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Community and Q&A

Lingering Chemical from Spray Foam Insulation

user-5280522 | Posted in Green Products and Materials on

I’ve read many articles on this subject, but I wanted to ask a more specific question as my case doesn’t seem to match the other’s horror stories with poorly-installed Spray Foam Insulation.

Our contractor came highly rated by a friend who is an architect in our area. He’s worked with this contractor on numerous occasions. I’d gotten quotes from ~5 different spray foam insulation vendors and this guy’s estimate was a good 50% higher than the others, but I felt he actually knew what he was doing. In conversations he seemed to say all of what I considered “the right” things. He does 100% spray foam insulation for high-end homes in our state of Connecticut.

They did a great job as far as the job site was concerned. They were extremely clean and really cared about keeping things orderly.

We had a very large job as our house is a two-story 5200 sq ft house.

They removed the blown-in insulation on the floor of the attic and sprayed BioBased 501w open cell foam on the underside of the roof deck (~10 inches on roof deck, and ~6″ on vertical walls).

Prior to spraying, they shut off the upstairs air handler that was housed in the attic and disconnected the ducts. They laid down plywood sheets on the floor and laid plastic on top of that, stapled to floor. All surfaces were covered. (A subsequent HVAC guy remarked that he’d never seen such a neat job of spray foam insulation installation.)

The foam was also covered with a fire-retardant paint (DC 315)

The contractor used an air handler in the attic that was attached to a removed window to vent the attic air to the outside.

The reason for this posting, however, is that we’re still smelling a chemical smell in the house when the vent is turned off. And this is now 2 months after the installation. Installation was done 2nd week of July and it’s now mid-September.

The smell is worse on hot days. It is not the dead fish smell that others have experienced, but it is evident.

It’s possible that I’m getting used to the smell, but my sense is that it IS getting better. Yesterday we had another 90-degree day and we could smell it and were worried, but I went into the attic and noticed that the 12-inch flexible tube out of the air-handler had detached and was not sucking air out at all.

That was actually encouraging because while there was a distinct chemical smell, it was less than it used to be. After re-attaching the air handler, the smell went away.

I know people have said the smell will never go away unless we take out the part that smells (assuming there’s an area that didn’t cure properly.)

However, I do feel that it is better. The contractor has assured me the smell will, eventually, go away.

I’ve read that if there is not adequate ventilation when the installation happens, initially, when the foam expands and forms it’s air bubbles it will pull in the accelerant gas that is present in the air. That slowly leaching gas can lead to a smell.

If this is what happened, it seems reasonable to me that the lingering (and decreasing) smell may just take awhile to go away, since this was a very large job. Plus the surface of the foam was covered in that thick, fire-retarding paint. If there is a gas in there that needs to come out to be replaced by fresh air, that paint has to be slowing the process, right?

Does this idea make any sense to any professionals on this list?

I have a call in to an air-quality tester to see if we can determine what the chemical smell is, and to set a baseline to test again later to verify whether it is, indeed, going away.

Looking for any guidance on this issue.

— Scott

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  1. GBA Editor
    Martin Holladay | | #1

    I don't have any encouraging information to share. Others in your situation report that the smell returns every summer, with the arrival of hot weather. Running a ventilation fan continuously undermines the purpose of the spray foam, which is to save energy.

    I don't recommend testing the air. Tests will tell you nothing. If you can smell the foam, you've identified the problem.

    A few people report that the smell eventually fades. Others report that it comes back with warm weather, every year.

    I would document the facts of your case in a letter to the contractor and a letter to the foam manufacturer. Others in your position have ended up insisting that all of the foam be removed. Good luck.

  2. user-1123621 | | #2

    I have been dealing with the odor problems in my house from the application (May-2013) of Demilec APX against the roof deck. I had to halt construction on the house, so I have not been able to live in the house. I had a sample of the foam removed from the attic chamber tested per Section 01350. This is the current standard to test products in California for VOC labeling. Eurofins and Berkeley Analytical do this test. My test resulted in a variety of VOC's. DEP (Diethly ethanephosphonate/CAS 78-38-6) had an extremely high emission rate. The rate is so high it is placed in the PAC 2 category. PAC stands for protective action criteria used by health professionals and first responders to evaluate the health impacts for a once in a lifetime exposure. For DEP that exposure is for only one hour. PAC 2 levels for DEP predict "Irreversible or other serious health effects that could impair the ability to take protective action". Those health impacts are for a one hour-once in a lifetime exposure. Occupational (work environment) or non-occupational (home environment) VOC levels have not been established for this chemical. These VOC levels were from a foam sample removed from house 7 weeks after installation. The chamber test is conducted at 73F where conditions in your attic get much hotter so you could expect higher emission rates in your attic. We are all told if installed properly the product is inert (not chemically reactive) after 24-72 hours. There are no know studies or trials to remediate the problem of continued off gassing of SPF. The only know solution is to remove the product, however this may not result in a complete elimination of the odor. My product was removed, but two follow-up IAQ studies of the attic show that DEP is still being emitted at much lower levels. One can only conclude the chemical has penetrated the wood truss system. My house requires the complete removal of the roof and truss.

    The problem with testing, is the B Side of the SPF mix is proprietary, so you don't know the chemicals to test for. Therefore, have the company do an extensive test for VOC's beyond those conducted in the section 01350 test. Have a sample of the SPF removed from your attic chamber tested and you will probably also need to independently test the fire coating.

