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Community and Q&A

Spray Foam Odor Remediation

chicago_spray_foam_customer | Posted in General Questions on

We had our attic in the Chicago suburbs done in 2019 to create 2 spaces:

1. A finished space with closed cell foam applied directly to the roof deck, finished with drywall, carpeting, and an HVAC supply
2. An unfinished space with open cell foam applied directly to the roof deck that contains our HVAC that services the 2nd floor.

In the spring of 2020 we noticed a “chemical” smell as it began to get hot and humid (seems stronger in the unfinished open cell section), and I can see from the forums here that we are not alone with this issue. We’ve had the installer out a few times to test the foam, and they are convinced it is fine and that the smell is coming from something else in the attic (I don’t quite buy this, as the attic is conditioned and so the materials up there – such as the insulation that remains underneath the attic floor – never gets hot). Absent a better explanation, I assume that a chemical reaction is taking place in the foam as it gets hot and sucks up moisture from the living space.

I’ve been dealing with this to date by using a duct fan to exhaust the air from the back of the unfinished section out of a window, the theory being that I’ll pull air in from the living space, through the smelly section, and out of the house, ideally before it gets sucked up by the HVAC return and dispersed to my 2nd floor. I’ve also now tried placing a dehumidifier in the attic to try and keep the moisture level lower, and will see if I notice an improvement in the spring after doing this all winter.

The intensity of the smell seems to be growing weaker, but I’m also not sure if I’m just getting better at ventilation, and this is obviously difficult to quantify.

I’m hoping for a more permanent solution, and from what I’ve read, removing the open cell foam would be possible, but it will be messy and might not solve the problem if the smell has leached into the wood of the roof deck.

I’m likely due for a new roof within the next few years, and I was wondering about adding some insulation from above, my theory being that if I can keep the foam from getting too hot, I can keep it from reacting and stop the smell without removing the existing foam.

Does anyone have any experience with this? I have no idea at this point how much it would add to the cost of my roof, but I’m definitely willing to spend a few bucks to never google “spray foam odor” ever again.

Any product recommendations? A friend brought this to my attention, I’m hoping to avoid any mistakes like the one I made when I had spray foam installed on my roof deck. I’m also considering solar panels if I’m going to do all of this work, so I’ll want to make sure that whatever I choose leaves me with this option.

Thanks for your time!

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  1. severaltypesofnerd | | #1

    Could you send some photos?
    You could explore air barrier approaches. Some 1/4" or 1/2" drywall for example could with good detailing pretty much keep the volatizing whatever in the ceiling structure. And add some fire resistance.

    You could try INTENSIVE summer ventilation, to hasten the volatizing process, seal it up for winter.

    You can do a duct pressure test, and seal up ALL the tiny imperfections in the ducting.

    Why two types of foam originally?
    Have you visited another house from the same installer, and smelled?

  2. chicago_spray_foam_customer | | #2

    Thank you for your reply!

    Here are some pictures:
    * stairs - Stairwell from the 2nd floor up to the attic
    * finished_space - Finished area with closed cell behind the drywall. The small door leads to an unfinished corner used for storage (no smell detected there)
    * view_of_landing_and_utility_door - View of the stairs leading up to the attic, you can see where I am exhausting the stale air out of the window. The door with the basketball net leads to the unfinished section of the attic
    * finished_space_2 - View of the utility room. You can see the HVAC supply to the left, and also a black 12" duct behind the doll house. That duct is meant to bring air into the unfinished section, and I have a box fan running on the other side to pull air in.
    * unfinished_space - Unfinished section with open cell foam and the HVAC unit. You can see on the right where I have the inline duct fan. It continues to the right to the finished section (and out the window). The duct to the left goes to the back of the attic so that I am ideally drawing air through the entire space. The filter duct taped to the HVAC return is a vain attempt to slow down air transfer from this return into my ductwork so that I'm not distributing this smelly air throughout the 2nd floor.

    I had tried the ventilation approach you suggested - initially that black duct was taped to the window to bring in outside air. The air should then be drawn through this unfinished room to the back of the attic, where the duct fun exhausts it out. I changed the approach slightly this summer when factoring in humidity to the problem, and this black duct now just pulls in air from the finished room. The idea is that this pulls conditioned air from the house through the attic and then exhausts it. I added the dehumidifier to attempt to control the humidity, which has been 60-70% for most of the summer (in line with the rest of the house).

    Regarding the two types of foam, someone had suggested doing this as a cost saving measure. Having educated myself a bit more, it sounds like I probably should have gone with closed cell throughout to keep moisture from migrating up to the roof deck. I haven't visited any other foamed houses.

    I'm considering 3 options:
    1. Continue doing what I'm doing today (i.e., ventilate so that the smell doesn't get into my ductwork), and hope the smell eventually goes away and I can stop doing this.

    2. Improve my existing ventilation by using an ERV/HRV to be more energy efficient. My goal would be to insert the fresh air into the ductwork or directly to the 2nd floor, and exhaust the stale air from the attic, pulling air up the stairs in the process. I'm not sure how feasible this is, or where I would need to locate the intake/exhaust.

