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Odor from Fire-Retardant Paint Applied Over Spray Foam

Brad964C4 | Posted in General Questions on

I’m an architect & designed a 2 story addition to a house 2 years ago. I just got a call from the homeowner about some trouble he’s been experiencing since it was built. I’ve never heard of this problem before & would appreciate any advice.
Rafters were insulated with open cell spray foam to create a conditioned space since an air handler & gas fired furnace are in the attic. A fire retardant paint was then applied over the spray foam. The paint odor was very bad at first & the owner was told the smell would subside….but it hasn’t in 2 years & is especially strong in summer. The odor is getting into the HVAC system & into the bedrooms below, which is a problem.
The HVAC installer says the mechanical equipment is sweating in the attic since there’s no air circulation & recommends ventilation, but I disagree….kind of defeats the concept of a conditioned attic.
I don’t know what was used for the fire retardant paint, but that seems to be the culprit. Has anyone else experienced anything similar?
Thanks in advance…..

Brad DeMotte

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  1. user-2310254 | | #1


    What client's climate zone (location)? Open cell foam in an attic is problematic in cooler parts of the country. (See So there could be a moisture/rot issue.


    You are using a combustion appliance in a conditioned space? Without a fresh air source!?

  2. Brad964C4 | | #2

    Project is in Southern NY, climate zone 4. I don't think the issue is moisture/rot.......I think the problem is improper installation of the foam as it didn't cure right.

    There is a gas fired furnace in the attic, but I haven't seen how it was installed. I'd assume it has a fresh air source, but will verify.


  3. user-2310254 | | #3


    Reports suggest bad foam jobs usually smell like rotten fish. This does not sound like that sort of situation. It probably would be worthwhile to hire a RESNET professional to inspect the project and determine what is going on.

  4. user-3039358 | | #4

    We just completed a new renovation with similar setup: open cell insulation with fire retardant paint in attic with air handler. The smell is very strong and is coming through the HVAC into the bedrooms. Insulation was installed ~6 months ago and this is in Massachusetts in the South Shore area. We think the odor is coming from the fire retardant paint but we are not sure.

    We are considering adding an exhaust fan in the attic, our HVAC contractor did not have any other suggestions. Have you had any luck on this issue?

    1. ma524 | | #8

      I am also in the south shore area and have the same exact problem. It has been 1 yr and I keep the attic extremely dry with a de-humidifier but when spring and summer roll around and the temp goes up, the smell becomes strong no matter the low humidity.

      Did you find a solution?

  5. Expert Member
    KOHTA UENO | | #5

    If you were interested in more information on high humidity issues in conditioned/unvented attics with spray foam, see the following:

    BSI-077: Cool Hand Luke Meets Attics

    Why do we have to worry about low-density open-cell SPF? It is very vapor open—around 30 perms per inch of thickness—and will allow moisture to pass through it and migrate to the underside of the roof deck (Photograph 5). This is not typically a problem as solar radiation drives this moisture back down out of the foam and back into the attic space air where it is usually removed by air change created by leaky ducts.

    So why not just use high-density closed-cell foam or apply a vapor retarder? Well, there are all sorts of other desirable properties associated with low-density open-cell SPF such as its fire performance and its “drying” properties and its “green” properties if “green” is your thing. For some folks blowing agents matter especially if they are “green”. And, I am not entirely convinced that in some climates that even high-density closed-cell foam with be without issues if there is no “communication”.

    Also, further information:

    BSI-016: Ping Pong Water and The Chemical Engineer

    Lots of attics insulated with open cell low density spray foam (Photograph 1, Photograph 2 and Photograph 3) are having problems – in hot humid climates, mixed humid climates, and cold climates. The problems are moisture related. The attics are “unvented” – open cell low density spray foam is installed directly on the underside of roof sheathing. The attics are humid. Very humid. Unacceptably humid. And the humidity collects at the upper portion of the attics.

    In terms of solutions:

    The HVAC installer says the mechanical equipment is sweating in the attic since there’s no air circulation & recommends ventilation, but I disagree….kind of defeats the concept of a conditioned attic.

    To clarify: by 'ventilation' is the intent 'cut openings in the roof to passively let air flow in and out,' or 'add a fan that moves a fixed amount of air'? I am hoping the latter was the intent.

    Two options that might be worth considering in isolation or together:

    - Per a previous commenter, add an exhaust fan, sending air from the conditioned attic to outdoors. This will increase air change in the attic (diluting odors), and draw conditioned air (assuming air conditioner running) from the main house into the attic (see the Cool Hand Luke 'communication' comments). Lastly, if the exhaust fan is large enough, airflow will generally go from the house into the attic, thus 'containing' the odors.

    - Add a dehumidifier. This will directly address the condensation problems occurring. Also, it is *possible* (not sure how likely) that this might reduce the odor issue. Odors are typically a function of temperature and humidity--we can't do much about the temperature, but reducing humidity might make chemicals 'less active' (less likely to react or evaporate).

  6. brad_glazier | | #6

    The sweating of the ductwork is the key to the mystery. There is a moisture issue in the space caused by insufficient air exchange. I would suspect that the old insulation/vapor retarder may still be in the floor of the attic space. They have in intent created a conditioned space but left out the means by which to condition it. Be sure to remove any insulation from the floor, tie the attic into the air handler of the main house to circulate/exchange air from the attic and/or install an air exchanger to control the humidity.

