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Community and Q&A

Vapor barriers

myadanny | Posted in General Questions on

Building department has questions on our spec for vapor barrier paint instead of 6 mill poly, on our new house build. We are in Zone 6, how we are going to seal at floor, roof and electrical boxes to form a continuous barrier? I can see at the roof the paint continues wall to ceiling, would the floor and electrical boxes be done with acoustic sealant?

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  1. Expert Member


    Air-barriers need to be continuous and all penetrations sealed. Vapour barriers don't. If you are using the drywall as an air-barrier, then you need to detail the penetrations to stop air movement, using gasketted outlets, and sealant. That has nothing to do with the paint. The paint is to coat the drywall to use it as your vapour retarder. A vapour retarder doesn't need to be sealed or continuous to work, and penetrations don't affect it.

  2. GBA Editor
    Martin Holladay | | #2

    Malcolm is right. You are confusing air barriers with vapor barriers. For more information, see these articles:

    "Questions and Answers About Air Barriers"

    "Do I Need a Vapor Retarder?"

    "All About Vapor Diffusion"

  3. myadanny | | #3

    So Martin how would I approach the building department that calls for an insulation and poly inspection that is taped and acoustic sealed?

    1. Expert Member
      MALCOLM TAYLOR | | #4


      I'm assuming this is in Canada, but the advice is similar for other places.

      Building codes distinguish between air and vapour barriers. If you are using your drywall as both, you need to show:
      - That the paint you have used yields a vapour barrier sufficient to meet the code requirement for permeability.
      - That you have sealed the perimeter of your drywall, and all penetrations, so it it acts as an air barrier. typically this is done by using gaskets or caulking at the bottom of your walls both to seal the sill plate to the subfloor, and between the drywall and framing behind. The penetrations are dealt with using a combination of exterior wall electrical boxes, foam and sealant.

  4. Peter Yost | | #5

    HI Dan -

    Need to know your location before recommending resources to support your approach, since codes vary by state, or even local jurisdiction but also by climate.

    IN the US - best code resource tends to be: Code Resource Center ( Building Codes Assistance Project (BCAP) -

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