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Drywall or plywood as a fire barrier over rigid foam insulation in rim joist areas

leeken | Posted in General Questions on

I have seen comments about a need to place drywall directly over the face of the rigid foam insulation for fire protection in the rim joist areas. If the basement is finished with drywall covering the ceiling and stud walls would that be sufficient for protecting the rigid foam from fire instead of placing drywall directly on the face of the rigid foam. In the blog “Three Ways To Insulate A Basement Wall” the detail for rigid foam insulation shows drywall on the ceiling and the stud wall but does not show drywall directly on the rigid foam insulation of both the rim joist area and the basement wall.

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  1. Expert Member


    Codes do not require any protection if the foam on the rim-joists or walls are within an enclosed space separated from the basement or crawlspace.

    1. leeken | | #3

      I appreciate your reply to my question. Thank you very much.

      1. Expert Member
        MALCOLM TAYLOR | | #5


        Sorry, I forgot to link to this article, which explains things in more detail:

  2. Expert Member
    BILL WICHERS | | #2

    If you're area isn't closed off as Malcolm mentions, you can also use mineral wool as a fire protective material over rigid foam in the rim joist area. You can use The Safe 'n' Sound version of mineral wool for this, which is slightly thinner (and a bit cheaper). Just cut pieces to fit between the joists, then press it in against the rigid foam for a tight fit.


    1. leeken | | #4

      Thank you for replying to my question. I really appreciate it.

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