We know that air from attached garages moves into houses, and we have some data on the size of the leakage area from the garage to the house, based upon field research. However, we are now working on a project involving garage-to-house air sealing in Canadian houses and I am looking for advice from people who have done this type of work, perhaps as part of weatherization programs. Does anyone have specific experience in sealing the garage-to-house leaks in attached garages? I am looking for information on cold climate houses that might be pertinent to Canadian stock. If you have published on the leak locations and sealing strategies, that sort of information would be great. Anecdotes are fine too. This seems to be an under-documented area.

The question that interests me the most is with suburban garages and bonus rooms above. These are notorious for having cold floors and discomfort. My instinct would be to rip the garage ceiling drywall off and redo the floor above properly, perhaps with foam. There must be others who have found less invasive and costly solutions. I would like to hear how you have done it.

Thanks for whatever information you have.

Don Fugler

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Sorry I don't know of any residential studies offhand but...

For fire & fumes only you can go with a second coat of drywall (both sets taped) with the seams offset & being very careful around any penetrations (check out commercial standards for more on this)

Best method though to take care of heat loss & fumes is to rip the drywall off & spray Closed Cell foam & take care of the fire / aesthetic aspects with drywall

Next option is 1"+ of Closed Cell foam followed up by blown fiberglass / cellulose

cheapest option - air seal the living snot out of everything - all seams, cracks, penetrations & finish off with blown cellulose or fiberglass (Owen Corning's EnergyComplete & some other manufacturers have rigs for doing this easily enough)

Don't forget to use a fire rated insulated door between the living space & garage


I believe I've seen papers that were done in Alaska for garages that were sealed.  If I can find them I will send the link.  They may have been from prior ACI or BPI related conferences.

I have a similar house - but live in a marine zone 4 environment.  Years ago I insulated with fiberglass -- walls, ceilings, etc.   If I were to do it again.  I would use Roxul. (Canadian right?)  Avoid the foam.  Remember, in addition to the VOC, CO, etc... the other major concern is fire.  Once the fire gets past the gypsum the foam would be adding fuel to the mixture -- even more than bare wood.   Roxul would add extra fire protection,  the desired insulation,  and sound dampening.

"Avoid the foam"???

VOC's - one should be ventilating that area & they should be gone before anyone regains access

CO - remember the "P" in the GWP piece stands for potential & with the fuzzy math they used... well that would earn most people an F in mathematics

Fire - well plenty of CC foam actually passes the flammability & smoke tests but just to play devils advocate and say it doesn't... by the time the fire gets past the drywall, everyone should be out of that house & the fire department should be showing up. If this same fire happened in the living area, by the time it would take to get to the foam, well you would already be dead

With that I am a big fan of Rockwool but the issue is any air movement allows CO, gas, & other fumes access into the living areas - if you can detail & do it right, you should be golden. The problem is most people are for getting things done quickly which doesn't fly so well in these cases 


Nice links below, I will have to check those out later - thanks

The reason I dislike foam in the garage -- even under a layer of sheetrock,  is that owners have the tendencies to puncture the and hang things from the ceiling.  I'm not sure the stats, but after the kitchen, I believe garages are near the top of the locations that fires break out in houses.  Generally there are not smoke detectors in a garage, that means that the fire could be smoldering and well on the way to expanding -- before owners are alerted... IF they are awake.  If they are sleeping - they may have little time to respond.  Worse - is that many owners don't keep the smoke detector batteries fresh.   

I would presume that the envelope would be well sealed.  Rockwool would never stop the air or fume access.  But with those areas sealed by another means - the rockwool could provide a safer insulation and sound dampening..

I also now park my vehicles out of the garage.  I have had one vehicle catch fire in a parking lot thirty minutes after it was parked, an electrical problem!   The vehicle was totaled.   Having seen the results of that - I would push for anything to buy an extra five minutes for the residents to get out of the house.  Because of the heat of car fires -- I don't think foam even with fire retardants.

So maybe the  better choice is a flash and bat...

Don,  I would also do an internet search or ask for queries about indoor air quality, Alaska (or province) and garage.  I know this has been studied and researched by a lot of the universities and building science groups.  The number one thing would be to protect the air quality -- avoid the bad stuff from the garage making into the house.   

Can you poke a small hole and put a borescope into the ceiling cavity and see what is up there...? 

How leaky is the building/garage?  Have you done any kinds of blower door tests?  

Are the houses very similar designs -- or is there a great deal of variation?  Can you use one or two as the model for the rest?

What are the rules from your building departments?  If you pull out the ceiling -- will that trigger the addition of a sprinkler system as part of the weatherization activity?

