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Spray Foam Off-Gassing

dipolojarvi | Posted in General Questions on

Hello everyone,

I’m in the process of replacing the roof on my 185os farmhouse in Maine. I had the ceilings in the attic sprayed with foam insulation about seven years ago. Now that the new roof is on with new weather shield wrap, it seems like the spray foam is offgasing again. The smell very strong in the attic.

Not sure what to do. Should I expect the smell to go away over time?



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  1. Expert Member
    BILL WICHERS | | #1

    Are you sure it’s the spray foam you’re smelling? After 7 years, any offgassing should have ended long ago.


    1. Jon_Harrod | | #2

      I'm wondering too if it's really spray foam you're smelling. Can you describe the smell? What type of foam was used (open or closed cell)?

  2. dipolojarvi | | #3

    Thanks for your replies.

    It's a chemical smell, and very potent. When I asked the roofer to go up and smell it with me, he also thought it smelled like the awful spray foam smell. WHen the shingles were removed there was a smell from some of the old paper that was used to cover the roof long ago. But all that was stripped off along with the old shingles. The roofers put down a layer of OSB over the orginal sheathing boards to make a nailable surface, then a layer of weather proofing, then the new shingles.

    The roofers finished the new roof on the main part of the house, but still have the smaller back part of the house to do.

  3. dipolojarvi | | #4

    From what I'm reading online, the smell may be coming from the shingles themselves or the weather shield that was used. It's terrible in the attic, which I was planning to convert to a bedroom!

  4. dipolojarvi | | #5

    Hello everyone,

    This problem has continued. It went away during the winter, then the smell has come back.

    The contractors are assuring me that the smell can't be from the new roofing materials. They have suggested that it might be coming from the spray foam and assume that the foam was not properly mixed and so never cured properly.

    They have suggested putting in a vapor barrier over the spray foam and then drywalling the area.

    Any suggestions would be welcome. I'm not even sure how to test the air quality.

  5. MattJF | | #6

    Get a blower and fog test done and see if there is a large path from the inside to outside roofing materials.

  6. dipolojarvi | | #7

    The roofers are suggesting that the new roofing made the attic so much tighter that it could be forcing the offgassing from the spray foam back into the attics and that improperly mixed foam is the culprit.

  7. MattJF | | #8

    Any photos on the inside of the attic available? Is there drywall or just open foam?

    I wouldn't expect new roofing to make things much tighter except perhaps a full roof of ice and water shield which is an adhesive sheet product. Is that the weather shield wrap you refer to?

  8. Expert Member
    BILL WICHERS | | #9

    What type of roof was applied? Some sealants (usually tar types) will smell when they heat up. The spray foam should have itself sealed the attic, so the “new roof made it tighter” argument should be moot. The one issue I could see would be if this was formerly a vented attic that the roofers sealed up. If that was done improperly, you could have other issues besides just smell.


  9. dipolojarvi | | #10

    It is just open foam, no drywall. The roof is architect shingles with ice and water shield. I'm not sure what sealants were used. The attic was vented, but vents were sealed and all walls were spray foamed to create a conditioned space. The smell came after the new roof. There was no smell of this type for the ten years with the spray foam. Someone just suggested that I put denny foil vapor barrier over the foam.

  10. ThirtyWest | | #11

    Did you say if this was open cell?

  11. Ehsptc | | #12

    Similar issue here. The foam is off ratio, but not necessarily everywhere. I used my nose when it was cooler outside to identify at least what I thought was the worst smelling area. I ripped a grape fruit size hole (initially before going bigger) and found the foam to be gold in color against the decking boards. It smelled horrible; exactly the same as the attic air when the outside temperature was greater than 84 degrees. The foam is being removed today.

  12. Expert Member
    BILL WICHERS | | #13

    That foam looks pretty much ok to me, but it’s hard to be sure from pics. It’s better to go by consistency — gooey is always a problem, but crumbly is too. Properly cured spray foam should be a pretty solid material (especially closed cell foam).

    Both mix AND temperature are important for proper curing. My guess is your application may have been on a very hot day and in too-thick lifts, which can result in poor curing on the inner part of the foam due to excessive heat.

    I think the key to a good installation with spray foam is an experienced installer. You basically want someone with OCD who obsesses about the process. The guy I like to use tweaks temperatures and pressures as he goes based on how the foam comes out of the gun and expands. He’s experienced, and spray foam is all he does. I’ve never had a problem with installations when working with people like this.


  13. dipolojarvi | | #14

    Hello everyone,

    Here's my proposed solution to this problem. Would you all please help me vet it? I really want to get this right.

