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Vapor barrier

Hobcon | Posted in Building Code Questions on

Is sherwin williams vapor barrier primer acceptable as a vapor barrier?

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  1. Expert Member


    Acceptable practically, or acceptable by building codes?

  2. Hobcon | | #2

    building code. I'm in southern maine and the code office isn't familiar with the product

    1. Expert Member
      Dana Dorsett | | #3

      Does the code office read and understand specs?

      Download and print the spec, circling the relevant portions.

      Per the spec :
      WVP Perms (US)
      As per ASTM E96 less than 1.0 perm
      grains/(hr ft2
      in Hg)

      Less than 1 perm = Class II vapor retarder.

      More short-form definitions from the US DOE:

      Where / what type of assembly is the local code office demanding a vapor a barrier?

      Maine's residential code is based on IRC 2015, which includes the use of Class-II vapor retarders on wall assemblies:

      With a Class I or Class II vapor retarder the roof/attic ventilation requirements are cut in half:

      The verbiage and relevant code sections didn't change between IRC 2015 and IRC 2018, so even if the local township has upgraded to the newer version it's still good.

  3. CMObuilds | | #4

    Think the thickness of the coat (mils) is important. One inspector asked to see the empty buckets so he knew the coverage wasn't skimped. He didn't do the math though, he was just trying to flex.

    1. Expert Member
      MALCOLM TAYLOR | | #5

      Note to self: Alway keep several empty paint buckets on site!

      1. CMObuilds | | #6

        Just write “vapor barrier paint” with a sharpie on some old buckets.

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