If I remember correctly - one of the biggest problems in the Alaska project --- had to do with the storage of the snowmobiles in the garage.  The VOC (gas fumes) while not strong - were actually making into the house.  The university had done long term air studies as part of their weatherization project.  Replacement air for the rest of the house was also a problem -- because it had been coming from the garage!





Canadian Mortgage and Housing Corporation (CMHC) has some research.   Building Sciences Corp has done a lot of work... (and they speak Canadian :-)) )  BSC would be a good group to contract with for consultations.  They know the buildings..


Thanks for the leads. I was the manager of the CMHC research. I recognize that we have established that garage-to-house air movement exists, and that it often brings in polluted air. What I am looking for now is the practical side of air sealing the garage leaks. Someone somewhere must have retrofitted a bunch of garages and has verified the reduction in leakage through blower door testing. That is the person for whom I am searching. If they exist ...

Don,  Building Sciences Corp may have paired up with the BuildAmerica program to test.  Your work at CMHC,  the northern state/province universities.   In Washington State -  the people at the WSU building/energy efficiency group may have done tests.  They've been pretty active with sealing experiments and blower door testing.

The Alaska University people might be good leads - lots of houses with attached garages or the garage is under a bedroom.  Plus the extreme cold - and the obvious air quality problems.  I do remember some of them going through trying to seal.

I will be doing the same project on my house this summer -- but one house is not a good enough sample - for anything except the two hundred other houses in my area built by the same developer in the 60's.

Ttwo blower doors?    If so does the garage have a separate door to the outside, or only one door into the house?   

Measure house with garage door closed (normal conditions),  measure house with garage doors open(living space only)?   This assumes the garage doors can seal up enough to make a difference...

You are trying to measure the leakage between the whole house and the garage - correct? 

Gary Nelson (Energy Conservatory) probably tested stuff like this years ago --

I've done a quick look to see if any papers were published recently...  most of the papers for northern climates point back to alaska and canada...  and the alaska papers point to research done in canada

If you are sending out weatherization crews and building possible checklists  of areas that I can think might be unique to older homes with a garage under the living space include:

1 - check the age of the plumbing!  If the piping is galvanized and 20+ years old,  it might be that your great sealing job will be torn up when the plumber comes out to replace the piping.

2. - garage doors, springs and opener mechanisms fail,  if old enough and have to remove portions of them to obtain access to the ceiling - you might have a problem re-installing them.  Conversely they could fail afterwards and the new garage doors and mechanism adds lots of holes to the newly sealed garage.

3.  in older house/garage combinations - the ceiling may have been installed years later by a prior owner - covering up access to wiring (junction boxes) -  these really need to be exposed for access.  So you'll need to look for them.

4. seismic tie downs that my be missing, any work like that (transfering seismic loads between floors) should be checked for for sealing -- if code requires the seismic hardening.


Thanks for those ideas. The garage door hardware on the ceiling could be a problem, and would be a big impediment if the ceiling were to be dropped to access the floor above. Junction boxes would have to be checked.

I was part of the team testing Canadian garages in the nineties. We used two blower doors to quantify interface leakage at that time. This last set of tests used a single blower door technique. It will be interesting to compare results.

the very big thing is sealing the return air.  When the fan is on and not sealed will suck the car gases in to the building.  I seal the return first.   To prove the return is sealed I use fog like used in the 70' disco days.   After the return is sealed then will dry pack the walls and above garage.   The return will be between .1 to .01 inch water col.  This can be a very big draw and I have seen 400 CFM of return just from garage.   With ducts using stud space for return will suck from every where and the  path of garage is lower than most duct work.   I was on one case where 6 people were killed with a 1966 mustang in the garage with door open but with lots of return air into garage will still let lot of CO2 into the building.  Sealing the return is the big thing and I feel should be first thing to seal in a  old building.  Just test out and test in and make sure the total stict presser is not to high.  

There have been several cases of CO poisoning fatalities relating to hybrid vehicles parked in attached garages.  Locations of fatalities are in New York and Florida.  See

http://www.nydailynews.com/news/toyota-sued-carbon-monoxide-tragedy... and



These fatalities should shine some urgency to the air sealing issue. Communicating this problem to customers is a very effective way to show how improtant air sealing can be.  Also see Lester Shen's recent post here:


I have gotten 6700 PPM CO off a hybrid that had a bad valve.  I have seen a 66' mustang 940 HP got 62,000 PPM CO. Flue gas meter go up to 8000 PPM CO, so to get the big number must use very high end testing meter.   With Garage door open still can get very high numbers. 


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