    Work with an Industrial Hygienist or an expert in indoor air quality. SPF is a chemical mixture, you are in a situation where you don't know if the SPF off gassing is toxic or harmful when exposed for the long term. In my case I have an extremely offensive odor and emitting of an organophosphate fire retardant. The odor could be one of the other chemical VOC's

    More information; I used Eurofins in Sacramento CA. For the foam sample I did the 24 hour VOC chamber test. The test was $400 without shipping. The foam sample is shipped in a mason jar & kept cool (gel ice packs in small lunch box sized cooler). They are a certified lab per CA 01350 criteria (there is a lot of good info/history about this test on the internet). This test has been adopted by other countries as it tests for 35 specific compounds (mostly known carcinogens). The 24 hour test also includes other VOC's such as aldehydes. If you know the specific VOC's of concern, discuss that with them beforehand and they may adjust the test or put more importance on them.

  3. GBA Editor
    Martin Holladay | | #3

    Did Demilec step up to the plate and take financial responsibility for your disaster?

  4. Andrew_C | | #4

    Good grief. I've been leery of using spray foam, but until now I'd thought that it was reasonable for basement rim joists only. After all, it's just a small area, and kinda tricky to airseal and insulate otherwise, so it should be okay, right? Nope, that's not going to happen in my house. If you know something is problematic, and that the fix is very difficult and expensive, and you still decide to go ahead with it...

    I feel badly for all the people that have been burned by bad spray foam installations. What a physical, emotional, financial mess.

  5. kaysmith | | #5

    Brad, we are having a similar problem - which I just posted on this forum. We also have a smell on hot sunny days - and it is not a fishy odor or an ammonia odor - it just has a distinct chemical smell. Can you keep us updated on your situation and if you find a solution? Is your attic humid as well?

  6. user-5280522 | | #6

    Kay, what brand of spray foam did you have installed? My situation is unresolved. I've been venting per the installer's recommendation and today was my first test of turning it off and closing the windows to see how bad the chemical smell is on the top floor.

  7. kaysmith | | #7

    Covestro - Bayer Bayseal Open Cell.
    Here is what I posted:
    It smells much stronger on hot sunny days - less so on cloudy days. We are seeing high humidity as well, which seems to make the smell worse.

  8. Rin4 | | #8

    Hi Scott,

    Did you ever find a solution to your problem? We just had spray foam applied a month ago with the promise of it being "odor free", etc, and it still smells so strongly of paint that I'm afraid to let my daughter sleep in her room upstairs. This is particularly strong during a sunny day as you mention. This is our dream home and it's been ruined by this horrible stuff. We had Bayseal Open Cell and I just want to know if this is something that eventually corrected itself over time or if you found relief any other way. Like I said earlier, this is our dream home and I live in fear of the top floor being full of toxic off-gassing from the fumes. We are getting pretty close to having the roof and trusses ripped off and replaced. Did you ever try the MemBrain or an air exchange or anything?

    1. BPortnoy1 | | #76

      Hi there. We are in same boat. What did you do and how was the process of removing? Thank you!

  9. user-7266153 | | #9

    Scott and Rin4,
    Has your smell gone away? I have had a sweet chemical smell for two years in a residential gym I built on my property. My son developed respiratory problems. So I had to ban him from the gym (and I built it for him). I tore out the walls and dug out the open cell foam as best I could and replaced it with rock wool. But the foam is still in the attic. I also added more fresh air ventilation. The smell got much better when I tore out the foam in the wells, but it is not gone. You smell it when you walk in, but it soon becomes unnoticeable. But still scared to let my son in there. I am hoping the last of the smell will finish offgasing and just go away. Did you smell go away?

  10. user-667537 | | #10

    Here's our experience. Approximately 2 years ago we added a second floor to our ranch hosue, which included an entirely new roof (as opposed to simply raising the existing roof). A hot roof was installed, using open cell spray foam. They used BASF Elastospray 8000.

    After the first winter, when things warmed up and we switched to air conditioning (we use a hydro-air system, so the AC shares the same ducts as the heat), we noticed some noxious odors. The term "chemical smell" would apply. I wrote it off as a byproduct of the recent renovations and didn't get too concerned about it.

    Now, this summer, when we switched from heat to AC, the same thing started happening. Clearly the hot, sunny weather causes something in the attic to become more active. Since it's almost two years since the insulation was installed we are now a bit more concerned, and started digging in.

    I contacted several people in different professions, but to make a long story short he's where we are.

    Our HVAC guy, whom we like a lot, said he was surprised that the town inspectors did not require the installation of an ERV or HRV since we are now almost 100% spray foam insulated, and there is very little air change happening in the house.

    The insulation installer came back and seemed pretty much 100% certain that what we are smelling is off-gassing of the fire retardant paint. (I was not even aware that a coat of paint had been applied) He said he encountered the same exact thing recently with another client's hot roof. They ran their AC fan for a couple hours a day with the windows open and things got better. He suggested we try the same thing and also offered to come back in a week or two with a large fan ducted from our attic if need be. I'm also running a small inline duct fan in the attic that vents to the outside by temporarily removing a section of the duct that exhausts our bathroom fans and putting the inline fan in its place.

    When I asked the insulation guy about an ERV, he enthusiastically said those should be required by code in these cases. He said houses just aren't breathing enough with so much spray foam installed.

    So, at this point my gut is telling me he's right, and we need to be more aggressive about turning over the air in the attic. We're going to give it a month or so and see what happens. We did notice some improvement after I had the little inline fan running for a few days, but we can't keep it that way indefinitely. And we are getting a quote for installation of an ERV.

    And by the way, I tried to contact BASF and got no response at all.

    PS: you'll notice in the images that there's some color variation of the foam. I was wondering what caused that, and became concerned that it was due to installer error. Evidently the fire-retardant paint was not applied uniformly, so now that will have to be addressed...

