Do I need an interior vapor retarder if the studs are filled with spray foam?
William Griswold| Posted inBuilding Code Questionson
For a new wood-framed single-family home that has spray foam insulation installed in wall, is an additional vapor retarder required to be installed on the interior side of wood studs?
The code does not address as far as i can see.
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Replies
William,
The code requires a vapor retarder (usually defined as a material with a permeance of 1 perm or less) on the interior of walls in some climates. However, the code does not specify what type of material you need to install to meet the code.
If you installed closed-cell spray polyurethane foam, you are all set; 2.5 inches of closed-cell spray polyurethane foam has a permeance of 0.8 perm. So the foam is the vapor retarder.
If you installed open-cell spray foam, you'll probably need to install a layer of vapor-retarder paint on your gypsum drywall to satisfy the code requirement for a vapor retarder.
For more information, seeVapor Retarders and Vapor Barriers.