Drywall Repairs and Vapor Barriers
While air barriers need to be continuous and without holes to work effectively, vapor barriers don’t have to be free of holes.
When patching drywall on an exterior wall, it’s almost impossible not to damage the vapor barrier. What can be done to ensure that a vapor barrier stays uninterrupted?
— Levi Hymes, via email
Martin Holladay: You don’t mention what type of vapor barrier you’re talking about, but I’m guessing that you are referring to a layer of polyethylene. While air barriers need to be continuous and without holes to work effectively, vapor barriers don’t have to be free of holes. A vapor barrier that is riddled with holes that make up 5% of the vapor barrier’s area is still 95% effective. Patch the polyethylene with housewrap tape if you can, but don’t worry about it too much. U.S. building codes don’t require an interior vapor barrier. In climate zones 5 through 8 and marine zone 4, most U.S. building codes require an interior vapor retarder (a more permeable layer than a vapor barrier). The requirement for an interior vapor retarder can be met with a layer of vapor retarder paint.