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Glass-fiber-faced polyiso used indoors

KayGP | Posted in GBA Pro Help on

I need some help ASAP. Long story short we are remodeling our attic. It is a conditioned space that used to be plaster and lath. We have filled the rafter bays with 3.5″ of Polyiso with a 1.5″ air gap for the soffit and ridge vents to do their job. 
My question is related to the 1″ glass fiber faced Polyiso that we are installing over the rafters as a base for installing shiplap. We purchased it as factory seconds so we don’t know the brand or actual type. It definitely looks to be coated glass fiber faced. The issue it that it has an odor. I have a feeling it was designed to be roof decking. My concern is for my families health. Could the smell indicate it is off gassing toxic fumes? We plan to prime it before putting the shiplap up.
Any thoughts on this would be so helpful. We’ve already begun putting it up but I want to stop but my husband doesn’t think it’s a big deal. I’m just really worried it could be harming us.


P.S. I can attach a picture if needed.

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  1. Expert Member
    Dana Dorsett | | #1

    Fiber faced polyiso under a torch down roof may have taken up some of the volatile asphalt from the roofing. In your vented roof stackup installing a sheet of 4-6 mil polyethylene between the polyiso and shiplap as an air barrier should keep any of that from entering your conditioned space. Some sort of broadsheet air barrier would be a good idea for this assembly anyway, since the seams of the used foam might not be easy to reliably air seal with tapes, and the ship lap is the opposite of air tight.

    Ship lap is unlikely to meet code requirements for a thermal barrier against ignition of the foam, so it may need a layer of half-inch gypsum or OSB between the foam board and ship lap, either of which could be detailed as an air barrier.

  2. Jon_R | | #2

    +1 on making sure that you have a good air barrier (verified with blower door testing). But I wouldn't use interior side polyethylene sheet in any house with AC.

  3. KayGP | | #3

    Thanks for the quick reply Dana.
    To clarify, the Polyiso was not reclaimed but factory seconds so it’s brand new. I’m attaching a picture of the facing so you can get a better idea of what we’re dealing with.

    The polyethylene is a good option to consider. We aren’t concerned about the air seal because we’ve done some serious sealing on the boards between the rafters with spray foam to seal it in. The 1” over the top is not only for extra R value but as a surface to attach the faux shiplap to.
    Code is not really an issue either as this is in a 120 year old home and nothing is to code in here so we are just doing the best we can.
    Do you think a thick coat of a paint primer such as Zinnser or Kilz2 could “seal” any off-gassing or odors?
    We just can’t figure out what is causing the odor and what the Facer material truly is.

    Thanks for all your help,

  4. Expert Member
    Dana Dorsett | | #4

    >"We aren’t concerned about the air seal because we’ve done some serious sealing on the boards between the rafters with spray foam to seal it in."

    That sealing method is known to fail in cut'n'cobbled foam applications.

    >"The 1” over the top is not only for extra R value but as a surface to attach the faux shiplap to."

    What is the faux ship-lap made of, how thick, and is it possible to air seal it? Is it sufficiently rated as a thermal barrier against ignition for the foam?

    >"We just can’t figure out what is causing the odor and what the Facer material truly is."

    Asphalted fiber facers are pretty common in the industry but if the color rendering in the picture is accurate it looks like something else. What does it smell like? Can you determine the manufacturer (are there any printed markings on the facers, company logos, part numbers, etc?)

  5. Expert Member
    BILL WICHERS | | #5

    You’re really better off building to code as you do improvement projects. Just because something else isn’t right doesn’t mean you shouldn’t try to complete new projects correctly. The fire codes are really there for your own safety so I strongly recommend putting in the ignition barrier. Drywall is pretty inexpensive, and you only need to do a quick tape and mud job to air seal it, you don’t need to finish it to a paintable surface since it’s going to be covered by the T and G boards.

    The cut and cobble foam seals can fail over time due to material shrinkage and the structure flexing (like when someone walks on the roof to do maintenance). You shouldn’t the cobbled insulation alone as your air seal.

    I’ve seen fire retardant panels before that look similar to the pic of the facer you attached. I can’t remember the name of the material at the moment unfortunately. You’re probably smelling whatever was used as a binder to hold that material together.


  6. KayGP | | #6

    Thanks for everyone’s input. The air sealing is really not a huge issue because as I mentioned before this is a 120 year old home. The rest of the house is plaster and lath and single pane windows so some air leakage in the attic is peanuts compared to what it was and what the rest of the house is like.
    If we wanted or needed to remodel to code we’d be better off tearing the house down and starting fresh lol. I do see the value in trying our best to meet fire codes for safety but the rest of the house is so far from it that it seems too little too late.
    Our biggest concern at the moment is whether or not this Polyiso is going to off gas harmful fumes to the family.

    In response to Dana:
    The Faux shiplap will be 1/4” plywood underlayment like this...

    I’m attaching some other pictures of the Facer... the only writing is a number and “this side down”
    The color is a dark gray and we’ve noticed that the smell is much stronger if the boards are damp, which they were from being under a tarp outside for a month. When the Facer is dry it smells faintly of new carpet. When the Facer is damp it’s an odd smell reminiscent of being at a water park on a hot water slide with chlorinated water and hot plastic. I know that’s strange but that’s the only thing the smell reminds me of.

  7. KayGP | | #7

    I contacted a company called Atlas who replied that their Coated glass fiber faced Polyiso is green guard certified so let’s hope that’s what we’ve got.

  8. KayGP | | #8

    So I contacted Atlas and these boards are not their product. The rep suggested maybe they are made by Firestone but from pictures it doesn’t look like it. I can’t figure out what this facer material is.
    I’m contemplating trying to sell them all and get something else. What type of facer would you recommend for indoor application?


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