  7. ma524 | | #7

    Hi Brad,

    Was a solution for your client ever found. Did they rid the attic of the paint smell and the HVAC is now pushing unscented air?

  8. walta100 | | #9

    Sadly ma524, we see this question often and almost never get a post about how the story ends.

    My wild guess is in a lawyer office signing a non-disclosure agreement so they can’t tell the story good or bad.


  9. Sudar | | #10

    I have the same issue. It been 1 year since the installation and the paint smells bad. I paid for it and now very sorry contactor used it on top of spray foam. This is ridiculous, read so much before doing spray foam, read about all the issues, and it's the stupid paint that ended up causing these nightmares

    Maybe I should have my ERV pull air from attic and dump fresh air there

  10. Sudar | | #11

    I am thinking pulling air out is the way to go since air from the house will get pulled to attic. If I provide fresh air to attic, I am risking of possibility of pushing attic air into the house.

    Ps. My spray foam guy has been in business for a long time, it's not like I picked some cheapo contractor. He did alot of houses with the same paint and smell went away. The difference is that in my case, house is not under construction and there is zero venting on the attic. But I still figured 1 year should take care of the smell......I guess I was wrong.

  11. brad_glazier | | #12

    This is 100% a failure to design for proper conditioning of the attic space. You have made this part of the interior envelop and it needs to be conditioned just as any other area of the house. Not a paint or foam issue purely a design issue. Install and HRV/ERV and include the attic space in the home ventilation system, problem solved.

    1. Sudar | | #13

      So you think it's OK that paint smells for 1 year? You think it will go away if I make an exhaust port in attic from my house ERV?

  12. walta100 | | #14

    Sudar It seems very unlikely that the paint is what smells.

    The paint was made in a factory under controlled conditions and samples were lab tested before the paint was shipped.

    Your foam was made in your attic at what ever the temp and humidity happened to be that day and the chemicals were mixed by setting adjusted by your installer in the field to what looks right that day.


    1. Sudar | | #15

      I am not 100% sure what the smell is, but it smells like oil based paint or something. When I used oil based stain blocker in room, it smelled similar and took like a week to get the smell out, and I only applied it to effected small area.
      So I understand that oil based paint can take a while to not stink but a year seems alot and something is wrong.

      In Home Depot now buying duct for ERV to do some venting

  13. Sudar | | #16

    Just spoke with building contractor that works with spray foam guy. He said when they do this job, it's the paint that always smells and takes a while to get the smell out even in vented area. Waiting for call back from spray foam guy......

  14. Sudar | | #17

    Spoke with spray foam contractor. He said paint is smelly but it's water based paint (none toxic) and the reason why it smells is because there is no ventilation. Also suggested I change HVAC filter since it can absorb the smell too (my filter is from last year, still pretty clean that's why I didn't bother)

  15. Sudar | | #18

    Paint manufacturer also said that space must be ventilated for several days with fresh air for paint to cure and smell to go away. Shouldn't come back after that. Going for vacation for 2 week soon. Will try to at least open the attic, maybe will help along with EVR running almost 24/7

    1. jshf_8 | | #19

      I'm experiencing this with my recently applied spray foam job in the attic. I have no ventilation up there so before going to the trouble of setting it up I would love to know if any of that helped

      1. Expert Member
        BILL WICHERS | | #20

        You NEED ventilation for the smell to go away. Ideally you want "cross flow" ventilation, with air coming IN one end of the attic and blowing OUT the other. I would setup some box fans to blow OUT from one end, with the other end open. This will depressurize the attic slightly, helping to keep the smell from leaking into your home. You want to run that setup for at least 2-3 days or so. I typically recommend doing the spray foam work at the end of the week, then airing things out over the weekend and taking a trip somewhere over that period.


        1. jshf_8 | | #21

          Thank you for the info - yeah the attic is completely encapsulated and I did leave the entry way open for a few days with a small fan running and the upstairs windows while we were away. While the smell isn't bad by any means and it has gotten better it's still very present every time I go up to the attic.

          I'm going to take your advice and try this again when we're away for this upcoming weekend with an extra fan at one end of the attic and another blowing air down towards a second floor window.

          1. Expert Member
            BILL WICHERS | | #22

            You need the fans setup for crossflow. That means not both blowing in, and not both blowing out, if they are at opposite ends of the space. You want air to come in one end of the attic and exhaust out the other. While it may seem that both blowing out will "suck out the smell", it doesn't actually work that way -- you need one blowing the smell out, and another open end (open window, open door, etc.) to let fresh air in to replace the smelly air you blew out. With air constantly moving through the space like that, you keep the concentration of the "smelly stuff" in the air low, which allows for the maximum amount of remaining "smelly stuff" to evaporate out of the installed materials. That's what you need to do to clear things up.


      2. jshf_8 | | #23

        Circling back - after a couple of weeks of ventilation where I attempted to get fresh air in to the attic to replace the existing stuff it has helped immensely and the smell is quite minimal now. It was probably the fire retardant paint just needing proper ventilation.

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