ARCHITECTURAL SERVICES DEPARTMENT
STUDY ON GREEN ROOF APPLICATION IN HONG KONG
FINAL REPORT
URBIS LIMITED
16 February 2007
Prepared by :
Derek Townshend
16 February 2007
Date
Alexander Duggie
16 February 2007
Date
Alexander Duggie
16 February 2007
Date
Checked by :
Approved for Issue by:
PART 1 – GREEN ROOFS OVERVIEW
1
INTRODUCTION............................................................................................................................................................6
1.1
1.2
DESCRIPTION OF THE STUDY.......................................................................................................................................................6
PURPOSE OF THE REPORT ...........................................................................................................................................................6
2
GREEN ROOFS – DEFINITIONS, BENEFITS AND CONSTRAINTS...........................................................................7
2.1
2.2
2.3
DEFINITIONS OF GREEN ROOFS ..................................................................................................................................................7
BENEFITS OF GREEN ROOFS (AESTHETIC, ENVIRONMENTAL, AND ECONOMIC).................................................................9
CONSTRAINTS OF GREEN ROOFS .............................................................................................................................................22
3
SHOWCASE EXAMPLES............................................................................................................................................26
3.2
3.3
3.4
3.5
3.6
3.7
3.8
UNTERENSINGEN, GERMANY .....................................................................................................................................................26
CHICAGO CITY HALL, USA ...........................................................................................................................................................27
ACROS BUILDING , FUKUOKA, JAPAN ........................................................................................................................................30
ROPPONGI HILLS, TOKYO, JAPAN ..............................................................................................................................................33
TAI LUNG LABORATORY, HONG KONG ......................................................................................................................................35
GUANGZHOU GREEN ROOFS, GUANGDONG, CHINA...............................................................................................................36
IFC2, HONG KONG.........................................................................................................................................................................39
4
FINDINGS OF DESKTOP RESEARCH.......................................................................................................................42
4.1
4.2
4.3
4.4
4.5
4.6
REVIEW OF INTERNATIONAL APPROACHES, STANDARDS, AND COVERAGE OF GREEN ROOFS ....................................42
REVIEW OF APPROACHES TO GREEN ROOFS IN HONG KONG .............................................................................................51
LOCAL ISSUES, CONCERNS, AND RESEARCH..........................................................................................................................53
CLIMATIC & ENVIRONMENTAL FACTORS INFLUENCING GREEN ROOF DESIGN & CONSTRUCTION IN HONG KONG....60
GREEN ROOF POTENTIAL IN HONG KONG................................................................................................................................62
GREEN ROOF BENEFITS TO HONG KONG.................................................................................................................................67
PART 2 – DESIGN & TECHNICAL GUIDELINES
5
GREEN ROOF SYSTEMS ...........................................................................................................................................70
5.1
5.2
5.3
5.4
ROOF TYPE SCENARIOS IN HONG KONG..................................................................................................................................70
BASIC COMPONENTS ...................................................................................................................................................................75
MAINTENANCE CONSIDERATIONS .............................................................................................................................................87
GREEN ROOF DESIGN CHECKLIST SUITABLE FOR HONG KONG ..........................................................................................88
6
INTENSIVE GREEN ROOFS (SKY GARDENS & PODIUM GARDENS) IN HONG KONG........................................94
6.1
6.2
CONSTRUCTION DETAILS............................................................................................................................................................94
SPECIAL CONSIDERATIONS FOR PODIUM GARDENS & SKY GARDENS ...............................................................................94
7
EXTENSIVE GREEN ROOFS (ECO-ROOFS) IN HONG KONG.................................................................................97
7.1
7.2
7.3
7.4
CONSTRUCTION DETAILS............................................................................................................................................................97
MODULAR TRAY SYSTEMS ..........................................................................................................................................................98
PLANT SELECTION FOR EXTENSIVE GREEN ROOFS ............................................................................................................101
EXTENSIVE GREEN ROOF PLANTING APPROACHES ............................................................................................................101
8
GREEN ROOF COST ESTIMATES FOR HONG KONG...........................................................................................103
8.1
8.2
CAPITAL COSTS ..........................................................................................................................................................................103
RECURRENT COSTS...................................................................................................................................................................107
PART 3 – CONCLUSIONS & THE WAY FORWARD
9
SUMMARY OF THE STUDY......................................................................................................................................110
9.1
9.2
9.3
9.4
BACKGROUND .............................................................................................................................................................................110
GREEN ROOF OPPORTUNITIES, CONSTRAINTS & CONSIDERATIONS FOR IMPLEMENTATION ......................................111
GREEN ROOF DIRECTIONS IN HONG KONG ...........................................................................................................................113
RECOMMENDATIONS AND THE WAY FORWARD....................................................................................................................114
APPENDIX I EXAMPLES OF PUBLIC BUILDINGS IN HONG KONG WITH GREEN ROOFS
APPENDIX II PLANT SELECTION MATRIX FOR GREEN ROOFS (INTENSIVE & EXTENSIVE)
APPENDIX III REFERENCES & BIBLIOGRAPHY
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List of Figures
2.1
2.2
2.3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.13
3.14
3.15
3.16
3.17
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
4.13
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
5.11
6.1
6.2
6.3
7.1
Warming Trends: Globally and in Hong Kong
Typical Roof Temperature Differences and Infra-red Imaging
Albedo values of roofing materials
Lauer Building, Unterensingen, Germany
Intensive Green Roof, Lauer Building, Unterensingen, Germany
Retrofitted Extensive Green Roof on Public Buildings, Chicago City Hall
Intensive Green Roofs on the ACROS Office Block Building, Fukuoko, Japan
Close-up view of Intensive Green Roofs on the ACROS Office Block Building
Conceptual Architecture for Green Roofs
Intensive and Extensive Green Roofs on the Roppongi Hills Main Building
Intensive Green Roofs at Roppongi Hills, Tokyo
Intensive Green Roofs at Tai Lung Laboratory, Yuen Long, Hong Kong
Specialized Sedum Cultivar
Site A – Feng Huang Shan Hostel and Adjacent Residential Buildings
Site B – Guang Wei Lu Residential Buildings
Site C – Dong Wang Market and Adjacent Residential Buildings
Example of Sedum Lineare in Shenzhen
Roof Garden at IFC2, Showing Trees, Seating and Water features
Roof Garden at IFC2, Showing Lawned Areas and Cafeterias
Plan of Roof Gardens at IFC2
Extensive Green Roof Research Project by Gammon-Skanska
Green Roof Research at University of Hong Kong
Green Roofs on Bus Shelters
Green Roof at Kadoorie Farm
Roof Greening of Noise Enclosures
Sun Paths for Hong Kong, Latitude 22°N
Landsat Image of Hong Kong (Shortwave Infra-red bands)
Green Roof Opportunities in the City Centre
Green Roof Opportunities in the New City Centre Areas
Green Roof Opportunities in Residential Areas
Green Roof Opportunities on other Structures
Green Roof Opportunities on other Structures
Green Roof Opportunities on other Structures
Roof Type Scenarios in Hong Kong
Sky Gardens
Podium Gardens
Existing and Low-Maintenance Buildings
Utilities on New Buildings
Basic Components of a Green Roof System (Intensive and Extensive)
Conventional (Intensive) and Lightweight (Extensive) Green Roof Systems
Exploded View of Shaped Level Difference - Extensive Green Roofs
Shaped Level Difference - Extensive Green Roofs
Examples of Typical Components
Simple Sprinkler Head Irrigation System
Details of Typical Intensive Roof Garden
Calculating Plant Weights at Maturity
Lifting Heavy Trees
Details of General Roof Build-up
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6.1
6.2
6.3
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
9.1
Details of Typical Intensive Roof Garden
Calculating Plant Weights at Maturity
Lifting Heavy Trees
Details of General Roof Build-up
Details of Parapet Edge Treatment
Details of Typical Drainage Inspection Chamber
Detail of Typical Penetration of Roof-top Utilities
Typical Extensive Green Roof Tray Systems
Prefabricated Extensive Greenroof (PEG) Tray System Developed in Singapore
Aesthetic Potential of Extensive Green Roof Tray Systems
Extensive Green Roof Planting Approaches
Some Typical Urban Forms in Hong Kong
List of Tables and Charts
2.1
Comparison of Extensive and Intensive Green Roof Systems
4.1
Extract from Portland’s Zoning Code
4.2
Cost Benefits analysis in Toronto (in CAD$)
4.3
Green Roof Temperature Measurements at the University of Hong Kong
4.4
Building types in Hong Kong
4.5
Benefits Applicable to Hong Kong
5.1
Considerations for New Buildings and Existing Buildings
5.2
Standard Soil Depths for Basic Vegetation Types
5.3
Characteristics of Inorganic Growing Media Components
5.4
Material Weights of Soils and Other Green Roof Components
5.5
Manual Irrigation Systems
5.6
Automatic Irrigation Systems
5.7
Maintenance Procedures for Hong Kong Green Roof Types
5.8
Green Roof Design Checklist for Hong Kong: PLANNING & FEASIBILITY
5.9
Green Roof Design Checklist for Hong Kong: COMPONENTS
5.10
Green Roof Design Checklist for Hong Kong: MAINTENANCE & MANAGEMENT
6.1
Trees and Palms for Intensive Green Roofs in Hong Kong
6.2
Plant Weights
7.1
Advantages and Disadvantages of Tray Systems
8.1
Comparison between Building and Green Roof Costs in Hong Kong
8.2
Comparison of International and Local Extensive Green Roof Cost Ranges
8.3
Typical Extensive Green Roof Capital Cost Breakdown (example from USA)
8.4
Costs Breakdown and Commercial Availability of Components in Hong Kong (HK$)
8.5
Comparison of Local Intensive and Extensive Green Roof Maintenance Cost Ranges
List of Abbreviations
AAC
Autoclaved Aerated Concrete
ACABAS
Advisory Committee on the Appearance of Bridges and Associated Structures
AFCD
Agriculture, Fisheries and Conservation Department
ArchSD
Architectural Services Department
ASLA
American Society of Landscape Architects
ASTM
American Society for Testing Materials (ASTM)
BD
Building Department
BEC
Business Environment Council
DE
Diatomaceous Earth
CAD$
Canadian Dollars
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CEC
CEPAS
CIBSE
CIRIA
CSO
CUHK
ECC
EIA
EIAO
EPD
EPDM
FLL
GFA
G-S
GIS
HDPE
HIPS
HK-BEAM
HK$
HKPSG
HKU
HPI
HyD
HVAC
IFC2
JPN
LECA
LegCo
MVAC
PGBC
PMMA
PlanD
PNAP
PP
PV
PVC
SC
SBR
SBS
SEBS
SCG
SFr
TPO
TPO
UHI
US$
Cation Exchange Capacity
Comprehensive Environmental Performance Assessment Scheme
Chartered Institution of Building Services Engineers
Construction Industry Research and Information Association
Combined Sewer Overflow
Chinese University of Hong Kong
Environmental Campaign Committee
Environmental Impact Assessment
Environmental Impact Assessment Ordinance
Environmental Protection Department
Ethylene propylene diene monomer rubber
Forschungsgesellschaft Landschaftentwicklung Landschaftsbau (German), translated as Landscape
Research, Development & Construction Society
Gross Floor Area
Gammon-Skanska
Geographical Information Systems
High Density Polyethylene
High Impact Polystyrene
Hong Kong Building Environmental Assessment Method
Hong Kong Dollars
Hong Kong Planning Standards and Guidelines
University of Hong Kong
Hydrophobic Pore-blocking Ingredients
Highways Department
Heating, Ventilation & Air Conditioning system
International Finance Centre 2, Hong Kong
Joint Practice Note
Light Expanded Clay Aggregate
Legislative Council
Mechanical, Ventilation & Air Conditioning system
Professional Green Building Council Hong Kong
Polymethyl-Methacrylate
Planning Department
Practice Note for Authorised Persons and Registered Structural Engineers
Polypropylene
Photo-voltaic solar panels
Polyvinyl Chloride
Site Coverage
Styrene-Butadiene-Rubber
Styrene-Butadiene-Styrene
Styrene-Ethylene-Butadiene-Styrene
Steering Committee on Greening
Swiss Francs
Thermoplastic Olefins
Town Planning Ordinance
Urban Heat Island
United States Dollars
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PART 1
Green Roofs Overview
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1
INTRODUCTION
1.1
DESCRIPTION OF THE STUDY
1.1.1
In May 2006, Urbis Limited was commissioned by Architectural Services Department to conduct a Study
on Green Roof Application in Hong Kong.
Objective
1.1.2
The environmental, social and visual contributions that green roofs can make towards creating
sustainable living in high-density cities are accepted worldwide. The objective of the Study is to conduct
a quick review of the latest concepts and technology on green roofs and recommend guidelines adapted
to suit local applications in Hong Kong to promote public understanding and awareness.
1.1.3
Upon satisfactory completion of the Study, the Government shall have a report and presentation package
providing an overview of the general approaches, representative examples of green roof application, a
better understanding of the benefits (environmental, aesthetic and economic) and constraints of green
roofs, and good practice design guidelines including installation and maintenance aspects for public
appreciation and understanding.
Background
1.1.4
The Steering Committee on Greening (SCG) chaired by Permanent Secretary for the Environment,
Transport and Works (Works) at its meeting on 17 February 2006 supported the notion that roof gardens
can be a means to improve urban greenery and subsequently endorsed the recommendation to carry out
a research study with a goal to provide the general public with information on visual impact and
environmental improvements. To this end, the Architectural Services Department (ArchSD) has
commissioned this study focussing on the technical aspects of rooftop landscaping.
1.2
PURPOSE OF THE REPORT
1.2.1
The purpose of the Final Report is twofold.
1.2.2
The first purpose is to present the findings of the desktop literature search into green roof application,
including:
♦
1.2.3
a brief review of the latest international and regional concepts and approaches, including policies
/ incentives and established standards (see Section 3 and Section 4.1);
♦ a search on available studies and records for percentage green roof distribution in major
Southeast Asia cities and Hong Kong (see the Bibliography and Section 4.1);
♦ a list of the benefits and constraints for the community and private sectors (see Section 2 and
Section 4.6) ;
♦ a list of the components of a green roof system (see Section 5); and
♦ a description of the climatic conditions and other environmental factors affecting application (see
Section 4.4).
The second purpose is to present the way forward for green roofs in Hong Kong, including:
♦
♦
♦
Recommending design guidelines applicable to Hong Kong (see Sections 5, 6, and 7);
Determining the range of capital and maintenance costs involved that might be expected in Hong
Kong, and determining the commercial availability of materials described in the findings (see
Section 8);
Recommending the way forward for the successful promotion and implementation of green roofs
in Hong Kong, covering technical, promotional and policy improvements. (see Section 10);
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2
GREEN ROOFS – DEFINITIONS, BENEFITS AND CONSTRAINTS
2.1
DEFINITIONS OF GREEN ROOFS
2.1.1
A ‘Green Roof’ development involves the creation of vegetated space integrated structurally on top of a
man made structure. The word ‘roof’ in this context refers to any continuous surface designed for the
protection of inhabitants from the elements, whether open or closed on the sides. The vegetated space
may be below, at, or above grade, located on a podium deck, a ‘sky garden’ on an intermediate floor
level, or at the very top level of the building, but in all cases the plants are not planted in the ground. Freestanding planters placed on top of a roof do not constitute the recognised international landscape industry
definition of a green roof, which is characterised by the integration of the vegetation containment structure
with the building roof structure. However, there are circumstances, particularly in retrofitting, where use
of planting in pots or planters may provide a practical solution and an acceptable greening effect.
2.1.2
There are two basic types of green roof systems, identified in the international landscape industry as
‘extensive’ and ‘intensive’, as described below. The advantages and disadvantages of both major types of
green roofs are summarised below in Table 2.1.
Extensive Green Roofs (Eco-roofs)
2.1.3
Extensive green roofs are characterized by their low weight, low capital cost and minimal maintenance.
The growing medium, typically made up of a mineral-based mix of sand, gravel, crushed brick, leica, peat,
organic matter and some soil, varies in depth between 50mm and 150mm. Due to the shallowness of the
soil and the desert-like micro-climate on many roofs, plants must be low and hardy, typically alpine, dryland or indigenous. Plants are watered and fertilized only until they are established and after the first
year, maintenance consists of two or three visits a year for weeding of invasive tree and shrub species,
mowing, safety, and membrane inspections. As a general rule, minimal technical expertise or practical
experience is required for installation and maintenance.
Intensive Green Roofs (Podium Gardens & Sky Gardens)
2.1.4
Intensive green roofs are characterised by greater weight, higher capital costs, more plantings and higher
maintenance requirements. Plants are grown and maintained in ways similar to ground level gardens,
with soil depths that vary according to plant requirements, ranging from a minimum of 200mm depth for
lawns to up to 2000mm depth for tree planting, with corresponding structural loading implications. Due to
increased soil depth, the plant selection can be more diverse including trees and shrubs, which allows a
more complex ecosystem to develop. Requirements for maintenance and watering are more demanding
and ongoing than with an extensive green roof.
2.1.5
Intensive green roofs are characterised by their use as a ‘garden’ in much the same way as people would
use a garden at ground level. Intensive green roofs are widely occurring in Hong Kong in the form of
podium level gardens.
General Application of Green Roofs
2.1.6
For existing roofs to be upgraded to “green roofs”, the proposed soil depth, 50-150mm, can be adopted if
structural limits allow. For new structures or developments, a minimum of 300mm soil depth should
generally be adopted to create a better physical condition for planting and to plant species with all-yearround greening effect.
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Table 2.1 - Comparison of Extensive and Intensive Green Roof Systems
Extensive Green Roof
Intensive Green Roof
Soil characteristics
Typical details
Brief
description
Advantages
Disadvantages
•
•
•
•
•
•
•
•
•
•
•
•
•
•
thin soil (50mm-150mm thick)
little or no irrigation
low maintenance ($0.8 to $2.25 /m²/year)
extensive application over large area for
optimal environmental benefits
lightweight (80 to 150 kg/m²)
low maintenance
suitable for retrofit projects
relatively inexpensive ($400 to 1000/m²)
suitable for large areas
suitable for roofs with 0-30o slope
can leave vegetation to develop
spontaneously
more limited choice of plants
usually no access for recreation or
other uses
may be visually unattractive to some,
especially in dry season
•
•
•
•
•
•
•
•
•
•
•
•
•
•
deep soil (200mm-2000mm thick)
irrigation
normal maintenance ($6.5 to $44 /m²/year)
intensive capital and maintenance input for
optimal benefits
diverse utilization of roof (i.e. for
recreation, growing food, as open space)
with direct benefit to owner
greater diversity of plants and habitats
good insulation properties
can simulate a wildlife garden on the ground
can be made very attractive
often visually accessible
relatively higher cost ($1000 to 5000/m²)
not usually suitable for green roof retrofit
projects
greater weight loading (300 to 1000 kg/m²)
need for irrigation and drainage systems
hence, greater need for energy, water
materials etc.
(Adapted from Peck Callaghan & Kuhn (1999), p14)
(Images: source and copyright © (above) EarthPledge (2005) and (below) Zinco Ltd.)
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2.1.7
It should be noted that the advantages and disadvantages described in Table 2.1 provide generic
information only. An individual green roof system may be a combination of intensive and extensive,
depending on factors such as:
♦
♦
location;
♦
budget; and
♦
structural capacity of the building;
client and/or tenant needs.
Accessible and Inaccessible Roofs
2.1.8
Green roof systems can be further classified as being either ‘accessible’ or ‘inaccessible’. An accessible
green roof is an outdoor open space intended for use by people as a garden or terrace. These types of
green roofs often involve surface planting, planter boxes, pathways, seating, water features, play areas
and shade structures. Since these roofs are accessible by tenants, employees and/or the general public,
certain safety requirements must be adhered to. These include emergency egress, guardrails and
lighting.
2.1.9
An inaccessible green roof is only accessible for periodic maintenance. The green space can be viewed
but not used, and as such, has no requirement for any special access or safety features any more than a
normal roof. Inaccessible green roofs can be flat, curved or sloped up to 30°. Sloped and curved roofs
need additional horizontal strapping to prevent slippage of the growing medium and plant layers when
they become wet.
2.1.10 Accessible and inaccessible roofs are normally associated with intensive and extensive green roofs,
respectively.
2.2
BENEFITS OF GREEN ROOFS (AESTHETIC, ENVIRONMENTAL, AND ECONOMIC)
2.2.1
There are many potential benefits of green roofs. These may be considered to fall into three main
categories, namely, Amenity and Aesthetic Benefits; Environmental Benefits and Economic Benefits,
although there is a great deal of crossover between categories.
2.2.2
Amenity & Aesthetic Benefits include: leisure and open space, visual aesthetic value; health and
therapeutic value; and food production. Environmental Benefits include: ecological and wildlife value,
water management; air quality, sound absorption; and reducing the urban heat island effect. Economic
Benefits include increased roof life, building insulation and energy efficiency; and green building
assessment and public relations.
2.2.3
These benefits operate at a range of scales. Some will only operate if relatively large numbers of green
roofs are implemented in any particular area and their benefits will only be apparent at the larger
neighbourhood or city scale. Others will operate directly on an individual building.
Private and Community Sector Benefits
2.2.4
Each of the above benefits may also be classified as either private and/or community sector benefits that
can then be used to promote the idea to different audiences.
2.2.5
Private sector benefits are those which offer some direct benefit to the developer or owner of a building,
and include items such as savings in energy costs, extension of the life of the roof, recreational use and
aesthetic improvements.
2.2.6
Community sector benefits are those that offer benefit to the wider community e.g. public recreational
use, storm-water management, urban climate mitigation, promotion of diversity & habitat.
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2.2.7
Many of the benefits described below accrue to both the community and private sectors. Mention is
made in the descriptions below regarding which benefits may be considered to accrue to the private
sector and which accrue to the general community.
Amenity & Aesthetic Benefits of green roofs
Leisure and Open Space
2.2.8
In a dense urban environment with limited areas of ground level open space flat roofs present enormous
potential in providing urban dwellers with the amenity and recreational space essential for healthy living.
The sights, fragrances and sounds of a garden add immeasurably to the richness of experience and
quality of life. Communal gardens also offer opportunities for social interaction between neighbours that
might not otherwise be available, in both residential and commercial developments.
2.2.9
In Hong Kong, podium decks are used ubiquitously to provide some of the active and passive open space
that is so essential for the well-being of the population. These roof open spaces may be private, for the
sole use of occupants of the development, or public spaces for the use of the general populace.
2.2.10 Such accessible roof open spaces are classified as intensive green roofs. Publicly accessible roofs
provide obvious community benefits. Privately accessed roofs offer private sector benefits by increasing
property values, whilst also offering community benefits by contributing to the general community wellbeing and by reducing strain on public recreational resources.
2.2.11 The provision of public and private open space in Hong Kong is regulated in accordance with the Hong
Kong Planning Standards and Guidelines (HKPSG), town plans gazetted under the Town Planning
Ordinance (TPO) and private lot Lease Conditions. Frequently, both Government and the private sector
achieve the required open space provision through the creation of intensive green roofs at podium level.
2.2.12 In Hong Kong it has been noted that some intensive green roofs on public buildings are not well
frequented by park users. Common factors which should be considered at planning design and operation
are:
♦
♦
♦
convenient access affecting park users, maintenance and management;
avoiding concealed locations which may lead to the misuse of facilities and further deter the
public from using them; and
minimising the noise of vent shafts occasionally placed close to gardens.
Visual Aesthetic Value
2.2.13 An obvious and significant benefit of a green roof (subject to good maintenance) is the potentially
attractive view offered to overlooking buildings. This is of great importance in a dense urban environment
such as Hong Kong, where views of roofs are often associated with grey concrete slabs and the various
paraphernalia of pipes, electrical and mechanical equipment and maintenance apparatus that usually
clutters roof spaces.
2.2.14 Visual aesthetic benefits are offered by both intensive and extensive green roofs. However, for the same
plan area, intensive green roofs offer potentially greater visual benefit than extensive green roofs,
because the former may include large trees and shrubs which offer a three-dimensional greening effect,
whereas the latter comprise only a thin two-dimensional ‘skin’ of green which may not be visible unless
viewed from above.
2.2.15 Although many developments in Hong Kong have views of attractive podium landscapes (intensive green
roofs), the potential visual benefits that extensive green roofs offer, have not yet been exploited in Hong
Kong. This is most likely because such benefits would not accrue to the developer who is paying for the
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creation of the green roof, but rather to his neighbours who overlook his roof. There is therefore little
financial incentive to the developer to develop extensive green roofs for visual benefits, unless the roof is
visible by his own occupants.
2.2.16 Visual aesthetic benefits may either be private, community, or both, depending on whether the roof is
viewed only by the building occupants and / or by the wider public. If adopted extensively in the city,
green roofs have the potential to aid visual green space continuity throughout the urban area.
Health and Therapeutic Value
2.2.17 Visual contact with vegetation has proven direct health benefits. Psychological studies have
demonstrated that the restorative effect of natural scenery holds the viewer’s attention, diverts their
awareness away from themselves and worrisome thoughts and elicits a meditation-like state 1. People
living in high density developments are known to be less susceptible to illness if they have a balcony or
terrace garden 2. This is partly due to additional oxygen, air filtration and humidity control supplied by
plants. The variety of sounds, smells, colours and movement provided by plants, although not
quantifiable, can add significantly to human health and wellness. This in turn can lead to some potential
savings in community expenditure on healthcare.
Food Production
2.2.18 Roof spaces offer opportunity for growing certain types of food in high density urban environments where
garden space is restricted. While food-producing plants may be substituted for ornamental plants in
conventional roof garden situations, extensive areas of thinner roof coverings are also viable for
production of herbs and vegetables.
2.2.19 Food production on roofs would:
♦
♦
♦
♦
♦
give occupants opportunity for full control of the growing regime in terms of growing medium,
fertilisers and integrated pest management;
give occupants access to fresh food that has not travelled long distances;
provide educational value through learning how to grow produce;
provide the therapeutic value of growing things; and
provide economic value through savings in food costs and potential increased property values
and rentals.
2.2.20 Roof spaces used for food production would usually be classified as intensive green roofs due to
maintenance requirements.
2.2.21 The benefits of food production may be appreciated by both the private sector (increased property values,
savings in food costs) and the community (social and therapeutic).
2.2.22 Overseas examples of food production on roofs occur in Russia, Thailand, Colombia, Haiti and Canada 3.
The Fairmont Hotel in Vancouver, Canada provides all the herbs used in the hotel, at an estimated yearly
cost saving of CAD$25,000-30,000 (HK$175,000-210,000). It also provides amenity space and gives rise
to higher room rates for those located adjacent to it.
2.2.23 One important cautionary negative note should be sounded in relation to food production on green roofs,
and that is the positive ability of plants to absorb pollutants in the atmosphere (see section on Air Quality
(1)
1
Ulrich (1992), pp96 & 94
(2)
2
Johnson (1996) p33
(3)
3
Dunnett & Kingsbury (2004), p24
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below). Whilst plants’ ability to absorb pollutants such as heavy metals may help to improve air quality, it
is a disadvantage if green roofs are to be used for food production in an urban area with poor air quality.
Given the current relatively poor state of Hong Kong’s air quality, it is therefore considered prudent not to
promote food production on green roofs in Hong Kong until such time as the ambient air quality improves.
Environmental Benefits
Ecological and Wildlife Value
2.2.24 The enhancement of biodiversity through the use of green roofs is closely linked to the type of vegetation
being used. If appropriate species are used, green roofs may provide an opportunity to provide natural
habitat for resident and migratory birds and insects. This is achieved through the provision of one or
more of birds’ basic needs – food, water, shelter, and a place to breed.
2.2.25 Although individual vegetated roofs may not serve all of these functions, they may still act as ‘stepping
stones’, creating links between larger habitats offered by nearby natural green areas, hillsides or parks.
2.2.26 Wildlife and ecological benefits are likely to be greater when the variety of soil depth, vegetation type and
character is greater, and thus intensive green roofs would tend to offer greater benefits than extensive
green roofs. The latter may still offer significant benefits since thin, relatively infertile soils tend to support
large numbers of plant species. The vigorous aggressive plants that dominate and out-compete more
delicate species in more fertile soils cannot get a hold, therefore enabling a much greater diversity of
plant species to co-exist.
2.2.27 Numerous studies have been done on the biodiversity and wildlife value of green roofs. One of the most
detailed studies has been carried out in Basle, Switzerland 4, in which the insect life and bird life on
seventeen green roofs was monitored. Key findings included the fact that there was little difference in
the number of spiders and beetles found on the roof and on the ground; that birds visited the roofs
primarily for food; and that roofs in urban areas were visited more frequently by birds than those in urban
fringe areas, implying the relative importance of green roofs in urban areas as a food source for birds.
2.2.28 The key message coming from the research is that diversity in planning and construction of a green roof
leads to diversity in plants and animals. Having a variety of heights and slopes, open stony un-vegetated
areas, a variety of vegetation types, and freely and poorly drained areas maximises their ecological value.
2.2.29 Ecological and wildlife benefits are usually a side-benefit resulting when a green roof is created for other
purposes, such as recreation provision. However, some green roofs have been created with ecology as a
prime factor. For example the award-winning green roof on an office building at the corporate campus for
The Gap at Cherry Hill, California 5, uses native grasses of relict coastal communities, linking the building
with the surrounding landscape and extending the distribution of the natural plant community into an
urban setting.
2.2.30 However, one potential drawback of adopting a ‘laissez-faire’ ecological style planting, in which plants are
not grown in a ‘gardenesque’ manner but rather left to ‘do their own thing’, is that this ecological style of
planting is best appreciated, from a visual standpoint, at large scales, and that at the relatively small
scales of green roofs, ecological planting is likely to appear untidy, ‘scruffy’ and un-maintained (especially
in the dry season when vegetation is likely to turn brown), and therefore likely to draw criticism from those
people (and they are many) who seek the ‘neat and tidy’ approach to landscape. This is particularly true
in Hong Kong where there is little experience of ecological planting in the urban context.
2.2.31 Ecological and wildlife benefits should be considered as wider community benefits since they do not
accrue at the building unit level (unless under another category such as visual).
(4)
4
Dunnett & Kingsbury (2004), p38
(5)
5
Dunnett & Kingsbury (2004), p37
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Water Management
2.2.32 In urban areas, man-made hard surfaces (roads, paving, roofs, etc.) are impermeable and drainage
schemes for these surfaces are devised to remove rainwater from them as fast and efficiently as possible.
As a result, around 75% of rain falling on an urban area is lost directly to run-off, compared with 5% in a
forest where the other 95% either infiltrates into the ground or is intercepted by vegetation 6.
2.2.33 This impermeable nature of urban paved areas and ensuing high run-off has created a number of
problems such as:
♦
♦
♦
♦
♦
♦
Flooding. With increasing urbanisation, increasing strain is placed on natural drainage systems
surrounding the urban area which cannot cope with the sudden surge of drainage water during
rainstorms, resulting in floods which cause significant disruption and financial damage to private
and public property. This has been a feature of the New Territories in Hong Kong during the new
town development of the past thirty years. This in turn leads to the need to canalise natural river
systems, with associated negative visual and ecological impacts.
The contamination of storm-water. As storm-water runs off impermeable surfaces, it picks up
particulates, oil, grease, heavy metals, rubber and garbage from roads, driveways, car parks,
pavements and roofs before it reaches storm drains. In a number of cities, including Toronto,
storm-water is the prime cause of water pollution in local rivers 7.
Combined sewage overflows. In older urban areas, sewage and storm-water systems are
sometimes combined, and surges in storm-water can lead to overspill of untreated sewage into
public streets.
Increase in water temperatures. Run off from paved areas is at higher temperatures than in the
surrounding natural drainage systems and large surges of run-off can negatively impact aquatic
plants and encourage algal blooms.
Drop in local water tables. This occurs because of the large proportion of natural precipitation
being discharged into the artificial drainage system, rather than infiltrating into the ground. This in
turn makes it harder for local vegetation to survive without artificial irrigation.
Heavy investment in artificial drainage systems. The large surges in storm drainage created by
impermeable surfaces result in the need to invest large sums of public money in storm-water
infrastructure that is capable of coping with these surges.
2.2.34 Roofs account for up to 50% of the impermeable surfaces in many urban areas (Hong Kong’s average
figures are expected to be lower) and as such have an important role to play in determining urban water
management and in mitigating potential adverse impacts on natural drainage systems.
2.2.35 Green roofs can influence roof water run-off in a number of ways. Water that falls on the roof can be
absorbed into pore spaces in the substrate or taken up by absorbent materials in the substrate. It can
also be taken up by the plants and either stored in plant tissue or transpired back into the atmosphere.
Some water may lodge on plant surfaces and subsequently evaporate away. Water may also be stored
and retained by the drainage system on the roof.
2.2.36 The two main resulting effects are firstly a reduction in total run-off (by absorbing water and returning it to
the air, the roof reduces the amount of water available for run-off); and secondly spreading the residual
run-off over a longer period (by storing it for a period before it runs-off, the roof acts as a buffer between
the weather and drainage systems). (These effects are reduced during long periods of heavy rainfall
(6)
6
Dunnett & Kingsbury (2004), p43
(7)
7
Peck, Callaghan & Kuhn (1999), p27
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when the green roof system reaches water saturation point.)
2.2.37 There are three significant benefits resulting from these two effects, namely:
♦
a reduction of pressure on urban drainage systems and downstream natural drainage systems (a
community benefit);
♦ significantly reducing downstream flood risk (a community benefit); and
♦ reducing cost of drainage schemes because smaller pipes are possible (a private sector and
community benefit).
2.2.38 Other water management related benefits of green roofs include:
♦
♦
♦
the absorption by vegetation of the pollutants in rainwater (a community benefit);
the possible use of recycled water for irrigation (a private sector and community benefit);
the possible integration of rainwater with a grey water system, exploiting the natural filtration
system offered by plants and / or gravel (a private sector and community benefit); and
♦ a reduction in the contamination of storm-water since there is less direct run-off from paved
surfaces (a community benefit).
2.2.39 Water management is a very significant benefit of green roofs, and currently the most important area of
research in roof greening, with a number of state funded research institutes and commercial bodies
actively involved 8.
Air Quality
2.2.40 Air pollution manifests itself in several forms including particulates (primarily from vehicle engines); heavy
metals (in vehicle and factory emissions); and ozone. (Particulate levels in Hong Kong are about 40%
higher than Los Angeles, the most polluted city in the USA.). Although not directly fatal in itself, air
pollution causes fatalities when respiratory problems already exist. The numbers of premature fatalities
attributable to air pollution can be large – an estimated 3 500 people per year in Hong Kong, which is
50% worse than the UK (per capita). The pollution-attributable heath care costs can also be high. In Hong
Kong this is estimated to be between HK$1 billion to HK$1.5 billion per year (which excludes the
subjective value put on lives lost which may push the total up to HK$19 billion per year). 9
2.2.41 Vegetation in urban areas can filter out fine air particles as the air passes over the plants, the particles
settling on plant surfaces, and subsequently being washed into the soil by rain. Foliage can also absorb
gaseous pollutants lodging the material in their tissue.
2.2.42 However, there is little research to establish the extent to which this mitigating effect of plants occurs,
although studies have shown that green roofs can trap up to 95% of cadmium, copper and lead and 16%
of zinc 10. Other studies have shown that 1 square metre of grass can remove 0.2 kg of airborne particles
per year. 11
2.2.43 Air quality benefits within a specific geographical area will only occur to a significant degree if large areas
of roofs within that locale are ‘greened’. Furthermore, intensive green roofs, with trees and large shrubs
presenting large three-dimensional surface leaf area will have a much greater effect than extensive green
roofs which have a relatively flat, ‘two-dimensional’ vegetation profile.
2.2.44 Air quality benefits, such as they are, should be considered as wider community benefits since they do
(8)
8
Dunnett & Kingsbury (2004), p46
(9)
9
Hedley, et al (2006), p1-2, Air Pollution: Costs and Paths to a Solution.
(10)
10
Dunnett & Kingsbury (2004) p50
(11)
11
Green Roofs for Healthy Cities Coalition, 2002.
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not accrue at the individual building unit level.
Sound Absorption
2.2.45 The hard surfaces of urban areas reflect sound rather than absorb it, and roofs are no different. Green
roofs, however, can absorb sound, with the substrate tending to block higher sound frequencies, and the
vegetation tending to block lower frequencies.
2.2.46 Research in Germany has revealed that a 10cm thick green roof at Frankfurt airport reduced sound
transmission into buildings by a minimum of 5 decibels. However, there is generally currently little
scientific evidence to provide guidance on exactly how much sound reduction is provided by green roofs
of different depths, although there is clearly some increased effect with increased depth.
2.2.47 Although building occupants may benefit from sound reduction due to green roofs, there may also be
some general reduction in ambient environmental sound experienced by building neighbours who benefit
due to the roof vegetation dissipating and dispersing the ambient sound waves that would otherwise be
reflected off a hard roof surface. However, this is also hard to quantify.
2.2.48 Reduction in ambient noise levels may be considered both as a private sector benefit and a community
benefit.
