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Pacific Northwest – vapor barriers with spray foam?

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  • November 10, 2024 at 10:00 am #2789
    Quinn Blackwood
    Member

    Working in Oregon and Washington. Getting conflicting info on whether we need a separate vapor barrier when using closed cell foam on exterior walls. Anyone doing work in the PNW have clarity on this?

    November 10, 2024 at 1:00 pm #2791
    Lisa Hutchinson
    Member

    In the PNW you are in climate zone 4C marine. Closed cell foam at 2 inches plus already functions as a vapor retarder Class II. Most code interpretations do not require an additional vapor barrier with sufficient closed cell.

    November 11, 2024 at 9:30 am #2792
    Amy Chambers
    Member

    Washington state has adopted specific amendments to the IECC. Most of WA west of the Cascades is zone 4C or 4A. Worth a call to the building department before the job.

    November 12, 2024 at 10:00 am #2794
    Quinn Blackwood
    Member

    Called my local AHJ – they confirmed no additional vapor barrier needed with 2 inch minimum closed cell on exterior walls. Thanks for pointing me in the right direction!

    November 12, 2024 at 2:00 pm #2795
    Lars Eriksen
    Member

    Good info. In Minnesota we are in zone 6-7 and the rules are different but the principle of getting local AHJ clarification applies everywhere.

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