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Community and Q&A

Exterior rigid foam and gable of unconditioned attic.

jamestimmerberg | Posted in Green Building Techniques on

I’m building a one-story home, with an unconditioned attic. I will be installing four inches of exterior rigid foam. Does the gable also require exterior foam? If not, what’s the most cost effective way to finish the gable?

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Does the gable also require exterior foam?"

    A. No.

    Q. "If not, what's the most cost-effective way to finish the gable?"

    A. Some builders feel that the easiest thing to do is just to continue the rigid foam all the up to the top of the wall, even though the rigid foam isn't needed. If you don't want to do that, you'll have to make furring strips that are 4 inches thick. Perhaps you could install 2x4s on edge (fastened with long ring-shank nails inserted through holes predrilled in the 2x4s), giving you 3.5 inches, and then install ripped pieces of 1/2-inch OSB or plywood on top of the 2x4s to give your 4 inches. It's not clear that this is easier than just extending the foam.

  2. Expert Member

    You can also flash the top of the foam and leave the finished gable where it is 4" back. Or instead of flashing, you can return the roof overhang across the gable end.

  3. iLikeDirt | | #3

    When I had my walls covered in rigid foam, the crew covered the gable end wall too. Unless your house has a really weird or steep roofline, it shouldn't be that much space so the extra cost and work should be minimal. And if they don't do that then they have to figure out another approach for thickening the exterior surface of the gable end wall to keep the cladding co-planar, which may be even more work. Finally, if you or someone else decides to condition the attic later, having rigid foam already on the exterior of the wall will reduce the amount of work for that project. Seems like a no-brainer to me.

  4. jamestimmerberg | | #4

    Thanks everyone.

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