Reducing Urban Heat Island Effect
2.2.49 The ‘Urban Heat Island Effect’ is the well documented phenomenon that urban areas are generally hotter
than the surrounding countryside due to a variety of factors including the large number of built structures
with heat absorbing properties; the reduction in evaporating surfaces; the lack of vegetation cover and
increased surface run-off; an increase in air pollutants; the heat production from buildings; and less
cooling wind because of shelter from buildings.
2.2.50 For example, the centre of Berlin on a clear windless night can reach 9°C (16°F) higher than the
outskirts 12. In Chicago, air temperatures range from 1°C to 2.7°C (3°F to 5°F) higher than the outlying
countryside. Another example is Tokyo which now experiences a mean temperature increase of 2.9°C
(5.2°F).
2.2.51 Hong Kong is no exception to the Urban Heat Island effect phenomenon. Research conducted by the
Hong Kong Observatory indicates that Hong Kong has been warming up during the past 118 years, in line
with the global warming trend. In the last ten years or so, the rural areas of Hong Kong have been
warming up at a rate of about 0.2°C per decade. At the Observatory Headquarters in the heart of urban
Hong Kong, the corresponding rise was about 0.6°C per decade. The difference of 0.4°C per decade
between temperatures in urban and rural areas can be attributed to the effects of urbanization. (Refer
Figure 2.1.)
2.2.52 Vegetation can have a cooling effect by dissipating some of the city heat through the process of evapotranspiration.
2.2.53 However, the effect of green spaces on urban climates has received little scientific attention. What
research has been done suggests that the larger the green area, the greater the degree of temperature
moderation within it. The cooling effect can also spread to adjacent areas (the so-called urban park cool
island effect) but this effect can be negated if the green area is surrounded by walls or if it lies in an area
of low-lying land from which the cool air will not spread.
2.2.54 The reduction of the heat island effect is the green roof benefit most difficult to quantify. Any such benefit
should be considered as a wider community benefit since it does not accrue at the building unit level.
(12)
12
Dunnett & Kingsbury (2004) p51
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2.2.55 Early research by the Toronto Green Roof Infrastructure Research and Demonstration Project (a project
that evaluates the environmental performance research of green roofs), released key findings in 2002.
Using 6% green roof coverage over 10 years (representing only 1% of Toronto’s total land area), it found,
could result in an average overall reduction of 1°C (1.8°F) in the urban heat island effect, with a reduction
of as much as 2°C (3.6°F) in some areas. However, development of new green roofs at an estimated
cost of CAD$ 45.5 million (HK$318 million) per year for ten years would be required to achieve this level
(6%) of green roof coverage.
Figure 2.1 Warming trends, globally and in Hong Kong stations
0.7
0.61
Temperature trend (°C/decade)
0.6
0.5
0.4
0.3
0.21
0.2
0.19
0.15
0.1
0
Global Mean
Hong Kong Observatory
Headquarters
Lau Fau Shan
Ta Kwu Ling
(Source: Adapted from results from Hong Kong Observatory)
Economic Benefits
2.2.56 Green roofs require greater structural loading, to varying degrees, and therefore require greater capital
cost. However, there are economic benefits which compensate for this as noted below.
Increased Roof Life
2.2.57 Studies have demonstrated 13 that green roofs, when properly constructed, can extend the life of a roof.
Degradation by ultraviolet light and the constant expansion and contraction caused by daily extremes of
temperature are the prime cause of the disintegration, cracking, delamination and splitting of roofing
materials. Green roofs insulate the materials from ultraviolet light and reduce the thermal extremes, thus
prolonging roof life.
2.2.58 German researchers have found out that reductions of diurnal temperature variations of up to 94% could
be achieved with green roofs, although that was heavily dependent on the type of vegetation used. This
high figure was achieved with a sward containing a wide variety of grasses and forbs similar to a
European meadow. Less bio-diverse grass swards achieved lower reductions, down to 12% in some
cases. Ground cover perennials were also trialled and again the bio-diverse mixes were most effective,
with a reduction in temperature variation of 90%. The better performance of bio-diverse mixes probably
(13)
13
Dunnett & Kingsbury (2004), pp29-32
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relates to the plants varied height structure and form, resulting in greater cushioning of air leading to
stronger microclimatic effects.
2.2.59 The second ‘Building Failure / Damage Report’ issued by the German government in 1988 identifies roof
greening as a solution to flat roof membrane failure. For example, a London department store installed a
roof membrane under planting in 1938 and 50 years later, the membrane was still in excellent condition 14.
2.2.60 Since lengthening of roof life will reduce an individual building’s life cycle costs, this might at first be
considered an economic benefit to the private sector. However, if the building developer intends to sell
the property once built, the long term savings would not accrue to him and therefore would not be an
incentive to invest the additional capital cost to install a green roof. Similarly, many homebuyers in Hong
Kong relocate after a few years, and the roof life of the property would probably have little or no impact on
the perceived property market value. Therefore this benefit may be better viewed as a community benefit
since longer building life-cycles offer economic savings at the community level.
2.2.61 It is important to note that the increased roof life benefit is dependent on proper green roof maintenance.
Horticultural attention is needed to ensure unwanted plant species (self-seeded trees in particular) do not
invade and cause damage. Regular maintenance such as checking the drains regularly is also needed to
preserve the healthy functioning of the green roof and to gain the benefits of an increased roof life.
Building Insulation and Energy Efficiency
2.2.62 One of the most important benefits that green roofs offer the private sector is the tangible economic
benefit resulting from reduced maintenance costs due to increased building insulation and energy
efficiency.
2.2.63 Green roofs can contribute to building insulation and energy efficiency in several ways:
♦
♦
♦
by trapping an air layer within the plant mass, the building surface is cooled in summer and
warmed in winter;
by covering the building with vegetation, summer heat is prevented from reaching the building
skin, and in winter, the internal heat is prevented from escaping; and
by acting as a buffer against wind moving along the building surface, which would otherwise
reduce the building’s energy efficiency.
2.2.64 A study in Singapore measured temperatures in an intensive green roof in the city over a range of
materials and vegetation 15. Temperatures were measured on the roof and indoors. The results showed
that over a typical 48 hour period, roof surface temperatures reached a peak of 57°C on exposed paved
surfaces, with a maximum diurnal fluctuation of 30°C, whereas the temperature measured under Raphis
(a common palm species) was only 27°C and the maximum diurnal fluctuation was only 3°C.
2.2.65 The net heat gain or heat loss was also calculated from a room beneath the different surfaces. Under the
unvegetated surfaces the room beneath the roof experienced a net heat gain over the period of a day:
even during the night heat was still entering the building because of the absorbed heat energy of the roof.
However, under the vegetated surfaces there was a net heat loss from the room. Interestingly, the rate of
heat loss from the room at night was the same under the vegetated surfaces as from the bare soil. This
indicates that in this situation there was little additional insulating benefit from the presence of vegetation
and that the main effect of plants is to reduce solar heat gain through shading during the day.
2.2.66 The shading effect of vegetation works even with low-growing plants such as sedums. Because green
roofs reduce temperatures in buildings partly through shading and partly through evapo-transpiration, the
(14)
14
Peck, Callaghan & Kuhn (1999) p30
(15)
15
Dunnett & Kingsbury (2004) p34
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plants have to be actively growing rather than in a state of heat-induced dormancy for the roof to be fully
effective. For this reason effective cooling by green roofs necessitates some irrigation to keep the plants
alive and green.
Figure 2.2 Typical Roof Temperature Differences and Infra-red Imaging
(Source (Left) Adapted from www.roofmeadow.com, Source (Right) Yok, T. P., & Sia, A., Selection of Plants for Green Roofs
in Singapore, p9 (Copyright © 2005 by National Parks Board, Singapore)
2.2.67 The insulating benefits of green roofs can provide immediate tangible savings in regular building
maintenance costs. This is of direct economic benefit to the building owner and can also benefit the
building developer (who builds then sells) due to the increased property value. There is also an economic
benefit to the community since less energy is required to satisfy the building’s needs, contributing to a net
reduction in the community’s overall power consumption.
2.2.68 Heat transfer through the roof and building walls into the rooms below is unique for every building making
it difficult to determine a general benefit for all green roofs. Factors that influence heat transfer include:
the external air temperature and humidity, the amount of direct radiation from the sun (overcast or not),
the building materials, the ratio of hard to greened surfaces, the roofing material and colour (see Figure
2.3), the depth of the soil, the type of vegetation used, the vegetation coverage and the colour of any
exposed soil, and the water content of the soil. Despite these difficulties, it is important to determine the
ultimate effects on internal room temperatures to determine what kind of energy savings can be expected.
Early research in Shanghai by ZHAO Ding-guo and XUE Wei-cheng shows that a room temperature
reduction of 2°C can be expected, at least on the top floor of any building. This research states that
other studies have found room temperature differences of 4-5°C. 16 Research by Dr. Nyuk Hien WONG,
at the National University of Singapore indicates that net annual energy savings are around 15%
(results applicable to a five-storey commercial building in Singapore – the closest available model and
climate equivalent to Hong Kong) 17.
2.2.69 The arguments for whether a cheaper, highly reflective “white roof” might give the same energy savings
as a green roof has been studied by the Centre for Climate Systems Research of Columbia University,
New York, and the Penn State Centre for Green Roof Research of Penn State University 18. Results
favour green roofs for two reasons:
(16)
16
ZHAO Ding-guo & XUE Wei-cheng (2005)
(17)
17
Wong (2002) http://www.nus.edu.sg/occ/pressrel/0209/020905.htm and (2002) http://www.bdg.nus.edu.sg/research/Rooftop.pdf
(18)
18
Gaffin, S. et al (2005) Energy Balance Modelling Applied to a Comparison of White and Green Roof Cooling Efficiency
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♦
♦
The equivalent energy-reflecting white surface (commonly referred to as its albedo) needs to be
so pure and radiantly white that keeping it so may require maintenance exceeding that of an
extensive green roof and be more hazardous for labourers too (see Figure 2.3 below)
With respect to the heat flow downwards into the room below, green roofs have shown
significantly lower temperatures than their surface temperatures simply because the rooms are
further insulated by the green layer above it. If this is factored into the equation then it becomes
obvious that pure white surfaces pale in comparison to green roofs when it comes to total energy
efficiency.
Figure 2.3 Albedo Values of Roofing Materials
(Adapted from Florida Solar Energy Center)
2.2.70 As green roofs and solar panels may often compete for the same rooftop space, there is also some
debate as to which technology best solves the city’s energy problems. Theoretical knowledge of photovoltaic (PV) semi-conductors suggests that these two technologies actually work best in tandem. 19 It is
well-known that PVs work more efficiently when the ambient temperatures are lowered to below 25°C (19)
19 Kohler, M., et al (Rio 02 – World Climate & Energy Event, Jan 2002) Photovoltaic-Panels on Greened Roofs - Positive Interaction Between Two Elements
of Sustainable Architecture http://www.rio02.de/proceedings/pdf/151_Koehler.pdf
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which in many cases can only be done cost-effectively through greenery. Similarly, PVs provide some
shade which expands the available plant palette and ameliorates the growing and soil conditions.
Research into this symbiotic relationship is early and ongoing. Apart from combined weight constraints,
there is little preventing solar panels being installed on frames above a green roof. In fact, combing the
routine inspections for both technologies may also provide a saving than if only one of the technologies
were used.
Green Building Assessment and Public Relations
2.2.71 It is estimated that half of the energy derived from fossil fuels is consumed by buildings. The challenge for
architects is to develop buildings that incorporate sustainable technologies and so reduce their pollution
and running costs. Three quarters of everyday energy use in buildings is accounted for, in more or less
equal proportions, by artificial lighting, heating and cooling. 20 Responding to this need are Green building
assessment schemes which exist in several countries, including Hong Kong. Their purpose is to
encourage environmentally sound building practice, and there is also considerable public relations value
in projecting an environmentally conscious image for a building development or organisation.
2.2.72 Green roofs can contribute to the credit rating of developments assessed under such schemes, and a
green roof can be a highly visible way in which a development can draw attention to its environmental
‘credentials’, which may contribute to increased property value.
2.2.73 In Hong Kong there is currently one private sector initiated green building assessment scheme in
operation, the Hong Kong Building Environmental Assessment Method (HK-BEAM), and one other
scheme currently being planned by the Government, the Comprehensive Environmental Performance
Assessment Scheme (CEPAS). Brief descriptions of these schemes are provided below.
Hong Kong Building Environmental Assessment Method (HK-BEAM)
2.2.74 HK-BEAM is a private sector voluntary initiative first implemented in 1996. HK-BEAM is currently
managed by the HK-BEAM Society, which was created in 2002, and is:
♦
an industry-led initiative to assess, improve, certify and label the environmental performance for
the life-cycle of buildings;
♦ a comprehensive standard and supporting process covering all building types, including mixeduse complexes, both new and existing;
♦ a means by which to benchmark and improve performance; and
♦ a voluntary scheme developed in partnership with, and adopted by the industry.
2.2.75 The aims of HK-BEAM are to:
♦
♦
♦
♦
♦
(20)
20
stimulate demand for more sustainable buildings in Hong Kong, giving recognition for improved
performance and minimising false claims;
provide a common set of performance standards that can be pursued by developers, designers,
architects, engineers, contractors and operators;
reduce the environmental impacts of buildings throughout the planning, design, construction,
management and demolition life cycle;
increase awareness in the building community, and ensure that environmental considerations are
integrated right from the start rather than retrospectively; and
be a driver for and a means by which to assure healthier, higher quality, more durable, efficient,
and environmentally sustainable working and living environments.
(Sir) Richard Rogers (1997)
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2.2.76 The HK-BEAM Society is a non-profit organisation that owns and operates, on a self-financing basis, the
HK-BEAM. The Society oversees the on-going development and implementation of HK-BEAM standards
for building assessment, performance improvement, certification and labelling. This is undertaken as an
industry-led, voluntary initiative to benefit the community.
2.2.77 Formalised in 2002, the HK-BEAM Society consists of individual and corporate members from all
disciplines in the private sector (owners, developers, facility managers, designers, researchers,
contractors, product and material suppliers, etc) with an interest in enhancing building environmental
performance.
2.2.78 Buildings are independently assessed and receive a HK-BEAM certificate and rating of Bronze, Silver,
Gold or Platinum, according to performance.
2.2.79 HK-BEAM defines over 100 best practice environmental criteria on the key aspects of Hong Kong's
buildings and provides a forum for the design / management team to work for the same environmental
goals:
♦ hygiene, health, comfort, and amenity;
♦ land use, site impacts and transport;
♦ use of materials, recycling, and waste management;
♦ water quality, conservation and recycling; and
♦ energy use, efficient systems and equipment, and energy management.
2.2.80 Adopted by almost 100 premises (covering some 60 million ft2), HK-BEAM Society claims that HK-BEAM
is one of the most widely used assessment and labelling schemes for buildings in the world.
2.2.81 Green roofs could potentially assist in gaining credits under several environmental criteria in the
assessment, including Ozone Depleting Substances; Water Pollution and Drainage; Microclimate around
Buildings; Landscaping; Planters on Buildings; Water Conservation; Recycling Facilities; and
Environmental Management Plan.
Comprehensive Environmental Performance Assessment Scheme (CEPAS).
2.2.82 CEPAS is a green building assessment scheme under planning by the HKSAR Government Building
Department (BD). BD’s intention is to create a user-friendly assessment scheme for buildings in Hong
Kong that is suitable for all types of new and existing developments. It is intended that CEPAS:
♦ be an assessment tool applicable for assessing entire building developments as well as individual
components or features of a building, and be able to assess all these at different stages in the
building life-cycle;
♦ form the basis of a green labelling system which can be adopted for both an incentive and nonincentive basis; and
♦ be a tool to encourage up-grading of the environmental performance of buildings in Hong Kong.
2.2.83 BD intends that CEPAS includes assessments on:
♦ holistic life-cycle including the planning, design, construction, maintenance and demolition stages;
♦ use of natural renewable resources and recycled / green building material;
♦ energy efficiency, in particular non-renewable types;
♦ construction and demolition waste minimisation; and
♦ indoor environmental quality.
2.2.84 In 2002, BD commissioned a consultancy study to develop the scheme. The study was completed in mid
2005, and it has been presented to various stakeholders, including LegCo and the Provisional
Construction Industry Co-ordination Board. The study recommendations have not yet been implemented.
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Benefits unique to Green Roofs
2.2.85 Some benefits that are similar to those described above may be achieved by using other (non-vegetative)
types of roofing material. However, many of the benefits described are unique to green roofs and cannot
be provided by other roofing materials. These include: Amenity & Aesthetic Benefits (i.e. leisure and open
space, visual aesthetic value, health and therapeutic value; and food production) and Environmental
Benefits (i.e. ecological and wildlife value; and air quality). Green roofs, in some locations, also provide
comfortable open spaces where elevated panoramic views of the city or surrounding landscapes can be
enjoyed.
Benefits of Intensive versus Extensive Green Roofs
2.2.86 The benefits of green roofs, both intensive and extensive, are roughly the same. Intensive green roofs
generally provide these benefits to a better degree and also provide additional functional open space
which is greatly needed in Hong Kong. Table 2.2 compares intensive and extensive green roofs and
highlights the main reasons for choosing one type of green roof over another.
Table 2.2 – Comparison between Intensive and Extensive Green Roof systems
•
•
•
•
•
•
Intensive Green Roof
Provides functional open space and can provide a local microclimate (with shade) that is user-friendly.
Increased amenity value can increase property values.
Greater plant range (including trees) that work reliably in Hong
Kong.
Is more visible and visually appealing.
Provides better environmental benefits (adding to ecology and
wild-life, water-management, air-quality improvements and the
reducing of Urban Heat Island effect).
Provides better building insulation benefits (sound absorption,
heat transfer and air-conditioning savings)
•
•
•
•
Extensive Green Roof
Low capital costs
Low maintenance costs
Light weight
Suitable for retrofit projects
2.3
CONSTRAINTS OF GREEN ROOFS
2.3.1
As intensive green roofs are widely occurring in Hong Kong it is apparent that any constraints presented
by the construction of intensive green roofs have already been overcome. The technical issues
associated with intensive green roofs are well understood by the local construction industry.
2.3.2
On the other hand, with no incentive and minimal knowledge about the emerging technologies, there are
very few examples of extensive green roofs in Hong Kong.
2.3.3
The constraints or barriers against the development of green roofs (which apply in Hong Kong to differing
degrees for intensive and extensive green roofs), may be considered to fall into four categories, each of
which is briefly described below, namely:
♦ Lack of knowledge and awareness;
♦ Lack of incentive / statutory mandate;
♦ Economic constraints;
♦ Lack of available roof area; and
♦ Technical issues and risks associated with uncertainty.
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Lack of knowledge and awareness
2.3.4
Although there is widespread knowledge and awareness in Hong Kong of intensive green roof
construction technology, there is very little awareness of extensive green roof technology.
2.3.5
The lack of extensive green roof pilot projects; the uncertainty within the market over costs and benefits;
the lack of local research on suitable plant species for low maintenance and/or inaccessible roof
applications; and the unfamiliarity among users and clients all act together as a barrier against the
development of extensive green roofs in Hong Kong.
2.3.6
In the Hong Kong context, the key groups of stakeholders who require additional knowledge on extensive
green roofs are:
♦ Policy Makers. Politicians and staff at all levels in government need knowledge of the costs and
benefits of green roofs.
♦ Professionals. The construction and building management industry needs to familiarise itself with
existing extensive green roof construction technology and adapt it to Hong Kong requirements.
More local research is required on suitable plant materials and substrates for extensive green
roofs.
♦ General Public. Public knowledge of the benefits of green roofs will create political demand for
government incentives as well as market demand for properties incorporating such green roofs.
Lack of Incentive
2.3.7
The development of the green roof industry in Europe is largely a result of legislation passed in Germany
in 1989 requiring new developments to install green roof systems. Without this statutory requirement, the
initial inertia caused by lack of knowledge and perceived technical problems would have been harder to
overcome.
2.3.8
Furthermore, several of the benefits described earlier in this chapter are long-term private sector benefits
or community benefits which would not accrue to a property developer who builds and sells immediately.
Since most property development in Hong Kong is of this type, it may be necessary to offer developers
more direct incentives to build extensive green roofs in Hong Kong.
Economic Constraints
2.3.9
There is a lack of understanding about direct tangible and long-term economic benefits of extensive green
roofs, and this uncertainty may mean that costs are thought to be higher than they actually are and
consequently the market fails to drive implementation.
2.3.10 Structural loading requirements require additional capital expenditure, the extent of which depends on the
nature of the green roof. Structural costs for extensive green roofs would represent a significantly smaller
percentage of overall construction costs than costs for intensive roof gardens which are already
widespread in Hong Kong.
2.3.11 Additional maintenance costs may be required, though this will vary greatly depending on the design.
Long-term maintenance costs of extensive green roofs should be a relatively small proportion of total
building maintenance costs, especially since damage to the building envelope will be reduced, but these
exact costs are not known. Long-term maintenance also requires initiative on the part of the owner /
manager.
2.3.12 Additional design costs may be required due to the need for specialist advice.
2.3.13 Additional infrastructure costs may be required, e.g. additional stairs for access and safety railings for
accessible roofs.
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Technical constraints and risks associated with uncertainty
Plan Area
2.3.14 Although, from a technical standpoint, there is no minimum area for a green roof, the smaller the roof is,
the harder it would be to create effective greening alongside other elements that have to be located on
the roof. This is a significant consideration in Hong Kong where building footprints are frequently quite
small.
2.3.15 Very small intensive green roofs may still provide useful benefits by virtue of their ability to create usable
space for leisure and amenity, and also generate comparatively large volumes of greenery from trees
growing out of a small floor plan.
2.3.16 On the other hand, the benefits of a small extensive green roof would be less than those of a small
intensive green roof, since the former’s ‘two-dimensional’ nature has less visual greening impact than the
latter’s ‘three-dimensional’ qualities; it cannot be used as leisure or amenity space; and the environmental
benefits of extensive green roofs described in Section 2.2.24 above are most effective when extensive
areas of roof are greened.
Altitude
2.3.17 Although there is no technical limit on the altitude of a green roof (since plant species may be chosen for
any given situation), significant changes in environmental and microclimatic factors occur as the altitude
increases, leading to significant constraints in design requirements and opportunities. Green roofs
located at higher levels above ground require plants suited to cool, windy, exposed locations, and will
present far more limited opportunities for human use.
Structural Loading
2.3.18 Although there is no technical reason why a sufficiently strong structure cannot be created for a green
roof, there may be financial constraints on the provision of a suitably strong structure. This is more likely
to be the case for intensive green roofs which require greater structural loading than extensive green
roofs.
Water Leakage
2.3.19 From a technical standpoint, there is no reason why leaks should occur any more than in a normal roof
system, (in fact they should be less likely to occur due to protection from weather, as noted in the section
on benefits) but if leaks do occur, they are potentially more difficult to trace.
Maintenance
2.3.20 If roofing components need replacement, a more complicated process is likely, since plant material and
growing medium would likely need to be removed and replaced.
2.3.21 Accessible roofs need on-going care. The more complex the planting scheme, the more care is required,
(e.g. pruning, etc.). However, this is already well understood and implemented on intensive green roofs
throughout Hong Kong.
Safety
2.3.22 Accessible roofs must have full perimeter safety protection. Adequate safety protection must be provided
for maintenance staff.
Plant Selection
2.3.23 Plant selection for use on intensive green roofs is well understood in the local landscape industry, and
there is a huge variety of ground covers, shrubs and trees that are commonly used on podium landscape
gardens in Hong Kong.
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2.3.24 However, the limited experience of extensive green roofs in Hong Kong means that there is uncertainty
on the correct plant species for use on this type of green roof in the local context.
2.3.25 The ornamental ‘neat and tidy’ approach to landscape that is prevalent in Hong Kong suggests that the
dry seasonal browning of ecological style planting on extensive green roofs may not be well received by
certain sectors of the general public. (For example, grass on natural hillsides in Hong Kong turns brown
during the dry season – which appears quite natural and not out of place - but grass planted as part of
slope greening measures along highways in urban areas seems to be expected to stay green all year
round and is frequently criticised for not achieving ‘greening’ objectives when it turns brown as part of its
natural cycle.) A desire for ‘neat and tidy’ and ‘always green’ landscape implies higher levels of
maintenance with associated costs.
2.3.26 Although requiring less maintenance than intensive green roofs, extensive green roofs still need to be
maintained to ensure that unwanted plant species (e.g. large shrubs or trees) do not invade the roof and
cause damage.
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3
SHOWCASE EXAMPLES
3.1.1
Provide below are seven showcase examples of buildings with successful green roofs, two from outside
Asia, two from Asia and three from Hong Kong and Guangdong.
♦
♦
Unterensingen, Germany, (Intensive and Extensive Green Roof)
♦
Chicago City Hall, USA, (Retrofitted Extensive Green Roof)
♦
Roppongi Hills, Tokyo, Japan (Intensive and Extensive Green Roof)
♦
ACROS Building , Fukuoka, Japan (Intensive Green Roof)
♦
Tai Lung Laboratory, Hong Kong. (Intensive Green Roof)
♦
Guangzhou Green Roofs, Gaungdong, China. (Extensive Green Roof)
IFC2, Hong Kong (Intensive Green Roof)
3.2
UNTERENSINGEN, GERMANY
3.2.1
This building provides examples of both intensive and extensive green roof systems.
Figure 3.1 Lauer Building, Unterensingen, Germany
The building with its green roof level, eight years after completion, showing both intensive and extensive green roof systems.
(Source and copyright © 2002 by Zinco Ltd.)
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3.2.2
When planning the new administration and research building in Unterensingen for the computer company
Lauer Systems´, it was decided to vary the architecture from the surrounding industrial buildings which
had monotonous flat roofs. An ambitious landscape design with a lot of green was requested. As the
footprint of the building was going to take up most of the development area, it was planned to provide
intensive landscaping on the three lower roof levels. Only the upper roof was provided with an extensive
landscape. The three intensive roof areas are landscaped to reflect the internal functions at each level,
providing outdoor areas for the Casino and conference rooms, to hold company picnics and other events.
3.2.3
Green roof characteristics are as follows:
3.2.4
♦
♦
♦
♦
♦
♦
Area:
Soil Depths:
Construction year:
Client:
Architects:
Design:
1200 m²
200mm to 700mm
1993
Knut Lauer
Kolb & Prassel, Hochdorf
Dieter Grau & Albrecht Hild
The landscaping consists of lawn, shrubs, bushes and trees in a design that made use of numerous
proprietary layers and substrates ranging from 200mm to 700mm, including special filter sheets, drainage
layers, insulation protection mats with root resistant waterproofing.
Figure 3.2 Intensive Green Roof, Lauer Building, Unterensingen, Germany
An avenue of trees surrounds a timber decked catwalk. The roof garden on the second floor is used by the employees during
breaks. A circular pergola with its seating acts as a central meeting area. (Source and copyright © 2002 by Zinco Ltd.)
3.3
CHICAGO CITY HALL, USA
3.3.1
This building provides an example of a retrofitted extensive green roof system. As a part of its effort to
become the “greenest city in America”, Chicago now claims more green roofs than any other US city.
The elaborate green roof on the century-old City Hall was among the first, and is now an important
research and demonstration site for studies on the benefits of green roofs, comparisons of green roof
technology, and the survivability of both native and non-native plant species.
3.3.2
Over 150 varieties of trees, vines, grasses, and shrubs are the subjects of ongoing experiments. Plants
are organized into bands of different colours, which change as the season progresses. These bands are
not merely aesthetic, but allow the same plant materials to be tried in various soil depths, slopes, and
drainage patterns. Although the roof is not accessible to the public, it is visible from more than thirty tall
buildings in the city centre. Limited tours are given to industry professionals.
3.3.3
The black tar roof of the adjacent Cook County Administration Building serves as a control for
comparative studies. Tests have shown that the average temperature on the City Hall green roof is 8°C
(78°F) cooler than on the Administration Buildings’ tar roof. Chicago’s City Hall green roof continues to
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provide the essential data that can ultimately support government incentives and investment in green
roofs as a way to mitigate the urban heat island effect.
Figure 3.3 Retrofitted Extensive Green Roof on Public Buildings, Chicago City Hall
Views showing the City Hall building before and after the addition of extensive rooftop gardens.
(Source and copyright © Earth Pledge, 2005)
Shrubs and climbers are also tested in these locations.
(Source and copyright © Earth Pledge, 2005)
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Annuals, bi-annuals and grasses are also being tested on this site.
(Source and copyright © Earth Pledge, 2005)
3.3.4
3.3.5
Green roof characteristics are as follows:
♦
♦
♦
♦
♦
♦
♦
♦
Area:
Roof Coverage %:
Soil Depths:
Costs:
Construction year:
Client:
Architect:
Landscape Architect:
2000 m² (22 000 ft²)
56%
100mm, 150mm, 450mm
US$ 490/m² (HK$3800/m²)
2001
City of Chicago
William McDonough & Partners
Conservation Design Forum
Interest in the City Hall roof and in the city’s support of green roofing has been so great that a multidepartmental team developed a brochure entitled ”A guide to Roof-top gardening” to respond to public
demand for information.
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3.4
ACROS BUILDING , FUKUOKA, JAPAN
3.4.1
This building provides an example of an intensive green roof system. The Asian Crossroads Over the Sea
(ACROS) building in crowded Fukuoka offsets the impact of its development on the adjacent Tenjin
Central Park with a series of elaborate stepped green roofs. The project is an articulate fusion of public
and private space, which more than doubles the size of the park whilst creating over one million square
feet of multipurpose space, including a museum, a theatre, shops and offices.
Figure 3.4 Intensive Green Roofs on the ACROS Office Block Building, Fukuoko, Japan
This building was designed for maximum greening and integrates with the Park below. The effect is reminiscent of the
hanging gardens of Babylon. (Source and copyright © Earth Pledge, 2005)
3.4.2
The city-owned land was the last large undeveloped plot in central Fukuoka and is next to the only park in
the area. The city chose to develop the site in a joint venture with private enterprise. The goal was to
create new public land equal to that lost to the development. The north face of the building is traditional,
with a formal entrance onto one of the most prestigious blocks in the city. On the south side, 15 vegetated
terraces climb the full height of the building. Each floor has landscaped gardens for meditation, relaxation
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and escape from the congestion of the city below. The top terrace is a grand belvedere, with views of the
bay of Fukuoka and the surrounding mountains. A series of reflecting pools are connected by water jets,
creating a climbing waterfall that masks the ambient noise of the city.
3.4.3
The design reconciled the developer’s desire for profitable site use with the public need for open space.
The nearby park and the ACROS building are visually and physically integrated, demonstrating how a
major building complex can co-exist with public green space.
Figure 3.5 Close-up view of Intensive Green Roofs on the ACROS Office Block Building
Roof-top utilities are bounded by walls covered in greenery. (Source and copyright © Earth Pledge, 2005)
3.4.4
3.4.5
(21)
In 2001, elaborate building heat measurements were taken which have helped to prove conclusively that
building efficiency, the surrounding areas, and the urban heat island effect can indeed be positively
influenced by architecture and urban forms that embrace greenery 21.
Green roof characteristics are as follows:
♦
♦
♦
♦
♦
♦
♦
21
Area:
Roof Coverage %:
Soil Depths:
Construction year:
Client:
Architect:
Landscape Architect:
9300 m² (100 000 ft²)
80%
300mm to 600mm
1995
Dai-Ichi Mutual Life Mitsui Real Estate
Emilio Ambasz
Niho Sekkei Takenaka Corporation
http://www.takenaka.co.jp/takenaka_e/news_e/pr0108/m0108_05.htm
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Green Roof Architecture
3.4.6
The ACROS building in Fukuoka, Japan illustrates the first steps in a new architectural approach where
buildings are shaped specifically to accommodate green roofs. If the complete benefits of green roofs are
to be realised for a city then a new kind of architecture, as implemented at ACROS, needs to be invented
that would maximise the amount of greenery a building can facilitate. It would need to be an architectural
style that does not see greenery as the amenity decorations for the incidental space left over on the site
or the incidental horizontal space created by its roof. Instead, an architectural style is needed that
integrates and welcomes the landscape in a truly ‘symbiotic’ relationship, where the building benefits as
much from the integration as the open space does. Looking closely at the ACROS building, the following
design principles can be observed:
♦ The architecture responds to the landscape below, respecting the scale of the park users below,
rather than boxing them in.
♦ The outer surface area of the building is maximised to accommodate greenery.
♦ Adequate natural lighting can still enter the building.
♦ Greenery on the building is designed to be visually accessible from ground level.
♦ The stepped layout allows for large planting to be installed without the danger of anything being
blown off and falling far to the ground.
♦ The stepped layout provides sound insulation to the sides of the building, not just the top.
♦ The stepped layout allows for easy access for building occupants and maintenance staff.
♦ Even the rooftop utility buildings have extensive green roofs installed. These are also screened
with a green wall (low enough for maintenance considerations).
Figure 3.6 Conceptual Architecture for Green Roofs
(Source and copyright © Urbis Ltd, 2006)
(LEFT) Menara Mesiniaga, Kuala Lumpur, Malaysia, 1992 (RIGHT) Hitechniaga HQ Tower, Malaysia (1995, not built)
(Source: Adapted from ‘Rethinking the Skyscraper – The Complete Architecture of Ken Yeang’.)
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3.5
ROPPONGI HILLS, TOKYO, JAPAN
3.5.1
This building provides examples of both intensive and extensive green roof systems. Roppongi Hills is an
experimental urban development in the heart of Tokyo. The complex was envisaged as a way to revitalize
a depressed downtown enclave, not only through economic development, but also by adding much
needed green space in a city that suffers from intense urban heat island effect. The Tokyo Metropolitan
Government worked with the developer Mori Building Company to design Roppongi Hills as an
entertainment district and a lush garden neighbourhood in the heart of the city.
Figure 3.7 Intensive and Extensive Green Roofs on the Roppongi Hills Main Building
This green roof includes intensive and extensive green roofs, arranged so that the public space is not obstructed by utilities.
(Source and copyright © Earth Pledge, 2005)
3.5.2
The area’s skyscrapers maximise the available space for housing, offices, and entertainment in the dense
city centre. Site planners were creative in their use of greenery, knitting together the complex with a
network of pathways, gardens, and green roofs. In a city with only 14% green space, Roppongi Hills has
twenty-six percent of its land area planted with vegetation.
3.5.3
The Keyakizaka complex rooftop boasts a rice paddy and vegetable plot, while the Sakurazaka roof
exhibits public art and street furniture in a garden setting. There is a 4000m² (43,000 ft²) traditional
Japanese garden, and most of the residential area is designed in a blended Japanese-British style.
Almost all the buildings, including the Asahi Television tower and the Virgin Cinema complex, have green
roofs. The variety of landscaping on the Rappongi Hills buildings showcases the potential for inventive
green and vertical urban development.
3.5.4
Green roof characteristics are as follows:
♦
♦
♦
♦
Area:
Roof Coverage %:
Soil Depths:
Construction year:
13000 m² (143 000 ft²)
26%
30mm to 1200mm (1.17 - 46.8 in)
2003
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♦
♦
♦
Client:
Architect:
Landscape Architect:
Roppongi 6 Chrome Redevelopment Association
Conran & Partners, JPI, KPF, and Mori Building Company
Yohji Saski & Dan Pearson
Figure 3.8 Intensive Green Roofs at Roppongi Hills, Tokyo
This green roof includes traditional rice fields.
(Source and copyright © Earth Pledge, 2005)
Buildings, footbridges and podium gardens are connected.
(Source and copyright © Earth Pledge, 2005)
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3.6
TAI LUNG LABORATORY, HONG KONG
3.6.1
This building provides an example of an intensive green roof system. Sustainability was critical to the
design of this building and included:
♦
♦
♦
♦
3.6.2
Arranging the building forms to harmonise with the site profile. They were also arranged to
optimise solar exposure as well as prevailing winds.
Keeping the building footprint as small as possible to minimize disturbances to the existing slope.
Arranging all building blocks to avoid felling existing mature trees.
Providing Roof-gardens and landscaped terraces which compensate for the trees felled.
The two-storey complex included; 8 laboratories for conducting a wide range of veterinary experiments,
2x level-three bio-safety laboratories (with supporting facilities to handle animal carcasses and to perform
post-mortem operations) and office accommodation and ancillary facilities for staff and technicians.
Figure 3.9 Intensive Green Roofs at Tai Lung Laboratory, Yuen Long, Hong Kong
Organic forms, natural materials and rooftop gardens were synthesized into a building that respects nature, minimises impacts
and compensates for losses. (Source and copyright © ArchSD, 2002)
(Source and copyright © ArchSD, 2002)
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(Source and copyright © ArchSD, 2002
3.6.3
Green roof characteristics are as follows:
♦ Areas:
400m² (of 780m² possible roof area, site area 2800m²)
♦ GFA:
1,107m²
♦ Roof Coverage %:
51%
♦ Soil Depths:
360mm
♦ Construction dates:
2002
♦ Clients:
AFCD (project manager: ArchSD)
♦ Architect &
Architectural Services Department
♦ Landscape Architect: Architectural Services Department
3.7
GUANGZHOU GREEN ROOFS, GUANGDONG, CHINA
3.7.1
These buildings provide examples of retro-fitted extensive green roofs in the Guangdong region and
demonstrate a particular Sedum cultivar suited for conditions similar to those found in Hong Kong. These
examples appear to be showcase examples for the Chinese Government.