    3. Add insulation from above when it comes time to replace the roof. It sounds like my main concern here (besides cost) will be moisture getting caught in the roof deck. Some quick forum perusal seemed to suggest that I want at least the same R value above as below.

    Thank you again for your thoughts!

    1. severaltypesofnerd | | #5

      I suggest asking the foam contractor to (a) have you visit another open cell foam attic and (b) do a core sample to verify proper curing of the foam deep below where it's visible.
      You can also take the core sample of open cell foam well away from the home, and smell it. Near the home the background smells are likely to be confusing, and your nose may become desensitized to the actual level of smell.

      1. chicago_spray_foam_customer | | #6

        I've had them out twice (though they never come at 4pm on a 90 degree sunny day...), and they have taken and tested a core sample that came back fine. They also cut into a few sections to visually inspect. The next step would be to take a larger square area all the way to the roof deck for testing. I'm hesitant to do this because I'll be left with a bare patch, and the installer clearly felt that the foam was good. If there is a bad section that is uncured, the odds of finding it with this sample seem unlikely. If I did go forward with this (probably next summer because I'd like them to come when it is hot), any advice on how I would fill in that gap?

        I put some of the foam sections that were cut away in glass jars and left them out in the hot sun. After heating them up, they did smell (though maybe not quite the same smell as in the attic). I get that I'm kind of cooking the plastic here, but isn't that what is happening to the foam up against the roof deck?

        1. severaltypesofnerd | | #9

          Open cell foam: no air seal. You can restore the R value with a can of spray foam.

          You could pull out two plugs.
          Send one with the installer.
          Keep one for experiments.
          Do it now when it's cold, and you can expose it to heat (or not) and figure out what's up.

          Note that foam on the roof is a good thing because of thermal bridging. You've already bought the big downside of foam: it burns. A bit more foam on the roof will help with insulation where the rafters are, and be unbroken sheets.

          1. chicago_spray_foam_customer | | #15

            Ah, so I could get away with a can of "Great Stuff" on the bare spot?

            My thinking on the insulation from above was that it would still be a net benefit anyway, but it sounds like I might need to be concerned about getting moisture trapped in the roof deck, so I'm not sure how much foam I'd want from above.

  3. mdhomeowner | | #3

    The attempted mitigation steps that I have seen for this issue are in line with what you are doing - try to make it so the gasses don't make it to the finished areas. In your case it looks like the kids playroom is right next to the foam, so don't be shy about overly ventilating and getting fresh air inside.

    You want to pull conditioned (cool and lower humidity) air from the house and into the foamed area and then outside. You also want a good source of make up air, I'd assume it would enter your house far from the attic. You may want to seal up the return in the foamed area, you don't want to be pulling that smell into your HVAC.

    I haven't heard of anybody adding insulation above the foam to try to protect it from the heat. That is interesting, but I'm not sure it would work unless there is a lot of insulation.

    Removal and proper remediation is extremely expensive, messy, difficult and a huge headache.

    1. chicago_spray_foam_customer | | #7

      Yeah, this is essentially what I'm trying to do now, though without a conscious effort to supply the make up air (it is an old house). I figure an ERV/HRV that exhausts the air from the attic seems like the next level of what I'm currently doing. I should do more to block off that return too, you're right. I didn't want to starve the unit, but that beats the alternative.

      I was hoping someone else might have experience with the insulate-from-above technique as a more permanent remediation. I'm not sure how hot the foam needs to be to react, but I assume really I'd just need to knock it down a bit. That being said, I only get one kick at this can, so I'd rather overdo it if I go this route (though I had no idea how expensive this is either).

      1. mdhomeowner | | #10

        How was the smell in the morning of the fall and spring? I wonder if the roof/foam temp with these extra boards in the summer will be similar to the current Temps at other times.

        Maybe you can extend that return into the finished space.

        Try taking that sample in a jar idea, but letting the sample air out for a little, then throw it back in the jar and leave it outside in the shade. After a day I'm guessing it will still smell. May even smell after 24 hours if kept inside.

        Hopefully you know what was installed. You can look up spec sheets to see appropriate temperature range. You can also read over the installation instructions and see if you see any steps that were missed.

        Some people say that talking to the manufacturer is worthwhile.

        1. chicago_spray_foam_customer | | #16

          Yeah, that's exactly what I'm wondering as well. It doesn't smell in the morning, and it worst on hot, sunny days. If I'm able to add some insulation from above to keep the foam slightly less hot, I'm wondering/hoping it will be more like the morning when it doesn't smell.

          I have a few samples of foam is jars, if I stick them in the sun they will smell. I'll have to see how it does in the morning etc., but it seemed like it still smelled even when it cooled down a bit (which is obviously not what I'm hoping for).

  4. pico_project | | #4

    Is it possible to cut out a large 4x4 square of the full depth to see anywhere near the end/middle still isn't cured or smells?

    1. chicago_spray_foam_customer | | #8

      The installer said that they can cut away a section like this and test it, though I'll then be left with a bare patch. If I can think of a good way to reinsulate that patch this would definitely be an option. I'm nervous about breaking the air seal by doing this.

