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Community and Q&A

FSK paper class A retardant, so no need for foil-face polyiso?

Apollo S | Posted in General Questions on

I’m separating FSK paper [foil-scrim-kraft paper] into its own question, since my original post got bit too long with other sub-topics.

So I am looking at what other options besides drywall and foil faced polyiso I can do in the crawlspace and basement.

As I was doing research, I found that FSK paper has same Class A ASTM-E-84 fire rating. So sound like it is a viable option for covering netted blown in cellulose in the floor rafters.
I know state insulation program contractor (here in MA) used FSK paper in my kneewalls to cover the netted densepack cullulose and said that was ignition barrier.

Here is the product I am talking about:

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  1. User avatar GBA Editor
    Martin Holladay | | #1

    Code requirements for protecting foam insulation in crawl spaces are interpreted differently in different communities. The only person who can answer your question is your local code official, whose code interpretation is the only one that matters.

  2. Apollo S | | #2

    Insulation does not require permit, so this is more about doing it the right way for me. Cellulose is Class A fire rated so is FSK paper. So I am looking at risk factors and using polyiso only where absolutely necessary and trying to keep the rest of the place insulated with stuff that does not burn - safer solution. Am I wrong?

  3. User avatar GBA Editor
    Martin Holladay | | #3

    If code compliance is not an issue, you can choose any product you feel comfortable with (as long as the product doesn't make it hard for you to sell your house when that day comes). I'm not familiar with this particular product (FSK paper), but I'm guessing that it is less flammable than ordinary kraft paper.

  4. Apollo S | | #4

    I tend to keep spec sheets for all the products I use. Our inspector is only part time and not exactly up to date on things (though we adopt latest code as soon as it comes out), so I already had to show him spec sheet for gas conversion gun for the oil furnace. I was surprised he had no idea what it was.

    I would much prefer to put up something like 1/2inch blueboard for my own peace of mind, since I have tested myself how polyiso and foam burn (cause I am curious about those things), but I realize there is moisture risk.

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