    1. PhilSchwarz | | #11

      MarcR, very similar situation here. Attic insulated with open cell spray foam coated with fire retardant paint, done by previous owner several years ago. Not able to obtain identity of the installer or the products used, at least not yet.
      House has hydro-air HVAC, separate air handlers (+ heating zones + AC coils/compressors) for first and second floors; first floor system has an HRV, but second floor does not, and there's very little air exchange between floors (only open space is a stairwell at one side of the house).
      House is *very* tight -- it got a 5-star HERS rating.
      During warm weather, we get a sweet-sharp sort of smell on the second floor, similar to what we smell year-round in the attic.
      If we open windows and turn on the ceiling fans the smell dissipates quickly. It only seems to accumulate when the upstairs is sealed tight (all windows closed).
      And it doesn't do so in the winter, when the attic is not getting heated by the outside weather and sun.
      Are you going ahead with installation of an ERV?
      Considering doing the same for our second-floor zone. Air handler for that zone is in the attic; ERV would be located there too.

      1. user-667537 | | #12

        Hi Phil. Sorry to hear you're experiencing this as well. It is very frustrating. We are hoping to install an ERV and waiting on a proposal from our HVAC guy. (been very hot here lately so he is understandably very busy with AC repairs)

        It turns out that the insulation contractor (I'll call him Sonny) who came to our house was not the installer on our job. He did our neighbor's insulation the year before we did our remodel; we used the same general contractor as the neighbor so there was some confusion. Now the GC says he cannot get any response from the actual installer.

        Anyhow, since it turns out that Sonny's company did not do our job, I asked him again if he still thinks it looks okay. He said it does, and still thinks we are only smelling paint fumes. He came back a few days ago (I told him we'd pay him for his help) and he put a big ventilator fan in our attic with flexible ducting running down to a window. (I guess I could have bought these things and done it myself had I really been thinking, but oh well) The fan has been running for approximately 48 hours now, but he said give it up to a full week. I turned it off once or twice and stuck my head up there but the odor remains, so I'm not very optimistic. But we are going to give it a full week...

    2. spup345 | | #27

      Marc thanks for the pics. Can I ask what CFM is that duct fan? I have a 4” bathroom exhaust fan and it looks like the 4” inline duct fans are only like 100cfm... can’t imagine that would do anything for a 1600sq foot attic...

      I may chip the foam away at the gable instead and vent out there then once the smell is virtually nil, I’ll just board up the gable and spray some Great Stuff and be done with the whole thing (with the inline duct just “as needed” from that point forward). Any opinions/thoughts?

  11. Expert Member
    BILL WICHERS | | #13

    I would be a little concerned about the spray foam application on this job. In your first pic you can see color variations with some yellowish striations in the mass of whiteish foam. A yellowish white color is normal for properly cured spray foam, but it should be EVENLY the SAME color.

    With the ventilator running, make sure there is a source of makeup air. The idea is to flow air THROUGH the attic, so the nasty old air is exhausted by the fan and new, fresh air is drawn in to replace it. While the fan is running you shouldn't be able to smell anything since the fan's airflow should overwhelm the spray foam (if that's where the smell is coming from). If a day or two after the fan is removed the smell returns, then I'd suspect a bad sprayfoam applications. If that's the case, you might try having a sample of the foam tested. It may be possible to apply some new spray foam to encapsulate the old (sealing in the smelly part), but I'm not sure how well that would work and I would definitely clear it with the manufacturer of the original foam before trying it.


    1. user-667537 | | #14

      Thanks for your thoughts, Bill. The whiter color is the paint, and the yellow is the spray foam; as I mentioned at the very end of my first post the paint was not applied evenly.

      I am not optimistic about the fan but we're giving it a try.

  12. Chicago_IL | | #15

    I know someone dealing with a similar issue. There's a chemical smell in their attic living space and it's stronger on warm, sunny days. Is this a health concern, or just an incovenience?

    1. Expert Member
      BILL WICHERS | | #16

      That's an "it depends". Since we're all construction people here, it's hard to really say anything about the health side. If the attic is sealed though, you might try airing it out for a while with some active (fan) ventilation. Sometimes that's all you need to do to clear things up. If the smell comes back again later, then you might have something going on with the material.


  13. Chicago_IL | | #17

    Thanks. It's been going on for a few years, even with having the foam removed. There's still some on the roof deck and trusses, so I'm assuming the foam is stuck in there. Trying to figure out the potential health issue to determine if the roof deck and trusses need to be replaced, or if additional ventilation would be enough. Any ideas or experiences with similar problems would be appreciated.

  14. spup345 | | #18

    Similar question but with a twist... I recently had to cut away 4-5 feet of open cell foam covered w fire retardant paint as my installer never removed the ridge vents from my roof and the foam has been slowly accumulating water over the past 5 years (Crappy ridge vents and wind blown rain).

    Anyway, there wasn’t much noticeable smell from the attic over the past few years however now that I cut away all that foam I am noticing a smell.

    Is it possible that cutting away the foam could somehow release odors from the Fire retardant paint or foam? I used a serrated one handed blade to cut the foam away (ie like a bread knife but sharper) and did it all by hand (nothing fast or mechanical that would have really heated up the foam).

    I would note the paint used had a VOC of < 50 grams per liter (DC315 retardant paint classified as a green product, you can google it). But my installer DID say the paint stinks despite having a low VOC and warned me that would smell but they had to apply it per code (he told me at the time he installed everything 5 years ago to not freak out about the smell as it’s the paint, not the foam). Could cutting the paint release the smell again perhaps?

