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.
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Have there been independent tests done to study the effectiveness of vapor barriers and house wrap or which materials work best? I just had my house re shingled with a new shingles and trusted that the shingler knew what he was doing. He said the new shingles were the latest and greatest as was the underlay.
Wait, in one article you say "Most buildings don’t need polyethylene anywhere."
Then you say, "...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."
The truth: Great air sealing is critical to a warm home. That's why blower door tests are done. 5%? Really? Would you cut a 16" hole every 4' in a wall and still call that "effective"? On older homes, that use vapor barriers for air sealing, that don't have dense pack insulation or other effective air barriers added, 5% is a very big deal.
We live in Orlando Fl our home is made of concrete walls with drywall on the inside and insulation with a vapor barrier in between. I want to hang curtain rods, but my husband is afraid it will damage the vapor barrier if I drill through the drywall into the concrete. The screws are too long to hang on just the drywall. Will this hurt the vapor barrier?