Air Sealing and Ventilation Improvements for Multifamily Buildings - Fitzgerald and Bohac

Editor's Notes

1. Probably the more appropriate title of this presentation is “how to achieve better air quality by sealing leaks between units and improving ventilation. Our focus is not necessarily on reducing energy, but what can be done to improve air quality in MF buildings. So we’ll talk about what the sources of contaminants are, how they get between units, what others have found regarding air leakage and air flows between units and then we’ll present information from our 6 building study in Minnesota.
2. So do you think the person in this apartment smoked a little bit? It’s either that or a lot of fired food. Secondhand smoke drift between units is one of the most significant sources of concern in apartment buildings and condos.
3. You could get rid of one of the SHS problem by converting the building to be smoke-free. There has been a strong effort in Minnesota and the “Live Smoke Free” program now has more than 500 smoke-free apartment buildings in Minnesota listed on their web site. They have a nice page that allows people to search for buildings in their area. They also have information for owners regarding steps to making their building smoke-free.
4. Survey of apartment owners indicates that cooking is the most common source of complaints. So even if a building goes smoke-free, you still have to deal with cooking and other odors that are transferred between units. Also, want to provide adequate ventilation in each unit to keep them fresh.
5. The cause of the problems are not just the sources, but that air and odors travel between units. You can see in these three studies with tracer gas measurements in apartments across the country that up to 35% of an apartment’s air comes from their neighbors.
6. Other studies that have looked at the leakage in apartment buildings have found 50% or more of the total leakage is to other apartments or to the common area.
7. So why is it that apartments share their air and their odors and other contaminants with their neighbors? What are the driving forces?
8. Just a little building science 101 here. In colder climates the main driving force is the stack effect. You have warm air in the building and colder air outside. Just like a hot air balloon, hotter air rises. In this case this tends to cause air to enter the building on the lower floors and exit out the top. This effect gets bigger with taller buildings, so it can be a big issue for taller MF buildings. That is unless the floors are air sealed or isolated from each other – and that doesn’t happen often.
9. The wind effect on buildings is pretty obvious. Air tends to enter on the windward side and leave on the downwind side. It is important to note that wind speeds are higher farther from the ground, so wind pressures are greater for the upper level of taller MF buildings.
10. The third effect is the mechanical system effect and sometimes that isn’t discussed much for single family houses. This is the imbalance of air flow in apartments. In most cases this occurs when there is more exhaust ventilation in one unit than an adjacent unit. Now in some buildings it makes sense to do this. Say for instance you have a pool attached to a school. You don’t want the chlorine smell from the pool to get into the school, so you run extra exhaust in the pool area which causes the pool to be at a negative pressure relative to the school and air flows from the school to the pool – not the other way around. Unfortunately, this same effect happens in MF buildings. Someone doesn’t like their neighbor’s cooking or smoking, so they turn on their bath fan. Unfortunately, that typically causes more air and odor to move into their unit. So turning on an exhaust fan has the exact opposite of the desired effect.
11. Sometimes smokers can be proactive. We’ve had buildings where the smoker got tired of their neighbor’s complaints so they opened a window when they smoked. Do you think that helps? Well on a cold day it probably helps the person in the unit below, but it doesn’t help their upstairs neighbor. When you open a window it causes the pressure to be about the same as outside which only increases the pressure difference from the smoker to the upper unit and produces more air flow (and odor) to the upper unit. Something to think about – another case where you intuition of what should help actually does not.
12. Of course you not only need the driving force, but also the pathways. For people that haven’t been involved in air sealing, the initial response can be – how does the air get from my unit to theirs? Solid floor no obvious leaks. But there are always leaks.
13. Unfortunately, most are small and spread out around the unit – access of occupied units can be a problem.
14. Baseboards or under walls can be an issue. 1/32” crack doesn’t seem like much but multiply that by 3’ and you have a 1 square inch leak. Multiply by 30’ and you have 10 sq inches.
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17. Add unit ERV/HRV as per Gord Cooke Stack vents
18. Put these 3 slides in with the LakeShore case study?