    1. Expert Member
      BILL WICHERS | | #19

      The paint probably acted to encapsulate the foam, sealing in some smell. When you cut through that paint layer, you made it possible for some smell to get out of the foam. The other possibility is that the spray foam didn’t cure properly deeper into the foam layer, and you cut into that.

      When applying any paints to spray foam, you really need to wait for a full cure of the spray foam first. Basically that means wait a few days before painting the foam.

      If the smell is still there after a few days, you could try painting over the part you cut to seal it again.


  15. spup345 | | #20

    Tyvm. Would uncured foam look and feel identical to cured foam? The pieces I removed were consistent in look and texture throughout.

    Assuming it was cured foam, is it possible to still have a smell like you state (trapped by the paint but harmless nevertheless)?

    Any possibility the paint would be the cause 5 years later or can it really only be the foam at this point?

    I do recall the installer waited a at least a day (if not two) before coming back to apply the paint.

    1. Expert Member
      BILL WICHERS | | #21

      Usually improperly cured foam is gooey.

      My guess is the paint just sealed in some residual odor. It’s strange that it still smells 5 years later, but I supposed it’s possible. Is it “really” smelly, like it was just installed, or does it just smell a little when you get right next to it to sniff? A little smell might just be because you disturbed it, similar to how if you break a piece of plastic it will sometimes smell a little for a short while.


  16. spup345 | | #22

    Ok definitely nothing gooey whatsoever. It’s basically like styrofoam at this point. Was very easy to break off in large chunks at a time. I really did cut a bunch out and from sheer exhaustion I only threw out the wet pieces (from the rain water). All the extra dry chunks are sitting on the floor of my attic because it would take another 15-20 garbage bags to throw it out. So it’s very possible with all of that exposed surface area now from all the cut pieces that it’s simply just cumulatively smelly. I will take the time to throw it all out. That should help give me my answer I think. I’ll keep you posted. It doesn’t sound like it’s from uncured foam though just using my own common sense and what you describe.

    The foam installer will be coming back to reapply in a month or so after I get the wet portions of plywood replaced and a new, dry, roof with !no ridge vent! put in (I was due for a roof replacement in next 5 years anyway, more cost effective just to do it now since they have 50 yr materials warranty now). I’ll also confirm how long they wait before applying the paint and how many passes they take to apply the 6-8” of foam. Again I’ll keep you posted. Thanks so much. Wish I had hindsight before I chose to go with foam...25-30% utility bill savings...feel like I would rather just pay the extra cash to heat my house next time...

    1. Expert Member
      BILL WICHERS | | #23

      The manufacturer of the spray foam will specify the maximum thickness (lift) that can be applied in one pass. Make sure your installation contractor doesn’t exceed that maximum as that’s one of the things that can cause big problems with a spray foam installation.

      Closed cell spray foam probably would have worked better in your application. Spray foam is a good product, but needs to be used in the correct applications like anything else. Open cell applied directly under the roof sheathing has been known to have moisture issues.

      Be sure to get those ridge vents sealed this time! Hopefully that will prevent you from having future problems.


  17. AntonioO | | #24

    Did I correctly note that all these customers had open cell foam installed under their roof decks? Is that noteworthy?

  18. spup345 | | #25

    Btw had it not been for the ridge vents I would have no issues at all with any of this. A $1000 oversight (Wish someone told me like NYSERDA inspector at end of job or NYSERDA foam installer at beginning of job... too much effort and $$ to try and sue someone here...) leading to a $4-5k fix (rip foam out, replace plywood, reapply foam).

    The rest of the foam that is dry has the plywood fine but I’ll let you know for sure when they reroof if my eyes deceive me.

    FWIW I chose open cell foam specifically because it allows water to eventually drip thru to show me a leak. Closed cell also sounded scarier re: chemicals and off gassing and difficulty in application at least when I read about it 5 years ago. If I had closed cell it’s possible the water would have gotten into the ridge vent and possibly hugged or permeated through the edges of the plywood keeping that wet, I never would have known, and eventually my plywood may have rotted across all my roof making things even worse than me having caught it now. Just me guessing...

    I confirmed just now w the same installer that they do wait several days before applying the paint. Will update later thanks everyone. Very helpful.

  19. spup345 | | #26

    Question - any reason why I couldn't chip away the foam at the gable and install a gable fan to pull the smell out, then once it (hopefully) is out, I'd only have to remove the gable fan & seal the gable? Yes I take an energy hit but more important to me my family doesn't take a health hit...

    The alternative is me buying one of these $800 AllerAir AirMedic Pro 6 MG Vocarb Air filters w/ 22lb activated carbon filter and sticking it in my son's room for a year.

    Or I do both and hope that the smell eventually goes away...

    1. spup345 | | #28

      FYI - quick update. Spoke w the foam manufacturer (UTC). His guess is the installer should have waited at least a week before spraying on the paint. May have done too quickly and locked in/retarded the full off gassing. Breaking apart the foam simply released it but once I ventilate it out it shouldn’t return. I tend to agree as the smell didn’t exist until I disturbed all the foam.

      Other point he made is the open cell is not really fully open cell. He said it’s like two hollow eggs next to each other with a small hole in them...if the hole of one egg is up against the solid part of the other it can really slow down the off gassing which is why he recommends folks wait at least a week before painting.

      Lastly he said if the foam was installed wrong it would be very obvious with gooey parts, non uniformity, etc. (which mine is not).

      Thanks all.

      1. Pat_F | | #38

        Hey George I’m located in the Hudson valley and hired an installer recently to spray foam my attic. The manufacturer is also utc. It’s been about 10 days so far and there is a very strong chemical smell especially on hot days. Do U know who u spoke to At utc? Do u know the name of the product. Was there a lingering smell after it was installed or only after u cut into it?

