Subscribe or Renew Membership Subscribe Renew

Offgassing of spray foams

offgridbuilder's picture

I used Great Stuff insulating foam sealant around all the windows of our latest project, a super-insulated off-grid home. Messy business but a good tight sealant.  I used the same product in the old cottage we are presently in, to seal various gaps and keep the cold winter winds out. The fumes, even though they are no longer noticeable, give me headaches and burning sinuses at night (the bedroom was one of the areas I worked on). We sleep with the window open a bit at all times, but the problem persists, two weeks later.

Question: does this spray foam, and others like it, stop offgassing eventually? We won't be moving in for months, so time is on our side. The main culprit is diisocyanate. Since the new house has a special emphasis on excellent indoor air quality (no MDF, particleboard, carpets, alkyd paints) I will tear out all that foam if it turns out to be a potential problem. Of course, there is not much else on the market I can use instead. Does anyone have any knowledge on this? Are there foams available in small quantities which use more innocuous propellants and solvents? Thanks, guys.   Paul

First off, even "Great Stuff" (post #205517, reply #1 of 12)

First off, even "Great Stuff" comes in several different varieties, with varying chemical compositions.

Dap used to sell (not sure if they still do) a low-expansion foam that was latex-based, containing far fewer volatile compounds.  Quite expensive, though, because a can only goes maybe 1/5 as far as a can of regular foam.

It may be that there are some commercially installed foams that have less outgassing, or with less obnoxious compounds.

In general, offgassing will follow an exponential curve, starting high and "decaying" over time, though never reaching zero.  Basically it will have a "half life" (could be minutes, hours, days, or weeks) and every "half life" the outgassing will be reduced by half.  So if it's a week then the outgassing will be reduced by a factor of 16 in 4 weeks.

Of course, the problem is that human sensitivity to odors and the like is roughly exponential in the opposite direction.  Reducing the chemical concentration by a factor of ten, say, may only reduce the perceived concentration by a factor of two.  Or, in some cases, reducing the concentration can actually cause an odor to smell stronger.

People differ a lot in terms of their sensitivity to volatile chemical compounds.  Mostly this has to do with the makeup of the DNA in the mitochondria in the body, and whether there are any "oddities" in the way the mitochondria consume (or not) the compounds.

(Also keep in mind that headaches and the like that come on when a house is sealed may be due to an increased CO concentration or some similar problem.  Check the furnace in your "cottage", and check other combustion appliances.)

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Dap foams (post #205517, reply #2 of 12)

Thanks, DanH. I looked up the Dap product and it is called "DapTex latex expanding foam sealant'. I haven't seen it around but I'll go find some and try it out. It is apparently VERY low expansion and doesn't go very far as you suggest, but I'll try it anyways. Paul

EPDM foam gasket? (post #205517, reply #3 of 12)

I haven't used it but Conservation Technologies has a gasket for this that folds in half and you tuck in the gap. I suspect it doesn't work with window mounting shims in the way though.


Certainly with any spray foam (post #205517, reply #4 of 12)

Certainly with any spray foam you should use some sort of backer for gaps over about 1/4" wide.  The spray foam layer only needs to be maybe 1/4-3/8" thick to do its job of sealing.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

I'm confused. You say you (post #205517, reply #5 of 12)

I'm confused.

You say you sleep with the window open a bit at all times.  Why even put the foam in?

for the energy tax credit. (post #205517, reply #7 of 12)

for the energy tax credit.

We have many parts if you're (post #205517, reply #6 of 12)

We have many parts if you're looking for anything. We also have instructional videos available

All homes need sealing (post #205517, reply #8 of 12)

I'm not sure if that comment about my sleeping with the window open was tongue-in cheek? We live in Central B.C. Canada, where winters can drop to minus 40 C.That's about the same in F, minus 40.  Summers can hit plus 37 C. That's about 99 F. It's important to have complete control over air infiltration, so we seal very carefully. The house has blow-in insulation which we did ourselves. A huge learning curve, so it took days with a rented Krendl machine. Walls are R48, Ceilings are R 67, floor is R36 using batts of Roxul mineral wool (great product!). Air infiltration can handicap all that hard work, so we take it seriously. This house stays nice and warm while the neighbours are slaves to their woodstoves. In the summer we stay cool (with no A/C) while the neighbours toss and turn at night and can't sleep.

My wife and I designed and built this home ourselves.Shallow frost-protected foundation, double-stud walls, Hardipanel siding, aspen wide-plank flooring, rainwater collection for toilet flushing, solar hot water, offgrid with 2.8kW solar array........There's no MDF, particle board etc. Cabinetry is all solid wood.  I'm just finishing the trimwork, so most of the spending is over. This house, 1080 sq. ft., has cost us $42,500, not including the solar PV and hot water. That's all materials; no labour. OK, no paid labour; we worked like dogs for five years. Not too shabby! As with any project, there are a few things I might do differently, but overall I think we ended up with a fine home.  Paul

The comment posted was dead (post #205517, reply #9 of 12)

The comment posted was dead serious. If you always sleep with the window open why even bother with air sealing the window in the first place ?  Surely you see that leaving the window open would allow in more air than would ever be let in by not sealing it

what did the off gasing odor smell like for you? (post #205517, reply #10 of 12)

I just used some of this in the walls behind the kitchen sink last night. This evening a strong acetone like smell came from that sink area. I suspect it may be the dow great stuff big gap filler I sprayed in some drilled holes. Usually this stuff is odorless, but that's always been on items I've sprayed that are open to the atmosphere and not behind closed walls. I wonder if the amount I sprayed in the wall was too much to cure and a lot of concentrated off gassing is leaking out whatever voids can be found. Just wanted to corroborate with you what the smell of its odor was. It's giving me headaches too.


I want to say I sprayed a good third to half can into those studs.

found the odor source (post #205517, reply #11 of 12)

Found a good tip from here. They too had a sudden acetone smell, eventually she traced it down to a leaking aerosol can. I went and revisited under the sink and bagged up all the aerosol cans and left them outside. Smell has since dissipated. I believe I also heard a very small leak from a can of scotch guard spray before I picked up the can. It was subtle and the sound stopped once I took hold of it so I'm not 100% sure that was it. But the strong odor tonight is definitely in line with how that scotch guard spray smells.


False alarm with the dow great stuff. Gotta be careful with the after this therefore because of this logic. But in this case it was a resonable suspicion to start with since the spray foam was really the only known change to the under the sink area. First ingredient listed in the Contains list was acetone. Whew, close one. Would have been horrible to sleep through it.