What is a Vapor Barrier? | |
A vapor barrier helps control the amount of moisture passing through the insulation and collecting inside exterior walls, ceilings and floors. In the winter, any moisture that passes through to these surfaces can accumulate and condense on the cold inner sides of exterior surfaces. Eventually, this condensation may blister the outside paint, form stains, or even damage the house structure. Whatever vapor barrier you choose, remember this important rule of thumb: in heating climates, install the vapor barrier toward the warm-in-winter side (living area) of the house. (In the Gulf Coast and Florida, local building practice may not call for an interior vapor barrier, or may call for the vapor barrier to be installed toward the outside in exterior walls. See installation instructions on package.) Types of Vapor Barriers Polyethylene When using unfaced insulation, install a separate vapor barrier using 4- or 6-mil polyethylene for most applications. Both 4- and 6-mil polyethylene are preferred because they are less likely to be damaged during construction. Kraft-Faced A kraft-faced vapor barrier is created by coating kraft with a thin layer of asphalt adhesive. The coated side of the kraft is then applied to the unfaced insulation material. The asphalt adhesive bonds the kraft and the insulation together. Foil-Faced A foil-faced vapor barrier is created by coating a foil-backed paper with a thin layer of asphalt adhesive. The coated side of the foil-backed paper is then applied to the unfaced insulation material. The asphalt adhesive bonds the foil-backed paper and the insulation together. NOTE: Never leave faced insulation exposed. The facings on kraft- and foil-faced insulation will burn and must be installed in substantial contact with an approved ceiling, wall, or floor construction material. If 4- or 6-mil polyethylene is used as a vapor barrier, cover with gypsum drywall or other approved interior material, as required by local codes, as soon as the insulation and polyethylene have been installed. Copyright 1996 Owens Corning. Reprinted with permission, HouseNet, Inc. |