        TIA, Pat

    2. Expert Member
      BILL WICHERS | | #29

      Yes, you can cut out a chunk of spray foam and then fix it later by foaming in the hole.

      It might be easier to get a cheap bathroom fan and some of the flexible plastic 4” dryer vent. Put the fan in the attic, then route the vent hose out an convenient spot to the outdoors. Wire the fan into an extension cord and let it run as long as necessary until the smell is gone. The fan will keep the attic under a slight negative pressure which should prevent the smell from leaking into the living spaces which is an added benefit.


  20. spup345 | | #30

    Thanks Bill. That is exactly what I just ordered last night. 4” inline 195CFM duct fan to re route my bathroom exhaust fan to that instead. I am lucky enough to have a (Relatively Unused) small bathroom under my other smaller attic so I’m going to run a new bathroom vent from there to the roof as well (since I’m getting my roof redone they will take care of that for me in a couple of weeks). So I’ll have two inline duct fans, one for each attic. I’ll keep u posted on how it goes.

    So far though, just w the gable foam cut open and a fan blowing out of the gable all night, my sons room is virtually odorless so it’s 100% working. If the duct fans have the samE results then I’ll be ecstatic.

    Be well. George

  21. spup345 | | #31

    Question re: venting attic on a go-forward basis:

    Right now my temporary floor fans are blowing out the temporarily exposed gable vents (1 in each attic - until foam is re-applied next month). It's def., thankfully, keeping VOC's/odors outside the house. However if there are lingering odors after foam is re-applied, I'd like a more "permanent" way to vent the attic if needed. The temporary workaround of disconnecting the bathroom exhaust duct and inserting an inline duct fan means bathroom moisture will go into the attic until it's re-attached. It's also a super tight working space for me to do the work as the ductwork is only ~5' from the eaves with foam overhead...

    Is an acceptable & more permanent workaround this?
    -Cut a round 6" hole in the foam at the gable vent and insert 6" solid duct w/ inline duct fan that I can turn on as needed (I'd make sure a vent flap is near the gable end of the duct obv). Can do the same through the roof instead if that's smarter than simply pointing the duct at the existing screened gable...that would allow me to place it anywhere in the attic instead of just at the end gable too (i.e. In the middle of the attic? if that matters)...

    I think 6" duct is better than 4" so I can get a ~500 CFM inline fan (6") instead of a ~200 CFM fan (4"). ...for my attic size (50' long, I think ~36' wide) I feel bigger would be better...

    Any thoughts on the above or a diff. suggestion? Hopefully never needs to be used, but would like a backup plan ready to go since I have that option w/ the new roof being put in & foam re-applied along ridge.

    1. Expert Member
      BILL WICHERS | | #32

      I’d go with the lower flow fan and the smaller hole. What you want is the MINIMUM airflow to keep the smell from getting into your house. This means you want just enough airflow to keep a slight negative pressure in the attic. More airflow than needed just means wasted energy and gains you nothing.


      1. spup345 | | #33

        Thanks - Indifferent as to through the roof or terminating at gable? And do you think I'm being crazy or makes some sense as a precaution even if there's a tiny performance hit (sanity check for me...)?

        1. Expert Member
          BILL WICHERS | | #34

          The usual ice dam precautions would apply, and don’t put the exhaust in a spot where it would just get sucked into a nearby intake vent. Aside from those, put the exhaust vent wherever is easiest.

          If you are bothered by a smell and the vent helps, then you’re not crazy wanting to run the vent :-). There will be a performance hit, since you’re intentionally blowing conditioned air out of the house which will suck in makeup air from outside. In your case, this should be a temporary system since you expect the smell to eventually go away. Once the smell is gone, remove the fan, then you go back to normal in terms of energy efficiency.


  22. spup345 | | #35

    Thanks so much, super helpful, really appreciate the guidance! Yes the roofer has in the contract they will apply GAF ice and water shield around all openings (and Geocel 4500 black caulk to seal base of vents to roof).

    1. Expert Member
      BILL WICHERS | | #36

      The ice dam issue I was referring to is that if you exhaust warm air under a soffit that can cause problems. You want your exhaust either through the roof or through a wall far enough from the eaves that you won’t have problems.


      1. spup345 | | #37

        Ah...that makes much more sense, thanks (that won't be an issue).

  23. ShedClassroom | | #39

    Any advice for me?
    I just had foam sprayed into a 10x12 shed. It’s been a few days and it has a definite “new paint” smell. Sort of bright, chemically, tip of nose type smell. Just like people described it here.
    I’ve been running a fan blowing air out the door and another pulling air through a small window.
    I was going to put up drywall, but I’m hesitant now because if this smell doesn’t go away, I’ll have to rip it all out!
    I just covered it all with 6 mil gray plastic sheeting so UV light wouldn’t brown the foam and I wouldn’t have to worry about my AC pulling in dust from the foam.
    It’s not sealed with tape, but I can do that. Was hoping it would dissipate, but today I ran the wall unit AC and it is still very much there. If I make sure the 6 mil is sealed will that stop the smell?
    My budget is tiny here, The spray foam and sheeting on such a small job was only around $700. The thought of sending out to a lab for $400 for a graduate student salary of zero is scary to me.
    I was going to use the space as my virtual classroom as I’m attending grad school remotely due to the pandemic.
    Was planning on being in the room for hours a day, now I’m scared to do that. Wishing I did freaking rolled insulation, but that had venting problems with the roof space.
    Aye, any advice y’all?

    1. Expert Member
      BILL WICHERS | | #40

      The polyethylene sheeting will slow down the offgassing of the spray foam, which is the opposite of what you want to do. There shouldn’t be dust coming off of the spray foam, either, since it should have cured into a pretty much solid mass.

