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Can moisture-resistant drywall, if sealed properly, be used as a vapor barrier?

Chris Rocheleau | Posted in General Questions on

They are basement walls and were sealed before framing and have Roxul rigid board behind the studs as a thermal break.

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  1. GBA Editor
    Martin Holladay | | #1

    There are really two questions here. The first question concerns whether drywall is a vapor barrier. The second question concerns the best way to insulate the interior of a basement wall.

    1. No, drywall is not a vapor barrier. Drywall is vapor-permeable. However, there is no need for most walls to have a vapor barrier. Some building codes require above-grade walls to have an interior vapor retarder -- which is a lesser standard than a vapor barrier. To meet this requirement, you can install a layer of vapor-retarder paint on the drywall.

    2. I don't recommend the use of Roxul mineral wool insulation to insulate basement walls on the interior. For advice on the right way to insulate a basement wall, see How to Insulate a Basement Wall.

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