Pacific Northwest – vapor barriers with spray foam?

[Quinn Blackwood]

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?

[Lisa Hutchinson]

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.

[Amy Chambers]

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.

[Quinn Blackwood]

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!

[Lars Eriksen]

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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