3.7.2
Emulating the extensive green roofs seen is Europe and Germany is dependent on finding plant material
which functions in much the same way (i.e. such as Sedums). Various local conditions (climate, typhoon
winds, vigour of local invaders, etc., as described in Section 4.4) make this a difficult exercise. However,
a cultivar of Sedum lineare has been developed in Guangzhou which shows promising results in
conditions very similar to Hong Kong.
Figure 3.10 Specialized Sedum Cultivar
(Source by Urbis Ltd., and copyright © ArchSD, 2006)
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3.7.3
This cultivar was derived from a plant species in Hunan province and has been developed over the last
10 years in Guangdong to suit local conditions and for a better aesthetic appearance. The original plant
species was leggy and sparse. The cultivar has been commercially available for the last 4 years. Like
Sedums in other parts of the world the cultivar appears robust and capable of withstanding harsh
conditions.
3.7.4
The main advantages of this cultivar are that:
♦ It establishes itself easily and fast, and is transported easily without soil. Early cost estimates
were quoted at HK$ 250/m², (including delivery, waterproofing, water retention layer, special soil
substrate, LECA drainage layer, and 3 months establishment maintenance)
♦ It grows on very thin soil substrates: 50-60mm
♦ It tolerates temperature extremes
♦ It prefers direct sunlight
♦ Minimal maintenance required
♦ It can apparently withstand long periods without watering and can also tolerate long periods being
water-logged.
♦ It can apparently tolerate varying soil conditions, but naturally prefers alkaline soils.
♦ It appears very vigorous and out-competes other invaders
3.7.5
The main disadvantages are:
♦ It is a single colour (grass green) and does not flower in the Hong Kong climate where it does not
get enough winter cold or long nights to trigger its reproductive/flowering mode.
♦ It does not tolerate being trodden on, taking more than a week to recover
♦ It is very vigorous and may out-compete other roof-top species
♦ It occasionally reverts to its old form requiring minimal maintenance to pluck those forms out.
3.7.6
This cultivar has apparently also been successfully installed in numerous cities in China, and is illustrated
below in three different sites in Guangzhou.
♦
♦
♦
SITE A: Feng Huang Shan Hostel and adjacent residential buildings, initiated by Guangdong
Province Agricultural Department Enterprise Unit.
SITE B: Guang Wei Lu residential buildings, initiated by Yue Xiu Municipal People's Government.
SITE C: Dong Wang Market and adjacent residential buildings, initiated by Bai Yun Municipal
People's Government.
Figure 3.11 Site A – Feng Huang Shan Hostel and Adjacent Residential Buildings
Sedums planted are 4 years old and show no signs of dying back or of being taken over by invaders (Source by Urbis Ltd.,
and copyright © ArchSD, 2006)
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Figure 3.12 Site B – Guang Wei Lu Residential Buildings
Examples in these locations are surviving in the heart of the city
(Source by Urbis Ltd., and copyright © ArchSD, 2006)
Figure 3.13 Site C – Dong Wang Market and Adjacent Residential Buildings
This example shows Sedums planted with bands of Rhoeo discolour for aesthetic effect. The Sedum is vigorous and is outcompeting the Rhoeo. More effective techniques will need to be developed if combinations of species are proposed in the
design. Due to its low tolerance for being trodden on, access paths need to be incorporated into the design of this type of
green roof.(Source by Urbis Ltd., and copyright © ArchSD, 2006)
3.7.7
Green roof characteristics for the 3 sites are as follows:
♦
♦
♦
♦
♦
Areas:
Roof Coverage %:
Soil Depths:
Construction dates:
Clients:
6000m², 3500m², and 23000m²
95%, 95% and 95%
30-40mm, 30-40mm, and 60mm to 80mm
May 2002, September 2005, and February 2006
Guangdong Province Agricultural Department Enterprise Unit, Yue Xiu
Municipal People's Government, and the Bai Yun Municipal People's
Government.
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Figure 3.14 Example of Sedum Lineare in Shenzhen
(Source and copyright © Yu Yu Environmental Protection Science and Technology Co. Ltd, 2006)
3.8
IFC2, HONG KONG
3.8.1
This building provides a local example of an intensive green roof system.
3.8.2
The IFC2 development contributes a number of open spaces which enhance the public realm of the
Central Business District. These comprise large urban public open spaces, two of which are Designated
Public Open Spaces and are accessible 24-hours a day.
3.8.3
The Second Public Open Space comprises a Podium Garden at Level 4, and the Harbour-side Terrace at
Level 3. Both the garden and the terrace serve community needs for more passive recreation spaces in
the Central Business District, and are fully integrated with adjoining retail and entertainment uses in the
retail podium.
3.8.4
As usable urban public open space is highly prized in the Central Business District, the usability of the
public open space is maximised by minimising low planting and planters which visually and physically
break up the space and inhibit free pedestrian circulation. ‘Greening’ is provided in the form of a series of
raised lawns, which can be used as informal recreation areas, and groves of semi-mature trees which
will, in time, create a virtually continuous shade canopy.
3.8.5
Selected trees comprise blocks of dark-foliage semi-mature Ficus altissima at the podium edge, and
larger blocks of light green foliage semi-mature, semi-deciduous Ficus rumphii which provide light shade
to seating areas. Cerbera manghas are planted along the Harbourside Terrace, and Plumeria rubra on
the roof of the retail bridges.
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Figure 3.15 Roof Garden at IFC2 Showing Trees, Seating and Water features
(Source and copyright © Urbis Ltd., 2006)
(Source and copyright © Urbis Ltd., 2006)
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Figure 3.16 Roof Garden at IFC2 Showing Lawned Areas and Cafeterias
(Source and copyright © Urbis Ltd., 2006)
3.8.6
Green roof characteristics are as follows:
♦
♦
♦
♦
♦
♦
Area:
Soil Depths:
Construction year:
Client:
Architect:
Landscape Architect:
13000 m²
600mm to 1200mm
2003
Central Waterfront Property Development Ltd.
Rocco Design Ltd
Urbis Limited
Figure 3.17 Plan of Roof Gardens at IFC2
Plan showing two public open spaces created as part of this private development (Source and copyright © Urbis Ltd., 2006)
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4
FINDINGS OF DESKTOP RESEARCH
4.1
REVIEW OF INTERNATIONAL APPROACHES, STANDARDS, AND COVERAGE OF GREEN ROOFS
Overseas Policy Approaches
4.1.1
Worldwide, green roof policies are not prescribed at a national level. However, it is often the case that
municipal regulations are borne from directives initiated at top level. This appears to be the case in
Germany, Canada, the USA, and Japan.
4.1.2
Germany has led the development of green roofs, particularly extensive green roofs. There are four
general categories municipal policies and incentives in operation in Germany 22, many of which have been
in place for over a decade:
♦
♦
♦
♦
4.1.3
(22)
Direct Financial Incentives. These financial incentives customarily take the form of subsidies
available to property owners and developers who build green roofs. As an incentive, this
approach can be tailor-made for any jurisdiction. It does not force property owners to create
green roofs; they act voluntarily through clear economic gains and are still encouraged to retrogreen existing buildings. It is an incentive that operates on a clear per square metre basis and is
proportional to the environmental benefits.
Indirect Financial Incentives. This approach uses Split Wastewater Fees and targets the storm
water runoff problem created by impervious buildings. Sewers collect wastewater from both
sanitary disposal and also storm-water disposal. This system provides monetary discounts to the
storm-water part based on the storm-water infrastructure savings that green roofs contribute. It
requires municipalities to split the municipal rates.
Ecological Compensation Measures. This is a policy that stems from the German “Intervention
Rule” which is based on the Federal Building Code, the Federal Nature Conservation Act, and the
Environmental Impacts Assessment Act. The Intervention rule is a decision-making process
applied at the land-use and development level. It follows a set of questions and prioritised options
aimed at complete restoration of natural balances that are disrupted. Avoidance, Minimization,
Compensation and Replacement are the terms used and are not unlike Hong Kong’s EIAO. In
Germany green roofs may be used in the Compensatory option but are very specific to what the
roof is compensating for and has proven difficult to monitor over the long term.
Integration into Development Regulations. Integrating development regulations is another tool
available to increase the coverage of green roofs. Local authorities may include green roofs in
their development regulations based either on Ecological Compensation Measures or based on
the German Federal Building Code. In some instances compulsory measures can be more
effective than voluntary incentives though typical protests against perceived additional costs may
be encountered. Its main benefit is that it requires no direct monetary input from government,
though monitoring may still incur an expense. Density bonus regulations (green roofs as
compensation for higher density) can also be integrated into development plans according to the
Land-Use Regulation. From the German experience, introducing regulations into new
development areas has proven especially effective while applying it to existing areas as retro-fit
projects has been difficult.
Apart from regulations and incentives, there are numerous other tools available to municipal authorities to
encourage green roofs. These include:
22
Ngan, (2004)
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♦
♦
♦
4.1.4
Competitions and Media Coverage,
Leading by Example - Greening Public Buildings, and
Performance Rating Systems.
Toronto has been pro-active in encouraging green roofs by installing green roofs on its municipal
department buildings, helping the green roofs industry, and embarking on a free green roofs advice
educational campaign.
City Policy Case Studies
Policy Case Study No. 1 - Portland, Oregon
4.1.5
In Portland, the motivation for developing green roofs has been concern about water pollution from
combined sewer overflow (CSO), particularly in light of major pollution of the Willamette River 23. Portland
promotes green roof development through a number of policies, but requires green roofs only on public
buildings. Portland has implemented the following strategies:
♦
♦
♦
♦
♦
♦
♦
♦
4.1.6
(23)
All new City-owned buildings are required to be built with a green roof that covers at least 70% of
the roof. The remaining roof area must be covered with Energy Star rated roofing material. When
practical, all roof replacements must also include a green roof. The City has internal green
building consultants to assist City buildings in meeting green building policy objectives. Most
public green roof projects have been financed by storm-water fees (see below).
The City Zoning Code offers developers floor area bonuses when they implement stipulated
options, like a green roof. The bigger the proportion of green roof coverage, the larger the bonus
offered. The owner must sign an agreement ensuring proper roof maintenance (although proper
long-term maintenance continues to be a concern).
Portland levies a storm-water management charge for commercial, industrial, and institutional
rate-payers that is based on the amount of impervious area on site (US$6.45 per 1000 square
feet of hard surface per month). There is an initiative under consideration to reduce charges by
35% for owners who install green roofs with coverage of at least 70%. Residences are charged
for storm-water management at a flat rate.
In the Central City District, developments must comply with architectural design guidelines, and
are subject to a general design review process prior to approval. A green roof in a design is
considered an asset and will assist the proposal being approved.
Portland provides education and outreach on green roof development, by providing technical
assistance to building owners and guided tours of green roofs. It also monitors green roofs.
Portland has funded green roof demonstration exhibits and test sites.
Green roofs are formally recognized as a Best Management Practice in the City’s storm-water
manual.
A citizens’ group called “Eco-roofs Everywhere” promotes green roof development for lower
income areas. It creates affordable demonstration projects, secures grants for small-scale
developments, and negotiates lower prices with vendors.
These efforts have been effective in promoting green roofs - Portland is considered one of the North
American leaders in green roofs. There were approximately 2 acres (0.81 ha) of green roofs in Portland in
2005, with about another 2 acres (0.81 ha) committed to be built. The City of Portland has promoted
23
City of Toronto Discussion paper (2005)
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green roofs so effectively that the private sector and some private citizens are starting to build or install
them on their own initiative. However, green roofs have not yet taken off in the industrial sector.
Table 4.1 Extract from Portland’s Zoning Code
33.510.210 Floor Area and Height Bonus Options
C.4
Rooftop gardens [Intensive Green Roofs] option. ……. For each square foot of rooftop garden area, a
bonus of one square foot of additional floor area is earned. To qualify for this bonus option, rooftop gardens
must meet all of the following requirements.
a.
b.
The rooftop garden must cover at least 50 percent of the roof area of the building and at least 30
percent of the garden area must contain plants.
The property owner must execute a covenant with the City ensuring continuation and maintenance of
the rooftop garden by the property owner. The covenant must comply with the requirements of
33.700.060.
C.10. Eco-roof [Extensive Green Roof] bonus option. Eco-roofs are encouraged in the Central City because they
reduce stormwater run-off, counter the increased heat of urban areas, and provide habitat for birds. An ecoroof is a rooftop stormwater facility that has been certified by the Bureau of Environmental Services (BES).
Proposals that include eco-roofs receive bonus floor area. A proposal may not earn bonus floor area for both
the eco-roof option and the rooftop gardens option; only one of these options may be used.
a.
b.
c.
Bonus. Proposals that include eco-roofs receive bonus floor area as follows:
(1) Where the total area of eco-roof is at least 10 percent but less than 30 percent of the
building’s footprint, each square foot of eco-roof earns one square foot of additional floor area.
(2) Where the total area of eco-roof is at least 30 percent but less than 60 percent of the
building’s footprint, each square foot of eco-roof earns two square feet of additional floor area.
(3) Where the total area of eco-roof is at least 60 percent of the building’s footprint, each square
foot of eco-roof earns three square feet of additional floor area.
Before an application for a land use review will be approved, the applicant must submit a letter from
BES certifying that BES approves the eco-roof. The letter must also specify the area of the eco-roof.
The property owner must execute a covenant with the City ensuring installation, preservation,
maintenance, and replacement, if necessary, of the eco-roof. The covenant must comply with the
requirements of 33.700.060.
Policy Case Study No. 2 - Chicago, Illinois
4.1.7
In Chicago, the motivation for developing green roofs is concern about the urban heat island (UHI) effect,
air quality and its effects on public health, and aesthetics 24. The Mayor has been a strong advocate of
green roof development. Chicago has a variety of policies and programs that encourage green roof
development, specifically:
♦
♦
(24)
24
The 2001 Regulation called the Energy Conservation Code requires that all new and retrofitted
roofs should meet minimum standards for solar reflection (0.25 reflectance). Chicago’s Bureau of
the Environment deemed that green roofs are an acceptable way to lower roof reflectivity,
mitigate UHI and improve air quality.
A “Building Green/Green Roof” policy applies to construction projects that receive public
assistance or certain projects that are subject to review by the Department of Planning and
City of Toronto Discussion paper (2005)
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♦
♦
♦
♦
♦
♦
4.1.8
Development. Through this policy, the City of Chicago grants a density bonus option to
developers whose buildings have a minimum vegetative coverage on the roof of 50% or 2000 sq.
feet (whichever is greater), usually in the form of a green roof.
Chicago has various City-sponsored green roofs, including demonstration sites, test plots, and
others. The City has partnered with green roof providers to build and compare test plots that use
different kinds of plants and material. It has issued a report on some of its findings.
Chicago has engaged the Chicago Urban Land Institute, a non-profit organization of real estate
professionals, in seminars and surveys. This helped to determine which kinds of incentives would
encourage green roof development.
Chicago offers a storm-water retention credit for green roofs, but does not levy a storm-water
impact fee.
The City has a website that supports green roof installation, and provides information and
technical assistance.
In 2005, Chicago offered a limited number of US$5,000 (HK$40,000) grants for building smallscale residential or commercial green roofs.
There was no requirement in 2005 for green roofs in the private sector.
As of June 2004, Chicago had more than 80 green roofs over municipal and private buildings in various
stages of installation. The total area of these roofs is over 1 million square feet (9.3 ha).
Policy Case Study No. 3 - Basle, Switzerland
4.1.9
In Basle, the motivation for developing green roofs is an interest in energy savings, and promoting
protection of biodiversity 25. Basle has promoted green roof development through a number of policies,
specifically:
♦
♦
♦
♦
In the mid-1990’s, after a public poll found general support for an electricity tax to promote energy
saving measures, and after consultation with stakeholders, Basle invested 1 million SFr.
(HK$6.4M) from electricity fees into a two-year incentive programme, providing a subsidy of 20
SFr./m² (HK$128/m²) of green roof. Another programme like this is planned for 2005/06
Since 2002, building regulations stipulate that all new and renovated flat roofs must be greened to
provide valuable habitat (primarily for invertebrates), using specified materials.
Basle provided a grant for research on the biodiversity protection benefits of green roofs. The
results of this study shaped the design specifications for green roofs in Basle.
Basle promoted the programme by holding a contest for the best looking green roof.
4.1.10 In 1996/7, there were 135 applicants for the green roof subsidy, and 85,000m² of roof-scapes were
greened, resulting in 4 GW/year of energy savings. As a result of the regulations for new and renovated
flat roofs, 15% of flat roofs in Basle have been greened. Basle is now exploring ways of enforcing proper
green roof quality.
4.1.11 Basle’s incentive programme concentrated efforts into a two year period, thereby raising the profile of
green roofs in the City. The incentive programme was well received, media interest was high, and Basle
received nationwide prominence as a result.
4.1.12 Basle’s green roof regulations did not meet with any significant resistance, because all stakeholders were
involved in the process from the beginning, and because of the success of the incentive programme.
(25)
25
City of Toronto Discussion paper (2005)
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Policy Case Study No. 4, Munster, Germany
4.1.13 In Munster, the motivation for developing green roofs has primarily been concern about storm water
management, and also interest in increasing green space 26 . Munster has promoted green roof
development through a couple of policies/programs:
♦
♦
Munster charges a storm-water fee, according to the amount of storm-water that runs off a
property and into the sewer system (i.e. if there is no run-off, there is no fee). The fee is reduced
by 80% or more when a green roof is installed. To implement this program, the Public Works
department sends property owners a bill stating the amount of pervious and impervious surface
area on the property, with the corresponding storm-water fee. The fees are used for maintenance
of the sewer system.
Munster has also had an evolving incentive programme for a variety of environmental measures
that can include green roofs. Subsidies were provided for green roof development, but this
programme ended in 2002, due to financial constraints.
4.1.14 Munster’s incentive programme was effective, resulting in a total of approximately 12,000m² of green roof
coverage by the end of the programme.
4.1.15 The storm-water fee has also been very successful, and it has been accepted well by the community,
however specific information about additional green roof development resulting from the fee is not yet
available. This programme does have a considerable administrative component, as pervious and
impervious areas for each property must be determined, verified, and in the case of adjustment,
reassessed. Costs for administration can be offset by the fee.
Policy Case Study No. 5, Stuttgart, Germany
4.1.16 In Stuttgart, the motivation for developing green roofs has primarily been concern about air quality, since
the city is situated in a basin-like valley where pollution tends to settle 27. Urban growth that has removed
vegetation from surrounding slopes has exacerbated the problem. There is also interest in mitigating
urban heat island effect. Stuttgart promotes green roof development in three ways:
♦
♦
♦
Stuttgart is greening the roofs of its public buildings. It has an annual budget allocation for green
roof development, and most green roofs are installed when the roof is due to be replaced.
Stuttgart has provided a financial incentive for green roofs since 1986. The programme has the
equivalent of HK$567,000 available each year, and pays for 50% of costs, or a maximum of the
equivalent of HK$196/m² of roof. The City provides a free consultation and a comprehensive
brochure to property owners explaining how to install green roofs.
Stuttgart has regulation requiring all flat and slightly sloped roofs (up to 12 degrees) of new
development to be extensively greened to certain standards. Trade-offs or compromises with
developers are common in the roof greening process.
4.1.17 All three approaches have been successful. 105,000m² of public roofs have been greened, and 55,000m²
of roofs have been greened through the incentive programme. No data is available on the amount of roofs
greened through regulation.
Policy Case Study No. 6, Toronto, Canada
4.1.18 After numerous investigations of other cities around the world, Toronto has recently embarked on its own
policies towards green roofs 28. These are generally motivated by all green roof benefits; the potential to
(26)
26
City of Toronto Discussion paper (2005)
(27)
27
City of Toronto Discussion paper (2005)
(28)
28
Toronto Policy and Finance Committee Agenda Meeting No.1, Jan 2006
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mitigate impacts on storm-water quality and quantity, improves buildings energy efficiency, reduces the
urban heat island effect, improves air quality, beautifies the city, provides natural green spaces in built-up
areas, holds grounds for gardening, food production and horticultural therapy, and increases passive
recreational space in densely-populated neighbourhoods. Toronto supports green roofs through various
initiatives:
♦
Toronto has stipulated that green roofs (with coverage of 50% - 75% of the building footprint) be
constructed on all new and existing City-owned buildings.
♦ Toronto has begun adapting its zoning by-laws and regulations relating to site plan control
applications to achieve green roofs.
♦ Toronto has begun with direct financial incentives programme for the retro-greening of existing
buildings. Pilot incentive programs in this regard have begun.
♦ Toronto has stipulated that a ‘green roofs resource person’ is identified in each of the municipal
divisions (Buildings, City Planning, Water, Facilities and Real Estate, Shelter, Support and
Housing Administration, and Technical Services).
♦ Toronto has actively embarked on a green roofs education and publicity campaign. These include
technical booklets on construction and maintenance, holding workshops for developers and
building owners, staff training, listing green roof suppliers and contractors, and establishing a
green roof ‘one stop shopping’ page on the city’s official website.
♦ Toronto has also added an element of competition to its green roofs drive by adding Green Roofs
as a Category for the Green Toronto Awards and has invited the Green Roofs for Healthy Cities
to hold its 2008 international conference in Toronto to highlight its showcase examples.
4.1.19 Toronto’s enthusiastic approach is very new (January 2006). The effectiveness of its approach should be
reviewed after it has been in place for some time.
4.1.20 Prior to the above-mentioned policies, Toronto hired a team from Ryerson University to undertake a study
of the municipal level benefits and costs of implementing green roof technology in Toronto. 29 The team
conducted an extensive literature review to identify and quantify the benefits related to green roofs. It also
collected information on the types of buildings in Toronto and their geographic distribution. The
information collected was modelled and applied to an inventory of existing flat roofs within the City for
aggregating the benefits on a citywide basis. The team also developed a method to compute the
monetary value of the benefits. A survey of the existing green roof technologies and standards was
carried out to improve upon the development of minimum requirements for green roofs.
4.1.21 The study quantified some of the many benefits associated with green roofs, based on currently available
research data, but recognized that the benefits that were not quantified (such as aesthetic improvement
of the urban landscape, increases in property values, use of green roofs for food production, and
increased bio-diversity) still have value. The study quantified the benefits from storm water flow reduction
- including impacts on combined sewer overflow (CSO), improvements in air quality, reductions in direct
energy use, and reductions in urban heat island effect. The benefits on a citywide basis were calculated
based on the assumption that 100% of available green roof area would be used. The available green roof
area included flat roofs on buildings with more than 350m² of roof area, assuming that at least 75% of the
roof area would be greened. The total available green roof area citywide was determined to be 5,000
hectares (50 million m²). The benefits were determined as initial cost savings related to capital costs, plus
a level of annual cost savings. These are shown in the table below.
(29)
29
Ryerson University, Environmental Benefits and Costs of Green Roof Technology for the City of Toronto, Oct 2005
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Table 4.2 – Cost Benefits analysis in Toronto (in CAD$)
Benefits
Initial Cost
Savings
Annual Recurrent
Cost Savings
Storm water
̇ Alternate best management practice cost avoidance
$79,000,000
̇ Pollutant control cost avoidance
$14,000,000
̇ Erosion control cost avoidance
$25,000,000
Combined Sewer Overflow (CSO)
̇ Storage cost avoidance
$46,600,000
̇ Reduced beach closures
$750,000
Air Quality
̇ Impacts of reduction in CO, NO2, O3, PM10, SO2
$2,500,000
Building Energy
̇ Savings in annual energy use
$21,000,000
̇ Cost avoidance due to peak demand reduction
$68,700,000
̇ Savings from CO2 reduction
$563,000
Urban Heat Island
̇ Savings in annual energy use
$12,000,000
̇ Cost avoidance due to peak demand reduction
$79,800,000
̇ Savings from CO2 reduction
$322,000
TOTAL
$313,100,000
$37,135,000
(Source: Environmental Benefits and Costs of Green Roof Technology for the City of Toronto, Oct 2005)
4.1.22 The report also presents its assumptions used in calculating City benefits as the minimum design criteria
for a green roof to achieve the stated benefits. The key considerations were that the roof system be
“extensive”, that it cover a significant portion of the roof, have a maximum storm-water run-off co-efficient
of 40%, and have a growing medium depth of at least 150 mm, where structural loads permit. Green roofs
with shallower growing media could be used on roofs where structural loading does not permit the 150
mm. depth, although it would be recognized that the benefits would be reduced.
4.1.23 Green roofs are an emerging technology and some questions need further exploration. These include
uncertainty related to some of the calculated benefits, the impact of less than 100% green roof coverage,
the impact of building-specific constraints, quantification of other social benefits and consideration of the
effectiveness of alternative technologies to green roofs. Moreover, the calculation of City program costs
would allow a complete cost benefit analysis of green roofs to the City. These questions are important
and will need to be considered further as the City develops its policy on green roofs. Nevertheless, there
is enough evidence of the benefits calculated in the report to show that there is a case for developing
public programs and promoting green roofs in Toronto.
Policy Case Study No. 7, Tokyo, Japan
4.1.24 After more than five decades of nearly unmitigated growth, only 14% of Tokyo’s land area remains green.
In fact, Tokyo has the lowest green-space-to-impermeable-surface ratio of any major metropolis. The
resulting heat island effect has caused Tokyo’s temperatures to increase at a rate five times faster than
global warming. Tokyo was once a temperate seaport but has become ever more tropical with the
number of hours above 30°C tripling. Energy consumption for cooling has increased by 15% from 1990 to
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1998, winters are shorter and the annual cherry blossom festival has been rescheduled due to an earlier
Spring. Palm trees and wild parakeets have appeared and small outbursts of Dengue fever have also
occurred.
4.1.25 In 2001 an Environment Ministry study found that the high ratio of impermeable heat absorbing surfaces
directly contributed to the city’s warming. In the face of intolerable temperatures, environmental and
health concerns, and a land-use policy that was impossible to change at this stage, the city turned to
green roofs as a solution. The urban heat island effect is therefore the city’s prime reason for establishing
green roofs.
♦
Tokyo began with an informal incentive program that provided a free consulting service. This was
followed by a subsidy program which resulted in 7000m² of rooftop greening.
♦ Tokyo then accelerated the process by mandating that all new-construction buildings were to
have green roofs. Private buildings larger than 1000m² and public buildings larger than 250m²
must green 20% of the rooftop or pay an annual penalty of US$2000. In the first year (2000 to
2001) this law had a dramatic effect - it doubled the net area of green roofs in the city from
52,400m² to 104,400m². New reports 30 indicate that green roof coverage is now 5 times what it
was in 2000.
♦ Tokyo has also set target goals, with the Green Tokyo Plan aiming at 1,200 ha (12,000,000m²) as
its ultimate goal.
♦ To promote the legislation, the city has constructed a green roof demonstration on the Tokyo
Council Building and other facilities.
4.1.26 Although the laws are forceful towards new buildings, they have been widely accepted by industry, an
aspect largely attributed to Japan’s cultural sense of social and civic responsibility. Before the legislation,
numerous surveyed companies were willing to convert to green roofs at their own expense. After the
legislation, full compliance has been found with no penalties issued.
4.1.27 Encouraged by improvements, the Japanese government has followed Tokyo’s lead. In 2003 the Ministry
of Land, Infrastructure and Transport announced revisions to the national nature conservation
regulations, mandating that all new constructions (multiple dwelling houses and offices buildings) green at
least 20% of their rooftops. This law went into effect in 2005.
Overseas Green Roof Standards and Regulations
4.1.28 As a means of successfully establishing Green Roof technologies in Hong Kong, the American Society for
Testing Materials (ASTM) has developed numerous testing regulations that may be suitable. Some of the
standards relevant to Green Roofs include:
♦
♦
♦
♦
♦
♦
♦
(30)
30
WK575 Practice for Assessment of Green Roofs
WK4235 Standard Guide for Selection, Installation, and Maintenance of Plants for Green Roofs
WK4236 Standard Practice for Determination of Dead Loads and Live Loads associated with
Green Roof Systems
WK4237 Standard Test Method for Water Capture and Media Retention of Geocomposite Drain
Layers for Green Roofs
WK4238 Standard Test Method for Maximum Media Density for Dead Load Analysis of Green
Roofs
WK4239 Standard Test Method for Saturated Water Permeability of Granular Drainage Media
[Falling-Head Method] for Green Roofs
WK5566 Standard Guide for General Principles of Sustainability Relative to Buildings
Oriental Daily, 25 September 2006
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♦
WK7319 Standard Guide for Use of Expanded Shale, Clay or Slate (ESCS) as a Mineral
Component in Growing Media for Green Roof Systems.
4.1.29 A more established green roof standards publication is the Guideline for the Planning, Execution and
Upkeep of Green Roof Sites, provided by the FLL (Landscape Research, Development & Construction
Society) in Germany. This guideline was initiated by the German Ministry of Planning, Building
Construction and Urban Areas who gave the FLL the responsibility of researching cost effective methods
for extensive and simple intensive green roofs. The guidelines were first published in 1990 and were
revised in 1995 and 2002 to incorporate latest technologies. It is now widely accepted as a technical
standard and is regularly referred to by the German DIN Standard. It covers the following topics:
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
Waterproofing;
Structural Loading;
Protection against root penetration;
Protection against mechanical damage;
Protection against corrosion;
Joints and borders;
Protection against emissions (such as on vent buildings);
Wind loads;
Fire Protection;
Protection against slipping and shearing;
Trafficable paved surfaces;
Landscape furniture (trellises, pergolas, lighting, ponds, etc);
Working layers: soil substrate, filter layer, drainage layer, protection layer, root barrier, separation
layers, anti-bonding layers;
Construction techniques;
Water retention (maximum water capacity, water permeability, discharge co-efficient, etc.);
Water storage and additional watering;
Drainage Layer (materials and types, physical requirements, granule size, structural stability,
behaviour under compression, water permeability, pH, carbonate content, salt content and
construction);
Filter Layer (materials and types, physical requirements, weight, cut-through strength, filtration
effectiveness, susceptibility to root penetration, weathering, resistance to soil-borne solutions and
micro-organisms, tensile strength, flexibility, frictional co-efficient, and construction);
Soil substrate (materials and types, physical requirements, granule size, organic content,
structural stability, behaviour under compression, water permeability, water storage capacity, air
content, pH, carbonate content, salt content, nutrient content, weed content, foreign substances,
and construction);
Application of Vegetation;
Erosion Protection;
Final care and readiness for handover;
Subsequent upkeep and maintenance
Warranties and periods of limitation;
Testing and monitoring methods; and
Reference Values for design loads.
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4.1.30 There are currently no existing British Standards for Green Roofs but the Construction Industry Research
and Information Association (CIRIA) is due to produce a Building Green report in late 2006 31. (CIRIA is a
not-for-profit organisation whose mission is to improve the performance of all concerned with construction
and the environment. This UK organisation works with industry to develop and improve practice, leading
to better performance by creating, sharing, and supporting the application of information and knowledge
across four research themes.)
Percentage distribution of green roofs in Hong Kong and Southeast Asian cities
4.1.31 It appears that no information exists on the percentage distribution of green roofs in Hong Kong.
4.1.32 In Shanghai green roof coverage has increased from 120 000m² to 450 000m² from 2003 to the end of
2005. Early research in Shanghai shows that a room temperature difference of 2°C can be expected in
the top floor of any building. This research states that other studies have found room temperature
differences of 4-5°C. 32 Currently about 100 green roof projects are being built in Shanghai 33.
4.1.33 To improve its image during the Olympics, Beijing is sponsoring ¥100/m² for green roofs on buildings
close to olympic venues. Beijing is aiming to achieve 300,000m² coverage per year. Other reports 34 say
that Beijing is hoping to cover 40,000,000m² for the 2008 Olympic Games. It is estimated that 60% of lowrises and 40% of high-rises could be covered.
4.1.34 Chengdu has so far been the most successful green roof city in China with 2 000 000m² already covered.
Conclusion
4.1.35 It should be noted that the above-mentioned standards, incentives and regulations for private and public
application of green roofs vary greatly. They depend on a city’s context, social values and individual case
settings. The International policy approaches quoted above have arisen from their own background of
social or environmental needs such as storm water management in Germany. In Hong Kong, thorough
investigation into community cost and benefits are required before evaluating the need for, and direction
of, policy and regulations.
4.2
REVIEW OF APPROACHES TO GREEN ROOFS IN HONG KONG
Policies in Hong Kong
4.2.1
Existing HKSAR government policies and standards influence the creation of intensive green roofs in the
public and private sector in both direct and indirect ways.
Government Policy on Green Roofs for Public Buildings
4.2.2
The Government’s greening policy is to uplift the quality of the living environment through active planting,
proper maintenance and preservation of trees and other vegetation. The target is to bring about
noticeable improvements in urban greenery, to enhance existing greened areas, and to maximize
greening opportunities during the planning and development of public works projects. In this regard, the
Government’s latest Policy Address 35 reads that “The Government will adopt the concept of greening of
rooftops whenever practicable in the design of new buildings. We are studying the wider application of the
concept with a view to encouraging more projects to adopt this approach.”
(31)
31
CIRIA http://www.ciria.org/buildinggreener/guidance_introduction.htm
(32)
32
ZHAO Ding-guo & XUE Wei-cheng (2005)
(33)
33
Oriental Daily, 26 September 2006
(34)
34
Positive News (Hong Kong Edition), Winter 2006 and http://www.msnbc.msn.com/id/7911618
(35)
35
Paragraph 55 of the Hong Kong Policy Address 2006-2007 http://www.policyaddress.gov.hk/06-07/eng/p52.html
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4.2.3
ArchSD has taken an active role in support of the greening policy and is targeted to provide roof-top
greening as far as possible to all new government building projects subject to the consent of the client
departments undertaking the after-care requirements.
4.2.4
Currently, ArchSD is undertaking this study on “Green roof application in Hong Kong”. The objective of
the Study is to conduct a quick review of the latest concepts and technology on green roofs and to
recommend guidelines adapted to suit local applications in Hong Kong to promote public understanding
and awareness.
Government Incentives to the Private Sector
Joint Practice Note No.1: Green and Innovative Buildings (JPN1)
Joint Practice Note No.2: Second Package of Incentives to Promote Green & Innovative Buildings (JPN2)
4.2.5
JPN1 (Feb 2001, revised Oct 2004) and JPN 2 (Feb2002, revised Feb 2006) are designed by
Government to protect and improve the built and natural environment by promoting the construction of
green and innovative buildings. ‘Green’ in this context refers to wider environmentally friendly
considerations, rather than vegetation.
4.2.6
The objective of the JPNs is to encourage the design and construction of buildings that encompass the
following features:
♦
♦
adopting a holistic life cycle approach to planning, design, construction and maintenance;
♦
maximising the consumption of energy, in particular those non-renewable types; and
♦
maximising the use of renewable resources and recycled / green building material;
reducing construction and demolition waste.
4.2.7
The JPNs set out the initial incentives that Government is providing to encourage the incorporation of
these features, and give guidance on how to apply for them under the Buildings Ordinance, the Lease
Conditions and the Town Planning Ordinance, as appropriate. Government’s intention is that the list of
features is continuously reviewed and expanded to keep pace with ongoing development of green
buildings.
4.2.8
The mechanism by which JPN1 and JPN2 promote certain ‘green features’ is by setting the criteria and
conditions under which these features may, upon application, be exempted from Gross Floor Area (GFA)
and Site Coverage (SC) calculations under the Building Ordinance, Lease Conditions and TPO, with
resultant economic benefit for the developer. ‘Communal Sky Gardens’ and ‘Communal Podium Gardens’
are listed among the green features to be exempted. JPN1 refers to residential developments and JPN2
refers to commercial developments.
4.2.9
However, the adoption of the incentive to include sky gardens has been relatively limited. The statistics
illustrating achievements since the issue of Joint Practice Notes on promotion of green buildings indicate
that between March 2001 and May 2005, only 19 out of 208 approved buildings plans provided
sky/podium gardens, while 191 and 130 came with balconies and utility platforms respectively. It is
surmised that the latter two were perceived by property buyers as usable areas, being private not
communal, and thus more popular.
Practice Note for Authorised Persons and Registered Structural Engineers No. 116 – Amenity Features
(PNAP116)
4.2.10 The purpose of PNAP116 is to provide incentive to private developers to include amenity features that are
not a statutory requirement but which enhance the quality of life for residents and users; encourage
efficient and effective building management; obviate the desire or temptation for unauthorised building
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works; and improve the environmental compatibility with the neighbourhood.
4.2.11 The provision of podium roof gardens and play areas is encouraged in PNAP116. Where these facilities
are under and within the perimeter of a domestic tower, they will be considered for exemption from GFA
calculations.
Indirect Encouragement of Green Roofs in the Public and Private Sectors
4.2.12 The provision of public and private open space in Hong Kong is regulated in accordance with HKPSG,
town plans gazetted under the TPO and private lot Lease Conditions. The HKPSG are non-statutory
guidelines, while the requirements of Lease Conditions and town plans are statutory.
4.2.13 Since there is very limited space available for the creation of such open space at grade, it is sometimes
the case that both Government and the private sector achieve the required open space provision through
the creation of intensive green roofs at podium level.
4.2.14 However, although many intensive green roofs have been provided at podium deck level, relatively few
have been provided at other levels of Hong Kong buildings.
