Q: When installing insulation, on which side of the wall should a vapor barrier be applied, the inside or outside?
A: Most insulation requires a vapor barrier on the inside of the house wall due to the increased humidity generated when the interior temperature is warmed during winter. Normal, everyday living can put from 5 to 10 pounds of moisture into the home each day. In the winter months this moisture can accumulate and condense on the cold inner sides of exterior surfaces. This can cause paint to blister, stains to form on drywall, even damage the building’s structure. Vapor barriers can help control the amount of moisture passing through insulation and collecting inside exterior walls and floors. A vapor barrier in the attic usually isn’t required as long as you have adequate ventilation.