      I would remove the poly sheeting and keep those fans going. If you have the spray foam exposed to the outdoors somewhere and that’s where your UV concerns are coming from, try using some cheap plywood (3/8” OSB or plywood sheathing, whichever is cheaper) to keep the spray foam in shadow while still allowing for free air movement. You need only to block direct sunlight, indirect light and weak reflections don’t cause problems.


      1. ShedClassroom | | #41

        Well, crap. Guess that’s $30 worth of sheeting and several hours of sweating in Texas heat down the drain. Is it normal for it to still smell after almost a week? Bear in mind, it’s Texas in the summer. 107 the other day. I have resigned myself to the fact that I may have to rip it out. If it keeps smelling.
        Thank you

        1. Expert Member
          BILL WICHERS | | #42

          The worst of the smell is usually gone in a few days, but it might still have a bit of smell for a few weeks — especially if it’s baking Texas style. It’s sumiaor to painting your house: the worst of the smell is gone in a few days, but even a week or two later you’ll still have that “freshly painted” smell if you go Away for a while and then come back so that you’re not used to it.

          Just make sure the spray foam isn’t sealed up so that it can finish any off gassing before you complete the structure.


          1. aunsafe2015 | | #43

            Zephyr, what amount of time is typically considered to be sufficient to allow open cell foam to finish off-gassing before covering with drywall?

          2. Expert Member
            BILL WICHERS | | #44

            I tell people to wait at least a weekend, so 2-3 days. That’s usually enough for the worst of the smell to go away. 1-2 weeks is more conservative if you want to be extra careful.

            Note that even after waiting you’ll still have a small amount of smell, a little like buying a new car. That small smell isn’t usually a problem, you just need to deal with the worst of the smell while the foam finishes curing.


          3. Adidoro | | #45

            I had the spray foam insulation done in December 2019 in the exterior walls of three bedrooms. Since that time the chemical smell is not gone although we scraped down the foam between the studs, we painted the studs with kill odour paint used by restoration people to stop the smell of a burned wood, we put pink insulation between walls, added vapour barrier, drywall, and painted. After a couple of days the chemical smell (not as strong as when the foam was present in between the studs) re-appeared in all three bedrooms. We also cleaned the ventilation system (air exchanger). The smell is still present. It's not continuously. It comes and goes depending of humidity, wind speed and direction, precipitations.
            My question for you is what else should I do to get rid of the odor? Do the chemicals infiltrate the wood? How long it takes to cure?
            I am thinking to knock down the structure of the walls and reframe them, which means lots of money to spend. Is this the only solution?
            Thank you for taking the time to answer my questions.

  24. Expert Member
    BILL WICHERS | | #46

    Adidoro, if the smell comes and goes with outdoor wind, then y0u have air leaks somewhere. Seal those leaks, and you'll likely stop that smell. My guess is there is some uncured spray foam out in the eaves somewhere, or otherwise around the perimeter of the wall where it's somewhat exposed to outdoor conditions through one or more air leaks. This is just a guess though.

    Spray foam should be pretty much cured in a matter of hours. I like to tell people to do the application on a Friday, then take the weekend to go travel so that there are 48 hours or more for curing and "airing out" the home. After that much time, everything should be fine with only minimal smell remaining that will dissipate as the indoor air is continously exchanged.

    A lot of the chemical smells we smell with things are from solvents, and many solvents can pass through plastic materials, including the usual polyethylene vapor barrier. If your only remaining option is to reframe the walls (a pretty extreme option), I'd try putting some 1/2" foil faced polyiso up on the indoor side, caulking it around the perimeter (ideally to the top plate, bottom plate, and corner studs) with urethane caulk, then drywall over that. The purpose of the polyiso here isn't to provide insulation, it's because you want the impermeable -- even to solvents -- foil facer. That aluminum foil facer is far, far less permeable to pretty much anything than any kind of plastic vapor barrier is.

    The polyiso step is an encapsulation step to basically seal the wall. You'll need to make sure to seal up any electrical penetrations too. Think of this as an extra super duper air sealing job, where you need to seal against contaminants and not just air.


    1. andy719 | | #47

      Bill, it looks to me like Adidoro is saying that the foam job was done 2 years ago and still smells. I didn't get the impression waiting a few hours would help him.

      1. Expert Member
        BILL WICHERS | | #49

        Yeah, I saw that -- there was another question about "what is the normal curing time", so I tried to cover both questions in one post.

        Two years is way more than enough time for spray foam to fully cure, so if it's still an issue, there is a problem.


  25. Adidoro | | #48

    Yes, the job was done 1 year and 5 month ago.
    After I open the windows in those bedrooms, in a short period of time, the odor is intensifying in the rooms. Is this another indication that the uncured spray foam went somewhere in-between the exterior siding and the framed wall? Maybe around windows? - air leaks, was your quess.
    My other question for you Bill, is about the wood. Can the chemicals infiltrate the studs and continue the off-gassing or the wood should be fine? This will help me decide if I go to the extreme solution, reframing the walls, or not.

    1. Expert Member
      BILL WICHERS | | #50

      I would expect that some of the material can get into the wood. I've never tested this to be certain, but wood is porous, so I'd expect it to be a bit of a sponge for these things if left in contact for a long time. The big question is "would the wood get back to normal in a short period of time once the problem material was removed?", and I don't really have an answer for that.

      I would try encapsulating the problem area before rebuilding the walls since I think encapsulation would be easier/faster/cheaper than a rebuild.