Current Green Roof Construction Practice in Hong Kong
4.2.15 Intensive green roofs (roof gardens) are a well established phenomenon in Hong Kong, usually as
landscape podiums in residential complexes. Many public open spaces are also built either wholly or
partially on structure (e.g. Harcourt Garden). The abundance of roof gardens in Hong Kong is a direct
response to the interaction of several factors, which include:
♦ Hong Kong’s dense urban environment and lack of space for passive and active recreation at
ground level;
♦ a market-driven desire for attractive landscaping of residential and, to a lesser extent, commercial
developments; and, perhaps most importantly,
♦ requirements in Town Planning Conditions and Lease Conditions for private sector property
developers to provide minimum standards of passive and active open space provision and
landscaped amenity within private property developments, which available space within the
development often dictates must be located on structure to a greater or lesser extent.
4.2.16 Extensive green roofs on the other hand, are notably absent in Hong Kong presumably because:
♦ there is no direct government requirement or industry incentive in Hong Kong for private
developers to build extensive green roofs; and
♦ the constraints of building extensive green roofs are perceived by property developers to
outweigh the benefits.
4.2.17 Apart from environmental and amenity benefits, Intensive Green Roofs provide what Hong Kong needs
most - valuable functional open space for human use. It is therefore not surprising that Hong Kong
already has as high a percentage of intensive green roof coverage as any other city. Extensive Green
Roofs, on the other hand, are limited in that they are used overseas mostly to improve the environment
and for building efficiency. Their popularity has yet to catch on in Hong Kong.
4.3
LOCAL ISSUES, CONCERNS, AND RESEARCH
Research on Intensive Green Roofs in Hong Kong
4.3.1
There does not appear to be any detailed organised research done locally into intensive green roofs –
neither into their construction technology, nor into attempting to quantify the benefits derived from them.
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Research on Extensive Green Roofs in Hong Kong
Gammon-Skanska / University of Hong Kong / Chinese University of Hong Kong
4.3.2
A small research project was initiated in 2004 by Gammon-Skanska (G-S) and is being conducted and
monitored by Dr. Sam C.M. Hui, a Building Science Researcher at The University of Hong Kong (HKU),
the environmental engineers at G-S, and latterly also Professor Chiu Siu-wai of the Chinese University of
Hong Kong (CUHK).
4.3.3
The project was initiated by G-S through a desire to moderate the temperatures inside their many site
offices located throughout Hong Kong, thereby creating more comfortable offices for their staff and
providing energy savings. After discussing potential technologies (solar panels, specialised ceramics,
green roofs etc.), G-S and Dr. Hui determined that green roofs would likely be the most successful.
4.3.4
The experimental green roof was installed on the sloping roof (approximately 25° degrees) of a G-S site
office in Tsing Yi (see Figure 4.1) and was designed to be lifted and re-used elsewhere. The growing
trays are 200mm deep and include a formula of Light Expanded Clay Aggregate and Pumice. Traditional
Sedum species were planted at first but these did not do well and were quickly invaded by unsightly
weeds. Consequently, a slow-growing lawn grass species was then planted which has proven far more
successful. With sufficient irrigation (lightly, twice per day with a tap operated drip irrigation system),
growth has been thick and lush and has effectively blocked out invader weeds. Currently, one side of the
roof is being maintained in a neat and tidy condition with irrigation, the other side is being allowed to
develop naturally with no irrigation.
Figure 4.1 Extensive Green Roof Research Project by Gammon-Skanska
Early photos of original Sedum planting before subsequent invasion by grasses and weeds.
(Source and copyright © Gammon-Skanska, 2004)
Recent photos showing one side covered in lawn and the other left to its own resources.
(Source and copyright © Gammon-Skanska, 2006)
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4.3.5
No research papers have been published yet by HKU, but the interim findings have demonstrated that the
energy savings have been worthwhile. Sound insulation tests have also shown a marked improvement.
According to Dr Hui, this experiment, although showing beneficial results pertaining to unique site office
conditions can not readily be extrapolated into usable data for common building conditions. The reasons
for this include:
♦ The site office has a built-in skylight which is not a good thermal insulator and distorts the
mitigating effects of the green roof.
♦ The irregular behaviour of people within the site office greatly affects the readings. This includes
how many people are active within the office, what machinery is operating, and how often doors
are opened and closed.
♦ The metallic roof of the site office has characteristics very different to conventional roofs.
4.3.6
CUHK started monitoring the ecological value of the roof in summer 2005. CUHK have noted the
colonisation of the ‘natural’ side of the roof with 20 plant species, and it seems to be developing its own
ecosystem, attracting a lot of insects which CUHK are monitoring.
CUHK intend to produce a paper summarising their observations. CUHK believe that several of the
invasive species offer potential for wider use in extensive roof gardens. CUHK also believe that they may
be able to formulate a substrate suitable for use on extensive green roofs in Hong Kong.
As a result of the research project, G-S is internally promoting the use of green roofs on their site offices.
However, the decision whether or not to install a green roof on any specific site office is made by project
managers on a project specific basis. This is because of the varying types of site offices (sometimes steel
containers are used) and the varying lengths of time that they would be in commission. From a purely
commercial standpoint, site offices in commission for short contract periods would not recoup enough
savings in energy costs to compensate for the initial fixed installation costs. The G-S site office has
recently been short-listed for a Green Building Award (2006) by the Professional Green Building Council
Hong Kong (PGBC) in the Research and Planning Section award category.
4.3.7
4.3.8
CLP / University of Hong Kong
4.3.9 CLP has also begun its own research into the benefits of green roofs which may prove effective,
especially for the cooling of its power substations (the first being installed at Sham Shui Po substation).
CLP has collaborated with Prof. Jim of the University of Hong Kong who has initiated his own
experiments at Hong Kong University. This green roof, shown below in Figure 4.2, uses different
substrate depths and species as part of its ongoing experiments. The research data gathered from this
recently installed green roof will only be available in months to come.
4.3.10 The site was divided into 3 study areas, each approximately 6m x 6m (total approx 108m²). The first area
uses a lawn grass, Zoysia japonica. The second area uses a common low ground cover, Arachis pintoi
The third area uses a common shrub, Duranta repens. The growing substrate consists of a lightweight
moisture reservoir 40mm thick with standard topsoil above (of varying levels for the grass, groundcover
and shrubs). Irrigation is achieved by a simple sprinkler system - 3 heads connected to a new rooftop
water-point with a simple automatic timer attached. Irrigation is done every day, weeding about once per
month and fertilizing four times per year. Systems for integrating dissolved fertilizer into the irrigation
system are currently being explored.
4.3.11 Each area has place for controlled weather and temperature monitoring equipment which measures
among other things the roof-temperature above, within and below the green roof. The findings from this
research will probably become the most accurate and relevant readings for Hong Kong to date. Research
so far shows a dramatic difference in roof temperatures during August, as shown below in Table 4.3.
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Figure 4.2 Green Roof Research at University of Hong Kong
Before (June 2006) & After (August 2006) photos of experimental green roof at University of Hong Kong.
(Source and copyright © Cheung Shing Yuk Tong Co., Ltd., 2006)
Table 4.3 Green Roof Temperature Measurements at the University of Hong Kong
Date
Max. Air Temp
Tiled Roof Surface Temp.
Roof Temp Below Duranta repens.
Roof Difference
2006-08-01
31.91°C
52.72°C
26.52°C
26.20°C
2006-08-09
32.70°C
46.83°C
28.68°C
18.15°C
(Source: Oriental Daily 25 September 2006)
Green Roofs on Bus Shelters
4.3.12 In January 2003 a bus shelter green roof feasibility exercise was conducted by First Bus Ltd. The green
shelter was installed in Causeway Bay and used common amenity species in a shallow growth medium
(165mm thick) of CDG, crushed clay brick and topsoil. The green roof was unfortunately removed at the
end of the experiment. No maintenance was required in the brief months after installation which occurred
during the rainy season. It was predicted that future bus shelters would require watering during the dry
season using mobile tanks (bowsers) or hand operated pumps. Interest in tram shelter greening has
followed on from this experiment and is under discussion between numerous parties.
Figure 4.3 Green Roofs on Bus Shelters
Before and After (June 2003) photos of bus shelter green roofs experiment in Causeway bay.
(Source and copyright © John YAU (Chun Wang), 2003)
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Green Roofs at Kadoorie Farm & Botanic Gardens
4.3.13 Construction of a green roof on a Kadoorie Farm wing began in April 2002 and was completed in July
2002. Its growing medium (approx. 150mm thick) uses a mixture of CDG, crushed clay brick and topsoil.
4.3.14 The example at Kadoorie Farm uses Zoysia japonica grass and is reported to be reasonably successful
with some maintenance. A drip irrigation system was installed on the roof and is used regularly. Grass
requires cutting and weeding by hand to stay neat and tidy (once per month in summer and every second
month during winter). Drains are checked every month.
4.3.15 The Farm will continue its investigations and studies into green roofs and has expressed willingness to
co-operate in research to determine suitable species for Hong Kong.
Figure 4.4 Green Roof at Kadoorie Farm
Before (April 2002) and After (July 2002) photos of a green roof at Kadoorie Farm.
(Source and copyright © John YAU (Chun Wang), 2002)
Green Roofs at EMSD Headquarters Building
4.3.16 In 2006, EMSD have undertaken some research into the thermal performance of green roofs on the retrofitted green roof at the EMSD Headquarters building in Kowloon Bay. The results were recently published
by the Energy Efficiency Office of EMSD 36 and indicated that:
♦
♦
The surface temperature of a vegetated area can be about 10°C to 15°C lower than that of a
concrete roof on a sunny day (results taken during Autumn/Winter, 5 November 2006 and 3
December 2006).
The thick roof structure of the EMSD Headquarters building (550mm thick, including the 150mm
concrete slab) insulates the rooms below from solar energy, and its heat storage capacity makes
it an effective thermal buffer (results applicable for Autumn/Winter).
Other Greening Studies Related to Local Application of Green Roofs
Sustainable Design
4.3.17 Buildings Department has recently begun a related study, Consultancy Study on Sustainable Design in
Hong Kong (Agreement no. BA/01/2006). The consultancy study is one of the follow-up initiatives after
The Report on the Engagement Process for a First Sustainable Development Strategy (2005) and A First
Sustainable Development Strategy for Hong Kong (2005).
4.3.18 The study objective is to review how new building design can promote more sustainable urban living
(36)
36
Report on Thermal Performance of Roof Green Features at EMSD Headquarters Building, Energy Efficiency Office, EMSD December 2006
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space in Hong Kong. According to the inception report of the consultancy study, the study would focus on
site/neighbourhood amenities at an area outside the building envelope and within the site boundary. Lack
of urban greenery is one of the generic problems to be addressed.
4.3.19 The Study’s most current task is the review of local legislation & practices and research on overseas
requirements & practices. At this stage, the effectiveness, deficiencies and constraints of related local and
overseas requirements and practices are being studied.
Greening of Highways Structures
4.3.20 Highways Department is currently engaged in a related study, Agreement No BSTR 1/2006, Investigation
Study for Greening of Highway Structures, which looks at different methods for greening and retrofitting
highways structures, including vertical greening, parapet greening & green roofs. The study is expected to
be completed by end 2006.
Greening of Noise Barriers
4.3.21 Highways Department has recently completed another related study, Agreement No HMW 1/2005 (EP),
Investigation Study for Greening and aesthetic Design of Noise Barriers, which covers aspects of
aesthetic design of noise barriers as well as greening. It covers green roofs briefly as part of the possible
treatments for noise enclosures and partial noise enclosures. One of its case studies highlights an
elaborate mountain-side cut-and-cover noise enclosure by CEDD on Route 8, Sha Tin Heights.
Figure 4.5 Roof Greening of Noise Enclosures
(Source and copyright © Urbis Ltd., 2006)
News Media Topics: Green Roofs versus At-grade Landscaping
4.3.22 Green roofs have been the subject of some recent public discussion in the press 37 . Three main
viewpoints have been expressed by the public, namely:
♦
♦
♦
(37)
37
that greenery at ground level which is lost to development should be re-provisioned to some
extent by green roofs on the developments;
that green roofs nevertheless should not be considered a satisfactory substitute for the provision
of the open space stipulated under Hong Kong’s town planning guidelines; and
that green roofs should not be used as an means or excuse for increasing densification of urban
development
SinTao Daily, Apple Daily, Oriental Daily and others (see the Bibliography)
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Intensive Green Roofs
4.3.23 Intensive green roofs can in some cases serve the same or similar purposes as gardens and open space
at ground level and their increased development in Hong Kong is to be encouraged.
4.3.24 However, intensive green roofs should not be considered as substitutes for ground level open space.
There are several reasons for this, as follows:
♦
♦
♦
♦
Certain types of open space require very large continuous landscape areas which would be very
difficult and expensive to provide as a green roof.
Although not impossible, it is very difficult and expensive to achieve significant naturalistic earth
mounding on green roofs, which therefore cannot achieve the same natural landscape character
as can be created at grade.
Trees which grow to large sizes (20m and upwards) require very large soil volumes to grow to
their full potential height. Although it is normal practice in Hong Kong to provide adequate soil
volumes for ‘average’ tree growth, it would be prohibitively expensive to provide sufficient soil for
all tree species to reach their full height potential. Therefore, in this respect, green roofs have
limitations - trees planted on green roofs can never fully substitute for ground level tree planting,
and similarly open spaces created on roofs cannot achieve the same landscape character as
certain types of open spaces created on grade.
Green roofs, if elevated, may be less easily accessible to the general public, less easy to
integrate with adjacent land uses, and therefore less used and less seen. (On the other hand,
depending on local circumstances, green roofs may present opportunities for creating high level
linkages between adjacent developments that may not be possible at ground level due to
severance by roads.)
4.3.25 Intensive green roofs present great opportunities to create landscape spaces where there is simply not
enough space to create ground level landscape. However intensive green roofs should be considered as
being complementary to ground level open space, not as a substitute for it.
Extensive Green Roofs
4.3.26 Extensive green roofs serve different purposes from at-grade landscape and intensive green roofs, and
cannot act as a substitute for either at-grade landscape or intensive green roofs.
4.3.27 Extensive green roofs provide a potential opportunity for new greening in Hong Kong that can
complement and significantly add to the greening provided by at-grade landscape and intensive green
roofs.
News Media Topics: Maintenance and Hygiene of Green Roofs
4.3.28 Articles referring to potential hygiene negatives associated with extensive green roofs have also been
mentioned in the press 38. In this regard, it should be noted that research (by CUHK at the GammonSkanska site office) only shows how pioneer species might rapidly colonise a derelict roof. Levels of
bacteria or insect populations are measured in a state of transition and do not necessarily reflect what
might be expected when a natural balance of climax-community species is achieved, or when a wellmanaged horticultural green roof is established and maintained. However, the point that green roofs, if
not planted incorrectly or left completely unattended may produce unfavourable conditions, is a concern
worth noting.
(38)
Ming Po, 13 October 2006 (Hong Kong newspaper). This article refers to the experimental research done by CUHK on the Gamman-Skanska site office
where one side of the roofs has been left to grow wild for ecological study. The article reports on the estimated 30%-40% energy savings of this particular
green roof but highlights other potential hygiene negatives. CUHK have distanced themselves from the conclusions and implications drawn by Ming Po.
38
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4.4
CLIMATIC & ENVIRONMENTAL FACTORS INFLUENCING GREEN ROOF DESIGN &
CONSTRUCTION IN HONG KONG
4.4.1
The local climate and environment have an important role to play in the design of green roofs in Hong
Kong.
Wind
4.4.2
Typhoons can cause serious damage to plants, particularly trees. Trees on green roofs need to be well
secured, particularly during establishment, to ensure that they do not blow over and cause damage.
Trees also cause additional wind loading on structures and green roof systems.
4.4.3
Trees will grow only as much as the soil volume allows, and consequently trees of the same species tend
to grow to smaller sizes on green roofs, where normally smaller soil volumes are available than at grade.
Nevertheless, tree pruning regimes need to be adopted for trees on green roofs to ensure that they do not
grow so large as to pose a safety hazard during high winds.
4.4.4
The dense high-rise nature of Hong Kong’s urban areas can create shelter at the podium deck level,
although this can also create problems if breezes cannot carry away localised air pollution from vehicles.
Conversely, high rise buildings can also create localised wind gusting problems due to strong downdraughts sweeping down building facades onto podium decks.
Rainfall
4.4.5
Hong Kong’s climate is characterised by high rainfall between April and September (wet season) and low
rainfall between October and March (dry season). Consequently this means roof designs must be
capable of shedding excess water in the wet season and retaining water in the dry season.
4.4.6
Much of Hong Kong’s natural hillside vegetation turns brown or yellow brown during the dry season, and
ecological style planting on extensive green roofs in Hong Kong might naturally do the same. However,
as noted in Section 2.3.25, this may not be well received by certain sectors of the general public.
4.4.7
Green roof systems must also be able to hold water without creating pools of stagnant standing water
which would encourage mosquito breeding and create a health problem.
Temperature
4.4.8
It is important to realise that the extensive green roof techniques gaining popularity throughout the world,
particularly in the cooler climates of Europe and North America, cannot be immediately transposed to the
warmer climates of Hong Kong without adjustment.
4.4.9
The reasons for this are several-fold:
♦
♦
♦
Extensive green roofs have been developed in Germany using low-maintenance alpine-meadow
vegetation, mostly Sedums. These species are temperate climate plants not well-suited to Hong
Kong’s sub-tropical conditions, particularly the higher temperatures.
Hong Kong‘s high rainfall and high temperatures during its summer months enables vegetation to
develop prolific growth rates. This results in higher maintenance requirements when compared
with cooler temperate climates.
The fast growth rate of local vegetation also means that it would generally out-compete Sedumlike species, making invaders on extensive green roofs a particular problem.
Shade
4.4.10 Many existing or planned roof spaces in the urban area that offer potential for development as green
roofs are shaded from the sun by surrounding tall buildings for much of the day. This influences plant
selection. Figure 4.6 below illustrates sun paths as a means for predicting shaded areas throughout the
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seasons.
Figure 4.6 Sun Paths for Hong Kong, Latitude 22°N
(Source and copyright © Urbis Ltd., 2006)
Altitude and Exposure
4.4.11 Temperature drops and wind exposure increases with height above ground level, and green roofs built on
upper floors of the types of high-rise developments common in Hong Kong would be subject to more
extreme weather conditions than those at lower levels, resulting in harsher growing conditions and less
suitability for human use.
Suitable Plant Species and Substrate for Extensive Green Roofs
4.4.12 Identifying appropriate plant species that suit the local climatic and environmental conditions prevailing in
Hong Kong, yet which possess the growth characteristics suited to extensive green roofs as exemplified
elsewhere in the world, is critical to the success of extensive green roofs in Hong Kong.
4.4.13 Similarly, identifying a suitable substrate that encourages growth of desirable species but discourages
undesirable species is also a key factor (cf. the infertile substrates used in European extensive green
roofs encourage alpine sedums and discourage many weeds).
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4.5
GREEN ROOF POTENTIAL IN HONG KONG
4.5.1
It is evident from the infra-red satellite image in Figure 4.7 where the built up areas in Hong Kong are
located. The hottest surfaces of the city show up as dark red-purple areas. Not surprisingly, it is the
heavily trafficked city centre and industrial areas which show the strongest heat readings.
Figure 4.7 Landsat Image of Hong Kong (Shortwave Infra-red bands)
(Source and copyright © 2006, www.Geology.com, prepared by Angela King using data from NASA)
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4.5.2
Photos illustrating the broad range of building types in Hong Kong are presented in Figures 4.8 to 4.14.
Figure 4.8 Green Roof Opportunities in the City (High Density)
Older areas in Hong Kong have small street block and lot
areas. The result is a multitude of thin finger-like buildings
with rooftop space cluttered with utilities. Retrofitted
green roofs will be difficult to accomplish in these areas.
Views from IFC, Central, looking East Towards Wanchai, Hong Kong Island
(Source and copyright © 2006 Urbis Ltd.)
Figure 4.9 Green Roof Opportunities in the City (Medium Density)
Newer areas in Hong Kong have larger lot
areas resulting in buildings with larger
footprints with more space for green roofs
Views from IFC, Central, looking North towards Tsim Sha Tsui
(Source and copyright © 2006 Urbis Ltd.)
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Figure 4.10 Green Roof Opportunities in Residential Areas
Village houses also offer
opportunities for green roofing.
Large residential complexes offer space
opportunities for green roofs.
Regular heights allow for an
environment without shadows which
affects species choice.
Views from above Sai Kung, New Territories and Tai Koo Shing,Hong Kong.
(Source Source and copyright © 2006 Urbis Ltd.)
Figure 4.11 Green Roof Opportunities on other Structures
Noise enclosures offer good
opportunities for green roofs,
though sufficient sky-lighting
should be considered.
Low-rise ferry piers are
another prime location for
visible green roofs.
(Left) Views of typical concrete noise enclosure. (Copyright © HyD).
(Right) Views from IFC looking at the Star Ferry Pier and Queen’s Pier (Source and copyright © 2006 Urbis Ltd.)
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Figure 4.12 Green Roof Opportunities on other Structures
Elevated footbridges, noise barriers, noise
enclosures, pumping stations, electrical
substations, warehouses, petrol stations and
even bus shelters are feasible locations for
green roofs.
(Left) Views from residential towers looking at DSD pumping station. In other rural areas, where the visibility of roofs is not
significant, roof greening may not always be as cost-effective as at-grade planting. (Source and copyright © Urbis Ltd., 2006)
(Right) View of bus shelter in Causeway Bay. (Source and copyright © John YAU (Chun Wang), 2002)
Figure 4.13 Green Roof Opportunities on other Structures
Elevated footbridges and covered walkways
offer numerous opportunities for green roofs.
There are many of these in Hong Kong. Their
highly visible location makes these structures
an ideal location for green roofing.
(Left) Views illustrating covered walkways in Admiralty, Hong Kong Island. (Source and copyright © Urbis Ltd., 2006)
(Right) Views showing network of covered walkways connecting ferry piers near to IFC2, Central, Hong Kong Island. (Source
adapted from GoogleEarth)
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Table 4.4 – Building Types in Hong Kong
Building Type
Old City Centre
(Sheung Wan,
Central, Admiralty
Wan Chai,
Causeway Bay)
(See Figure 4.8)
New City Centre
(Kowloon)
(See Figure 4.9)
CDA high-rises
(See Figure 4.10)
Older Residential
towers
(See Figure 4.8 &
Figure 4.10)
Industrial buildings
Village Houses
(See Figure 4.10)
Other Low-rise
structures
(See Figure 4.11,
Figure 4.12, and
Figure 4.13)
Description
Rooftop
Space
avail.
Need for
Urban
Greenery
(H/M/L)
(H/M/L)
Multiple level sky-rises (mostly offices)
ranging from 10 to 40 storeys. Rooftops are
often exposed and windy. Scenic views of
city are common on some buildings.
Rooftops are larger with less utilities and
obstacles cluttering the area. Building
owners can often afford green roofs or roof
garden.
Multiple level sky-rises (mostly offices)
ranging from 10 to 50 storeys (max 80). Sun
and shade is unpredictable and often shady
on lower rooftops. Rooftops are often
exposed and windy. Scenic views of city are
common on some buildings. Rooftops are
often cluttered with utilities and obstacles.
Building owners can often afford green roofs
or roof garden.
New high-rises (residential or office blocks)
ranging from 20 to 40 storeys with garden
podiums levels below (5 storeys, mostly
retail shops). Buildings are usually of a
similar height making rooftop access to the
sun constant (though podium gardens may
often be shaded. Rooftops are often
exposed and windy. Podium gardens can
sometimes be vulnerable to down-drafts
created by the building faces. Building
owners can often afford green roofs or roof
gardens.
Older High-rise residential towers ranging
from 15 to 30 storeys. Building owners can
sometimes afford green roofs or roof
gardens.
Intensive Green Roofs are needed
and should be promoted for all new
buildings.
Low
Covered Pedestrian Walkways and
Footbridges, Covered roads and noise
enclosures,
vent
buildings,
power
substations, stadiums, service reservoirs
and pump houses.
High
Extensive Green Roofs should be
promoted for existing buildings.
Intensive Green Roofs are needed
and should be promoted for all new
buildings.
Medium
High
Extensive Green Roofs should be
promoted for existing buildings.
The practice of installing Intensive
Green Roofs on Podium Levels
should be continued.
Extensive Green Roofs should be
promoted for all existing buildings.
Medium
Medium
Medium
Medium
Intensive Green Roofs are needed
and should be promoted for all new
buildings.
Extensive Green Roofs should be
promoted for existing buildings.
Intensive Green Roofs and public
accessibility should be promoted for
all new buildings.
Older buildings ranging from 10 to 15
storeys. Building sizes are often wider than
other buildings. Building owners can
sometimes afford green roofs or roof
gardens.
Buildings range from 1 to 4 storeys. Building
owners can sometimes afford green roofs or
roof gardens.
Recommendations
High
MediumLow
HighMedium
Medium
MediumLow
High
Given the large areas available,
Extensive Green Roofs should be
actively promoted for existing
buildings and for all non-accessible
buildings.
Given the surrounding greenery,
lower need for greenery and
probable budgetary constraints,
Extensive Green Roofs should be
actively promoted.
Given the lack of accessibility to
rooftops as well as the large areas
available, Extensive Green Roofs
should be actively promoted.
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4.6
GREEN ROOF BENEFITS TO HONG KONG
4.6.1
An analysis of the benefits that Hong Kong might experience is presented in Table 4.5. (Also see
Sections 2.2 to 2.6)
Table 4.5 – Benefits Applicable to Hong Kong
KNOWN GREEN
ROOF BENEFITS
WHO
BENEFITS?
HOW DO THEY BENEFIT?
HOW SIGNIFICANT IS THE
BENEFIT?
AMENITY & AESTHETIC BENEFITS OF GREEN ROOFS
Public /
Building
occupants /
Property
Owners
Additional passive recreational space is
added to the city where the public or
building occupants can escape from the
busy streets below. Property Owners may
benefit from increased property prices
High
Leisure and Functional
Open Space
Visual Aesthetic Value
Public / building
occupants / HK
government
The city is more appealing to look at. The
government gains from a better image of
the city
High – but only if a significant number
of visible roofs are covered.
Public
Therapeutic benefits of calming the
observer.
Moderate to High – but depends on
location.
Roof Garden
Grower
Food cost reductions and therapeutic value
of gardening.
Low – not expected to run at any
appreciable scale in the city centre.
Public
Healthier air to breathe. Scenic visibility
might be improved with a reduction of city
smog.
Moderate – but only if large areas are
covered
Public
Air-conditioning costs might be reduced
(reduction in pollution associated energy
production)
Moderate – but only if large areas are
covered
Wildlife
Habitat creation
Moderate to Low – depends on
location and species used
HK government
/ Wildlife
Potential costs on storm-water
infrastructure can be reduced.
Contaminated storm-water entering the
ocean is reduced.
Moderate to Low – most locations in
Hong Kong are close to the sea
making storm-water infrastructure a
relatively small issue for the city
compared to other cities. Presence of
Green Roofs is unlikely to change
drainage engineers calculations
Building
Occupants
Slightly quieter environment. (only 5dB)
Low – benefits are likely to be only on
the top floors below the green roof and
from noise from above.
Building
Occupants
Air-conditioning costs might be reduced by
around 15%
High – though benefits are likely to be
appreciated by upper floors only
Property
Owners /
Developers / HK
government
They benefit from an improved image of
being environmentally friendly and
sustainable
Moderate – (noted from GammonSkanska site office publicity). This
benefit is equally applicable to
Government’s image.
Property
Owners/
Building
Occupants
Property owners may derive roof cost
savings but only if they intend to own and
maintain the building in the long-term. This
is not the case for most developers. Roof
life costs are therefore a low incentive to
developers.
Low – most developers in Hong Kong
build to sell and would therefore not
see the benefits gained years later.
Health and Therapeutic
Value
Food Production
ENVIRONMENTAL BENEFITS
Air Quality
Reducing Urban Heat Island
Effect
Ecological and Wildlife
Value
Water Management
Sound Absorption
ECONOMIC BENEFITS
Building Insulation and
Energy Efficiency
Green Building Assessment
& Public Relations
Increased Roof Life
Moderate –for Government owned
buildings this issue becomes more
relevant.
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4.6.2
It is clear from the above that Green Roofs offer distinct benefits for Hong Kong. Clear community
benefits that would be enjoyed by the public include: increased public open space; increase visual
amenity; improved air quality and a reduced urban heat island effect.
4.6.3
However, the direct financial benefit for developers and property owners is less easy to determine since
although overseas data suggests that green roofs provide tangible financial benefits for the private sector,
there is no hard data from local research to substantiate this in the local Hong Kong context.
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PART 2
DESIGN & TECHNICAL GUIDELINES
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5
GREEN ROOF SYSTEMS
5.1
ROOF TYPE SCENARIOS IN HONG KONG
5.1.1
In Hong Kong there are three main green roof scenarios – Sky Gardens, Podium Gardens (New
Buildings) and Existing/Low-maintenance Buildings.
♦
♦
♦
Sky Gardens are found on top of any high-rise buildings (usually 20 storeys and above). Sky
Gardens are usually designed as part of the building and may be intensive or extensive green
roofs depending on usage.
Podium Gardens are usually 2 to 5 storeys up forming the base of a residential or office tower.
These gardens are usually intended for full access by the building occupants or the public and
are therefore always intensive green roofs.
Existing and low-maintenance buildings include existing office and residential towers and other
buildings such as public infrastructure buildings. Due to weight constraints and the need for low
maintenance extensive green roofs would generally be prescribed.
Figure 5.1 Roof Type Scenarios in Hong Kong
(Left) Sky Gardens (Source and copyright © EarthPledge, 2005)
(Centre) Podium Gardens, (Source and copyright © ArchSD, 2005)
(Right) Existing Buildings (Source and copyright © Urbis Ltd., 2006)
Table 5.1 Considerations for New Buildings and Existing Buildings
NEW BUILDINGS
• Costs can be saved in the design stage, as part of the existing
contract.
• Roof slabs can be designed to take heavier soil depth loads.
• Irrigation and water supply can be built into the roof from the
beginning
• Waterproofing can be part of the concrete roof slab rather than
using a membrane tanking system (see Section 5.2.2).
• Utilities can be arranged to maximise the green roof area.
• Favourable marketing opportunities may arise from the
inclusion of green roofs.
• extended side walls to protect green roofs from excessive wind
may be incorporated at the design stage
• barrier-free access (e.g. elevators) can be incorporated into
the design if public access is considered.
EXISTING BUILDINGS
• Building requirements may limit growth medium
depth.
• The age and condition of the existing building
and roof affects the feasibility of a green roof.
• Installation of rooftop water points may be
needed.
• Installation of new drainage points may be
needed.
• Waterproofing needs to be considered as an
additional layer.
• Roof-top utilities placed in ad-hoc arrangements
can limit the area of green roofs.
• Access may be difficult and additional safety
devices may need to be installed (Barrier-free
access may be impossible to retro-fit).
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Sky Gardens
5.1.2
As Sky Gardens are found on high-rise buildings, they will have unique factors influencing their design.
♦ Extreme growing conditions are often present. Wind is of particular importance and in some
instances may rule out large trees. Conditions are also very exposed, enduring direct sunlight
and temperature extremes. This may stunt the growth of some plants. Trees may be protected
from high winds using wind screens. Structural anchorage as well as regular pruning of trees is
important to avoid typhoon damage.
♦ Safety is always a concern on high buildings. Railings for safe access are essential. The potential
for lightning strikes also needs to be considered
♦ Rooftop utilities are often located in positions that compete for space. It is essential to group
rooftop utilities to maximise the space available for greenery. Refuge floor requirements are
another building requirement that could potentially compete for space. Preserving panoramic
views of the surrounding city is also an important factor affected by rooftop utilities.
♦ Water pressure at roof top locations may also be a problem which may require complex tanks
and/or pumps. Possible access by the public is another issue.
♦ Hauling of materials and plants is a potential and expensive complication. Large trees are
particularly difficult to move.
♦ Waterproofing is critical on any roof and should be protected continuously from damage during
construction, and after establishment. Special leak detection systems may be installed.
♦ Critical plant selection is needed that includes non-invasive root systems and suits site-specific
microclimates.
Figure 5.2 Sky Gardens
( Left: source and copyright © EarthPledge, 2005) (Right: source and copyright © Greenlink Küsters Ltd.)
( Left & Right: source and copyright © ArchSD, 2005)
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Podium Gardens and Conventional Roof Gardens
5.1.3
Podium Gardens are usually 2 to 5 storeys high and are generally built for functional open space. As such
numerous unique design issues need to be considered.
♦
♦
♦
♦
♦
Safety is always a concern on roof gardens that are intended for high public usage. Railings for
safe access are essential and may even include wind screens or clear panel noise barriers made
of PMMA (Polymethyl-Methacrylate) for a quieter experience (see Figure 5.3 below). Designs
need to address the potential for creating mosquito problems. Playground equipment may be
considered and needs to be designed with safety in mind. Structural anchorage as well as regular
pruning of trees is important to avoid typhoon damage.
Podium floors are also often designed as refuge floors which may compete for space.
Waterproofing is critical on any roof and should be protected continuously from damage during
construction, and after establishment. Special leak detection systems may be installed.
Critical plant selection is needed that includes non-invasive root systems and suits site-specific
microclimates. Podia are often very shady or receive full sunlight for brief periods during the day.
Planting design needs to accommodate distant viewers who may look down onto the roof garden
as well as the users of the garden. Variety, colour and scale of the planting design is therefore an
important consideration.
Figure 5.3 Podium Gardens
( Left & Right: source and copyright © ArchSD)
( Left & Right: source and copyright © ArchSD)
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Existing and Low-Maintenance Buildings
5.1.4
Existing and low-maintenance buildings are designed and retro-fitted primarily for environmental &
building efficiency performance. Design issues usually revolve around loading, existing roof status,
maintenance access and safety, soil depth, and successful low-maintenance species.
♦
♦
♦
♦
♦
State of the existing roof is critical. The allowable weight and safety margins need to be critically
assessed. The loading for extensive green roofs ranges from 80 to 150 kg/m² though loading may
occasionally allow for Intensive Green Roof components at some locations. The state of the
existing waterproofing is another major consideration.
Waterproofing is critical on any roof and should be protected continuously from damage during
construction, and after establishment. Special leak detection systems may be installed.
Safety for maintenance access also needs to be considered. This may take the form of additional
railings, a clear gap away from the edge or safety harnesses.
Critical plant selection is needed that includes plants that 1) do well in lightweight and shallow
soils, 2) are wind tolerant, 3) are drought tolerant, 4) are pollution tolerant, and 5) have noninvasive root systems.
Growing media generally needs to be 1) super light-weight, 2) inert, 3) well-drained, 4) wellaerated, 5) fire resistant, and 6) nutrient retentive. Despite being lightweight the growing media
should provide adequate anchorage for all plants and also be resilient to wind erosion.
Figure 5.4 Existing and Low-maintenance Buildings
( Left: source and copyright © ArchSD) (Right: source and copyright © Greenlink Küsters Ltd.)
(Left & right: source and copyright © Greenlink Küsters Ltd.)
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Utilities on New Buildings
5.1.5
Rooftop utilities can significantly influence the design, cost and eventual success of any green roof.
Utilities on extensive green roofs can, if oddly placed, result in wastage of up to 30%. Rooftop utilities on
intensive green roofs are even more important because they can significantly hinder the creation of userfriendly roof-top spaces.
5.1.6
The arrangement of rooftop utilities on all new buildings is therefore an aspect that should receive
significant consideration during the early design phase of a building. This is particularly important in the
Hong Kong context where tall finger-like buildings are largely cluttered with rooftop utilities.
5.1.7
The example in Figure 5.5 below shows how a variety of greening techniques (intensive and extensive),
and a well thought-out use of level changes, can be adopted to achieve an uncluttered appearance.
Users of the space are able to enjoy unobstructed panoramic views of the city – one of the few unique
advantages that green roofs offer over at-grade greenery. Similar principles were followed at Roppongi
Hills, Tokyo, as seen in Figure 3.7 and Figure 3.8.
Figure 5.5 Utilities on New Buildings
(Source and copyright © Urbis Ltd., 2006)
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5.2
BASIC COMPONENTS
5.2.1
Green roofs are feasible on any properly designed roof deck, including steel, wood, concrete, plastic or
composites, as long as the necessary structural considerations are met. The basic components of green
roof systems are basically the same for intensive and extensive green roofs and are presented below in
Figure 5.6 and Figure 5.7. Numerous specialised layers may vary from the illustration below and may
cater for unique conditions such as steep slope scenarios. The basic functions of these systems include:
♦ weatherproofing the roof,
♦ protection of the roof surface from root penetration,
♦ drainage, and
♦ support and growth of the vegetation layer.
Figure 5.6 Basic Components of a Green Roof System (Intensive and Extensive)
(Source and copyright © Urbis Ltd., 2006)
Figure 5.7 Conventional (Intensive) and Lightweight (Extensive) Green Roof Systems
(Source and copyright © Urbis Ltd., 2006, Adapted from images from Greenlink Küsters Ltd.)
