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Fire code

BPortnoy1 | Posted in Building Code Questions on

Hello. In my attic I have paper faced fiberglass. The paper is covered by foil faced thermax with the foil faced out. It says combustible on the foil. The thermax itself is fire rated but I’m wonder if it is a sufficient fire barrier to the Kraft paper code wise. There are other issues related to assembly in my attic I’m aware of but trying to determine if this is another one. See photos. Thank you

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  1. Expert Member
    BILL WICHERS | | #1

    Note that only one side of thermax is rated to face towards the interior of the space, so make sure you installed the sheets in the correct orientation.

    I would say the thermax sheets provide protection for whatever is behind them, which could include “regular” polyiso, or Kraft faced batts. The reasoning is that the ignition barrier provided by the thermax should protect anything behind it, not just the polyiso of the sheet of thermax itself. Code wants listed ASSEMBLIES though, and thermax isn’t listed that way, so you could technically have a compliance issue here if you have someone who goes by the literal reading of the code. The only way to be sure what will be acceptable in your area is to ask your local building department people. Most building departments will accept thermax as a sufficient covering using the same logic i explained earlier, but you don’t want to find out they won’t accept it after you’ve built everything so it’s worth asking first.


  2. BPortnoy1 | | #2

    That all makes sense. I appreciate the time you took to reply! Do you know if the foil side is the rated side?

    1. Expert Member
      BILL WICHERS | | #3

      If you look at the edge, the rated side is slightly thicker than the other. The thicker faced side faces towards the interior of the habitable space.


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