    A bit of context first:

    In my situation there doesn't seem to be anything wrong with the spray foam. It is closed cell, seems to be very well connected to the substrate. Also I just had a very experienced energy efficiency team here for a blower door test and they said the foam looked fine. That the energy sealing seemed really good. There are just a few gaps where an old chimney was removed, that they suggested I fill with storebought foam.. They said they thought the offgassing was from the roof and is getting in through tiny gaps in the spray foam, which wasn't super smooth in the application, so finding those targeted tiny gaps would be difficult. They also reminded me that it would be best if the foam were covered with a flame retardant paint or drywall, since it is such a big space and could make a good living area.

    After the blower door test was done, the energy efficiency people said that the my house is overall very tight and could use some ventilation to change the air throughout the year (they suggested putting an exhaust fan in the bathroom).

    I thought I could fix that overall problem as well as removal of the offgassing if I drywalled the attic and treated it as the room from which the exhaust would happen. I could install a bathroom fan that vented through one of the old gable vents. There are two attics that this plan would apply to. The added benefit is that as attics they're dusty stagnant air spaces, so I thought this way I'm doing the house an overall service while removing the smells.

    Here's a drawing to illustrate what I mean.

    I've also attached a picture of the foam and rafter combination.

    Other people I've talked to have suggested completely redoing the roof and installing sleepers to create airflow and make the gasses go away. The gasses are only present on hot summer days..

    1. Expert Member
      BILL WICHERS | | #15

      Is this tied in with your other post about roofing materials? You really need to identify the problem first before coming up with "solutions". If there was no smell until the new roof went on, then I'd suspect you're smelling new roofing materials in the hot sun, which will probably be a tar-like smell for asphalt shingles. Fancy venting on the inside isn't going to do anything about a problem on the exterior, a might actually make things worse by pulling in smelly outdoor air.

      Wait a week or two to see what happens. Usually new materials will "bake out" over a period of time and stop smelling.


      1. dipolojarvi | | #16

        Thanks Bill. This is related to the other post. I forgot that I had not just continued this conversation.

        Identifying the problem has been surprisingly challenging. The smells do only happen on hot days. But it is not a tar smell, and it has occurred across late summer of 2019, then summer of 2020, and has started again. The smell occurs on the inside of the house when the windows are closed, so it is not coming from the outside air.. The smell was strongest that first year. it has got a bit less each year. The smell seems to come from the meeting place between the old pine boards and the new OSB. Once I sealed the area where an old chimney had been, where the new sheathing was exposed over the, the smell decreased a bit. In short, though, these are no longer truly new materials.

        One other solution offered is just to seal the hatches to the attics with good gaskets, so the smells stay in the attics and keep windows open in the summer to continue to let the offgassing take its natural course over time.

        1. jablo | | #17

          Closed spray foam was installed in 2017 in my reputable very experienced installer, unfortunately he didn't know the difference technique installing closed cell and open cell. all installers like this., they compromise health of homeowners
          Because he sprayed to thick layers foam is off gassing this is very toxic.
          My 5 year old contracted crohn's disease.
          Because your house is tight all smells stay and accumulate.
          I would spray paint foam with good primer latex sealer)
          I would install
          Erv (Zhender)
          With intakes close to source of smell.

          1. dipolojarvi | | #19

            How would I know if it is the foam still off gassing? Did you have a VOC test done? The foam was done about ten years ago, and I never smelled this smell until the new roof was put on two years ago.

            Was the off-gassing you had intermittent in the same way mine is? I only smell it on hot days in the spring, summer and early fall.

  14. Ehsptc | | #18

    I'm not an expert, but I have had this problem and there is no reason to believe that it will stop off gassing ever. The space is closed and if the foam is off ratio, it will never cure. Such was my situation and I had it ripped out after a year of trying things to stop the offgassing.

    1. dipolojarvi | | #20

      Thanks. Also asking if you did a test to see if it was the foam that was smelling. Since the foam was installed so long ago and never had a smell before the new roof, I have thought it couldn't be the foam.

      Was the off-gassing you had intermittent in the same way mine is? I only smell it on hot days in the spring, summer and early fall.

  15. dipolojarvi | | #21

    Hi, everyone, Thanks for staying with me on this very stressful problem. I've checked some parts of the foam where boards were pulled away after the install (shows some of the depth). I sure don't see anything gooey. The foam on those boards has no smell at all.

    1. Expert Member
      BILL WICHERS | | #22

      Spray foam that hasn't properly cured will generally be either gooey (the worst issue), or crunchy (much less of an issue in terms of smelliness). You can sometimes get a "cruncy outside with a chewy center" if the installers applied the foam in too-thick "lifts" (layers).