Note: Intensive green roof weights of 300-1000kg/m² refer to the most shallow soil depth needed for amenity groundcover or
lawn grass (300mm). A soil depth conducive for successful tree growth (1500mm deep) is likely to weigh around 3300kg/m²,
excluding the weight and wind-loading pressure of the trees.
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Waterproofing:
5.2.2
Waterproofing is arguably the most important pre-requisite of a green roofing system. For waterproofing
to remain effective it must be root resistant over the long term and should fulfil the necessary standards
(such as the German FLL standards). Alternatively, if the waterproofing is not root resistant then the
green roof system must include a separate root barrier. Numerous waterproofing systems exist. These
include:
♦ Bitumen/asphalt roofing felt or bituminised fabrics. These materials generally have a limited life
span of 15 to 20 years and degrade from temperature changes and ultraviolet radiation (which
are largely mitigated if greening is applied above). A separate root protection barrier must be
applied with such membranes.
♦ SBS modified bituminous membrane sheets set in SEBS polymer modified bitumen and coal tar
pitch/polyester built-up systems. These are a more robust system suitable for green roofs.
However, they are only root resistant if a layer of copper is put inside the membrane or if it is
treated with chemicals. This kind of waterproofing is commonly used in Europe for Intensive
green roof application.
♦ Fluid Applied Membranes. These are available in hot or cold liquid form and are spray painted
onto the surface. They do not suffer from jointing problems and are easier to apply vertically or to
difficult shaped surfaces. Often a protection board (PVC sheet or expanded polystyrene) may be
added above this layer. On flat roofs a layer of gravel, concrete slabs or sand may be added to
protect the membrane from temperature fluctuations and UV radiation. (These gave rise to the
observations of spontaneous plant colonization which sparked initial research on extensive roof
greening in Germany.)
♦ Single-ply roof membranes. These membranes are rolled sheets (sometimes tiles) of inorganic
plastic rubber material overlapped at the joints and sealed with heat, or with solvents if Ethylene
Propylene diene monomer rubbers (EPDM) are used (requiring very clean and dry conditions).
These membranes can be very effective if applied properly but are weakest at the seams
between sheets and tiles. The PVC and butyl rubber are prone to UV degradation and should be
covered at all locations. Thermoplastic polyolefins (TPOs) are also specified for green roof
waterproofing and are often considered more environmentally acceptable. PVCs, EPDMs and
TPOs are generally root-resistant. These kinds of membranes have a long proven track record in
the green roof industry but rely on correct installation.
♦ Concrete admixture water-proofing. Concrete admixture waterproofing or Hydrophobic Poreblocking Ingredients (HPI) are not well known in the green roof industry because they are
applicable only to newly cast concrete roofs. From a construction and waterproofing viewpoint
they perform better than PVC membranes and are generally cheaper too (see Table 8.2). With
this system the concrete itself becomes permanently waterproofed in a more robust form which
cannot be punctured, torn or damaged (a risk often associated with other waterproofing
techniques when other sub-contractors are working on upper layers). Attachments to the roof
slab (such as tree anchors) are also easy to install and do not form weak spots as they would
through membrane waterproofing. However, when using HPIs it is important to find an admixture
that; 1) is effective at limiting water-absorption, 2) has a long and proven track record, 3) is
guaranteed for a long time and is guaranteed despite workmanship which may occur above the
slab, 4) chemically does not break down over time, 5) does not leach out under pressure, and 6)
does not compromise the performance of the concrete. Another type of concrete admixture is
crystal growth waterproofing which works by growing crystals within the pores of the concrete
matrix. It is best used as a concrete admixture when the concrete is being cast but can also be
effectively used as coating which penetrates into existing concrete. As a coated waterproofing its
effectiveness may be dependant on the type and porosity of the concrete used.
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5.2.3
On new roofs the ideal is to double-waterproof the system using waterproofed concrete as well as a more
flexible waterproofing layer above. Each waterproofing system has its own advantages and
disadvantages but by combining the two systems far greater reliability is achieved. For example, although
concrete admixtures are more robust and more repairable, the negative side of concrete waterproofing is
that under certain conditions, where concrete expands and contracts, cracking is inevitable. These cracks
would most likely be covered using a flexible system (PVC, etc). For existing roofs, where waterproofing
the concrete system is impossible, it is still advisable that any levelling screed is also waterproofed.
5.2.4
On existing roofs it may be determined that the existing waterproofing is sufficient and that the green roof
layers may be added without additional waterproofing. An assessment like this must be undertaken by a
suitably qualified professional and/or the liability of failure removed from the green roof contractor’s
responsibility.
5.2.5
When using liquid or sheet membranes, attention needs to be given to the following locations where
water leakage is often present 39:
♦
♦
♦
♦
♦
♦
Right angled bends such as corners or at the junction between a roof slab & a parapet wall: In
these locations it is preferable to fix a triangular fillet prior to laying the membrane. This will form
an obtuse angled junction, which is less likely to tear as a result of any subsequent movement
that may take place, than a right angled one.
For the prevention of rising damp: the membrane should be continued between 150mm & 300mm
vertically up the side of a parapet wall at the perimeter of a roof, above the roof level & dressed
into a horizontal groove & sealed. It should not just be stuck onto the side of the wall. The same
principle applies to plinths & machine bases on the roof.
For pipe or service duct penetrations: Carry any liquid waterproofing material up the side 150300mm above the roof level. With sheet material, trim carefully around the base of the pipe &
seal with a liquid applied sealant compatible with the membrane material. In some cases, suitable
fasteners (such as jubilee clamps) may be used to secure the membrane to the pipe.
Where the parapet is made of block or brickwork, rather than concrete: The waterproofing should
be taken up the inner face of the parapet wall & beneath the coping on the top of the parapet. If
this is not done, water will pass down through the brickwork & migrate behind the membrane at
roof slab level.
Prevention of degradation: The surface of the membrane may need to be covered with tiles,
lightweight mortar screeds, or reflecting paint in order to prevent UV degradation & radiant heat
absorption into the roof slab.
Surface abrasion tears: Special care must be taken to ensure that waterproofing does not lie on a
concrete/screed surface that is too rough. Expansion and contraction as well as the weight
pushing the waterproofing onto this surface can cause punctures or abrasion holes. A separation
layer is generally advisable.
Root Barrier
5.2.6
(39)
As mentioned above, a separate root protection barrier is needed if the waterproofing layer contains
bitumen, asphalt, or any other organic material. It is important that this separation is continuous because
any penetration of roots also provides access for micro-organisms which can actually attack these
organic oil-based materials. Root Protection membranes are usually made of PVC rolls that are around
1mm thick. Intensive green roofs may need a far more robust root protection system capable of
withstanding the penetration of tree roots. These are often thick hard plastic sheets or even metal sheets
(usually copper) for exceptionally vigorous roots (such as from some Ficus trees or bamboos). For
39
Adapted from notes by Dr. Chris Stanley (May 2005, Hong Kong Concrete Repair Association).
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extensive green roofs with limited rooting, a single layer of 0.4mm thick HDPE membrane can also be
installed without welding as long as the overlap is at least 1.5m (FLL approved).
Protection Layer
5.2.7
Between the waterproofing and drainage layer a protection layer is often advised. This is usually a nonwoven geo-textile that protects the waterproofing from mechanical damage. Extensive green roofs usually
use a 300gr/m² polypropylene layer. A stronger protection layer (ranging from 400-800 gr/m²) is advised
for green roofs with higher strain or loadings. The application of protection layers is more critical if the
drainage layer uses a more primitive granular mix.
Drainage Layer
5.2.8
The main purpose of the drainage layer is to drain excess water or underflow as rapidly as possible to
prevent prolonged saturation. The operative word is excess, meaning that drainage is only necessary if
the growing medium has reached saturation point. In fulfilling its main purpose, the drainage layer also
protects the waterproof membrane. If drainage is inadequate then problems to the waterproof membrane
may occur due to continuous contact with water or wet soil.
5.2.9
The drainage layer also helps to aerate the substrate. Providing internal airflow, below and through the
substrate it also helps to reduce the vacuum which occurs due to wind uplift along the edges of an
extensive green roof.
5.2.10 Green roof vegetation, particularly on extensive green roofs, is selected to be drought resistant and suited
to free-draining soils. Prolonged saturation of the soil is likely to cause plant failure and rotting.
5.2.11 A permanently wet green roof is also likely to lose its thermal insulating properties.
5.2.12 The drainage layer may also double up, in some instances (as shown in the Figure 5.5), as an irrigation
mechanism, referred to as irrigation by diffusion. In such cases the troughs of the drainage layer, which
are able to store water (away from the substrate), are actually able to provide water to the substrate
through diffusion into the substrate which draws water up when dry.
5.2.13 Drainage layers are only applicable to flat or slightly angled surfaces (<5°). The addition of drainage
layers on steeper slopes may in fact remove water too quickly and be disadvantageous to plant growth.
5.2.14 There are three main types of drainage materials:
♦ Granular Materials. These are usually coarse granules of gravel, stone chips, broken clay tiles,
clinker, scoria (lava rock), pumice, expanded shale, or LECA. They contain large pockets of air or
pore space between them when packed together in a layer or a space. It is this pore space that
allows water to run freely through. This is the most low-tech drainage system but in some cases
may be all that is necessary to lift the main substrate above the draining water. Often these layers
may be lighter than the main growing substrate and can be used to lighten its overall load
because they are still used as part of the root zone. A disadvantage of using granular materials
(like LECA) is that they can easily be unevenly dispersed by workmanship occurring above. A
wheel-barrow track, for instance, might cut into this layer completely compromising its function in
that location.
♦ Porous mats. These mats operate in a similar way to horticultural capillary matting. They are
made from numerous materials including recycled materials such as clothing and car seats and
behave much like sponges, absorbing water into their structure. There is the danger that these
materials may absorb too much moisture from the growing substrate or become too light when
dry. Some materials (e.g. recycled foam) may decompose or shrink over time. Having no nutrient
holding potential these materials may require continual fertilizing.
♦ Lightweight plastic or polystyrene drainage modules. A great variety of proprietary products exist
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which operate in slightly different ways. Most are thinner than 25mm. Some include the ability to
store water while others do not, and some can be filled with granular media. These interlocking
modules are rigid enough to support the growing medium and vegetation which are kept away
from the roof, and provide a permanent free-flowing lightweight drainage layer beneath. In some
designs they store reserve water allowing plants to derive additional moisture. To prevent
collapse during and after construction attention must be given to the strength that these drainage
media offer. Thickened HDPE or High Impact Polystyrene (HIPS) may be considered in some
circumstances.
5.2.15 Drainage outlets are an important consideration (existing roofs will already have their own drainage points
installed). These need to be kept clear to fulfil their functions, especially from growing substrate. Drainage
outlets should be connected by vertical piping to the surface of the growing medium so as to avoid and to
clear blockages.
5.2.16 Drainage layers include a filter mat above, which prevents fine material being washed into the drainage
which would negate its purpose and may also block the drainage outlets. Non-woven filter layers are ideal
for most circumstances (having superior filtration) though woven versions may be considered for heavy
duty applications. It is important that edges of the filter mat are taken up the edge of the planting medium.
5.2.17 If suitable soils are used, sloped green roofs (3°-10°) may drain naturally without the need for a drainage
layer. For slopes above 10° it is advisable to include a drainage board that actually holds water in its
specially designed pockets as the natural drainage may be too rapid.
Growing Medium / Substrate / Soils
5.2.18 Finding the right soil mix for roof gardens is a critical aspect to its success. The general requirements of
all growing media are the same:
♦ efficient moisture retention,
♦ excess water is easily drained,
♦ well aerated
♦ able to absorb and supply nutrients,
♦ retains its volume over time; and
♦ provides adequate anchorage for plants.
5.2.19 Additional requirements that are important for green roof growing media include the following:
♦ light weight;
♦ water retention capacity;
♦ inert in a sub-tropical climate (i.e. artificial materials do not degrade); and
♦ fire resistant properties.
5.2.20 Light weight characteristics may be achieved using natural, artificial, or waste minerals. Lava (scoria) &
pumice, perlite, vermiculite, light expanded clay aggregate (LECA), rockwool, diatomaceous earth (DE) 40
and numerous other materials are used. These may offer some other advantages, such as greater water
absorption, but this light weight advantage usually comes at a cost, such as retaining soil volume or
nutrient holding capabilities.
5.2.21 In extensive green roofs general garden soil or topsoil on its own is generally not suitable because it is
too heavy and too fertile. However, thin layers of topsoil have been seen to be successful when used
above lightweight, well-drained mediums below. Therefore, in the extensive green roofs developed in
(40)
40 Diatomaceous earth is a lightweight bio-mineral consisting of the fossilized remains of diatoms, a type of hard-shelled algae. It is similar to pumice with
high water-retention and nutrient holding characteristics. It also has mechanical properties that act as natural insecticide (the fine silicate powder absorbs
lipids from the waxy outer layer of insects' exoskeletons, causing them to dehydrate). This is a feature that might be considered desirable for extensive
green roofs, which are designed to have high mineral and low organic soil contents.
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Europe, substrates are geared towards light-weight alpine-like meadow vegetation (i.e. Sedum species).
These prefer well-drained, low fertility soils where they have developed survival techniques to secure their
niche. German research indicates that the ideal growing medium comprises 30%-40% substrate and
60%-70% percent pore space. Most commercial substrates are based on tailor-made non-organic mineral
components. Clay and organic materials are sometimes added for their moisture and nutrient-holding
capacities but noting the types of vegetation commonly used, and the negative aspects of these materials
(potential clogging of the drainage systems and shrinkage of organic matter) these are usually applied
sparingly.
5.2.22 Fire resistant properties are important, particularly for extensive green roofs where the maintenance
regime may involve minimal irrigation permitting the roof to remain dry for long periods in the dry season.
5.2.23 The depth of growing medium/substrate or soil for various vegetation types is critical to its success.
Common vegetation soil depths are illustrated below in Table 5.2. A list of the regular materials is
presented in the Table 5.3 below showing the characteristics of each. Table 5.4 provides the weight
characteristics of the various growing media as well as other green roof components for comparison.
Table 5.2a Standard Soil Depths for Basic
p Vegetation Types – Extensive Green Roofs
250
millimeters
200
150
100
50
0
Moss-Sedum
40-80mm
Sedum-mossherbaceous
plants
60-100mm
Sedumherbaceousgrass plants
100-150mm
Grassherbaceous
plants
150-200mm
Table 5.2b Standard Soil Depths for BasicpVegetation Types – Intensive Green Roofs
2500
millimeters
2000
1500
1000
500
0
Large Trees
Medium
Tall Shrubs Small Trees
Medium
1500Trees
& Medium
& Small
Shrubs
2000mm
1000Palms
Palms
300-500mm
400-700mm 600-1250mm 2000mm
(Source Adapted from the FLL’s Guideline for the Planning, Execution and Upkeep of Green-Roof Sites)
Lawn
200-350mm
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Table 5.3 Characteristics of Inorganic Growing Media Components
Materials
Comments
Natural minerals
Sand
Lava (scoria) & pumice
Gravel
Perlite
Vermiculite
Fine texture can result in lack of pore space and problems of saturation of the substrate if
drainage is poor. Conversely, coarse sands can be so free-draining as to require constant
irrigation.
Lightweight and valuable if locally available.
Relatively heavy.
Particles tend to collapse over time (Hitchmough 1994).
Very lightweight, but has no water- or nutrient-holding capacity and may disintegrate over time
(Hitchmough 1994).
Artificial minerals
Light expanded clay
aggregate (LECA)
Expanded shale
Rockwool
Lightweight, produce large amounts of pore space because of their size, and absorb water
because of their porous nature.
Very lightweight but energy-intensive production and no nutrient-holding capacity.
Recycled or waste materials
Crushed clay brick or
tiles, brick rubble
Crushed concrete
Stable and uniform, some nutrient and moisture retention. Brick rubble may contain mortar and
cement, which will raise the pH of the substrate.
Limited moisture retention and nutrient availability, alkaline. However, cheap and available in
quantity as a demolition material.
Subsoil
Heavy, low fertility, readily available as by-product of construction.
(Source: Adapted from Dunnett & Kingsbury (2004), p73)
Table 5.4 Material Weights of Soils and Other Green Roof Components
Materials Weight (Saturated Weights Where Applicable) - x 100 for kg/m³
Soil Substrate Material
Gravel
Pebbles
Pumice
Sand
Crushed Brick
Sand and gravel mix
Topsoil
Weight of 1cm
layer (kg/m²)
16-19
19
6.5
18-22
10-13
18
17-20
14
Other Materials
Stone
Granite
Concrete (precast)
Concrete (reinforced)
Brick (solid with mortar)
Concrete (lightweight)
Autoclaved Aerated Concrete
Lightweight Foamed Concrete
Weight of 1cm
layer (kg/m²)
23-30
26.6
21
24
18
13-16
6.5
7
Topsoil (lightweight)
Water
10
Hardwood timber
7.3
Lava
8
Softwood timber
5.7
Cast iron
Perlite (expanded)
5
Vermiculite (expanded)
0.6-1.6
Steel
LECA
3-4
Aluminum
Rockwool
(1.7 dry) 10
Extruded Polystyrene fill
Note: the mixing of particles of different size will tend to make moisture capacities and final weights unpredictable.
(Source: adapted from Dunnett & Kingsbury (2004), p60, Also refer to http://www.simetric.co.uk/si_materials.htm and
Chapter 13, ‘Reference Values for Design Loads’ of the FLL Design Guidelines )
71
78
27
0.7
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Light-weight fills and thermal insulating layers
5.2.24 Lightweight fills are used primarily on Intensive Green Roofs to create differences in level. Another use
may be to create sculptural contours to hide utilities or to liven up the flat surfaces commonly associated
with extensive green roofs.
5.2.25 Lightweight fills are usually made of some expanded material which has a lot of air in it. As such they are
often very good thermal and acoustic insulators. In extensive green roofs they are sometimes used only
for these reasons - as a thermal insulating layer (see Figure 7.1).
5.2.26 Most light-weight fills are relatively soft and are not physically durable enough to last over long periods if
exposed to outside elements 41. Lightweight fills can be made of a variety of materials:
♦
Extruded Polystyrene Sheets are the most established material. These are becoming less
popular because of their environmental impacts during manufacture and eventual disposal.
Polystyrene is also flammable. Its main benefit is its ease of handling, low cost and extremely
light weight.
♦ Polystyrene Cement is the process of mixing polystyrene beads into cement. Traditionally this
process produced an inconsistent material because the beads floated before the cement could
set. Experiments using coated beads are proving more successful and may be on the market
soon. This material is cheap and easy to produce and form on site but, depending on its
composition, has a maximum depth (e.g. around 350mm).
♦ Autoclaved Aerated Concrete (AAC) is a special kind of pre-cast concrete. This material arrives
on site in pre-cast panels or blocks. It is made from a mixture of cement, lime, water and sand
that expands by adding aluminium powder, much like baking powder in cakes. It is then steamcured in a pressurized chamber (an autoclave) at 300°C. It is often used as a walling system but
is also perfectly suited as a lightweight fill for roofs. AAC’s benefits are that it: 1) is easy to
handle, work and shape (using only hand tools), 2) uses non-toxic natural materials which are
completely recyclable, 3) is airtight, and 4) can be re-inforced with steel if needed to create
additional load-bearing panels or roofs.
♦ Foamed Concrete is a special in-situ concrete which mixes foaming chemicals into the cement
with a special mixer on site. The proportions of foam may be adjusted for various applications but
care must be taken to produce a mix that is stable for its purposes (700kg/m³ is considered
stable, though foamed concrete may be pushed to 420kg/m³ for other applications). From a
density and workability point of view it is very similar to AAC but has the advantage of being
poured in-situ if needed.
♦ Other Cements (perlite, vermiculite, and LECA) are other forms of lightweight cements. Perlite
and vermiculite are mined mica minerals. Perlite, vermiculite and LECA are all expanded in a
heating process much like popcorn. Being the constituents of clay, they all have nutrient-holding
capacities (known as cation exchange capacity - CEC) and are therefore used effectively as
lightweight soil mixes. However, perlite and vermiculite can also be mixed easily with concrete to
create a very favourable lightweight fill. In Hong Kong these minerals are not readily available
and/or are not of a high quality that expands well. Experiments using LECA in cement are
currently being conducted and may prove to be an effective lightweight fill in the near future.
5.2.27 Composite concrete lightweight fills are physically more durable than other lightweight fills (polystyrene)
but are much more porous than normal concrete. This makes them vulnerable to carbonation and other
concrete weathering processes which makes waterproofing very important. Quality waterproofing is
feasible on lightweight concretes using sterates.
(41)
41 Discussions with Redland Precast Concrete Products Limited and Dr. Chris Stanley of the Hong Kong Concrete Repair Association. Also see
http://www.hkcra.com.hk/tech_waterproof_05.htm
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Figure 5.8 Exploded View of Shaped Level Difference - Extensive Green Roofs
Recently opened HQ of American Society of Landscape Architects, ASLA (July 2006). The dullness of a flat roof (particularly
on retro-fitted extensive green roofs or where little colour is possible) is often simply accepted without question. Lightweight
constructions, as shown above, illustrate techniques for creating unique level differences for extensive roof gardens. These
structures may be used for concealing rooftop utilities or, with enough area, may be used for defining elaborate spaces. They
convert the flat canvas technique into an endless range of sculptural possibilities. (Adapted from images from ASLA, 2005)
Figure 5.9 Shaped Level Difference - Extensive Green Roofs
Opportune structural beams may be used for spots of heavier loading where small shrubs, palms or trees may be planted with
conventional soil while being surrounded by lightweight extensive green roof planting. Lightweight fills may be used to smooth
out the level differences using slopes or terraced contours. Terraced contours allow for a distinct separation of planters if
vigorous growth habits and competition between species is foreseeable.
(Left: Source and copyright © Greenlink Küsters Ltd.) (Right: source and copyright © Urbis Ltd., 2006)
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Figure 5.10 Examples of Typical Green Roof Components
Inspection chamber for regular checking of the drainage
layer. Drainage gullies should always have inspection
chambers above.
(Source and copyright © Greenlink Küsters Ltd.)
Special paving drainage unit used if the drainage layer
continues below the paving.
(Source and copyright © Greenlink Küsters Ltd.)
Protection layer/moisture retention mat being installed
above the waterproofing/root barrier in Europe.
(Source and copyright © Greenlink Küsters Ltd.)
Drainage layers being installed at HKU
(Source and copyright © Cheung Shing Yuk Tong Co.
Ltd., 2006)
Light weight fills or additional thermal insulation layers are
usually installed below the drainage layer.
(Source and copyright © Earth Pledge, 2005)
Inorganic growing medium in Stuttgart, made from
recycled construction and industrial waste, including
crushed clay tiles and steel mill slag. (Source: Urbis Ltd)
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Irrigation Systems
5.2.28 Irrigations systems and plant water requirements are highly dependent on site location, water supply and
pressure, maintenance access, size of planter, type of vegetation and the expected lifespan of plants and
the irrigation system. There are three principal ways of irrigating green roofs:
♦
Manual Hose Irrigation - a 20m hose pipe connected to water points located at 40 metre
spacing;
♦ Fully Automatic Irrigation Systems - a programmed system that irrigates at set times,
running continuously with minimal supervision; and
♦ Semi-Automatic Irrigation Systems - a programmed system with various manual override
options that are activated per day or as needs require.
5.2.29 Manual watering (with hose) is reliable, robust and tried-and-tested. Its main draw-back is its high labour
costs. Automatic irrigation systems are systems that are controlled (usually electrically) to irrigate areas of
planting without human intervention. They are able to deliver precise water quantities at very specific
times.
Table 5.5 – Manual Irrigation Systems
ADVANTAGES
DISADVANTAGES
•
•
•
•
• High labour costs.
• Installation of water points may be needed.
• Watering needs to occur during working
hours when more evaporation occurs.
• Water usage is not optimised and efficiency
may be difficult to monitor.
• Water dispersion may be unevenly
distributed.
Reliable and robust.
Tried-and-tested.
Low installation costs.
Labour does not need to be skilled.
Table 5.6 – Automatic Irrigation Systems
ADVANTAGES
DISADVANTAGES
• Reasonably reliable.
• Low recurrent costs.
• Watering can occur at times best suited to
minimize evaporation.
• Water usage is optimised, is easier to control
and to monitor.
• High installation costs.
• Space required for pumps and other
infrastructure such as electrical controllers.
• Components are more delicate and planting
of vegetation needs more care not to
damage pipe-work.
• Skilled operators are needed to understand
programming of control systems.
5.2.30 The layouts of Automatic Irrigation Systems are dependent on a number of factors: the dispersion height,
the irrigation length, the specific plant requirements and the soil volume needing saturation. Most critical
are the dimensions of the planters to be irrigated. This affects the available water pressure, which in turn
affects the irrigation pipe size, the need for booster-pumps, and in some cases special dispersal
mechanisms.
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5.2.31 For any automatic irrigation system the delivery or dispersal mechanism also needs to be considered.
These are also largely dependent on site location, water supply, water pressure, maintenance access,
size of planter, type of vegetation and expected lifespan. The two major dispersal mechanisms are
described below:
♦
♦
Sprinkler Heads - Sprinkler systems are generally cheaper and are used where water falling on
leaves is desired (i.e. typically grasses, etc) or where long jets of water are the only means to
irrigate a wide surface area. These range from small sprinklers called Bubblers to Spray Heads,
to Rotary Nozzles, to Rotars, and eventually to high-volume delivery systems called Impacts for
very large areas (mostly lawned sports fields). Sprinkler heads are not as accurate as other
dispersal systems with water being lost due to wind and evaporation. Sprinkler Heads need to be
elevated above their immediate vegetation to be able to spout to their desired distance. This
makes them vulnerable to vandalism and damage where people may walk, which necessitates
the need for pop-up versions. The smallest of this type of dispersal mechanism is a bubbler,
which covers an area of about 1.2m delivering a high flow in a small area. Generally, Sprinkler
heads do not perform efficiently in very windy locations, a constraint associated with many green
roofs.
Drip Irrigation – Drip Irrigation Systems are about 30-40% more expensive than sprinkler systems
but offer a more efficient water dispersal method by delivering water at or near the plant root
zone. For tree planting slotted subsoil pipes or special leaking pipes may be installed within the
tree pits. For shrub and ground covers, they are normally installed above the soil (but below the
mulch layer). By applying water directly to the soil, minimal water is lost through evaporation. Drip
irrigation pipes laid on the soil surface are generally sufficiently concealed by the planting to avoid
being visible to the public, but still visible enough to avoid damage during general plant
maintenance. Drip irrigation delivers a low flow to a small area. Drip irrigation lines are vulnerable
to UV light and if constantly exposed they need to be replaced approximately every 2 years. This
is a constraint often associated with many green roofs.
Figure 5.11 Simple Sprinkler Head Irrigation System
A simple sprinkler head system with a very basic timer is low-cost and sometimes all that is needed. (Example shown at HKU)
(Source and copyright © Cheung Shing Yuk Tong Co. Ltd., 2006)
5.2.32 The infrastructure associated with very large areas includes the following:
♦ Central Pump Room – This is usually situated at ground level with water being fed from municipal
sources. The main pump provides any additional pressure that may be needed, which is
especially relevant on elevated structures and very long planters. Space for this pump room
needs to be adequately catered for during the initial design stage. The pump room needs space
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for maintenance, the actual pump, the reservoir tank and control systems. (The accurate
dimensions of these components depend on the available water volume and pressure which
cannot be determined until detail design investigations are initiated.)
♦ Primary Line - From the pump room, a primary line stretches along the longest length of the
planter. This is usually a 2 inch PVC pipe buried within the planter.
♦ Lateral Emitter Lines - Attached to the primary line are the feeding lateral emitter lines to disperse
the water. These lateral emitter lines would often be looped systems connected to the primary
line. The total linear length of the entire loop must not exceed 45m. Emitter heads would be
attached to the pipe at intervals appropriate for the desired dispersion. At the connecting point of
each loop, a valve box is needed. Space for each valve box (approx. 500mm x 400mm x 300mm
high, which includes a valve, filters and control mechanism) needs to be accommodated. An
electrical cable (24V) also needs to be incorporated into the system to control each of these
valves.
5.2.33 Semi-automatic Irrigation systems are constructed in much the same way. The only difference is that the
control system is geared for manual override which means that an operator is responsible for turning it on
every day as needs be. Another possible semi-automatic feature might be the manual control of the
lateral feeder lines. This could be manually controlled electrically (i.e. the operator flips a switch for each
line at the main controller situated in the pump room) or manually controlled at water valves along the
route of the planter.
5.3
MAINTENANCE CONSIDERATIONS
5.3.1
Maintenance is an aspect that will determine the success of green roofs in Hong Kong. The maintenance
requirements of green roofs are determined by many factors – height, micro-climate, soil types, soil
depth, irrigation, species used and access (access is often the most crucial factor influencing
maintenance costs. Green roof design should focus heavily on this aspect).
In the FLL, it is the maintenance requirements (not the soil depth) that determine whether a green roof is
defined as being extensive, intensive or in-between (semi-intensive). Turf grass, for example, is
considered a semi-intensive or intensive green roof, even if installed on a shallow lightweight growing
medium.
Extensive green roofs are built for low-maintenance. Generally, the species used are native and adapted
to harsh conditions (low water, exposed conditions) where they thrive and out-compete other species.
This aspect of extensive green roofs is often misunderstood. A cavalier approach to maintenance, such
as over-watering or over-fertilizing, may in fact change the growing environment making it more prone to
weeds and ultimately adding to the green roofs maintenance requirements.
Intensive green roofs are directly comparable to the maintenance of amenity planting in at-grade locations
and are not elaborated on in this study.
5.3.2
5.3.3
5.3.4
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Table 5.7 Maintenance Procedures for Hong Kong Green Roof Types
Extensive
Extensive
Green Roofs
on Existing
Roofs
Maintenance
Procedure
Sky Gardens
Podium
Intensive
Notes
Waterproofing Inspection
x1 per year
x1 per year
Inspection for water penetration through the concrete
Drainage Inspection
x1 per month
Every 2 months
Litter
X1 per week
None - As necessary
Plant Health Inspections
x6 per year
2 /yr
Replacement planting
As necessary
As necessary
Irrigation
780 l/m²/yr
Low to none
Pruning
x2 per year
N/A
Lawn Mowing
x9 per year
N/A
& Rough Grass cutting
x0 to x3 per year
x0 to x3 per year
Fallow grasses require less cutting than turf grasses.
Fertilizing
x1 to x2 per year
Every 4-5 years
May be increased for horticultural practices which remove
biomass from the system, such as lawn mowing
Disease & Pest Control
X4 per year
X4 per year
Weeding
X9 per year
None to x3 per year
Inspection of drainage outlets
Includes removal of litter and emptying of bins. Depends
largely on the type of green roof, visitor numbers & occasional
litter that may fall on the roof.
Includes checking for insect and fungus infestations.
Particularly relevant during establishment period
Based on 15 litres per week (reduced from 25 litres due to
HK’s high rainfall during summer) for amenity planting.
Depends largely on design and turf grass species used.
Includes regular inspections.
Weeding for extensive green roofs should be virtually none if
installed correctly. Self-seeded trees may be a problem in
urban fringe areas.
5.4
GREEN ROOF DESIGN CHECKLIST SUITABLE FOR HONG KONG
5.4.1
Numerous decision-making steps need to occur before a green roof can be considered on any building.
These ordered questions are presented below as a checklist for consideration:
Table 5.8 – Green Roof Design Checklist for Hong Kong: PLANNING AND FEASIBILITY
Category Checklist Questions
Notes, Tips and References
a. General
What are the client’s objectives for implementing a green
roof? What are the city’s main objectives for implementing
green roofs?
What kind of budget does the client have for both capital
and recurrent costs?
Who will see or appreciate the green roof?
Is a green roof justified in the local context?
See Section 8 for Capital and Recurrent
Costs
Green roofs not visible to the public may be
designed less for visual appeal and more for
ecological or building efficiency performance.
In some cases (such as rural areas, where
the benefits of green roofs may not be
appreciated) a thorough investigation into the
needs for a green roof need to be assessed.
At-grade planting may prove more effective
in terms of visual results, and low capital and
recurrent costs.
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Table 5.8 – Green Roof Design Checklist for Hong Kong: PLANNING AND FEASIBILITY
Category Checklist Questions
Notes, Tips and References
Will the green roof be applied to special structures with
special maintenance requirements or special access?
b. Type of
Roof
c. Roof
Space
d. Roof Pitch
Is the roof new, existing, or in need of replacement or
major repair?
Can the existing waterproofing accommodate new layers
and workmanship above without the need for new
waterproofing? If so, who takes responsibility for the
waterproofing?
Is there sufficient space on the roof to incorporate a
significant area of plants, access pathways, rooftop
utilities, safety railings or devices, and access via ladders
or staircases, etc?
On new buildings, have the rooftop utilities been arranged
to optimise the functional open space and to maximise the
amount of greening?
Is or will the roof be flat or sloped?
Has slippage of the growing medium been considered?
How is drainage affected by slope?
Have the surface flows and water penetration rates been
considered? Is the drainage layer below the growing
substrate capable of removing excess water effectively?
e. Winds and
Climate
Will severe winds be a problem?
Have the wind limits of the site been determined?
The greening proposals for Highways
structures should be assessed on a case-bycase basis and should take into account
local site conditions and also the guidelines
provided in the Transport Planning and
Design Manual.
A deteriorating roof may be the most
opportune and most cost-effective time to
replace the roof with a green roof.
Due consideration should be given to space
needed for refuge floor areas.
Drainage layers on some pitched roofs may
not be necessary as the medium is able to
drain very easily by itself. In some cases
drainage through the medium may be too
fast. The drainage requirements under these
circumstances are best left to experienced
specialists.
Simple methods like timber battens and grids
may be used to curb to problem up to pitches
of 30 degrees. Steeper pitches may require
special substrate mixes and devices.
Some wind problems occur as a result of
vortexes at the edge of the roof created by
updrafts from the face of the building. From
the outset, the building may be designed to
limit this problem using irregular or ‘rougher’
faces (plant covered balconies, for example).
High wind uplift is most severe near the
edges and corners.
Are the green roof layers vulnerable to wind shear?
Does the waterproofing layer need to be bonded to the
roof beneath?
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Table 5.8 – Green Roof Design Checklist for Hong Kong: PLANNING AND FEASIBILITY
Category Checklist Questions
Notes, Tips and References
Has the wind erosion of the soil mix been considered?
Lightweight media like LECA, Vermiculite
and Perlite are considered by some to be too
light for green roof applications. However, if
these are covered with heavier topsoil then
this risk is minimised.
Wind vortex problems may also be mitigated
by angling and extending the shape of the
parapet coping. Erosion problems may
necessitate the use of anti-erosion netting
placed just below the soil surface. These are
the same systems commonly used on slopes
in Hong Kong.
f. Accessibility
Has the staking or weighting down of trees been
considered? If so, how does this interface with the
waterproof layer if it needs to connect directly to the
structure?
Are additional lightning conductors needed to avoid
striking people or trees?
Is or will the roof be accessible or inaccessible?
How will the roof be accessed?
g. Structural
Limits
If the roof is to be accessible, does it have space and
loading capacity for additional railings, lights, paving, etc.?
If accessible by the public will it be secure and safe?
Have durable lightweight materials been used for the
walkways?
What are the structural loading limits of the roof?
Have the loading calculations been done by a Registered
Structural Engineer or suitably qualified person?
Has the dead load included all components (structure,
paving, pipes, HVACs, etc)?
Have the live load estimates included all components (rain,
wind, people)?
Has the dead weight of the green roof materials and plants
been included? Do the soil substrate weights include
moisture content at saturation point?
Has plant weight at maturity been included, particularly for
trees?
Have maximum loading capacities for the roof been
separated into different areas?
Are polystyrene or other lightweight materials being used
to increased depth without adding significant weight?
Has the green roof manufacturer provided detailed
information and attested to the fully saturated weight?
Accessibility and safety for maintenance also
needs to be considered. Difficult or unsafe
access during construction and maintenance
may increase the labour insurance
premiums.
Special cases may require the erecting of
temporary scaffolding for maintenance.
The typical loadings of extensive green roofs
range from 80 to 150kg/m² while intensive
green roofs range from 300 to 1000 kg/m².
I.e. loading directly above support beams
and walls may allow for significant increase
in soil depth (See Figure 5.8)
(e.g. Autoclaved Aerated Concrete, Foamed
Concrete, Extruded Polystyrene, etc.)
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Table 5.8 – Green Roof Design Checklist for Hong Kong: PLANNING AND FEASIBILITY
Category Checklist Questions
Notes, Tips and References
Will any roofing components be removed from the roof
which allows for additional weight?
h. General
Design
Have structural joints been incorporated into the green roof
design from the beginning?
Have maintenance paths been incorporated as part of the
design?
In Hong Kong ‘air-gap’ tiles with elevated
points are often laid above the structural slab
and sealed together. Their construction and
condition might determine whether they are
removed for a retro-fitted green roof which
may affect the weight calculations.
Structural movement joints need to be
accessible for maintenance.
Roof gardens on bridges may require large
concrete slabs on either side of the joint
which should be recognised early in the
design stage.
Maintenance paths are especially relevant
for extensive green roofs because they often
create a distinctly visible intersection within
the green roof canvas.
