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Community and Q&A

Exposed XPS foam board in crawl space and attic?

kieran973 | Posted in General Questions on

I just had some insulation added to my basement rim joists, crawl space, and attic. The insulation company put mineral wool along the rim joists, but they used XPS foam board in the crawl space and the attic. Specifically, the foam board is on 1.) the inside of three crawl space walls, 2.) the attic side of the door which leads from an upstairs bedroom into the walk-up, unfinished attic, and 3.) on top of and around the edges of the whole-house fan in the attic floor. The foam board is Owens Corning Foamular 250. It has a “Greenguard Gold” rating. But it also says on the board itself that it needs a thermal barrier, per local code. All of this board is exposed with no thermal barriers placed over any of it. Should the insulation company have covered it with gypsum board or something? Thanks

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  1. Expert Member


    Yes. Contractors can't come and work on your house leaving it with code violations. Their only excuse could have been if they had explicitly told you further work was necessary to finish the job, and that another trade would have to perform it.

  2. kieran973 | | #2

    Wow, OK. Thanks for the heads up. I guess I'll have to figure out why this was left exposed, and why the company didn't say anything about it....

  3. plumb_bob | | #3

    Depends what building code you are working under. BC Building Code allows exposed foamed plastics in crawl spaces and attics in SFDs and other simple buildings.

    1. Expert Member
      MALCOLM TAYLOR | | #4

      Good point. I'm assuming he is under the IRC. It's worth finding out what the local code says.

      From my reading of I'm not sure that the BCBC allows it to be exposed in attics and crawlspaces either:
      "Foamed plastics that form part of a wall or ceiling assembly shall be protected from adjacent space in the building, other than adjacent concealed spaces within attic or roof spaces, crawl spaces, wall assemblies and ceiling assemblies"

  4. andy719 | | #5

    As always with code questions, the answer is it depends. Did you hire an insulator or a licensed GC? Did you file for a permit? That wouldn't change the code but might change who's responsibility it was to meet it.

    What code are you using? The 2018 IRC has different rules for attics, crawls, and rims. Each of them has exceptions for foam tested to a certain fire resistance level. I believe the DOW (blue) product has met that testing requirement, but the OC foamular (pink) has not. An inspector might ask you to provide that documentation though.

  5. Jon_R | | #6

    Seems like it is usually sufficient left exposed:

    If not, consider adding 3/8" gypsum as an ignition barrier. Or just go to 1/2" and also meet the thermal barrier spec.

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