      I suspect in your case, Ilmari, it's probably something other than the spray foam that is causing the issue. Spray foam that is 10+ years old should be long past smelling, unless you cut into it maybe. In most cases, the smell is gone within a few days to a few weeks. If it IS spray foam that you're smelling, I'd look around the places the crew either started or stopped applying foam, since these are the places most likely to have the mix not quite right if the majority of the project appears to be OK.

      Anytime you seal up a space, it's possible for small issues to become more noticeable since the lack of ventilation allows things to accumulate and get up to more noticeable levels. A slight depressurizing fan should eliminate any problems if this is the case.

      BTW, I don't see how spray foam would cause crohn's disease -- the usual issues with spray foam are respritory, notable an acquired sensitivity to isocyanates.

      It's also worth pointing out that there are many, many spray foam installs that are fine. It is true that there are some problem installs, but they're pretty rare. If you've had spray foam in for years, then you change something and notice a problem, the problem is likely related to the recent change and not a years-old spray foam installation.


  16. 1910duplex | | #23

    I have closed cell foam against my attic ceiling, with rockwool batts covering it and drywall covering eave walls. This is the second summer post-installation. At the beginning of it getting hot again, there is a smell in the attic again, sort of sweet smelling is how I would describe it? I wouldn't want to have a bedroom there, but it's not so strong that it comes into the living space below. I do open up the windows in the attic some days, and that helps.

    I do not believe my foam cured improperly. I think it is the nature of putting a lot of new plastic in this environment.

    There is some science to suggest that air pollution can be a contributing factor for Crohn's Disease, but they're talking more like auto exhaust, not plastics in your house.,development%20or%20exacerbation%20of%20CD.

  17. jablo | | #24

    I think toxic smell can cause many diseases. toxic smell are the cause for many autoimmune diseases
    Professional foam testing and air samples with interpretation is around $15G
    And they probably tell you if there are any foam chemicals


    If your smell is like fishy,
    Natural tree resin,
    I can bet is foam.

    I did ventilate my unvented attic. I have placed air intakes
    In the source of smell
    And supply in the bedrooms and kitchen.

    Seems to be working.
    But im not 100% sure if gases dont go through erv membrane.
    To solve this I have installed
    20 lb active carbon filter after
    Unusual but after all that set up my family and me stopped getting sick

    I have hcho meter with 12 hour histogram.
    And if levels don't go to normal level during night,
    That means air is bad.
    Day time peoples activities can cause very high spikes

    You can do simple test just cut out a piece a 2 3 inches deep and smell it.


    1. Expert Member
      BILL WICHERS | | #25

      Smell alone doesn't cause disease, but certain chemical compounds can. There are exposure limits for things, stuff like that. With spray foam, it's the isocyanates that can cause some issues. I don't know all the details, aside from knowing you can get an aquired sensitivity to the stuff if you're exposed long enough -- then you are basically allergic to it after that.

      The stuff that "off gasses" is usually a solvent. Many solvents can go through membranes, even polyethyelene sheet. This is similar to how used motor oil can often go right through a plastic trash bag without visibly damaging the bag itself. The only way to reliably block these solvents is to use a metal foil barrier, like the foil facing on foil faced polyiso. Negative pressure will often work well, and it usually doesn't take much. The downside is the energy use to run the fan, and keep that fan running for a very long time if not forever.


  18. acama23 | | #26

    Hello! I'm writing to see what has been done to remediate this situation. I too had spray foam installed about a month ago and have had a constant smell in my attic. Indoor air quality tests identified that there is 1-4 Dioxane in the air which our env. services contractor says is linked to spray foam.

    The manufacturer of the foam as well as the contractor both indicate that the smell should not be there.

    I'm unsure how best to remediate. The manufacturer and contractor have been less than helpful with ideas on the best way forward.

    Should I engage in legal services? I'd hate to go that route but suspect that ventilation alone (which was already tried for 4-5 days straight about a week ago) didn't touch the smell. It has been cold here but on the warmest day since the install the smell was oppressive.

    I appreciate your help with this.

  19. jablo | | #27

    Number of days you provided multiply by years
    Then smell intensity decline

    1. acama23 | | #28

      Can you explain?

      1. jablo | | #29

        That happened in my case
        Smell eventually degraded about 5 years after installation
        I guess outer layers have offgassed because if you cut thru smell is there
        And on a hot day intensifies a lot

        Manufacter representative was lying that is no big deal it will get better after 2 weeks of ventilation
        Same lye was pushing installer
        "Very experienced "
        After those years I belive toxic smell is within legal limits but problem is we become alergic to foam offgasing
        The worst part is that little kids getting sick first
        You cannot have laboratory conditions in the field
        Temperature (air, substrate, foam itself) ratio of component, thickens of the foam in 1 pass
        Anything is off you don't have full reaction of component
        And what is left is very very harmfull
        It is like you can't paint car on the street perfectly

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