Table 5.9 – Green Roof Design Checklist for Hong Kong: COMPONENTS
Category Checklist questions
Notes, Tips and References
i. Insulation
and Lightweight fills
j. Waterproofing
k. Root
Barrier
l. Drainage
Layers and
Drainage
Is additional thermal Insulation necessary?
Are lightweight fills needed or desired to create level
differences?
What kind of insulation or lightweight fill is required?
What kind of waterproofing will be used?
Are leak detection tests planned prior to installation?
Does the waterproofing have any guarantee? With
different contractors building the green roof-scape layers
above the waterproofing is this guarantee still valid?
How is waterproofing quality control ensured? How will the
various sub-contractors co-ordinate to ensure that the
water-proofing layer is not compromised during their
construction?
Does the green roof system need an additional root
barrier? Or does the waterproof membrane fulfil this
purpose?
Are the root barriers tied into flashings and roofing
terminations?
How effective is the root barrier?
Has the root repellent system been tested or approved by
a relevant overseas body, the FLL for example?
If the slope is more than 21° have mechanisms such been
installed to prevent slippage of the layers?
What will the drainage layer be made of?
Polystyrene (flammable, not environmentally
friendly but very lightweight) or lightweight
cement mixtures (heavier, more robust and
environmentally friendly). See Section
5.2.25
Membrane tanking or concrete admixtures,
see Section 5.2.2.
A protection board above the waterproofing
may be considered.
If laid loose root barriers should overlap at
least 1.5m to prevent lateral root growth.
Cheaper but heavier granular layers,
lightweight plastic drainage mats made for
water storage, or more robust plastic
drainage grids engineered for rapid removal
of excess water and for heavy loads.
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Table 5.8 – Green Roof Design Checklist for Hong Kong: PLANNING AND FEASIBILITY
Category Checklist Questions
Notes, Tips and References
Has the drainage been designed for major storm events?
Are there at least two roof outlets or overflow drains? In
the event of a major storm event will the vegetation be
drowned? If so, for how long?
Does the drainage capacity increase closer to the drains?
Has the drainage layer adequately catered for the average
rainfall events?
m.Filter Layer
n. Growing
Medium /
Substrate
o. Plant
Selection
Has a drainage specialist investigated the impacts?
If rain water is being retained within the substrate
(moisture reservoir layer) or drainage layer, how long will it
last? Will it last till the next rainfall or will irrigation be
needed in-between?
If the drainage layer stores water, has its loading capacity
been considered during the structural calculations?
Is the filter layer lightweight, rot-proof, inexpensive, easyto-install and permanent?
Is the filter layer effective? Non-woven is preferable.
At the edges and seams, is the filter cloth appropriately
overlapped?
Is the filter layer designed to properly deal with the edges
and curbs?
Has the growing media been specified by an experienced
professional?
Has the medium been well-established and tested?
Does the growing medium have the characteristics specific
to the green roof design? (weight, water absorption,
stability, resistance, drainage and surface area)
How is the growing media being transported to the roof?
Has the plant material been specified by an experienced
professional?
Will any new plants be introduced into Hong Kong? Have
these been approved by AFCD?
Will any new plants be imported into Hong Kong? Have
the necessary Plant Import Licences / Phytosanitary
documents been acquired from AFCD?
Do the selected plants work in the local area and specific
rooftop environment?
Has full consideration been given to growth rates,
sensitivity to airborne pollutants, ability to withstand wind,
drought tolerance, and fire resistance?
Are they readily available for supply? If not how long?
Will seeds be used, cuttings, mats, modules plugs or fully
grown plants?
On lower areas, has the sun exposure hours and shade
hours been considered?
p. Irrigation
With heavier downpours (such as occur in
Hong Kong) a thicker drainage layer is
recommended, i.e. 25mm thick rather than
12mm, used abroad.
See Section 5.2.18
See Table 7.2 for potential species suitable
for extensive green roofs in Hong Kong. Also
see Table 6.1 for a list of known trees that
are suitable for use in Hong Kong’s Podium
Gardens and Sky Gardens.
Plants from countries other than mainland
China may need to fulfil more stringent
requirements.
These affect the price but mature at different
rates.
This is particularly relevant to podium
gardens and green roofs proposed on
elevated walkways within the city.
Have the irrigation needs been established, particularly
during the dry season?
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Table 5.8 – Green Roof Design Checklist for Hong Kong: PLANNING AND FEASIBILITY
Category Checklist Questions
Notes, Tips and References
Will additional roof-top water points be needed? Or will
tanks and pumps be needed?
What kind of irrigation system is needed?
How will irrigation be timed?
Sprinklers are cheaper but are inefficient in
windy conditions. Surface drip irrigation is
more expensive and is vulnerable to UV
(automatic, semi-automatic or manual)
Table 5.10 – Green Roof Design Checklist for Hong Kong: MAINTENANCE & MANAGEMENT
Category
Checklist questions
Notes, Tips and References
q. Management
Has a detailed management plan and budget been
established?
Are any special arrangements required for access? (e.g.
scaffolding)
Who is responsible for management and maintenance?
How will access be managed?
Will horticultural training be necessary
Will litter bins and associated maintenance be required?
Will temperature reductions be measured to determine
building energy efficiency changes? Who will coordinate measurements and data collection?
r. Maintenance
In government projects the agents
responsible are not necessarily LCSD by
default. For clarification refer to ETWB TCW
No. 2/2004 (Maintenance of Vegetation and
Hard Landscape Features
http://www.etwb.gov.hk/UtilManager/tc/C2004-02-0-1.pdf ).
It is advisable to resolve maintenance
responsibilities before implementation.
Access for maintenance and the public
needs to be controlled. Green roofs not
intended for public access might attract
curiosity visitors.
Dedicated horticultural maintenance staff are
usually required for intensive green roofs.
Maintenance for Extensive green roofs is
easy enough for building maintenance staff
to be done. In most cases an introductory
lecture of 2 hours by an experienced green
roof contractor is all that is necessary.
Baseline measurements before construction
need to be taken. Teams or qualified
professionals may use pyrometers,
scintillometers, infra-red cameras or thermal
imaging cameras (very expensive) to
determine building temperatures.
How will the plant species selection affect
maintenance?
How often will drains be inspected?
How often will plant health be inspected?
How often will the building’s waterproofing be checked?
How often will irrigation need to be switched on? How
often will the irrigation system need to be checked?
How often will weeding be necessary?
How often will fertilizing be necessary
How often will tree-staking need to be checked?
How often will mowing need to be done?
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6
INTENSIVE GREEN ROOFS (SKY GARDENS & PODIUM GARDENS) IN HONG KONG
6.1
CONSTRUCTION DETAILS
Figure 6.1 Details of Typical Intensive Roof Garden
(Source: adapted from drawings of PTI roof garden park, CNR Chatham & Salisbury Road, TST. copyright © Urbis 2006 and
adapted from drawings from LF Sam Ltd.)
6.2
SPECIAL CONSIDERATIONS FOR PODIUM GARDENS & SKY GARDENS
The Importance of Trees
6.2.1
Any urban greening proposals, including green roofs, should consider the inclusion of trees. Compared to
other types of greening, trees are generally the most effective in terms of:
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
the amount of greenery they provide versus the ground surface area they occupy (though roots
may occupy substantial underground space);
their provision of shade;
their rates of evapo-transpiration;
their total leaf surface area and ability to filter air-bourne particulates and gaseous pollutants;
their life-expectancy;
their sensitivity to climatic and air quality fluctuations
their visual mass;
the ecological habitats they create;
their long term maintenance and water requirements; and
their price
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6.2.2
Trees greatly enhance the various benefits offered by green roofs. Trees define spaces and provide
micro-climates conducive to the creation of amenity spaces on rooftops, which may ultimately enhance
the value of the property. A plant selection matrix of trees, palms and palm-like trees applicable for
intensive green roofs in Hong Kong is presented in Appendix II.
Trees in Roof Gardens
6.2.3
When including trees in roof gardens the following key aspects should be considered.
♦ Provision of adequate soil volume for healthy growth and anchorage is critical. A simple rule of
thumb is that 1.2m soil depth should be provided, although smaller trees may grow in shallower
depths, provided that the lateral extent of soil is widened to compensate.
♦ Soil depth may be locally deepened at tree locations (either by mounding the soil surface or
locally deepening the planter). Trees may be located over structural columns to take advantage
of loading efficiency.
♦ Tree anchoring may be by staking or tying down of the root ball but in all cases must not interfere
with the integrity of the waterproofing.
♦ Species selection is critical. Trees need to be selected which have a strong branching system,
are flexible in high winds and have leaves that do not appear battered when exposed to strong
winds.
Calculating Plant Weights
6.2.4
Calculating plant weights at maturity (particularly for trees) is an important consideration during the initial
design stages of a green roof. There is no industry standard for calculating tree weights. The simple
method presented below in Figure 6.2 was adapted from the successful techniques used for the
importing, transporting, and installing of large trees to Penny’s Bay and Hong Kong Disneyland.
6.2.5
Tree weight calculations consists of three components; stems, branches and roots. Weight calculations
for roots can simply use the entire volume of the soil multiplied by an average soil density (1750kg/m³).
The proportion of the roots (around 20%) can be ignored because the heavier density of soil builds in an
adequate safety margin. The above-soil weight calculations are based on a tree being simplified into a
consistent cylinder, where the volume is easy to calculate (¶.r² x H), multiplied by the density of hardwood
(650kg/m³). The estimated radius at the branching height (usually ⅓ of the estimated total height) is
considered a usable average for the volumetric calculations of the assumed cylinder.
Figure 6.2 Calculating Plant Weights at Maturity
Note: The technique presented is for general reference only.
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6.2.6
It should be noted that the above calculations do not factor in wind loading which needs to be added to
the weight loading calculations. Additional wind loading results from the horizontal force of the wind being
transferred to the roots of the tree, resulting in a downward pressure on one side and an upward pressure
on the other side. This is best left for suitably qualified engineers and experts to determine. Also not
included are tree supports and anchorage which may become exceedingly heavy with larger trees.
6.2.7
Determining plant weights during construction is also important. These weights need to be calculated to
determine labour and transport costs and to ensure the balancing of cranes that may be used to lift heavy
trees. Table 6.2 below presents a very general indication of typical weights for a variety of plant materials.
Table 6.2 Plant Weights
Plant Type
Description
Root Ball Size
and Depth
Estimated
Planting
Weight
TREES
Light Standard Tree
Stem dia. 35mm, total height 2.5m
Root ball dia. 350mm, depth 300mm
54 kg
Standard Tree
Stem dia. 60mm, total height 3.5m
Root ball dia. 350mm, depth 300mm
58 kg
Heavy Stand. Tree
Stem dia. 150mm, total height 3.5m
Root ball dia. 400mm, depth 350mm
119 kg
Semi-mature Tree
Stem dia. 200mm, total height 5.5m
Root ball dia. 1000mm, depth 600mm
961 kg
Specimen Trees
Stem dia. 200mm, total height 7.0m
Root ball dia. 1000mm, depth 600mm
991 kg
Stem dia. 250mm, total height 8.0m
Root ball dia. 1200mm, depth 800mm
1884 kg
Stem dia. 300mm, total height 10m
Root ball dia. 1500mm, depth 1000mm
3640 kg
PALMS & BAMBOO
(well formed and with good fronds)
Palms
Stem dia. 30mm, clear trunk ht. 300mm
Root ball 200mm, depth 250mm
14 kg
Stem dia. 40mm, clear trunk ht. 700mm
Root ball 200mm, depth 250mm
15 kg
Stem dia. 80mm, clear trunk ht. 1500mm
Root ball 350mm, depth 300mm
57 kg
Stem dia. 100mm, clear trunk ht. 3000mm
Root ball 500mm, depth 450mm
174 kg
Stem dia. 120mm, clear trunk ht. 4500mm
Root ball 1000mm, depth 600mm
881 kg
Stem dia. 150mm, clear trunk ht. 7500mm
Root ball 1300mm, depth 800mm
1997 kg
Stem dia. 170mm, clear trunk ht. 9500mm
Root ball 1800mm, depth 1000mm
4721 kg
Stem dia. 175mm, clear trunk ht. 1500mm
Root ball 350mm, depth 300mm
75 kg
Stem dia. 210mm, clear trunk ht. 2000mm
Root ball 350mm, depth 300mm
97 kg
Stem dia. 50mm, overall height 600mm
container dia 400mm, depth 450mm
103 kg
Small Shrub
Stem dia. 10mm, Overall height. 400mm
container dia 130mm, depth 150mm
4 kg
Medium Shrub
Stem dia. 15mm, Overall height. 600mm
container dia 150mm, depth 200mm
6 kg
Small Gnd covers
Average dia. 350mm
Pot grown dia.125mm, depth 150mm
3 kg
Medium Gnd covers
Average dia. 500mm
Pot grown dia.150mm, depth 200mm
6 kg
Large Gnd covers
Average dia. 1200mm
Pot grown dia.200mm, depth 300mm
Note: Calculations use thick-diameter trees, a wood density of 650kg/m³ and soil density of 1750kg/m³.
(Source: Adapted from values provided by Asia Landscaping Ltd.)
17 kg
Bamboo Palms
Bamboo
SHRUBS
GROUND COVERS
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7
EXTENSIVE GREEN ROOFS (ECO-ROOFS) IN HONG KONG
7.1
CONSTRUCTION DETAILS
Figure 7.1 Details of General Roof Build-up
(Source: Adapted from technical drawings for Eco Park, Hong Kong, from Sarnafil Ltd.)
Figure 7.2 Details of Parapet Edge Treatment
(Source: Adapted from technical drawings for Eco Park, Hong Kong, from Sarnafil Ltd.)
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Figure 7.3 Details of Typical Drainage Inspection Chamber
(Source: Adapted from technical drawings for Eco Park, Hong Kong, from Sarnafil Ltd.)
Figure 7.4 Detail of Typical Penetration of Roof-top Utilities
(Source: Adapted from technical drawings for Eco Park, Hong Kong, from Sarnafil Ltd.)
7.2
MODULAR TRAY SYSTEMS
7.2.1
Recent years have seen the introduction of tray systems into the extensive green roof market. These
come in a variety of shapes and sizes and offer some advantages, particularly for maintenance. Figure
7.5 illustrates a typical large tray system (1.17m x 1.17m) needing equipment to install but being tightly
connected to allow for additional soil to be installed above the bounds of the tray. Figure 7.6 illustrates a
smaller and possibly more versatile system that can be installed manually. It appears to be completely
self-contained and has drainage connected directly to roof outflow pipes rather than relying on the
existing waterproofing. Although planting designs may be restricted by the rigidity of a grid system, welldesigned plant variety, as seen below in Figure 7.7, needs to be used to create a pleasant design.
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Figure 7.5 Typical Extensive Green Roof Tray Systems
(Source: adapted from GreenTech ITM™ Module by GreenTech, Inc.)
Figure 7.6 Prefabricated Extensive Greenroof (PEG) Tray System Developed in Singapore
(Source and copyright © ZinCo Singapore Pte Ltd., using a patented design developed by Singapore’s Housing &
Development Board and United Premas Ltd.)
Figure 7.7 Aesthetic Potential of Extensive Green Roof Tray Systems
GreenGrid™ modular rooftop garden
(Source and copyright © Weston Solutions, Inc.)
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7.2.2
Tray Systems, like extensive green roofs in general, are suitable for retro-fitted green roofs. Despite the
apparent ease of construction, tray systems have negative characteristics which must be also be
considered.
Table 7.1 - Advantages and Disadvantages of Tray Systems
♦
♦
♦
♦
♦
♦
♦
♦
♦
7.2.3
Advantages
If the growing medium is completely
contained, then the modules (only if
small enough) can easily be removed
and put back in place without disturbing
the plants.
Plants are pre-planted and may be
used for instant effect. Seasonal or
festive effects may make use of this
advantage though it would be a costly
exercise.
Onsite installation is quicker. Downtime
due to inclement weather is reduced.
Onsite installation can be done by less
experienced labour as quality is
maintained more at the plant
propagation nursery rather than by the
onsite contractors.
Alterations may be easier and
installation in stages is easier.
Concerns over various sub-contractors
(if different) interfering with each other’s
layers, such as the waterproofing layer,
are reduced.
Tray systems may be well suited to
sloped roofs.
Trays systems may be well suited to
being specially mounted above some
roof top utilities (e.g. pipe work).
Designers may experiment or refine the
planting design on site by mixing and
matching the different pre-grown
planting modules.
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
Disadvantages
In years to come, older module designs may not be
available making replacing of parts difficult.
Plastic trays will eventually deteriorate in the sun, even
UV-resistant plastic. This compromises the aging
benefits that green roofs offer over conventional roofs.
There is also the possibility that cheap copies using
inferior short-aged plastics may flood the market.
Transportation and stacking difficulties and expenses
may be higher, especially for larger tray systems. Larger
cranes may be needed in many cases. (Only onsite
installation may be quicker).
Being self-contained, trays may be slightly more prone to
drying out, requiring more watering and care. (Tray
systems must have adequate soil depth and water
reservoir layering to overcome this).
Some tray systems have fixed soil depths which limits
the overall design.
Planting designs and maintenance pathways layout are
largely dictated by the uniform squares of the trays. The
exposed grids lines may also detract from the aesthetic
qualities of a continuous landscape.
As trays may be easier to dismantle they may invite
developers to be only half-committed to green roofing.
If modules are rigidly connected or buried with soil above
then the removal may be as cumbersome as normal
extensive green roofs.
There is the possibility of roots growing through drainage
holes in open module systems and compromising the
roof slab below (particularly from undesirable selfseeding weed trees).
Uneven roof surfaces below the tray system may collect
water. As this water may not evaporate away fast
enough it may create breeding grounds for mosquitoes.
Major conditions/scenarios for choosing a modular tray system might include the following:
♦
♦
♦
♦
♦
If regular removal for inspection is foreseeable;
If the plastic used is guaranteed over the long term;
If long-term roofing cost benefits are not a concern;
If an instant effect is needed; and/or
If liability issues between sub-contractors is a concern.
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7.3
PLANT SELECTION FOR EXTENSIVE GREEN ROOFS
7.3.1
In the early days of roof greening in central Europe the species used were generally the more showy or
resilient components of dry meadow communities or species chosen from the extensive flora popular as
rock-garden plants. Trialling of species for their suitability for roof greening was a major part of the early
research work. German researchers set up trials, with plants being evaluated by a panel, which assessed
them for appearance of growth and ground coverage. Sedums consistently rated high, along with lowgrowing grasses such as many Festuca and Koeleria species. Sedums have since become the standard
plant for shallow-substrate roof-greening systems due to their drought tolerance, year-round good looks,
ease of propagation, and suitability for shallow substrates. The trials also revealed surprises. Some
species were found to be unsuitable for their sensitivity to competition with grasses. Others were
excluded for the opposite reason – invasiveness. 42
7.3.2
The task of selecting suitable plant species for roof greening has arguably hardly begun, and it offers
potentially enormous rewards. 43 Unfortunately, there has been a limited range of research into widening
the planting possibilities on roofs. While many German green-roof companies carried out their own
research into suitable species for low-input green roofs, they are now doing very little additional research.
In parts of the world where green roofs are a new phenomenon, there is a tendency to repeat the use of
these species. 44 It is essential for proper local investigations to be done to find the most appropriate
species.
7.3.3
It is important to note that new technologies are emerging, especially in the field of façade walls. Although
the maintenance of these systems is largely unknown (probably notably higher than extensive green
roofs), they do offer an urban greening method that uses epiphytes, of which Hong Kong has many
suitable species.
7.3.4
A collection of species that have extensive green roof potential are listed in Appendix II. Year-round
greenery is theoretically possible in all plant species presented. This is dependant on the local conditions,
maintenance and watering. Plants adapt and grow well in ideal and consistent environments. Highly
responsive maintenance/irrigation regimes aims to ameliorate stressful impacts (excessive heat and dry
periods for example) allowing plants to flourish. Maintenance and irrigation that responds poorly to
extreme conditions might result in plants appearing less desirable during such periods. Plants listed in
Appendix II generally look well even during harsh conditions, allowing appearance to be maintained with
minimal maintenance. However, some species will perform better than others. Species with succulenttype characteristics (i.e. those with C4-photosynthesis or CAM- photosynthesis), which have special
mechanisms for preserving water, generally appear better during extreme periods. Plant family names
are also included in Appendix II as these reveal such features. Succulents-type plants include
Crassulaceae, Agavaceae, Cactaceae, Dracaenaceae and Portulacaceae.
7.4
EXTENSIVE GREEN ROOF PLANTING APPROACHES
7.4.1
This section suggests planting options commonly associated with extensive green roofs. Extensive green
roofs are designed for their low maintenance and/or ecological functioning and generally follow four basic
approaches:
♦ Mono-culture Planting. This type of planting is simple and usually uses one plant species en
masse. It is the easiest to prescribe and install. It is argued that mono-culture plantings are
visually uninteresting but in some circumstances a uniform appearance may be appropriate.
From an ecological viewpoint they may be susceptible to total die-back if drought or disease
(42)
42
Dunnett & Kingsbury (2004) p102
(43)
43
Dunnett & Kingsbury (2004) p103
(44)
44
Dunnett & Kingsbury (2004) p80
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♦
♦
♦
severely affects the species in question.
Pattern Planting. This type of planting is used primarily for its visual effect but uses more than one
species. As an open canvas, a wide range of designs are possible. The usual design elements
may be used for good effect: a play with materials and colours; a play with proportion and
balance; a play with texture, pattern and line; and the use of rhythm and repetition. This approach
may require higher maintenance levels than other planting approaches.
Mixed Planting. The approach uses a mix of species to create a random but colourful carpet. It is
a relatively safe approach as the successful growth of various species will eventually find there
own equilibrium. This approach does not necessarily use indigenous species and in most parts of
the world uses a mix of sedums.
Plant Communities Planting. This approach is based on natural habitats. Plants are chosen and
combined in proportions approximating nature and their occurrence in the wild. Community-based
planting tends to be self-sustaining, requiring low maintenance inputs for their upkeep. By their
nature, they would be informal with a naturalistic appearance. This approach may often use wild
grasses and may be considered untidy by some. Some examples from overseas have seen the
careful and diverse selection of plants that flower almost year-round. This approach strives to use
indigenous plants to fulfil a green roof’s maximum ecological potential.
Figure 7.8 Extensive Green Roof Planting Approaches
Monoculture planting (Source: Urbis Ltd.)
Pattern Planting
(copyright © Earth Pledge, 2005, photo Peter Philippi)
Mixed Planting
(Source and copyright © Earth Pledge, 2005, photo by City
of Portland)
Plant Communities Planting - planting design by Dunnett.
(Source and copyright © Dunnett & Kingsbury (2004),
p101)
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8
GREEN ROOF COST ESTIMATES FOR HONG KONG
8.1
CAPITAL COSTS
8.1.1
Capital Costs are largely dependent on labour, materials and access difficulties. However, compared with
entire building costs in Hong Kong 45, green roofs costs, both intensive and retrofitted extensive, are very
small. This is illustrated in Table 8.1 below.
Table 8.1 Comparison between Building and Green Roof Costs in Hong Kong
$24,000
$20,000
$17 700 / m²
Luxury Houses
$16,000
$12,000
$8,000
$5000 / m²
$4,000
$3600 / m²
Low-cost Housing
Average $2000/m²
$1,000 / m²
Average $500/m² $400 / m²
$1,000 / m²
$0
HK Building Costs
Intensive Green
Roofs HK
Extensive Green
Roofs HK
12%
Percentage of Total Building Costs
10% Int.
10%
8%
6%
4%
2.56% Int.
2.22% Int
2%
0.28% Int
0.08% Ext.
0.55% Ext
20 Storey
Standard
Apartment
@ $9000 /m²
(Podium)
0.64% Ext.
0.27% Ext.
0%
40 Storey
5 Star Hotel
@ $17600 /m²
2.56% Ext.
1.11% Int.
20 Storey
Standard
Apartment
@ $9000 /m²
(Rooftop)
12 Storey
Industrial
Building
@ $6500 /m²
3 Storey
Infrastructure
Building
(excl. industrial
equipment)
@ $6500 /m²
The lower table illustrates the range that green roofs will play in the overall costs of buildings ($500/m² for extensive green
roofs, and $2000/m² for intensive green roofs). It illustrates that on luxury skyscraper buildings, green roof costs are virtually
insignificant. On low-rise infrastructure buildings green roof costs might reach 10% of the total costs if elaborate Intensive
Green Roofs are considered).
(45)
Approximate Building Costs in Hong Kong, 1st Quarter 2006 (Davis Langdon & Seah, Quantity Surveyors)
http://www.dlsqs.com/modules.php?name=News&file=article&sid=279
45
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Extensive Green Roof Capital Costs
8.1.2
Table 8.2 shows the range of capital costs for extensive green roofs in North America, Germany and
Hong Kong. A range of $400/m² to $1000/m² (average $500/m²) is estimated for Local Extensive Green
Roof costs 46 and relates to retrofitting costs. The costs for new construction extensive green roofs
currently have no precedents in Hong Kong. However, American research 47 indicates that new
construction extensive green roofs costs are around 60 to 70% that of retro-fitted projects.
Table 8.2 Comparison of International and Local Extensive Green Roof Cost Ranges
$2,000
$1,850
$1,800
$1,600
$1,400
HK$ / m²
$1,200
$1,000
$1,100
$1,000
$1,100
$800
$680
$670
$600
$400
$600
$400
$200
$0
North American
Extensive Green Roofs
(new markets)
German/European
Extensive Green Roofs
(well-established markets)
Local supplier's quotes
using reputable imported
proprietory products
Local Supplier's quotes
using local materials
Note: All costs quoted in Hong Kong Dollars
8.1.3
A typical breakdown of the costs involved is illustrated below in Table 8.3. The specialised growing
substrate is clearly the most expensive part.
Table 8.3 Typical Extensive Green Roof Capital Cost Breakdown (example from USA)
Drip Irrigation
5%
Root Barrier & Waterproofing
16%
Plant Materials
31%
Mulch (20mm), Soil Substrate
(100mm), Drainage (10mm)
48%
(Source: calculated from component priced at www.greenrooftops.com)
(46)
46
(47)
Figures based on quotes from local suppliers with some experience in Hong Kong and in China
Portland Bureau of Environmental Services (2002), indicates that a new construction would cost around HK$800/m² to HK$1200/m² (US$10/ft²-US$15/ft²)
while a retrofitted green roof might cost around HK$1200/m² to HK$2000/m² (US$15/ft²-US$25/ft²).
47
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8.1.4
The costs of extensive green roofs are generally affected by the following:
♦
♦
♦
♦
♦
♦
♦
♦
♦
Access constraints to the site during construction
Whether the project is a new construction or a retro-fit project.
The slope of the roof.
Status of the existing roof (if a retro-fit project).
The number and arrangement of rooftop utilities, affecting labour and wastage.
The materials used, and the type of plant material used. This affects labour costs (plants may be
individually planted, seeded, or have pre-grown sedum or turf mats applied).
Irrigation needs.
Growing medium depth.
Access or safety components that need to be added
Intensive Green Roof Capital Costs
8.1.5
The costs of intensive green roofs are highly variable and therefore difficult to assess 48 . They are
estimated to be at least double the cost of an extensive green roof (if only soft-landscaping costs are
considered).
8.1.6
Costs for intensive green roofs can be divided into two broad categories – soft-landscaping (with a unit
cost of $800/m²) 49 and hard-landscaping (with unit costs of $3200/m²) 50 which together give a general
value of $2000/m² for easily accessed intensive green roofs. The lowest value, with very easy access
and mostly soft-landscaping is estimated to be around $1000/m². The general high-end range has been
assessed at $5000/m² and is based on a green roof having a highly thematic design, difficult access (5
storey podium) and where the landscaping contract and crane operations are brought in separately. 51
8.1.7
The costs of intensive green roofs are generally affected by the following:
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
Access constraints to the site during construction
The ratio of hard- to soft-landscaping
The amount of specialised thematic designs and materials including water-features, canopies,
etc.
Whether the green roof is part of a larger building contract or not. This affects the availability of
building equipment already on site. For example, costs can be drastically affected if cranes are
brought in just for landscaping (large cranes, reaching a 6 storey high podium, will cost about
$400,000 to erect and dismantle, and will have a running cost of $100,000 per month) 52.
Whether the contract needs to be built in access-limiting stages. When a site is being used by the
public (often requiring pedestrian diversions), costs may be increased by these inconveniences.
The size and maturity of the trees being installed and the type of vegetation being prescribed
(palms, bamboo, trees)
The depth of the topsoil
Irrigation needs.
Lighting
Access or safety components that need to be added
(48)
48 Green roof garden design and soil depth might dramatically influence the structural design of a building with cost implications that are not possible to
separate. The green roof cost range provided does not consider such extreme cases and is based on costs occurring above the roof slab.
(49)
49
Costs based on two public accessible roof gardens being currently being built above new KCRC and MTR stations
(50)
50
Costs based on hard-landscaping costs of a new publicly accessible roof gardens currently being built above an MTR station
(51)
51
Costs based on elaborate and thematic roof garden being built as part of Macau’s casino complex
(52)
52
Based on construction costs of a new casino complex in Macau
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General Green Roof Capital Cost Breakdown
8.1.8
Table 8.4 below offers a typical breakdown of the costs involved for intensive and extensive green roofs.
Although this table may provide a good indication for budgetary purposes, it should be noted that pricing
of green roofing is normally by a global rate or item, rather than by each individual component of the
green roof design.
Table 8.4 Costs Breakdown and Commercial Availability of Components in Hong Kong (HK$)
Basic Green Roof
Components
Supply
Costs HK$
Install &
Labour
Costs
HK$
Additional Costs ‡
- due to height and
access
constraints, etc.
Additional Notes & Descriptions
PLANT MATERIALS
Cost is dramatically influenced by size of
trees and site access. Semi-mature trees
may need external cranes.
Trees (Standard Size)
$180 / tree
$100 / tree
$200 / tree
Shrubs
$20 / shrub
$10 / shrub
$20 / shrub
Climbers
$10 / plant
$10 / plant
$20 / plant
Groundcovers
$8 / plant
$6 / plant
$6 / plant
Sedums (Specialized
species)
$60 / m²
$10 / m²
$20 / m²
Grasses
$40 / m²
$10 / m²
$20 / m²
Mulch (50mm)
$20 / m²
$10 / m²
+$20 / m²
Topsoil
$170 / m³
$160 / m³
+$100 / m³
3:1 (CDG: conditioner)
Sand
$100 / m³
$160 / m³
+$350/m³
River Sand
Lava (scoria) and Pumice
$500 / m³
$160 / m³
+$350/m³
(Sourced from Inner Mongolia)
Gravel
$180 / m³
$160 / m³
+$350/m³
Perlite
$1500 / m³
$160 / m³
+$350/m³
Vermiculite
$480 / m³
Included
+$350 / m³
100mm Vermiculite pellets (3mm 6mm) with 300mm soil mix - Supply, mix and
lay to Ground level works only.
LECA (Light Expanded Clay
Aggregate)
$530 / m³
Included
+$350/m³
100mm LECA with 300mm soil mix - Supply,
mix and lay to Ground level works only.
+$350/m³
Price depends on availability of brick rubble
in the area which is crushed on site.
GROWING MEDIUM
Crushed clay Brick or tiles,
Brick rubble
Moisture Reservoir Panel
within growing medium
(40mm THK)
$200 / m²
Included
Included
$10/m²
Included
Included
PROTECTION & DRAINAGE
LAYERS
Filter Layer
The more expensive layers with specialized
dimples is to be used specifically when water
retention is required.
$120 / m²
Drainage Layer
$84 / m²
Non-woven fabric is better. Filter layer is
often built onto the drainage layer.
Included
Included
$60 / m²
Other lower costs systems are made for
more rugged situations and are designed for
very heavy loading and rapid removal of
excess water.
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Basic Green Roof
Components
Supply
Costs HK$
Install &
Labour
Costs
HK$
Additional Costs ‡
- due to height and
access
constraints, etc.
Additional Notes & Descriptions
Separate Root Barrier / Root
herbicide layer
$60 / m²
Included
Included
OPTIONAL. - Seperate root barrier is needed
if waterproofing layer does not provide this
function
Waterproof Layer (PVC
membrane) and root layer.
$130 / m²
Included
Included
PVC layer. Costs include Moisture retention
mat above and separation layer below
Integrated Cement
Waterproofing (Admixtures
and Impregnations)
$34 - $68/m²
(150mm slab)
Thermal Insulation Layer
(Expanded Polystyrene)
$45 / m²
None
None
Robust and effective when used as an
admixture to concrete (i.e. for new roofs).
Needs a concrete layer of 150mm for
effective guarantee.
Included
Included
OPTIONAL. May be needed if additional
thermal insulation is desired.
OTHER COMPONENTS
Paved areas
$200 - $800
/m²
Included
Included
Autoclaved Aerated Concrete
$650 /m³
$350 /m³
Included
Lightweight Foaming
Concrete
$800-1000 /m³
Included
Included
Concrete roof slab
$1650 /m³
Included
Included
Concrete roof beams
$3050 /m³
Included
Included
Extension of Concrete
Columns
$2700 /m³
Included
Included
Concrete walls
$2000 /m³
Included
Included
Railings added to parapet
$1000 / ln.m
Included
Included
Drip Irrigation System
$70/m² to
$100/m²
Included
Included
Sprinkler Irrigation System
$55/m² to
$70/m²
Included
Included
Commonly termed Y-Tong blocks in Hong
Kong
Standard S/S Railings. Free-standing railings
with concrete footings = $1200 / ln.m
Price does not include additional tanks and
pumping systems. It includes dispersal
mechanism, controllers, timers and rain
sensors.
Note ‡ - Additional Costs due to height & access constraints, are based on a typical 20 storey residential block in Hong Kong.
8.2
RECURRENT COSTS
8.2.1
Maintenance requirements for Intensive green roofs are directly comparable to the maintenance of atgrade parks, except for the difficulties associated with height access by maintenance staff. These
proportions may vary considerably but are generally in the order of 30% which brings the local
maintenance costs for intensive green roofs to between $6.5 per m² per year to $44 per m² per year 53.
8.2.2
Estimated maintenance costs for extensive green roofs are based on industry experience in Beijing and
Shanghai (Shanghai is considered a close approximation to Hong Kong) 54 . If installed as a proper
Extensive Green Roof, maintenance should only require 1 minute per m² per year. This may increase but
will very rarely exceed 3 minutes per m² per year. Translated into local labour costs this equates to
between $0.8 per m² per year and $2.25 per m² per year. These values are typical for typical building
rooftops. Very difficult access (such as on some highways structures) may have even higher maintenance
(53)
53
Based on LCSD Term Contract rates and discussions with Tarzan Ltd.
(54)
54
Discussions with Peter Küsters (FLL representative in Asia) of Greenlink Küsters.
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values for extensive green roofs.
8.2.3
It is estimated that the maintenance of hybrid or semi-intensive green roofs, where more common
amenity planting is used on thin lightweight substrates, will result in a maintenance cost range above true
extensive green roofs but below the lowest range of Intensive green roofs, i.e. between $2.25 per m² per
year to $6.5 per m² per year. Examples might include the turf grass and Duranta repens planted at HKU
(see Figure 4.2), the amenity planting tried on bus shelters (see Figure 4.3) and the turf grass planted at
Kadoorie Farm (see Figure 4.4).
Table 8.5 Comparison of Local Intensive and Extensive Green Roof Maintenance Cost Ranges
$48.00
$44.00
$40.00
$36.00
$32.00
$28.00
$24.00
$44 /m²/yr
TYPICAL EXAMPLES IN HONG KONG
Posssible Costs Added
• very difficult access
• dangerous work conditions
• small areas
• refuse collection (high traffic)
• problematic pests
• high maintenance plants
• electricity & lighting
WAN CHAI POLICE HQ
$20 /m²/year (excluding non-horticultural maintenance)
15/F high access, high security, lift access only
TYPICAL RESIDENTIAL PODIUM
$13 /m²/year (excluding non-horticultural maintenance)
lower level but often limited to lift access only
$20.00
$16.00
$12.00
IFC2 PODIUM
$9 /m²/year (excluding non-horticultural maintenance)
low level, large areas, various access points
Conventional Cost Range
(Horticultural Costs only)
MIDDLE ROAD CHILDREN'S PLAYGROUND
$7 /m²/year (excluding non-horticultural maintenance)
low level, large area, wide stair access, lift access.
onsite maintenance storage rooms
$8.00
$4.00
$6.5 /m²/yr
$0.00
Intensive
Green Roof
Labour Costs
$2.25 /m²/yr Conventional Cost Range
$0.8 /m²/yr (Horticultural Costs only)
Extensive
Green Roof
Labour Costs
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PART 3
Conclusions and the Way Forward
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9
SUMMARY OF THE STUDY
9.1
BACKGROUND
9.1.1
There are two main types of green roofs:
♦ Intensive Green Roofs (with deep soils, wide plant choice but requiring more capital and
maintenance resources); and
♦ Extensive Green Roofs (that are lightweight, have a narrow plant range, and are geared for low
maintenance).
The Study finds that the green roof industry is well established in Europe, particularly Germany and is
rapidly becoming popular in North America and in some parts of Asia.
