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Best Rim Joist and Header insulation with exterior rigid foam

walldocmp | Posted in General Questions on

I have 2″ of polyiso rigid foam insulation installed on the out side of my house in zone 6. What would be my best bet be for insulating the basement rim joist? Also would using polyiso in window headers be a bad idea?


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  1. GBA Editor
    Martin Holladay | | #1

    The 2 inches of polyiso should keep the rim joist warm enough that you don't have to worry about moisture accumulation or condensation on the rim joist. That means that you can choose from a wide range of insulation materials for the interior insulation: open-cell spray foam, rigid foam, fiberglass, or mineral wool.

  2. walldocmp | | #2

    Thanks. What do you think about using rigid foam in door and window headers when there is exterior rigid foam?

  3. GBA Editor
    Martin Holladay | | #3

    I think it's fine.

  4. walldocmp | | #4


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