  26. user-2310254 | | #51

    Annoying smells can ruin your quality of life. If the odor source is inside the walls, you might be able to solve this program by increasing ventilation and slightly overpressuring the interior of the home. One of the experts might be able to suggest a way to test this strategy to gauge its effectiveness.

    1. Expert Member
      BILL WICHERS | | #52

      A small manometer could measure the presure differential if you pressurize your living space. That part is easy. Testing for smell would be a bit more difficult, since a nose isn't exactly a piece of calibrated test gear :-)

      Pressurizing the house isn't a bad idea though, and would work well in conjunction with an encapsulated wall. The only downside would be the energy use of the fan doing the pressurizing. If trying this, make sure the air intake is somewhere far away from the source of the smell, and consider an activated carbon air filter too which will help filter out any smells from the intake air.


  27. Adidoro | | #53

    My next question maybe will sound stupid. If two years is way more than enough time for the spray foam to fully cure, what is still off-gassing inside the walls?
    Bill, you mentioned the probability for some uncured foam to go out towards siding/around the perimeter of the walls/windows where it's somewhat exposed to outdoor conditions. Is the smell going to disappear if I do all this pressurizing the bedrooms procedure? Or I have first to take the siding down to reach the plywood sheets from outside, remove the foam, if present, and then do the pressurizing of the bedrooms?
    Thank you.

    1. andy719 | | #54

      Just curious, have you ruled out other potential sources? You mentioned an air exchanger, when was that installed and what did you use for ducting? Was it pvc by chance, pvc tubing has been mentioned as a source of bad smells on this site many times as well. I only ask because I'm planning to spray foam my home rim joists and bonus room floor soon, and posts like this scare me tremendously. Any other possible sources, like glue-down vinyl floors or neighboring facilities?

      1. Adidoro | | #56

        Andy719, we had ZERO smell in the house prior to the spray foam insulation event. No pvc tubing for the air exchanger. After the foam was applied and the odour was very strong, first thing was to pay for a clean up of the entire air exchanger system. Also, why the chemical smell is just in the 3 bedrooms, not the entire house?

    2. Expert Member
      BILL WICHERS | | #55

      Uncured spray foam is due to a bad mix at install time. This is most common around the beginning of the project, so you're most likely to find uncured residue near wherever they first started spraying. Sometimes you get a little problem at the end too, and at places where they have to change out tanks of material. The "middle" part, between those things previously mentioned, is the area of least potential issues.

      Once the spray foam is mixed properly, it should fully cure regardless of where it goes as long as conditions are right for application (not too cold or hot, etc.). My guess is if you have any uncured material, it will be near the end of a wall, probably near the top or bottom of that last stud bay. Basically wherever they started or stopped the application. Uncured residue will usually be gooey in consistency, so it's easy to spot. Poke it with a stick to see for sure -- properly cured foam won't be gooey or sticky.

      I've heard of improperly cured spray foam that seems hard, but still smells. I haven't seen this problem myself, so I can only guess as to what is going on, but I'd suspect it's something of a "crispy outside with a chewy center", and would probably mean the spray foam was applied in too-thick "lifts" (layers), so the inner part overheated and didn't cure properly.

      Properly cured spray foam is very stable, and shouldn't have any potent, lingering smell.

      Pressurizing the home will force all the air leaks to go OUT, towards the outdoors, not IN, towards the interior, so all the smells will be forced out, away from your living spaces. That's how pressurization would work. Note that you need only a very, very small amount of pressure to make this work, far less than what would be dedectible by people. The pressurization doesn't make the smell go away, it will only keep the smell from coming inside where it will be a problem for the occupants.

      BTW, Andy719 has a good point -- be SURE it's the spray foam that is the source of the smell before you start taking your walls apart.


      1. Adidoro | | #57

        Thank you, Bill. Unfortunately, I cannot check what part of the walls have uncured foam and what parts are fine, because we scraped down the foam after 2 months. The only parts left that were exposed to the foam are the studs and the plywood sheets. This made me think that I have to redo all the framing of the walls. I have some photos taken before we scraped down the foam (attached to this post)
        Like you have mentioned, some foam maybe went out between the plywood, towards the siding. In this situation I have to take down all the siding, the tyvek wrap and whatever-else is over there to reach to the plywood from outside the house and check for existing foam trapped there.

        1. Expert Member
          BILL WICHERS | | #58

          From what I can see, that doesn't look like a bad install. You might try poking a few holes here and there to see if there are any soft spots. I'd try encapsulating things first, use foil faced polyiso (you need the metal facer to block any solvents), sealed at the perimeter of the wall and taped with foil tape. You may find that encapsulating the wall gets rid of the problem.


  28. madrunner | | #59

    I unfortunately have a similar issue with chemical smell on hot summer days, which are typically very humid in Midwest. If our house is sealed with windows closed the smell comes down into attic into main living space on top floor of split level. The AC also brings the smell down because the air handler is in the attic and vents come down through top floor ceiling, although the system is sealed and I've had it checked over to try to reduce attic air from entering the system. We had the attic spray foamed with Certainteed closed cell foam 7 yrs ago. I contacted the company and shared pics and they suggested some parts may be "overcured" and to take it up with installer as they no longer manufacture spray foam. Any thoughts on how to solve this issue? Is the smell dangerous?

    1. Expert Member
      Michael Maines | | #61

      Madrunner, "overcured" is a quaint way to say that the exothermic reaction was too hot, usually due to installations that are too thick or an imprecise mix that leaves uncured resin. Sometimes that causes huge bubbles within the foam, sometimes it starts a fire, and sometimes it just leaves uncured, smelly resin.