9.1.2
9.1.3
In Hong Kong Intensive Green Roofs are already well-established in the form of podium gardens.
Extensive Green Roofs, on the other hand, are better-suited to retro-fitting projects which have their own
technical constraints, and are not yet well-established in Hong Kong. Despite Intensive Green Roofs
being well-established, a consolidated approach to green roof techniques and standards is still needed.
9.1.4
The benefits of Green Roofs are numerous and well-researched overseas. All of the benefits are of some
value to Hong Kong, in varying degrees. These benefits include:
♦ Amenity and Aesthetic Benefits including:
̇ Leisure and Functional Open Space
̇ Visual Amenity Value; and
̇ Health and Therapeutic Value
♦ Environmental Benefits including:
̇ Ecological and Wildlife Value,
̇ Water Management,
̇ Reducing the Urban Heat Island Effect, and
̇ Air Quality.
♦ Economic Benefits including:
̇ Increased Roof Life,
̇ Building Insulation & Energy Efficiency,
̇ Green Building Assessment & Public Relations)
9.1.5
Although all green roof benefits will be noticeable, the major benefits for Hong Kong are considered to be:
♦ Increased Leisure and Functional Open Space.
♦ Increased Visual Amenity.
♦ Improved Building Insulation & Energy Efficiency. 55
♦ Green roofs at a significant scale also contribute towards numerous city-wide environmental
benefits. These include improved water-management, air quality and mitigation of the urban heat
island effect. 56
(55)
55
Research by ZHAO Ding-guo (2005 at the Environmental Science Research Institute, SAAS, Shanghai, 201106, China) & XUE Wei-cheng shows that a
reduction of 2°C for internal room temperatures can be expected, though other research claims values of 4°C to 5°C under different circumstances.
Research by N.H.WONG (2005, National University of Singapore) shows a net annual saving of 15% for air-conditioning costs on a 5 storey building.
Local findings show similar results and indicate that the surface temperature of a vegetated area can be about 10°C to 15°C lower than that of a concrete
roof on a sunny day in November/December (readings at EMSD HQ building) and about 18°C to 26°C lower during August (readings at HKU).
(56)
56
Research (Green Roofs for Healthy Cities Coalition, 2002) indicates that 1 square meter of grass can remove 0.2 kg of airborne particles per year.
Research on the ACROS building in Fukuoko, Japan illustrates that the environmental benefits of intensive green roofs extend beyond the building footprint
and may play a significant role in mitigating the urban heat island effect.
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9.2
GREEN ROOF OPPORTUNITIES, CONSTRAINTS & CONSIDERATIONS FOR IMPLEMENTATION
Opportunities
9.2.1
Hong Kong’s urban form, context and climate are unique. In the CBD, buildings are tall and finger-like,
providing minimal roof-greening opportunities. However, other parts of the city have larger street blocks
and buildings with more suitable roof greening opportunities. Hong Kong also has numerous roofgreening opportunities on other infrastructure buildings, such as covered walkways, noise enclosures,
ferry piers, pumping stations and vent buildings. Typical Building types in Hong have been listed in Table
4.4.
9.2.2
Consequently, the potential opportunities for green roofs in Hong Kong may be broadly categorised into
three main green roof scenarios – Sky Gardens, Podium Gardens (New Buildings) and Existing / Low
Maintenance Buildings:
♦
♦
♦
Sky Gardens are found on top of any high-rise buildings (usually 20 storeys and above). Sky
Gardens are usually designed as part of the building and may be intensive or extensive green
roofs depending on usage.
Podium Gardens are usually 2 to 5 storeys up forming the base of a residential or office tower.
These gardens are usually intended for full access by the building occupants or the public and
are therefore always intensive green roofs.
Existing and low-maintenance buildings include existing office and residential towers and other
buildings such as public infrastructure buildings. Due to weight constraints and the need for low
maintenance extensive green roofs would generally be prescribed.
Figure 9.1 Some Typical Urban Forms in Hong Kong
(Source and copyright © 2006 Urbis Ltd.)
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Constraints
9.2.3
As intensive green roofs are widely occurring in Hong Kong it is apparent that any constraints presented
by the construction of intensive green roofs have already been overcome. The technical issues
associated with intensive green roofs are well understood by the local construction industry. On the other
hand, with no incentive and minimal knowledge about the emerging technologies, there are very few
examples of extensive green roofs in Hong Kong.
9.2.4
The constraints or barriers against the development of green roofs (which apply in Hong Kong to differing
degrees for intensive and extensive green roofs), fall into four categories, namely:
♦
♦
♦
♦
♦
Lack of knowledge and awareness – There is generally a lack of knowledge about extensive
green roofs. Also, knowledge of the benefits of all green roofs has previously never been
consolidated and used effectively in building design decision making. Greenery in the city is
generally approached from an amenity and cosmetic point of view only.
Lack of incentive / statutory mandate - Many of the benefits would not accrue to property
developers who build and sell immediately;
Economic constraints - There is a lack of understanding about direct tangible and long-term
economic benefits of extensive green roofs. Green roof structural loading requirements require
additional capital expenditure. Additional maintenance costs may be required.
Lack of available roof area – Many of Hong Kong’s buildings, especially the tall finger-like
buildings in the CBD, are often so cluttered with roof-top utilities that green roofs may be
impractical.
Technical issues and risks associated with uncertainty – This is particularly relevant for extensive
green roofs (especially the retro-fitting of existing green roofs).
Considerations for implementation in Hong Kong
9.2.5
From a physical and climatic point of view, Green Roofs in Hong Kong have their own unique difficulties.
These include:
♦
♦
♦
♦
9.2.6
high winds,
high summer rainfall with low winter rainfall,
high & exposed buildings, and
Hong Kong has little experience in using low-maintenance plant species that fit the defining
criteria of extensive green roofs.
Other major considerations for implementation include capital and recurrent costs.
Capital Costs in Hong Kong
9.2.7
In Hong Kong, green roof costs (for both Extensive and Intensive Green Roofs) are not high relative to
total building costs, which range from $ 3,600 /m² (for low-cost housing) to $ 17,700 /m² (for luxury
houses). For comparison, green roof prices are listed below and include all components above the roof
slab, and all hard- and soft-landscaping components.
♦
♦
Intensive Green Roofs usually range from $ 1,000 /m² to $5,000 /m² (market average: $2000/m²).
Extensive Green Roofs usually range from $ 400 /m² to $ 1,000 /m² (market average: $500/m²).
Recurrent Costs in Hong Kong
9.2.8
Recurrent costs are notably also not high. The labour associated with intensive green roofs is directly
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comparable with the maintenance associated with at-grade park operations which range from easily
accessed sites to very inaccessible or remote sites. The maintenance requirements for extensive green
roofs are untested in Hong Kong. Beijing and Shanghai experience shows that as little as 1 to 3 minutes
per m² per year is needed for extensive green roofs (if designed correctly and with low-maintenance
plants). These facts translate into the following figures:
♦
♦
Intensive Green Roofs usually range from $6.5 /m²/year to $44 /m²/year (average: $20/m²/year).
Extensive Green Roofs are estimated to range from $0.8 /m²/year to $ 2.25 /m²/year.
9.3
GREEN ROOF DIRECTIONS IN HONG KONG
9.3.1
The application of green roofs should be based on a rational evaluation of the specific needs of each
building and its users, while still striving to accomplish the city’s environmental needs. A balanced
understanding of green roof costs and effectiveness is required.
9.3.2
This study has comprehensively covered the costs and technical aspects of green roofs, showing that
green roofs (extensive and intensive) are economically and practically feasible in Hong Kong. However,
the effectiveness of some benefits of green roofs is unfortunately more difficult to quantify. This is
because they deal with aspects, such as some environmental and economic benefits, which are difficult
to quantify.
♦
♦
♦
9.3.3
The social benefits (i.e. Amenity and Aesthetic benefits) of green roofs are generally well
understood, with the public and planners commonly identifying and emphasizing the need for
more hospitable, pedestrian-friendly and greened environments in Hong Kong.
Unfortunately, some environmental benefits of green roofs, such as improving air quality and
reducing the Urban Heat Island effect, are extremely complex issues to quantify. To know all the
causes of these urban problems is difficult enough, let alone determining what scale of mitigating
impact green roofs would have. Further research in this field is essential.
Some economic benefits of green roofs, such as building insulation and energy efficiencies, also
require more in-depth local knowledge before they can be fully factored into any cost-benefit
assessment. Of all the technologies available (solar panels, double skins, green roofs etc.), it
remains to be determined which will be the most cost-effective for Hong Kong’s context.
However, it is considered unwise to delay the implementation and encouragement of green roofs simply
because of these unknowns, especially when one considers the following points:
♦
♦
♦
Of all the technologies that a city or building might employ to solve its problems it would appear
that green roofs offer the most benefits. The aesthetic and amenity benefits of green roofs are
also a major aspect that other technologies are not likely to contribute to the city.
Early research (with regards to pollution control and mitigation of the urban heat island effect) is
already beginning to prove that green roofs on a large enough scale can noticeably improve a
city’s environment. Overseas research in this field is ongoing and is likely to deliver useful results
in the near future.
Early research from a building-energy-saving’s point of view shows that green roofs, as a living
skin, are more cost-effective than the whitest surface possible (see Section 2.2.69). Green roofs
also help to lower ambient temperatures, making solar panels more effective, which suggests that
green roofs are likely to be an integral part of this technology if adopted (see Section 2.2.70). It
should also be noted that green roofs reduce energy demands, which in the field of resource
efficiencies, is considered more sound than simply adding additional components and
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♦
maintenance to a building to cater for high energy demands.
It is intuitively felt that a return to natural systems (in whatever small way) should be of some
environmental benefit to the city.
9.3.4
Considering the above, it is apparent that Green Roofs offer noticeable benefits for Hong Kong and could
become an integral part of the city’s solutions. For now, the main benefits to aim for are considered to be:
♦ An improvement to the city’s appearance and amenity,
♦ An increase in the usable green space, and
♦ An improvement on building energy savings.
9.3.5
As such, it is considered that Intensive Green Roofs should be promoted as the prime direction for the
future of green roofs in Hong Kong. Extensive Green Roofs could be considered for retro-fitting projects
and situations where Intensive Green Roofs are not practical.
9.3.6
The long term objective of green roofs is to achieve collective environmental benefits through city-wide
application of green roofs. Various steps are needed to achieve this. They are presented below and are
divided into Short, Medium and Long Term Goals.
9.4
RECOMMENDATIONS AND THE WAY FORWARD
Short Term Recommendations
9.4.1
Dissemination of information through the media is recommended to actively promote green roofs and to
foster better understanding of their potential benefits.
9.4.2
Trade Shows demonstrating green roof technologies are recommended for Hong Kong.
9.4.3
Engaging with stakeholders (including real estate professionals, construction industry representatives,
developers and suppliers) is recommended to encourage green roof development in Hong Kong.
9.4.4
Government should lead by example by continuing to implement green roofs on all new buildings, and to
review the retro-fitting of green roofs for existing roofs.
9.4.5
Introducing rating systems and elements of competition should be maintained and strengthened by
expanding the role of green roofs in CEPAS and HK-BEAM labelling systems, especially after local data
and research on building efficiencies is available.
9.4.6
Pilot schemes and further research is needed to fulfil the need for more local information. Information is
needed to more accurately determine: 1) changes to ambient temperature, building surface and interior
temperatures; 2) changes in pollution and particulate levels; and 3) changes in water runoff. The goal is
to accurately determine building energy efficiencies applicable to Hong Kong’s unique climate and
building forms. Further horticultural research is also needed to determine the viability of different species
for extensive green roofs.
Medium and Long Term Recommendations
9.4.7
Collating citywide scientific data on green roofs is recommended. This would involve doing cost-benefit
analysis studies to establish the geographical extent to which green roofing could be achieved in Hong
Kong, and the resultant benefits that would be enjoyed by the community. This could take the form of a
G.I.S. study. Monitoring of green roofs on a regular basis is also recommended. This would provide
knowledge of the progress over time and would assist the formulation of effective policies and incentives
to promote green roofs.
9.4.8
Developing reliable standards (e.g. similar to Germany’s FLL Guidelines) is suggested to promote
industry confidence and to prevent low-quality products and construction from entering the market.
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Although podium gardens are well-established in Hong Kong, there are still no standards ensuring quality
in this field. The development of standards should cover extensive and intensive green roofs.
9.4.9
Reviewing Government policy is suggested to maximise the amount of greening possible in the city, after
collective environmental/economic benefits have been proven and supported by public consultations.
There are numerous green roof policies around the world that may be considered and adapted for Hong
Kong’s needs. These policies used abroad should always be viewed in the context of each city’s physical
composition, social values and individual case settings. The approaches adopted elsewhere should not
necessarily be copied directly in Hong Kong. Also, Hong Kong requires a thorough understanding of the
costs and benefits, technical standards, horticultural requirements and unique market forces before
evaluating the need and direction of policy and regulations. It is therefore premature, at this stage, to
make recommendations on policy. There are many concepts tried elsewhere that may be considered.
These include: 1) Direct Incentives to the Private Sector, such as cash grants towards capital costs, 2)
Indirect Incentives to the Private Sector, such as GFA bonuses for the provision of green roofs, or even 3)
the introduction of the Polluters Pay Concept, based on the “eco-tax/carbon tax” concept against
polluters, where the provision of a green roof might be used to reduce this tax because of its contribution
towards energy efficiency.
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Appendix I
Examples of Public Buildings in Hong Kong with Green Roofs
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NAME OF FACILITY
TYPE OF
BUILDING
1.1.
Roof top planters along covered walkway
High Court
1.2.
Roof top garden at Pier 2
Pier
1,318
1.3.
Roof top garden at Pier 3
Pier
1,640
1.4.
Roof-top garden at Arbuthnot Road FEHD Refuse
Collection Building
Refuse Collection Station
91
1.5.
Sitting-out Area at Centre Street Market
Market
800
1.6.
Joint Users Building at Rock Hill Street, Kennedy Town
2.1.
Bowrington Road Market Roof-top Children’s Playground
2.2.
New Police Headquarters, Wan Chai (at 15/F)
2.3.
Tang Shiu Kin Hospital
Hospital
3.1.
Sitting-out Area at 2 Podium Levels
(not open for public)
Municipal Services
Building
3.2.
North Point Government Offices
3.3.
Meng Tak Primary School at Chai Wan
3.4.
Braemar Hill Fire Station
3.5.
Roof-top garden at Ex-Chai Wan
Refuse Collection Point
3.6.
Meng Tak Primary School, Cheung Man Road, Chai Wan
School
3.7.
Lei Yu Mun Museum
Museum
4.1.
Roof-Top Garden at Stanley Sports Centre
Municipal Services
Building
4.2.
Water Sports Centre at Stanley Main Beach
DISTRICT
1. Central &
Western
2. Wan Chai
3. Eastern
4. Southern
5. Yau Tsim
Mong
6. Kowloon
City
Market Complex
TOTAL
AREA m2
PHOTO
APPENDIX I: EXAMPLES OF PUBLIC BUILDINGS IN HONG KONG WITH GREEN ROOFS
90
1,200
892 m2 at 6/F
338 m2 at 8/F
44
470
4.3.
Wah Fu Fresh Water Service Reservoir
Service Reservoir
5.1.
Amenity Plot at the Podium of 3/F, Fa Yuen Street Sports
Complex
Municipal Services
Building
5.2.
Roof Top Garden Phase 1,II, III at Kowloon Park
Kowloon Park
4,928
5.3.
Middle Road Children’s Playground
At the roof-top of KCRC
East Tsim Sha Tsui
Station
5,671
5.4.
Transport Link in Tsim Sha Tsui East
5.5.
Tsim Sha Tsui Promenade Beautification
5.6.
Reprovisioning of CAS & FSD Facilities, West Kowloon
Reclamation
6.1.
Kowloon Hospital – Phase 1 Redevelopment
6.2.
New EMSD Headquarters
6.3.
Education Resource Centre cum Transport Interchange
6.4.
Kowloon Tong Fire Station, Ambulance Depot & Fire
Command HQ
6.5.
Podium garden, Civil Engineering and Development
Department (Ho Man Tin)
Government Office
6.6.
Podium garden at Hung Hom Phase 1
Residential
471
6.7.
Podium garden at Homantin South Phase 1B
Residential
87
38
Municipal Services
Building
1,043 (planted
area)
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TYPE OF
BUILDING
7. Wong Tai
Sin
6.8.
Primary School at Sheung Shing Street, Ho Man Tin
School
6.9.
Education Resource Centre cum Transport Interchange
School / PTI
7.1.
Ngau Chi Wan Market Roof Top Children’s Playground
Municipal Services
Building
7.2.
A 36-classroom Primary School in Sze Mei Street, San Po
Kong
School
7.3.
Special School for Physically Handicapped Children at
Ngau Chi Wan
School
7.4.
Diamond Hill Crematorium
Crematorium
800
7.5.
Podium garden at Lok Fu Phase 7
Carport
480
7.6.
Podium garden at Wang Tau Hom Phase 12
Commercial
30
7.7.
Podium garden at Wang Tau Hom Phase 13
Residential
533
7.8.
Podium garden at Wang Tau Hom Phase 14
Residential
502
8.1.
Tsun Yip Street Cooked Food Market Roof-top Rest
Garden
Market
8.2.
Yee On Street Market Rest Garden
8.3.
Podium at 2/F in Ngau Tau Kok Municipal Services
Building
8. Kwun
Tong
8.4.
Shun Lee Departmental Quarter
8.5.
Lei Yue Mun Museum
8.6.
Podium garden at Lam Tin Phase 7 & 8
Residential
8.7.
Podium garden at Lei On Court at Lei Yue Mun
Residential
8.8.
Podium garden at Lei Yue Mun Phase 1
Residential
8.9.
Podium garden at Sau Mau Ping Commercial Centre
Commercial
8.10.
Two 36-classroom Primary Schools in the Eastern Harbour
Crossing, Yau Tong
School
8.11.
Special School for Physically Handicapped Children at
Ngau Chi Wan
School
9.1.
Public Health Laboratory at Nam Chong Street,
Shamshuipo
Medical Facility
9.2.
Re-provisioning of MHAHK Pak Tin Children Centre at
Cornwall Street, Sham Shui Po
School
9. Sham
Shui Po
9.3.
Primary School at Site 10, West Kowloon Reclamation
School
9.4.
Secondary School at Site 10, West Kowloon Reclamation
School
9.5.
Podium garden at Un Chau Street Phase 1
Carport
1177
9.6.
Podium garden at Un Chau Street Phase 3
Residential
282
9.7.
Secondary School at Lai Hong Road
School
10.Kwai
Tsing
10.1.
Wo Yi Hop Road Cooked Food Market Roof-top Sitting-out
Area
Cooked Food Market
10.2.
Lai King Departmental Quarter
Municipal Building
10.3.
Princess Margaret Hospital Lai King Building
Hospital
10.4.
Public Mortuary at Area 26E, Kwai Chung
10.5.
An 18-Classroom Primary School at Tai Pak Tin Street,
Kwai Chung (Non-Standard)
Complex
Municipal Services
Building
TOTAL
AREA m2
PHOTO
NAME OF FACILITY
DISTRICT
1,450
1,100
1,400
2,212
998
590
1,160
School
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TYPE OF
BUILDING
10.6.
Infectious Disease Centre Attached to Prince Margaret
Hospital
Hospital
10.7.
Re-provisioning of Victoria Prison at Lai Chi Kok Old Staff
Quarter
Prison
10.8.
Podium garden at Kwai Chung Estate 5 & 7
Planting on Footbridge
50
10.9.
Roof-top garden at Shek Lei Phase 10
Refuse Collection Point
126
10.10. Kwai-Chung Ambulance Depot
TOTAL
AREA m2
PHOTO
NAME OF FACILITY
DISTRICT
Hospital Facility
10.11. Public Mortuary at Area 26E, Kwai Chung
11.Islands
12.Tuen Mun
10.12. Improvement Works to Departmental Quarters for the
Disciplined Services in Kwai Chung & Kwai Yung Court,
Kwai Chung
Municipal Building
10.13. Princess Margaret Hospital Radiotherapy and Accident &
Emergency Department
Hospital
10.14. Welfare Complex at Lai King Headland, Kwai Tsing
Public Facility
11.1.
Praya Street Sports Centre Roof-Top Sitting-out Area
Municipal Services
Building
11.2.
Primary School in Area 20, Tung Chung
School
11.3.
Secondary School in Area 20, Tung Chung
School
11.4.
Secondary School in Area 40, Tung Chung
School
11.5.
Second Secondary School in Area 40, Tung Chung
School
12.1.
Kwong Choi Market Root-top Garden
Kwong Choi Market
1,450
12.2.
Tuen Mun Riverside Park
Roof-top Garden
21,800
12.3.
Tuen Mun Cultural Square
Town Hall Complex
13,700
12.4.
Tuen Mun Hospital
Hospital
12.5.
Castle Peak Hospital
Hospital
12.6.
Primary School at Hing Ping Road
School
12.7.
Immigration Services Training School & Perowne
Immigration Centre
Municipal Building
12.8.
Primary School in So Kwun Wat, Area 55A
School
12.9.
Second Primary School in So Kwun Wat, Area 55A
12.10. Community Complex at Tseng Choi Street
411
School
Public Facility
12.11. Rehabilitation Complex at J/O Tsun Wen Road & Leung
Shun Street, Tuen Mun
13.Yuen
Long
12.12. Primary School at Hing Ping Road, Tuen Mun
School
13.1.
Tai Kiu Market Sitting-out-area
Government offices cum
market complex
13.2.
Yuen Long Civic Centre
Public Facility
13.3.
International Wetland Park & Visitors Centre in Tin Shui
Wai
Eco-tourist centre
13.4.
Primary and Secondary school at Tin Shui Wai
School
13.5.
A Special School in Area 32, Tin Shui Wai
School
13.6.
Primary School in Area 12, Yuen Long
School
13.7.
Boundary Crossing Facilities in Shekou China, Shenzhen
w. Corridor/Deep Bay Link
13.8.
Podium garden at Tin Shui Wai Area 101 Phase 1
Residential
1,480
10,000
128
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13.9.
14.Tsuen
Wan
15.Sha Tin
NAME OF FACILITY
TYPE OF
BUILDING
Podium garden at Tin Shui Wai Area 102 Phase 7
Commercial Centre and
Carport
TOTAL
AREA m2
PHOTO
DISTRICT
840
13.10. Yuen Long Civic Centre
Public Facility
14.1.
Tsuen King Circuit Children Playground
Market Complex
14.2.
Primary School in Ma Wan
School
14.3.
NT South Regional Police Headquarters & Operation Base,
Tsuen Wan
Government Offices
14.4.
Podium garden at Lei Muk Shue Phase 3 & 4
Commercial & Carport
15.1.
Sha Tin Government Office
Government Offices
15.2.
New Laboratory Building at Shatin Sewage Treatment
Works
Municipal Facility
15.3.
Podium garden at Shatin Area 11 – Shek Mun
Residential
102
15.4.
Podium garden at Shatin Area 14B Phase 2
Carport Building
670
15.5.
Podium garden at Shatin Area 14B Phase 5
Commercial Centre
580
15.6.
Podium garden at Shatin Area 4D Phase 2
Carport Building
570
15.7.
Science Park at Pek Shek Kok Phase 1C - Building 9)
15.8.
Science Park at Pek Shek Kok Phase 1C - Buildings 7 & 8
15.9.
Science Park at Pek Shek Kok Phase 1C - Building 6
2,525
678.4
15.10. Science Park at Pek Shek Kok Phase 1B - Building 4
15.11. Science Park at Pek Shek Kok Phase 1A - Building 1
16.North
17.Tai Po
18.Sai Kung
15.12. New Lab. Building at Shatin Sewage Treatment Works
Municipal Facility
15.13. Government Complex in Lee On Estate, Area 108, Ma On
Shan
Government Offices
15.14. Roof garden at Primary School in Shatin Area 11
School
15.15. Roof garden at Primary School in Shatin Area 11
School
16.1.
Shek Wu Hui Complex Podium Garden
Municipal Services
Building.
16.2.
Fanling Departmental Quarter
Government Offices
16.3.
Fanling Magistracy Building
Government Offices
16.4.
Retro-fitting of Air-conditioning and General Improvement
Works to Shek Wu
16.5.
Tai Lung Veterinary Laboratory
Medical Facility
17.1.
Amenity area at the podium of Tai Po Complex (landscape
area 500 m²)
Complex
17.2.
Market Complex at Area 1, Tai Po
Market
17.3.
Refuse Collection Point, Fong Ma Po, Tai Po
Refuse Collection Point
17.4.
Redevelopment of Hong Chi Pinehill Schools
School
18.1.
Sai Kung Waterfront Park
Podium of the park
18.2.
Primary School in Area 65, Tseung Kwan O
School
18.3.
Secondary School in Area 50, Tseung Kwan O
School
18.4.
Podium garden at Tseung Kwan O Area 73A Phase 1
Commercial Centre
2380
2,830
1216
435
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Selected Images of Public Buildings in Hong Kong with Green Roofs
1.2 – Roof top Garden at Pier 2
(Central & Western District)
(Source and copyright © by Urbis 2006)
1.3 – Roof top Garden at Pier 3
(Central & Western District)
(Source and copyright © by Urbis 2006)
2.1- Bowrington Road Market Roof-top
(Wan Chai District)
(Source and copyright © by Urbis 2006)
2.2 – New Police Headquarters
(Wan Chai District)
(Source and copyright © by ArchSD)
2.3 – Tang Shiu Kin Hospital
(Wan Chai District)
(Source and copyright © by ArchSD)
3.2 – North Point Government Offices
(Eastern District)
(Source and copyright © by ArchSD)
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Selected Images of Public Buildings in Hong Kong with Green Roofs
3.6 – Meng Tak Primary School
(Eastern District)
(Source and copyright © by ArchSD)
4.3 – Wah Fu Fresh Water Service Reservoir
(Southern District)
(Source and copyright © by ETWB)
5.3 – Middle Road Children’s Playground
(Yau Tsim Mong District)
(Source and copyright © by Urbis 2006)
5.6 – Reprovisioning of CAS & FSD Facilities
(Yau Tsim Mong District)
(Source and copyright © by ETWB)
6.1 – Kowloon Hospital
(Kowloon City District)
(Source and copyright © by ArchSD)
6.2 – New EMSD Headquarters
(Kowloon City District)
(Source and copyright © by ArchSD)
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Page vii
Selected Images of Public Buildings in Hong Kong with Green Roofs
6.5 – Podium Garden, CEDD HQ, Ho Man Tin
(Kowloon City District)
(Source and copyright © by CEDD)
6.8 – Primary School at Sheung Shing Street
(Kowloon City District)
(Source and copyright © by ArchSD)
6.9 – Education Resource Centre cum Transport
Interchange
(Kowloon City District)
(Source and copyright © by ArchSD)
7.2 – Primary School at Sze Mei St. San Po
Kong
(Wong Tai Sin District)
(Source and copyright © by ArchSD)
8.4 – Shun Lee Departmental Quarter
(Kwun Tong District)
(Source and copyright © by ArchSD)
8.7 – Podium Garden, Lei On Court
(Kwun Tong District)
(Source and copyright © by Housing Dept.)
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Page viii
Selected Images of Public Buildings in Hong Kong with Green Roofs
8.8 – Podium Garden, Lei Yue Mun Phase 1
(Kwun Tong District)
(Source and copyright © by Housing Dept.)
10.2 – Lai King Departmental Quarter
(Kwai Tsing District)
(Source and copyright © by ArchSD)
10.3 – Princess Margaret Hospital
(Kwai Tsing District)
(Source and copyright © by ArchSD)
10.10 – Kwai Chung Ambulance Depot
(Kwai Tsing District)
(Source and copyright © by ArchSD)
10.11 – Public Mortuary at Area 26E
(Kwai Tsing District)
(Source and copyright © by ArchSD)
10.12 – Princess Margaret Hospital,
Radiotherapy and Accident & Emergency Dept.
(Kwai Tsing District)
(Source and copyright © by ArchSD)
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Page ix
Selected Images of Public Buildings in Hong Kong with Green Roofs
12.4 – Tuen Mun Hospital
(Tuen Mun District)
(Source and copyright © by ArchSD)
12.5 – Castle Peak Hospital
(Tuen Mun District)
(Source and copyright © by ArchSD)
13.3 – International Wetland Park
(Yuen Long District)
(Source and copyright © by ArchSD)
13.9 – Podium Garden, Tin Shui Wai Area 102
(Yuen Long District)
(Source and copyright © by Housing Dept.)
15.1 – Sha Tin Government Office
(Sha Tin District)
(Source and copyright © by ArchSD)
15.4 - Podium Garden, Sha Tin Area 14B, Phase
2
(Sha Tin District)
(Source and copyright © by Housing Dept.)
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Page x
Selected Images of Public Buildings in Hong Kong with Green Roofs
15.5 - Sha Tin Area 14B, Phase 5
(Sha Tin District)
(Source and copyright © by Housing Dept.)
15.7 – Science Park, Building 9
(Sha Tin District)
(Source and copyright © by ArchSD)
15.8 – Science Park, Buildings 7 & 8
(Sha Tin District)
(Source and copyright © by ArchSD)
15.11 – Science Park, Building 1
(Sha Tin District)
(Source and copyright © by ArchSD)
15.14 – Primary School in Area 11, Shatin
(Sha Tin District)
(Source and copyright © by ArchSD)
15.15 – Primary School in Area 11, Shatin
(Sha Tin District)
(Source and copyright © by ArchSD)
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Page xi
Selected Images of Public Buildings in Hong Kong with Green Roofs
16.2 – Fanling Departmental Quarter
(North District)
(Source and copyright © by ArchSD)
16.3 – Fanling Magistracy Building
(North District)
(Source and copyright © by ArchSD)
16.5 – Veterinary Lab. at Tai Lung Farm
(North District)
(Source and copyright © by ArchSD)
18.2 – Prim School, Area 65, Tseung Kwan O
(Sai Kung District)
(Source and copyright © by ArchSD)
18.3 – Sec. School, Area 50, Tseung Kwan O
(Sai Kung District)
(Source and copyright © by ArchSD)
18.4 – Tseung Kwan O Area 73A, Phase 1
(Sai Kung District)
(Source and copyright © by Housing Dept.)
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Page xii
Appendix II
PLANT SELECTION MATRIX
FOR GREEN ROOFS
(INTENSIVE & EXTENSIVE)
APPENDIX II: PLANT SELECTION MATRIX FOR GREEN ROOFS (INTENSIVE & EXTENSIVE)
Interesting Fragrance
Interesting Foliage
Conspicuous Flowers
Slow Growing
Medium Growing
Fast Growing
M
Deciduous
H
Evergreen
Pollution Tolerant
(Chinese Name)
Wind Tolerant
Species Name
Size SMALL
Common Name
Size MEDIUM
APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (INTENSIVE)
Trees
Araucaria heterophylla
Norfolk Island Pine (南洋杉)
Callistemon viminalis
Tall Bottle-brush (串錢柳)
M M
Cassia surattensis
Sunshine Tree (黃槐)
M M
Cinnamomum burmannii
Cinnamon Tree (陰香)
M M
Eleaocarpus hainanensis
Hainan Elaeocarpus (水石榕)
M
L
Weeping Fig (垂榕)
H
H
Golden Chinese Banyan (黃金榕)
H
H
Garcinia spicata
Fortune Tree (福木)
H
H
Hibiscus tiliaceus
Sea Hibiscus (黃槿)
H
H
Dragon Juniper (龍柏)
H
M
Golden Rain Tree (複葉欒樹)
M
L
Ficus benjamina
Ficus microcarpa ‘Golden Leaf’
Juniperus chinenisis cv.Kaizuca
Koelreuteria bipinnata
Lagerstroemia speciosa
Queen Crape Myrtle (大花紫薇)
M M
Magnolia grandiflora
Southern Magnolia (荷花玉蘭)
M
L
Michelia x alba
White Jade Orchid Tree (白玉蘭)
M M
Michelia champaca
Yellow Jade Orchid Tree (黃玉蘭)
M
L
Nagi (竹柏)
M
L
Wild Bean (水黃皮)
H
M
Buddhist Pine (羅漢松)
M
L
Nageia nagi (syn. Podocarpus nagi)
Pongamia pinnata
Podocarpus macrophyllus
Schefflera actinophylla
Syzygium jambos
Umbrella Tree
(傘樹)
M M
Rose Apple (蒲桃)
M M
Thuja orientalis
Chinese Arborvitae (扁柏)
M
L
Thespesia populnea
Portia Tree (恆 春 黃槿)
H
M
H - High, M - Medium, L – Low,
Unless other-wise noted, plant photos are sourced from Urbis’ plant library.
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Page ii
APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (INTENSIVE)
Trees
Araucaria heterophylla
Callistemon viminalis
Cassia surattensis
Norfolk Island Pine
Tall Bottle-brush
Sunshine Tree
(南洋杉)
(串錢柳)
(黃槐)
Cinnamomum burmannii
Eleaocarpus hainanensis
Ficus Benjamina
Cinnamon Tree
Hainan Elaeocarpus
Weeping Fig
(陰香)
(水石 )
(垂 )
Ficus microcarpa ‘Golden Leaf’
Garcinia spicata
Hibiscus tiliaceus
Golden Chinese Banyan
Fortune Tree
Sea Hibiscus
(黃金榕)
(福木)
(黃槿)
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APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (INTENSIVE)
Trees
Juniperus chinenisis cv.Kaizuca
Koelreuteria bipinnata
Lagerstroemia speciosa
Dragon Juniper
Golden Rain Tree
Queen Crape Myrtle
(龍柏)
(複葉欒樹)
(大花紫薇)
Magnolia grandiflora
Michelia x alba
Michelia champaca
Southern Magnolia
White Jade Orchid Tree
Yellow Jade Orchid Tree
(荷花玉蘭)
(白玉蘭)
(黃玉蘭)
Nageia nagi
Pongamia pinnata
Podocarpus macrophyllus
(syn. Podocarpus nagi)
Wild Bean
Buddhist Pine
Nagi
(水黃皮)
(羅漢松)
(竹柏)
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Page iv
APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (INTENSIVE)
Trees
Schefflera actinophylla
Syzygium jambos
Thespesia populnea
Umbrella Tree
Rose Apple
Portia Tree
(鴨腳木)
(蒲桃)
(恆 春 黃槿)
Thuja orientalis
Chinese Arborvitae
(扁柏)
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Page v
M
Cycas revoluta
Sago Palm (蘇鐵)
H
M
Hyophorbe lagenicaulis
Bottle Palm (酒瓶椰子)
H
M
Hyophorbe verschaffeltii
Spindle Palm (棍棒椰子)
H
M
Neodypsis decaryi
Triangle Palm (三角椰子)
H
M
Pandanus veitchii
Veitch Screwpine (露兜)
H
M
Phoenix dactylifera
Edible Date Palm (中東海棗)
H
M
Phoenix hanceana
Date Palm (刺葵)
H
M
Phoenix sylvestris
Silver Date Palm (銀海棗)
H
M
Phoenix roebelenii
Dwarf Date Palm (日本葵)
H
H
Livistona chinensis
Chinese Fan Palm (蒲葵)
H
H
Wodyetia bifurcata
Foxtail Palm (狐尾棕)
H
M
Washington Palm (華盛頓葵)
H
M
Interesting Fragrance
H
Interesting Foliage
Coconut Palm (椰子)
Conspicuous Flowers
Cocos nucifera
Slow Growing
M
Medium Growing
H
Fast Growing
Bismarck Palm (霸王棕)
Deciduous
H
(Chinese Name)
Evergreen
Pollution Tolerant
H
Species Name
Size SMALL
Betel Palm (檳榔)
Common Name
Size MEDIUM
Wind Tolerant
APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (INTENSIVE)
Palms & Palm-like Trees
Areca catechu
Bismarckia nobilis
Washingtonia robusta
H - High, M - Medium, L – Low,
Unless otherwise noted, plant photos are sourced from Urbis’ plant library.
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APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (INTENSIVE)
Palms and Palm-like Trees
Areca catechu
Bismarckia nobilis
Cocos nucifera
Betel Palm
Bismarck Palm
Coconut Palm
(霸王棕)
(椰子)
Cycas revoluta
Hyophorbe lagenicaulis
Hyophorbe verschaffeltii
Sago Palm
Bottle Palm
Spindle Palm
(蘇鐵)
(酒瓶椰子)
(棍棒椰子)
Neodypsis decaryi
Pandanus veitchii
Phoenix dactylifera
Triangle Palm
Veitch Screwpine
Edible Date Palm
(三角椰子)
(露兜)
(中東海棗)
(檳
)
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APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (INTENSIVE)
Palms and Palm-like Trees
Phoenix hanceana
Phoenix sylvestris
Phoenix roebelenii
Date Palm
Silver Date Palm
Dwarf Date Palm
(刺葵)
(銀海棗)
(日本葵)
Livistona chinensis
Wodyetia bifurcate
Washingtonia robusta
Chinese Fan Palm
Foxtail Palm
Washington Palm
(蒲葵)
(狐尾棕)
(華盛頓葵)
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Plant Selection Matrix for Extensive Green Roofs
This list is derived from existing local knowledge and other overseas sources with humid climatic
conditions similar to Hong Kong. It should be noted that plants from these overseas sources (Singapore)
do not encounter the dry winters that Hong Kong experiences, making the species they use, possibly not
suitable for Hong Kong. They are presented below as having a good chance for success in Hong Kong
and also as worthy candidates for planting trials in Hong Kong. This list also includes grasses,
ornamentals and annuals even though these vegetation types may not have the ecological functions and
low-maintenance features which characterize extensive green roofs. Plant species are listed according to
low-maintenance, soil depth, wind tolerance and pollution tolerance - the order of characteristics that best
defines extensive green roofs.
