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Possible foam insulation smell in warm/humid days

JohnP2020 | Posted in General Questions on

Hello all,

I hope I can get some advice on the below.

I have a chemical smell in my house and from everything that I have been reading, I suspect it might be related to the foam insulation. I wonder if you have any advice, or if it could be anything else besides the foam insulation.

Last year (2019), I have added a second floor to part of a split level home in Connecticut. As part of this renovation, I have changed all of the windows, siding and added blown-in insulation in the existing structure. For the existing roof rafters we added open-cell foam insulation.  This area has no smell at all.

The new addition, has foam insulation (open-cell) both in the walls and between the roof rafters. In the new structure only, there is a chemical smell (not fish or ammonia smell) when humidity is over 65% and it over 70 degrees outside, however there is no smell in the attic (new structure), only inside the rooms. The structure was completed in November 2019. The isolation went in on Sep. 11, 2019 and the drywall was installed on Sep. 15, 2019. As the smell persisted, the contractor opened two walls (in different rooms) to cut out 12×12 pieces of insulation and a 12×12 piece from the attic and sent it to be tested by the manufacturer. The insulation itself did not smell at all when we opened the wall and it looked  OK and harden. And now with the walls open, the insulation itself does not have a smell.  Is it possible to have the smell from the insulation as it emits gases, overtime and they accumulate in the room? Or could it be something else?

Please see attached the insulation data sheet.

Thank you in advance,


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  1. Expert Member
    Michael Maines | | #1

    John, did you install new carpeting or cabinetry? Are your doors and trim solid wood or mdf? Do you have gas-burning appliances?

  2. JohnP2020 | | #2

    Hi Michael,

    No carpeting, we have wood floors which have a water base finish. Regarding cabinetry, we only have a vanity in the bathroom; it does not smell. It is not a "new" smell or paint smell. No gas burning appliances. We have propane for heating and hot water, but that's in a different part of the house, which has no smell.



  3. JohnP2020 | | #3

    Just an update. Now we also have the smell from fireproof paint covering the foam insulation on the rafters being pulled into the AC system. Yesterday we had to shutdown the AC system because the smell was so strong. Should the fireproof paint still smell? It was applied in late September 2019. And it clearly smells stronger on hotter and humid days.

  4. GBA Editor
    Brian Pontolilo | | #4

    Hi John.

    Temperature and humidity are factors in off-gassing, however I'm used to hearing these stories end with one of two results. The first is that the off-gassing smells were existent when the spray foam was first installed and with some time and ventilation, dissipated. The second is that the off-gassing and smells persisted and were determined to be the result of a bad installation.

    I'm curious about the factor of the time of year that you had the installation done (moving into cooler weather). At this point I suspect the best thing for you to be doing is ventilating the house well, for your own safety, and because this could perhaps be some delayed off-gassing and will eventually subside (I don't actually know if delayed off-gassing is a thing; I'm speculating). I hope some others chime in with their knowledge and experience.

  5. JohnP2020 | | #5

    Thanks Brian. The insulation was applied in mid-September hence my concern. It had enough time to ventilate. Also, the heating and AC system have an ERV, which should bring in enough fresh air. And, there was no smell during winter, fall and early spring. The smell started in May. We sent samples of insulation from the attic and walls from two separate rooms to the manufacturer. Hope to have results soon. We also brought in the GM, the insulation contractor and the HVAC contractor. All seem very defensive, which makes me think, there is actually a real problem.

  6. JohnP2020 | | #6

    Just an update: the foam insulation installer decided shaved off a thin slices of the insulation covered by the fireproof paint - in both attics. They think that at least some of the smell is from the paint. We shall see. They recommend to let the insulation bread out for a couple of weeks before they paint it again.

  7. JohnP2020 | | #7

    Does anyone recommend a company that could test the foam insulation?

  8. tommay | | #8

    A lot of these stories out there. My take is that there are microscopic bubbles within the foam, the air in these bubble heat up to a point where the pressure forces the cooked foam outward causing the out gassing, which is why the surface itself, for the most part, doesn't really smell depending on the path the gas takes. Perhaps taking a core sample on a hot day and smelling the interior of the foam sample may give you some indication. Or take a hair dryer and heat up a small section and test it that way.

  9. JohnP2020 | | #9

    Thank you Tom. The smell was gone for a couple of day and almost wanted to celebrate, but it is back today. I will definitely try your suggested method.

  10. JohnP2020 | | #10

    I have a closet in which the smell is very strong - possibly because it is a smaller space. I plan to remove the drywall and the insulation from the outside wall and see if that will eliminate the smell. Is there any guidance on how to effectively do this? And on how to clean the plywood and 2X6 frame. I am afraid that the smell might be embedded in the plywood and the wood frame. Thank you.

  11. JohnP2020 | | #11

    I just wanted to updated everyone. We eventually had to remove all the foam insulation from inside the walls. Not the easiest project, as the drywall had to be removed and replaced in the process. The installer agreed to remove it all and replace it with Rockwool. They also replaced the drywall in that area and repainted. There is no smell now. I wish I would have done this sooner.

    About 6-7 weeks ago (if not more) I sent samples of the insulation to the manufacturer who stated (after long delays) they independently tested and there is nothing wrong with the insulation. However, they are unwilling to provide the lab report - which makes me believe that there was something wrong with their product. I plan to independently test it.
    Prior to this they sent an "industry expert/consultant" to my house to inspect the insulation. He suggested to repaint the walls with Kiltz primer - I guess he wanted to seal the smell inside the walls. Obviously, this was the worst advice. He denied that there is anything wrong with the insulation and the smell in the house could be from anything - unlikely in the an addition that was built less than a year ago. He had a goal in mind before he entered my house - to convince me that there is nothing wrong with the insulation, so the manufacturer is not liable.

    Be aware of foam insulation and the foam insulation manufacturers; they will do anything to convince you that there is nothing wrong with the insulation and they will never assume any kind of responsibility. Conduct your due diligence well. A bad product or a bad installation job could cost you time, money and it is emotionally draining. Not to mention the impact on your health. I would never use foam insulation inside the walls. I believe it makes sense to install it on the roof rafter and if something goes wrong, you can easily inspect and remove. Not so easy from inside the walls.

    Stay well, stay safe and stay away from foam insulation - at least 6 feet apart ;)

    1. JC72 | | #12

      Thanks for the update. Personally I love the concept of spray foam and I know of one builder which allegedly uses it for all their homes with some success but time and time again the products seems ill suited for cost-effective application in the field.

      On a side note. Don't be surprised that the manufacturer said there was nothing wrong with the foam. When it comes to spray foam in the vast majority of cases the issue is installer related (Improper spray technique, Improper mix, applied at improper ambient temperatures, moisture level of the wood is too high).

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