      If it is still there after 7 years as far as I know your only options are to further seal it in place with more foam or an interior membrane, or to fully remediate the foam from your house. A friend of mine recently went through full remediation and it's not fun, to say the least.

      Not that it helps you, but this is one of several reasons I only use spray foam when it's the only reasonable way to complete a project, and even then I stick with contractors I know and trust.

      1. mdhomeowner | | #63

        Do you have any information about fully remediating misapplied spray foam?

        I can't find anybody that has done it before. So far I'm just getting contractors that are guessing at what to do, and guessing at an end result.

  29. user-2310254 | | #60

    I'll give your post a bump. I'm no expert, but something looks off with the installation.

  30. vikihymer60 | | #62

    I too have suffered from home being destroyed by spray foam. I am elderly and poor so not much I can do. What I want to know is why there is not a class action suit against spray foam industry so people can be compensated for their losses? This industry seems to be protected? Why is that? Is it going to take the loss of many lives as well as homes before something is done? King

    1. mdhomeowner | | #64

      Try contacting the EPA. They throw up their hands and say they don't look into it any more. I wonder why that is.

      What kind of product was installed, and what attempts to fix the problem have been done?

    2. Expert Member
      Michael Maines | | #65

      It's all about the money, of course. Many of us do what we can to warn people of the potential dangers and risks of spray foam, but when it cures properly it works well and solves some problems. And there is a lot of industry money to promote it.

    3. Expert Member
      BILL WICHERS | | #66

      The problems are usually due to bad installations, not any problems with the spray foam itself. Due to this, the installers are usually to blame and not the manufacturers, and the installers are often small private contractors. If you have problems with a bad installation, you'd need to go after the installer, and probably file a claim with their insurance.

      Since there is no inherant flaw with the product, a class action suit isn't really appropriate. The vast majority of spray foam installations go in fine, and in some niche applications, spray foam is really the only option. I advise against the use of spray foam in places where it doesn't really gain you anything (like in walls), but for things like unvented roof assemblies, spray foam is often the best, and sometimes the only, option.


      1. mdhomeowner | | #67


        I'll agree that the installation errors are the problem. But at that point, what does it matter?

        Good luck with insurance and lawyers. I'm obviously jaded, but the minimal chance of there being issues still means that it happens to some people. And when it does you are going to waste magnitudes more money and energy than you would have ever saved by using spray foam.

        1. Expert Member
          BILL WICHERS | | #68

          Problem installations are a very small percentage of total installations. People complaining on the Internet amplify their bad experiences, which gives a false impression of there being "lots" of problems out there. The reality is that most installations are fine, but people with good experiences are less likely to talk all over on forums about things. Spray foam is very low risk, just get a good installer.

          Insurance isn't usually too much a problem IF you handle things correctly. It's a good idea to ask to be named "additionally insured" on your contractor's policy, and get a copy of the Accord form showing that. This lets you go directly to the insurance company if you have problems, bypassing the contractor. This avoids the "the contractor dissapeared and never calls me back" problem. You don't usually need a lawyer for this.

          For a bit of irony for this thread, I have a cathedral ceiling here that had the venting messed up by my roofing contractor (who was honest about the problem, and it was easy to miss). As a result, his insurance paid to reconstruct the roof (lots of water/mold problems due to no venting). Part of that meant the insurance company paid for the installation of closed cell spray foam in the roof assembly when it was rebuilt.


          1. Expert Member
            Michael Maines | | #69

            Spray foam may be low risk but far from zero risk, and like plane crashes and mass shootings, when it goes badly, it goes very badly. I personally know of several projects where it didn't cure properly; on an order of magnitude I'd estimate that one out of 100 installations is a problem. A friend of mine just had to have her entire brand new 4000 sq.ft. house torn apart, foam removed and everything put back together because the foam didn't cure properly. No other insulation product has that kind of result of a poor installation. No other insulation product comes close to the negative environmental impact, either, and no other insulation product requires the installer to use a supplied-air respirator during installation.

  31. Arizonaplace | | #70

    Hello- did you ever find out about the chemicals and your air quality test? We have the same problem here in Phoenix with our spray foam. It makes our house smell. The company said they did it right but we don’t know!

    1. mdhomeowner | | #72

      What you are looking for will be based on what you had installed. See if you can get the installer what was actually installed. This would be a good time to start getting everything in writing.

      It seems like the amine catalyst is the root of the smell in most cases, and manufacturers claim that chemical is a trade secret.

      The CPSC has a database of complaints. Some people put the chemicals found in the air in those complaints.

      Bud Offerman at has a lot of information available for indoor air quality. On the right side of the website is a publication about SPF emissions. It is pretty thorough with a variety of chemicals that he tests for.

  32. Deleted | | #71


  33. walta100 | | #73

    Sadly, we never get to see a post telling us how this all-too-common type of story ends.

    My guess is most home owners end up getting a lawyer and the first thing the lawyer say is stop posting on the internet and years later the case gets settled with the home owner signing a non-disclosure agreement preventing them from posting


    1. Expert Member
      DCcontrarian | | #74

      That's a safe guess.

  34. 1910duplex | | #75

    We had closed cell HFO foam put in our attic a little more than three years ago, and it can still smell sweet on hot humid days in the attic... but never comes down into the living space (and we also now have a ducted minisplit in the attic, even one that failed the first duct blaster test.)

    For this reason, I would never recommend it in walls of rooms you are going to live in... but it did make a big difference in our heating bill, I think, and insulating at the attic floor wasn't an option b/c we have a staircase into the attic, no way to airseal properly between the second floor and the attic.

    I don't think there are any health concerns from the smell, unless you have developed chemical sensitivies (and then it's the same as being exposed to perfume or cleaning products or whatnot)

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