Pollution Tolerant
Growth Rate ( F / M / S )
Autumn Zephyr-lily
(蔥蘭)
8
L
H
M
F
Zephyranthes grandiflora
AMARYLLIDACEAE
Rose-pink Zephyr-lily
(風雨花)
8
L
H
M
F
Bryophyllum
‘Crenatodaigremontianum’
CRASSULACEAE
Dancing Butterfly
森之蝶舞
8
L
H
H
F
Singapore
Bryophylum fedtschenkoi
CRASSULACEAE
Lavender Scallop, Grey
Sedum
(花葉落地生根)
8
L
H
H
F
Singapore
AGAVACEAE
Mauritius Hemp, Green
Aloe
(黃紋萬年麻)
8
L
H
M
M
CRASSULACEAE
Panda Plant, Pussy Ears
(月兔耳)
8
L
H
H
M
Singapore
CONVALLARIACEAE
Variegated Lily Turf
(闊葉麥門冬)
8
L
H
M
F
Singapore
Portulaca oleracea
PORTULACACEAE
Purslane
(馬齒莧)
8
L
H
M
F
Native to HK but not
common, Singapore
Portulaca pilosa
PORTULACACEAE
Kiss-Me-Quick, Shaggy
Purslane
(毛馬齒莧)
8
L
H
M
F
Native to HK but not
common, Singapore
CACTACEAE
Clumpy Mistletoe Cactus
8
L
H
M
F
Singapore
Sansevieria trifasciata
‘Golden Hahnii’
DRACAENACEAE
Golden Birdsnest
(金邊短葉虎尾蘭)
8
L
H
H
M
Sansevieria trifasciata
‘Hahnii’
DRACAENACEAE
Bird Nest Sansevieria
(短葉虎尾蘭)
8
L
H
H
M
Sansevieria trifasciata
‘Laurentii’
DRACAENACEAE
(金邊虎尾蘭)
8
L
H
H
M
Sedum acre
CRASSULACEAE
Biting Stonecrop, Wall
Pepper, Golden Moss
(金氈景天)
8
L
H
H
F
Common Name
(Chinese Name)
USED in HONG KONG
Wind Tolerant
AMARYLLIDACEAE
Family Name
Interesting Foliage
Maintenance ( H / M / L )
Zephyranthes~candida
Species Name
Conspicuous Flowers
Minimum Soil Depth (cm)
APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
ADDITIONAL
NOTES
(Special
Requirements,
Location of
known use on
Extensive Green
Roofs, etc.)
Low-maintenance Groundcovers
Furcraea foetida
‘Mediopicta’
Kalanchoe tomentosa
Liriope muscari
Rhipsalis
mesembryanthemoides
Singapore
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Pollution Tolerant
Growth Rate ( F / M / S )
Variegated stonecrop
(佛甲草)
8
L
H
H
F
Singapore and
Shenzhen
Sedum lineare
‘Variegatum’
CRASSULACEAE
Variegated Sedum
(白佛甲草)
8
L
H
H
F
Singapore
Sedum mexicanum
CRASSULACEAE
Mexicum Sedum
(松葉佛甲草)
8
L
H
H
F
Singapore
Sedum nussbaumerianum
CRASSULACEAE
Coppertone sedum
(銘月)
8
L
H
H
F
Singapore
Sedum sarmentosum
CRASSULACEAE
Stringy stonecrop
(垂盆草)
8
L
H
H
F
Singapore
Sedum sexangulare
CRASSULACEAE
Tasteless Stonecrop
(六楞景天)
8
L
H
H
F
Singapore
8
L
H
H
F
Native to HK but not
common, Singapore
Sesuvium portulacastum
Common Name
(Chinese Name)
Sea Purslane
AIZOCEA
海馬齒
USED in HONG KONG
Wind Tolerant
CRASSULACEAE
Family Name
Interesting Foliage
Maintenance ( H / M / L )
Sedum lineare
Species Name
Conspicuous Flowers
Minimum Soil Depth (cm)
APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
ADDITIONAL
NOTES
(Special
Requirements,
Location of
known use on
Extensive Green
Roofs, etc.)
COMMELINACEA
Purple Heart
(紫鴨跖草)
8
L
H
H
F
Tulbaghia violacea
ALLIACEAE
Wild Garlic, Society
Garlic
(蒜味草)
8
L
H
H
F
Zephyranthes rosea
AMARYLLIDACEAE
Fairy Lily, Cuban Zephyrlily
(玫瑰蔥蓮)
8
L
H
M
F
Singapore
Alternanthera ficoidea
‘White Carpet’
AMARANTHACEA
8
L
M
M
F
Singapore
Commelina diffusa
COMMELINACEA
8
L
M
M
F
Murdannia nudiflora
COMMELINACEA
8
L
M
M
F
Native to HK but not
common, Singapore
Murdannia vaginata
COMMELINACEA
Sheathed Murdannia
(細柄水竹葉)
8
L
M
M
F
Native to HK but not
common, Singapore
Portulaca grandiflora
PORTULACACEAE
Ross-moss
(松葉牡丹)
8
L
M
M
F
Arachis duranensis
FABACEAE
Groundnut
(蔓花生)
10
L
H
H
F
Arachis pintoi
FABACEAE
Amarillo
(多年生花生草)
10
L
H
H
F
Axonopus compressus
POACEAE
Carpet Grass
(地毯草)
10
L
H
H
F
Stenotaphrum dimidiatum
POACEAE
Glabrous Stenotaphrums
(光鈍葉草)
10
L
H
H
F
Wedelia chinensis
ASTERACEAE
(COMPOSITAE)
Wedelia
(蟛蜞菊)
10
L
H
H
F
Wedelia trilobata
ASTERACEAE
(COMPOSITAE)
Wedelia
(三裂葉蟛蜞菊)
10
L
H
H
F
Scutellaria indica
LAMIACEAE
Skullcap
(韓信草)
10
L
H
M
M
Tradescantia pallida ‘Purpurea’
New:Setcreasea purpurea
Alternanthera 'White Carpet'
(白莧草)
Diffuse Dayflower
(節節草)
Naked Flowered Murdannia
(裸花水竹草)
Singapore
Grass
Native to Hong
Kong
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Wind Tolerant
Pollution Tolerant
Growth Rate ( F / M / S )
MELASTOMATACEAE
12-stamened melastoma
(地菍)
10
L
M
M
M
For shady areas,
Native to HK
Vitex rotundifolia
VERBENACEAE
Beach Vitex
(單葉蔓荊)
15
L
H
H
F
Native to Hong
Kong
Crinum asiaticum var.
sinicum
LILIACEAE
Chinese Crinum
(文殊蘭)
15
L
H
M
M
Native to Hong
Kong
Hymenocallis littoralis
LILIACEAE
Spider lily
(蜘蛛蘭)
15
L
H
H
F
MELASTOMATACEAE
Chinese Osbeckia
(金錦香)
15
L
H
M
M
AGAVACEAE
Spear sansevieria
(虎尾蘭)
15
L
H
H
M
Alternanthera bettzickiana
AMARANTHACEAE
Calico-plant
(紅草)
15
L
M
M
F
Cyathula prostrate ‘Bloodred Leaves’
AMARANTHACEAE
Blood-red Leaves
(紫杯莧)
15
L
M
M
F
VERBENACEAE
Lantana
(馬纓丹)
15
L
M
H
F
Nephrolepis exaltata
NEPHROLEPIDACEA
E
Sword-fern
(腎蕨)
15
L
M
M
M
Ophiopogon jaburan
LILIACEAE
Jaburan Lily-turf
(花葉沿階草)
15
L
M
M
F
Ophiopogon japonicus
LILIACEAE
Blue Grass
(沿階草)
15
L
M
M
F
Asparagus densiflorus cv.
Sprengeri
LILIACEAE
Springer Asparagus
(天冬)
20
L
H
H
F
MYRTACEAE
Dwarf Mountain Pine
(崗松)
20
L
H
H
F
Native to Hong
Kong
COMMELINACEA
Creeping Basketplant
(舖地錦竹草)
8
M
M
M
F
Singapore
LABIATAE
Swedish ivy
(瑞士常春藤)
8
M
M
M
F
Singapore
Rhoeo discolor
COMMELINACEAE
Oyster Plant
(蚌花)
10
M
M
M
F
Rhoeo discolor ‘Compacta’
COMMELINACEAE
Dwarf Oyster Plant
( 矮蚌)
10
M
M
M
F
LYTHRACEAE
False Heather
(細葉萼距花)
15
M
M
M
F
Iris tectorum
IRIDACEAE
Crested iris
( 鳶尾)
15
M
M
M
M
Liriope spicata
LILIACEAE
Lily turf
(山麥冬)
15
M
M
M
F
Native to Hong
Kong
Epipremnum aureum
(old name: Scindapsus
aureus)
ARACEAE
Ivy-arum
( 綠蘿 )
15
M
L
M
F
Requires semishade and high
water requirements
AMARANTHACEAE
Songuinea
20
M
M
M
F
Osbeckia chinensis
Sansevieria trifasciata
Lantana sellowiana
Baeckea frutescens
Callisia repens
Plectranthus verticillatus
Cuphea hyssopifolia
Aerve songuinolenta
USED in HONG KONG
Maintenance ( H / M / L )
Melastoma dodecandrum
Interesting Foliage
Common Name
(Chinese Name)
Species Name
Conspicuous Flowers
Family Name
Minimum Soil Depth (cm)
APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
ADDITIONAL
NOTES
(Special
Requirements,
Location of
known use on
Extensive Green
Roofs, etc.)
Native to Hong
Kong
Native to Hong
Kong
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Page xi
H
M
F
USED in HONG KONG
H
Interesting Foliage
Growth Rate ( F / M / S )
20
Conspicuous Flowers
Pollution Tolerant
Common Name
(Chinese Name)
Wind Tolerant
Family Name
Maintenance ( H / M / L )
Species Name
Minimum Soil Depth (cm)
APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
ADDITIONAL
NOTES
(Special
Requirements,
Location of
known use on
Extensive Green
Roofs, etc.)
( 血莧草 )
Zoysia japonica
POACEAE
Zoysia Grass
(朝鮮草)
Grass
Note 1: L=Low, M=Medium, H=High, F=Fast, M=Medium, S=Slow.
Note 2: Annotations reading “Native to HK but not common, Singapore” refers to species that are indigenous to Hong Kong
(Checklist of Hong Kong Plants, 2004, AFCD) but are not yet widely used and/or may not be commercially available yet.
These species have been successful in Extensive Green Roof planting trials in Singapore. As they are indigenous, these
species have a very good chance of also being successful on Extensive Green Roofs in Hong Kong.
APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
Aerve songuinolenta
Alternanthera bettzickiana
Songuinea
Calico-plant
Alternanthera ficoidea ‘White
Carpet’
(紅 )
Alternanthera 'White Carpet'
(血莧
)
(白莧
)
Arachis duranensis
Arachis pintoi
Groundnut
Amarillo
Asparagus densiflorus cv.
Sprengeri
(蔓花生)
(多年生花生 )
Springer Asparagus
(天冬)
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APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
Axonopus compressus
Baeckea frutescens
Carpet Grass
Dwarf Mountain Pine
Bryophyllum
‘Crenatodaigremontianum’ †
(崗松)
Dancing Butterfly
(地毯
)
(森之蝶舞)
Bryophylum fedtschenkoi †
Callisia repens
Commelina diffusa
Lavender Scallop, Grey Sedum
Creeping Basketplant
Diffuse Dayflower
(花葉
地生根)
(舖地錦竹
)
Crinum asiaticum var. sinicum
Cuphea hyssopifolia
Chinese Crinum
False Heather
(文殊蘭)
(細葉
(節節
)
Cyathula prostrate ‘Blood-red
Leaves’
Blood-red Leaves
距花)
(紫杯莧)
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APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
Epipremnum aureum
Furcraea foetida ‘Mediopicta’ †
Hymenocallis littoralis
(old name: Scindapsus aureus)
Mauritius Hemp, Green Aloe
Spider lily
Ivy-arum
(黃紋萬年麻)
(蜘蛛蘭)
Iris tectorum
Kalanchoe tomentosa †
Lantana sellowiana
Crested iris
Panda Plant, Pussy Ears
Lantana
(鳶尾)
(月兔耳)
(馬纓丹)
Liriope muscari †
Liriope spicata
Melastoma dodecandrum
Variegated Lily Turf
Lily turf
12-stamened melastoma
(闊葉麥門冬)
(山麥冬)
(地菍)
(綠蘿)
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APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
Murdannia nudiflora †
Murdannia vaginata †
Nephrolepis exaltata
Naked Flowered Murdannia
Sheathed Murdannia
Sword-fern
(裸花水竹 )
(細柄水竹葉)
(腎蕨)
Ophiopogon jaburan
Ophiopogon japonicus
Osbeckia chinensis
Jaburan Lily-turf
Blue Grass
Chinese Osbeckia
(花葉沿階 )
(沿階
)
(金錦香)
Plectranthus verticillatus †
Portulaca grandiflora †
Portulaca oleracea †
Swedish ivy
Ross-moss
Purslane
(瑞士常春藤)
(松葉牡丹)
(馬齒莧)
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APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
Rhipsalis
mesembryanthemoides †
Rhoeo discolor
Clumpy Mistletoe Cactus
(蚌花)
Sansevieria trifasciata ‘Hahnii’ †
Spear sansevieria
Sansevieria trifasciata ‘Golden
Hahnii’ †
(虎尾蘭)
Golden Birdsnest
(短葉虎尾蘭)
Portulaca pilosa †
Kiss-Me-Quick, Shaggy
Purslane
Oyster Plant
(毛馬齒莧)
Sansevieria trifasciata
Bird Nest Sansevieria
(金邊短葉虎尾蘭)
Sansevieria trifasciata
‘Laurentii’ †
Scutellaria indica
Sedum acre †
Skullcap
(金邊虎尾蘭)
(韓信 )
Biting Stonecrop, Wall Pepper,
Golden Moss
(金氈景天)
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APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
Sedum lineare
Sedum lineare ‘Variegatum’
Sedum mexicanum †
Variegated stonecrop
Variegated Sedum
Mexicum Sedum
(佛甲
)
(白佛甲
)
(松葉佛甲
)
Sedum nussbaumerianum †
Sedum sarmentosum †
Sedum sexangulare †
Coppertone sedum
Stringy stonecrop
Tasteless Stonecrop
(銘月)
(垂盆 )
(六楞景天)
Sesuvium portulacastum †
Stenotaphrum dimidiatum ‡
Tradescantia pallida ‘Purpurea’
Sea Purslane
Glabrous Stenotaphrums
(New name: Setcreasea
purpurea)
(海馬齒)
(光鈍葉
)
Purple Heart
(紫鴨跖
)
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APPENDIX II - PLANT SELECTION MATRIX FOR GREEN ROOFS (EXTENSIVE)
Tulbaghia violacea †
Vitex rotundifolia
Wedelia chinensis
Wild Garlic, Society Garlic
Beach Vitex
Wedelia
(蒜味 )
(單葉蔓 )
(蟛蜞菊)
Wedelia trilobata
Zephyranthes candida †
Zephyranthes grandiflora †
Wedelia
Autumn Zephyr-lily
Rose-pink Zephyr-lily
(三裂葉蟛蜞菊)
(蔥蘭)
(風雨花)
Zephyranthes rosea †
Zoysia japonica
Fairy Lily, Cuban Zephyr-lily
Zoysia Grass
(玫瑰蔥蓮)
(朝鮮
)
† Plant photos from Selection of Plants for Green Roofs in Singapore, copyright © 2005, National Parks Board of Singapore
http://www.nparks.gov.sg/book_1.asp ‡ copyright © 2004 Antonie Van Den Boss
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Appendix III
References & Bibliography
APPENDIX III: REFERENCES AND BIBLIOGRAPHY
III.1
MAJOR PUBLICATIONS.
III.1.1 Dunnett, N. & Kingsbury, N. (2004) Planting Green Roofs and Living Walls, Timber Press, Portland,
Cambridge
III.1.2 EARTH PLEDGE (2004) Green Roofs – Ecological Design and Construction, Schiffer Publishing
III.1.3 Nielsen, S. (2004) Sky Gardens – Rooftops, Balconies, and Terraces, Schiffer Publishing, Atglen, PA,
USA
III.1.4 Ngan, G. (Dec 2004) Green Roof Policies: Tools for Encouraging Sustainable Design
III.1.5 Snodgrass, E..C., and Snodgrass, L.L. (2006) Green Roof Plants – A Resource and Planting Guide,
Timber Press, Portland
III.2
RELEVANT GOVERNMENT PUBLICATIONS (LOCAL, INTERNATIONAL, AND INCLUDING POLICY)
III.2.1 Agriculture, Fisheries and Conservation Department (Hong Kong)
♦
♦
Introduction to Import Control, summarising the Plant (Import and Pest Control ) Ordinance,
Chapter 207, Laws of Hong Kong
http://www.afcd.gov.hk/english/publications/publications_qua/files/importcontrol.pdf
Checklist of Hong Kong Plants, 2004
http://www.hkherbarium.net/Herbarium/checklist2004/checklist2004_E.htm
III.2.2 Buildings Department, Lands Department & Planning Department (Hong Kong), Joint Practice Notes:
♦
♦
♦
III.2.3
JPN No.1 - Green and Innovative Buildings
http://www.pland.gov.hk/tech_doc/joint_pn/jpn01_e.pdf
JPN No.2 - Second Package of Incentives to Promote Green and Innovative Buildings
http://www.pland.gov.hk/tech_doc/joint_pn/jpn02_e.pdf
JPN No.3 - Re-engineering of Approval Process for Land and Building Developments
http://www.pland.gov.hk/tech_doc/joint_pn/jpn03_e.pdf
Buholzer, B. & Wark, R. (June 2006) Regulatory Options for Promoting Green Roofs in British Columbia
http://commons.bcit.ca/greenroof/download/Green%20Roof%20Regulatory%20Options.doc
III.2.4 Buildings Department
♦
♦
♦
PNAP- Practice Note for Authorized Persons and Registered Structural Engineers
http://www.bd.gov.hk/english/documents/pnap/Pnap116.pdf
Code of Practice for Structural Use of Concrete 2004 (particularly clause 2.3 on Design
Loads) http://www.bd.gov.hk/english/documents/code/concrete/e_concrete2004.htm
Wind Effects in Hong Kong 2004
http://www.bd.gov.hk/english/documents/code/windcode2004.pdf
III.2.5 Case studies of green roof regulations in North America 2006 (April 2006)
http://commons.bcit.ca/greenroof/publications/2006_regulations.pdf
III.2.6 Environmental Benefits and Costs of Green Roof Technology for the City of Toronto (Ryerson University,
Oct 2005) http://www.toronto.ca/greenroofs/pdf/fullreport103105.pdf
III.2.7 Building Green - a guide to using plants on roofs, walls and pavements, (by Johnston, J. & Newton, J
(2004, 1st pub. 1996) for London, United Kingdom)
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http://www.london.gov.uk/mayor/strategies/biodiversity/docs/Building_Green_main_text.pdf
III.2.8 Environment, Transport and Works Bureau Technical Circulars (Hong Kong)
♦
♦
♦
♦
♦
♦
♦
♦
Cyber Manual For Greening (ETWB TCW No. 11/2004)
http://www.etwb.gov.hk/UtilManager/tc/C-2004-11-0-1.pdf
Allocation of Space for Urban Street Trees (WBTC No. 25/1992)
http://www.etwb.gov.hk/UtilManager/tc/92/wb2592.doc and
http://www.etwb.gov.hk/UtilManager/tc/92/wb25921.doc
Tree Planting in Public Works (WBTC No. 07/2002)
http://www.etwb.gov.hk/UtilManager/tc/2002/wb0702.doc
Tree Preservation (ETWB TCW 03/2006) http://www.etwb.gov.hk/UtilManager/tc/C-2006-030-1.pdf
Management and Maintenance of Natural Vegetation and Landscape Works, and Tree
Preservation (WBTC No. 14/2002) http://www.etwb.gov.hk/UtilManager/tc/WBTC-1402(Rev.%20on%205%20May%202004).doc
Community Involvement in Greening Works (ETWB TCW No. 34/2003)
http://www.etwb.gov.hk/UtilManager/tc/C-2003-34-0-1.pdf
Maintenance of Vegetation and Hard Landscape Features (ETWB TCW No. 2/2004)
http://www.etwb.gov.hk/UtilManager/tc/C-2004-02-0-1.pdf
Registration of Old and Valuable Trees, and Guidelines for their Preservation and Appendix
A (ETWB TCW No. 29/2004) http://www.etwb.gov.hk/UtilManager/tc/C-2004-29-0-1.pdf and
http://www.etwb.gov.hk/UtilManager/tc/Appendix_A.JPG
III.2.9 Environmental Protection Department (Hong Kong)
♦
Preparation of Landscape and Visual Impact Assessment under the Environmental Impact
Assessment Ordinance (EIAO Guidance Notes No. 8/2002)
http://www.epd.gov.hk/eia/hb/materials/GN12.doc
III.2.10 Global warming - the Hong Kong connection (Hong Kong Observatory, 1 August 2003)
http://www.hko.gov.hk/wxinfo/news/2003/pre0801e.htm
III.2.11 Greenbacks from Green Roofs: Forging a New Industry in Canada (Canada Mortgage and Housing
Corporation) http://greenroofs.org/pdf/Greenbacks.pdf
III.2.12 Handbook on Skyrise Greening in Singapore (National Parks Board of Singapore and National University
of Singapore, 2002) http://www.nparks.gov.sg/publications/handbook_sg.shtml or
http://www.nparks.gov.sg/book_2.asp
III.2.13 Hong Kong Planning Standards and Guidelines on Urban Design Guidelines (PlanD, last modified 2006),
Hong Kong
III.2.14 NParks Pilot Green Roof Project (Housing Development Board (HDB), Singapore, November 2003)
http://www.hdb.gov.sg/fi10/fi10296p.nsf/PressReleases/2487237DEDB5E488482570830023FF70?Open
Document
III.2.15 Introductory Manual for Greening Roofs (Public Works and Government Services, Dec 2002), Canada
ftp://ftp.tech-nv.com/pub/SERVICE_LIFE_ASSET_MANAGEMENT/PWGSC_GreeningRoofs_wLinks.pdf
III.2.16 Majid, H. A., Singapore set to be leader in vertical greening in Asia Pacific (Channel NewsAsia, 24 March
05) http://www.wildsingapore.com/news/20050304/050324-2.htm
III.2.17 Operation Manual, Volume V: Arboriculture (LCSD, Sept 2003), Hong Kong
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III.2.18 Planning Department (Hong Kong), Hong Kong Planning Standards and Guidelines.
♦
♦
♦
Chapter 4: Recreation, Open Space & Greening
http://www.pland.gov.hk/tech_doc/hkpsg/english/ch4/ch4_text.htm
Chapter 11: Urban Design Guidelines
http://www.pland.gov.hk/tech_doc/hkpsg/english/ch11/ch11_text.htm
Ch12 Miscellaneous Planning Standards & Guidelines
http://www.pland.gov.hk/tech_doc/hkpsg/english/ch12/ch12_text.htm
III.2.19 Portland Zoning Codes, (22 April 2006), Title 33, Planning and Zoning Chapter 33.510, Central City Plan
District http://www.portlandonline.com/shared/cfm/image.cfmid=53363
III.2.20 Recreation and Amenities Manual, Volume II: Horticulture (LCSD, July 2001), Hong Kong
III.2.21 Standard Requirements for Handover of Vegetation on HyD SIMAR to Highways (Rev. A) (Landscape
Unit, HyD), Hong Kong.
III.2.22 Tan, P.Y., & Sia, A., Selection of Plants for Green Roofs in Singapore (National Parks Board of
Singapore, 2005) http://www.nparks.gov.sg/publications/greenroof.shtml or
http://www.nparks.gov.sg/book_1.asp
III.2.23 Thermal Performance of Roof Greening Features at EMSD Headquaters Building (Energy Efficiency
Office, EMSD, December 2006), Hong Kong
III.2.24 Toronto: Policy and Finance Committee Agenda Meeting No.1 (23 Jan 2006)
http://www.toronto.ca/legdocs/2006/agendas/committees/pof/pof060123/agenda.pdf
III.2.25 Toronto: Making Green Roofs Happen (Nov 2005) http://www.toronto.ca/greenroofs/policy.htm#making
III.3
GREEN ROOF RELATED RESEARCH
III.3.1 Chan, A. T., et. al., (Univeristy of Hong Kong, 2001) The Air We Breathe: Air Pollution in Hong Kong
III.3.2 Camp Dresser & McKee International Inc. in association with GHK (HK) Ltd, (Electrical & Mechanical
Services Department, Hong Kong, Dec 2002) Study on the Potential Applications of Renewable Energy in
Hong Kong - Stage 1 Study Executive Summary
http://www.hk2030.gov.hk/eng/environmental/pdf/renewable_energy.pdf
III.3.3 Chong, K.P., and Kadoorie Farm & Botanic Garden (Hong Kong Institute of Landscape Architects annual
journal, 2006) New Native Shrubs and Groundcovers for Ornamental Planting
III.3.4 Gaffin, S. et al, (Centre for Climate Systems Research, Columbia University, New York, and Penn State
Centre for Green Roof Research, Department of Horticulture, Penn State University, 2005?) Energy
Balance Modelling applied to a Comparison of White and Green Roof Cooling Efficiency
http://www.roofmeadow.com/technical/publications/GaffinetalPaperDC-0009.pdf
III.3.5 Hitchcok, D., (Houston Advanced Research Centre, July 2006) Strategic Plan for Urban Heat Island
Mitigation in the Houston Region
http://files.harc.edu/Projects/CoolHouston/Presentations/UrbanHeatIslandMitigation.pdf
III.3.6 Hedley, A. J., et al., (University of Hong Kong, June 2006) Air Pollution: Costs and Paths to a solution,
http://www.civic-exchange.org/publications/2006/VisibilityandHealthE.pdf
III.3.7 Hui, S. C. M., (2006) Benefits and potential applications of green roof systems in Hong Kong, paper
submitted to 2nd Megacities International Conference 2006, 1-3 December 2006, Guangzhou, China
III.3.8 Kohler, M., et al (Rio 02 – World Climate & Energy Event, Jan 2002) Photovoltaic-Panels on Greened
Roofs - Positive Interaction Between Two Elements of Sustainable Architecture
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http://www.rio02.de/proceedings/pdf/151_Koehler.pdf
III.3.9 Livingroofs.org in association with Ecology Consultancy, Green Roofs - Benefits and Cost Implications - A
Report for Sustainable Eastside (Birmingham City Council, March 2004) http://www.sustainableeastside.net/Green%20Roofs%20Report%202.07.05.pdf
III.3.10 Takenaka Corp. Heat Island Phenomenon Proven to Be Alleviated by Rooftop Greening: ACROS
Fukuoka Step Garden Creates Winds (Takenaka, August 2001)
http://www.takenaka.co.jp/takenaka_e/news_e/pr0108/m0108_05.htm
III.3.11 Tang, T., (Business Environment Council, April 2005) Living Under Blue Skies - A Review of Air Pollution
in Hong Kong and the Pearl River Delta,
http://www.bec.org.hk/fileLibrary/_A%20Review%20of%20Air%20Pollution%20in%20HK%20and%20PR
D%20(April%202005).pdf
III.3.12 Rosenzweig, C., & Solecki, W., et al., (Columbia University, New York, and Hunter College, New York,
2005) Mitigating New York City's Heat Island with Urban Forestry, Living Roofs, and Light Surfaces
http://ams.confex.com/ams/pdfpapers/103341.pdf
III.3.13 Wong, N. H. (Research Brief, Dept. of Building, School of Design and Environment, National University of
Singapore, 2002) Study of Green Roofs in Singapore http://www.bdg.nus.edu.sg/research/Rooftop.pdf
also see http://www.nus.edu.sg/occ/pressrel/0209/020905.htm
III.3.14 Wong, N. H. (Dept. of Building, School of Design and Environment, National University of Singapore,
2002) A Study of Urban Heat Island (UHI) in Singapore
http://www.bca.gov.sg/ResearchInnovation/others/UHI%20_2004-001_%20rev.pdf, also see
http://www.nus.edu.sg/corporate/research/gallery/research34.htm
III.3.15 Wong, N. H. (Innovation Magazine, Vol 3 Number 2) Urban Heat Island Effect: Sinking the Heat
http://www.innovationmagazine.com/innovation/volumes/v3n2/free/coverstory2.shtml
III.3.16 ZHAO Ding-guo & XUE Wei-cheng (2005, Acta Agricultural Shanghai journal), Effect of greening on light
roofing on lowering temperature
III.4
GREEN ROOF STANDARDS
III.4.1 American Society for Testing Materials (ASTM) http://www.astm.org, also see
http://www.astm.org/SNEWS/JANUARY_2002/green_jan02.html
III.4.2 ASTM (an article on the history of standards and the ASTM)
http://www.roofmeadow.com/technical/astm.shtml
III.4.3 Business Environment Council Ltd http://www.bec.org.hk
III.4.4 Wark, C. G. & Wark, W. W. (The Construction Specifier; August 2003 Vol. 56, No.8) Green Roof
Specifications and Standards; Establishing an emerging technology
http://www.greenroofs.com/pdfs/newslinks-803_construction_specifier.pdf
III.4.5 Guidelines for the Planning, Execution, and Upkeep of Green-Roofs (Release 2002, English version, by
the FLL, Forschungsgesellschaft Landschaftentwicklung Landschaftsbau (Landscape Research,
Development & Construction Society)) http://fll-ev.de/shop/product_info.phpproducts_id=10&cPath=4
III.4.6 Hong Kong Building Environmental Assessment Method (HK-BEAM) http://www.hkbeam.org.hk/general/home.php also see Latest HK-BEAM Standard for New Buildings http://www.hkbeam.org.hk/fileLibrary/_4-04%20New%20Buildings%20(Full%20Version).pdf and Latest HK-BEAM
Standard for Existing Buildings http://www.hk-beam.org.hk/fileLibrary/5-04%20(full)%2021feb05.pdf.
III.4.7 Hong Kong Professional Green Building Council (PGBC) http://www.hkpgbc.org
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III.4.8 Hong Kong Concrete Repair Association (HKCRA) http://www.hkcra.com.hk, also see Waterproof
Concrete - Is it really necessary? By Dr. Chris Stanley, May 2005,
http://www.hkcra.com.hk/tech_waterproof_05.htm
III.4.9 International Green Roofs Association, Regulations and Guidelines for Green Roofs, http://www.igraworld.com/green-roof-guidelines/index.html
III.5
OTHER PUBLICATIONS, RELATED WEBSITES, SUPPLIERS, ETC.
III.5.1 Approximate Building Costs in Hong Kong, 1st Quarter 2006 (Davis Langdon & Seah, Quantity
Surveyors) http://www.dlsqs.com/modules.php?name=News&file=article&sid=279
III.5.2 ASLA Green Roof Project http://www.asla.org/land/050205/greenroofcentral.html
III.5.3 Being Green On Top (Magazine: IMC Building Services Professional, July-August 2006 ed.),
www.imcmedialtd.com
III.5.4 Beijing to Plant Rooftop Grass to Clean Away Smog (January 10, 2005, Environmental News Network By Reuters) http://www.enn.com/ch_clim.html?id=53
III.5.5 Bio-Lung (2005, Marumo Publishing Co. Ltd., Japan)
III.5.6 Bio-lung, a Massive Greening Wall at EXPO Plaza (EXPO 2005, Aichi, Japan)
http://www.expo2005.or.jp/en/eco/bio-lung.html
III.5.7 Burkhardt,P., (July 2006) ASLA Retrofits Headquarters with Green Roof
http://archrecord.construction.com/news/daily/archives/060706asla.asp
III.5.8 Chan, T., CIBSE Hong Kong Branch (Oct 2005) Climate Change - What Hong Kong is Doing Now
http://www.cibse.org.hk/pub/16/2005%20CIBSE%20-%20Thomas%20Chan.pdf
III.5.9 Chan, S.T., (Hong Kong Institute of Landscape Architects annual journal, 2006) Skyrise Greenery in
Hong Kong
III.5.10 Garden Landscapes in the Sky, ZinCo Singapore Pte Ltd.
III.5.11 GreenTech Systems http://www.greentechitm.com/pdf/RoofTop.pdf
III.5.12 Green Roofs: A Horticultural Perspective (by Kate Jenrick, Mar 2005, Dissertation, Royal Botanic
Gardens, Kew) http://www.livingroofs.org/NewFiles/KHJ_dissertation.pdf
III.5.13 Green Roof Design 101 Introductory Course – Participant Manual (2005, Green Roofs for Healthy Cities)
www.greenroofs.org
III.5.14 Higgins, D., et. al., Hybrid Green Roof For Es2: A Feasibility Study (Nov 2004)
http://www.adm.uwaterloo.ca/infowast/watgreen/projects/library/f04greenroof1.pdf
III.5.15 Holladay, A., (April 2006), Green roofs swing temperatures in urban jungles (USA Today)
http://www.usatoday.com/tech/columnist/aprilholladay/2006-04-24-green-roofs_x.htm
III.5.16 Hui, C.M. (Sam), (1995 Hong Kong University), Overall Thermal Transfer Value in Buildings, 1995, Hong
Kong http://www.arch.hku.hk/research/BEER/hkottv/hkottv.htm
III.5.17 It isn’t Easy Being Green (Landscape Architecture Australia magazine, Issue 110)
III.5.18 Kallwall Nanogel technology http://www.kalwall.com/nano3.htm, http://www.kalwall.com/nano1.htm,
http://www.kalwall.com/42.htm, http://www.kalwall.com/expandtraditional.htm,
http://www.kalwall.com/whats_new.html, http://www.kalwall.com/nano5.htm,
III.5.19 Miller, C. (March 2006 for Roofscapes Inc.) Extensive Green Roofs (Whole Building Design Guide)
http://www.wbdg.org/design/greenroofs.php
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III.5.20 Ngan, G. (Dec 2004) Green Roof Policies: Tools for Encouraging Sustainable Design,
http://www.gnla.ca/assets/Policy%20report.pdf
III.5.21 Powell, R. (1999, Thames & Hudson) Rethinking the Skyscraper – The Complete Architecture of Ken
Yeang
III.5.22 Rockdelta Green Noise Barrier http://www.rockdelta.com
III.5.23 Rogers, (Lord) Richard (1997, Faber and Faber, edited by Philip Gumuchdjian) Cities for a Small Planet.
III.5.24 "Sky Oasis" Rooftop Greenery Completed on Roof of Head Office Building (Mido Building) - Effectiveness
of Three Types of Gardens Verified (Takenaka Corporation, Apr 2002)
http://www.takenaka.co.jp/takenaka_e/news_e/pr0204/m0204_04.htm
III.5.25 TED (Trade and Environment Database) Case Studies: Japan Air Pollution
http://www.american.edu/TED/japanair.htm
III.5.26 Role of Green Roofs in Managing Thermal Energy (Green Roofs Inc.)
http://www.roofmeadow.com/technical/publications/Thermal_Effects.doc
III.5.27 Rooftop Greenery: Growing Plants on Buildings to Absorb Heat (Oct 2001, Trends in Japan) http://webjapan.org/trends01/article/011003bus_index.html
III.5.28 Sky Garden Green Roof Systems http://www.greenrooftops.com
III.5.29 Velazquez, L. S., Modular Green Roof Technology: An Overview of Two Systems
http://www.greenroofs.com/pdfs/exclusives-modular_presentation03.pdf
III.5.30 World's Largest Green Wall - the 'Bio-Lung' - Debuts at Aichi Expo 2005 (June 2005, Japan for
Sustainability) http://www.japanfs.org/db/database.cgi?cmd=dp&num=1029&dp=data_e.html
III.6
LOCAL GREEN ROOF NEWSPAPER FEATURES
III.6.1 SingTao Daily (Hong Kong), 28 August 2006
III.6.2 SingTao Daily (Hong Kong), 7 September 2006
III.6.3 Apple Daily (Hong Kong), 25 September 2006
III.6.4 Oriental Daily (Hong Kong), 25 September 2006
III.6.5 Oriental Daily (Hong Kong), 26 September 2006
III.6.6 Ming Po (Hong Kong), 13 October 2006
III.6.7 Positive News (Hong Kong Edition), winter 2006 http://www.msnbc.msn.com/id/7911618
III.6.8 Apple Daily (Hong Kong), 31 October 2006
III.6.9 South China Morning Post, 21 December 2006
III.6.10 Apple Daily (Hong Kong), 23 December 2006
III.6.11 Headline Daily (Hong Kong), 27 December 2006
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