Q: My home has about 6 inches of fiberglass insulation in the attic, and I’m planning to add more. Should I use faced insulation?
A: No; only use unfaced fiberglass insulation. The facing acts as a vapor retarder that helps reduce the amount of moisture entering a wall, ceiling or floor. In hot climates, your original layer of insulation should already have a vapor retarder facing the living area of your home. If you add a second vapor retarder with another layer of faced insulation, any moisture that does get through the first layer may condense on the second. This can cause water stains on the ceiling and could lead to mold and structural damage. When the joist cavity is full, install the second layer of unfaced insulation perpendicular to the first, covering the ceiling joists to reduce heat loss through the wood. Otherwise, install the second layer right on top of the first layer, between the joists.