      1. pico_project | | #13

        Couldn't you just 1 part (can) foam that small void left by the sample?

        1. Expert Member
          BILL WICHERS | | #14

          If you just take core samples, which is all that is really needed to test the quality of the foam, you can very easily fill the small hold with canned foam. That's what I always do. All you have to do is start with the straw at the bottom of the hole, then slowly pull the straw out as you're foaming so that the hole gets evenly filled to the full depth. Sometimes a SLIGHT mist of water sprayed into the hole first will help the canned foam to cure properly at the depths of the hole.


  5. Expert Member
    BILL WICHERS | | #11

    My guess is that you might just be 'baking out' the spray foam a bit. Open cell spray foam is sponge-like, and my guess is the heat is driving some old residual stuff out of the open cell structure. The foam itself might be fine. Before you do anything drastic, I suggest running some strong cross flow ventilation, with a fan pulling air OUT at one end of the space, and a vent or window letting air IN at the opposite end. This arrangement will maximize the ventilation in the space, and will help keep a slight negative pressure in the space which will help to keep any fumes from leaking into the occupied areas. I would run this setup for at least 2-3 days to see if there is any improvement. I wouldn't expect humidity levels to make much difference, I think it's the heat driving this.

    You don't need to cut out a large section of the foam to check for curing issues -- all you need are core samples. An easy way to do this for thin sections is to use a small 1" or so hole saw to cut out pieces by hand, but that usually only works for foam of 1.5" or less thick. For thicker areas, try using some scrap 1" EMT electrical conduit with the end cut at a slight angle of maybe 20-30 degrees or so. Poke the conduit into the foam while rotating it back and forth to help it cut through, and keep doing this until you get all the way through the foam. Pull the pipe out, which should have a core sample in it (you might need to rock the pipe back and forth to break off the end of the core from whatever the spray foam was sprayed against). Use a wood dowel to push the core out of the pipe. You're looking for one of two things in the core: gooey/sticky areas, or burned-looking crunchy areas. Either is a sign of improper curing, and which one you see lets you know which part of the foam mixture was excessive. If the foam looks similar all the way through, with no goo or crunchiness, it's probably OK. I would check several random areas of the foam to be sure you didn't just get lucky with the first sample, and BE SURE to try to test the areas where the installers first started spraying, and also where they finished. Mix problems most commonly show up at the very beginning or very end of an installation when they are starting or stopping their spray foam rig.

    Hopefully there is nothing wrong but some lingering stink trapped in the foam, and ventillation will clear that up over time. If you do have curing problems with the foam itself, then you'll want to consider more drastic remediation steps. I would not do anything drastic until you know for sure if the foam is OK.


    1. severaltypesofnerd | | #12

      +1 on starting with core samples, and a strong cross ventilation while weather permits.

    2. chicago_spray_foam_customer | | #17

      The ventilation strategy you describe is what I had been doing the past few summers. I'm using a duct fan to exhaust air from the back of the attic, and then bringing air in from open windows and a box fan. This summer I switched to exhausting conditioned air and putting a dehumidifier up there, which did seem to reduce the smell.

      One strategy would be to continue to try to get it hot and humid to finish "baking out" the foam. Or I can try to keep it from getting hot enough to react (insulate from above). I'm hoping for a strategy more like the latter so that I have a more permanent solution. At this point I'll also explore an ERV/HRV and try to ventilate the space as well because I've become a bit paranoid, and this doesn't sound like a bad thing to do anyhow.

      The installer has taken and tested a few samples, and also visually inspected a few pieces that they've cut away. Their position is that the foam itself is fine.

  6. user-5946022 | | #18

    My attic is also sprayed with open cell foam, and I also smelled it on very hot days. What I can report regarding my situation:
    - Sprayed in 2018 late spring/ early summer
    - Smelled ALOT in summer 2018-2019
    - Smell reduced somewhat in summer 2020 with humidity control
    - Reduced smell in summer 2021 when I got more serious about humidity control
    - Further reduced smell in summer 2022 with strident humidity control - sensors all over tied to a smart home system. Smell noticeably increased when the dehumidifier broke. In fact I noticed the smell a few hours before I deduced the dehumidifier was not longer properly dehumidifying. Looking back at my logs, as soon as humidity near the ridge went over about 59% the smell came back.

    Overall, I would say the smell has significantly reduced over time. Even with the dehumidifier broken, it was not nearly as bad as it was a few years ago.

    My roof also has a vapor diffusion vent, for whatever that is worth. That will supposedly prevent the roof deck from rotting. You have to be concerned about both the smell and the roof rot, and I would be especially concerned about roof rot in a climate like Chicago.

    1. chicago_spray_foam_customer | | #19

      Wow, I don't think the humidity in my house has been below 60% all summer, so I think it would be more difficult for me to control the summer humidity.

      Glad to hear that this smell is going away in time for someone else in a similar situation. We have forced air heat so my house is usually pretty dry in the winter, but I'm going to make sure with the dehumidifier up there this year.

      Thanks for the note about the diffusion vent, something else to look into as I'm hopefully not rotting my roof as well.

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