A vapor barrier is any material used during damp proofing, which helps to resist moisture through a floor, ceiling or wall. Depending on the material used, there is a different moisture vapor transmission rate that will help prevent permeability. A vapor retarder is categorized with impermeable (oil-based paint, vinyl wall coverings, plywood or asphalt-backed kraft paper), semi-permeable (heavy asphalt-impregnated building papers, latex-based paints or unfaced expanded polystyrene) or permeable (unfaced fiber glass insulating, unpainted stucco, polymer-based exterior air barrier films).
Moisture moves through a building several ways including by heat transfer, by diffusion through materials and through air currents. A vapor retarder helps to reduce this problem. The most effective installation is during construction, however many experts believe it may be impractical to design a home around this type of assembly. The goal of these materials is to control the wetting of building on both the interior and the exterior. In many countries such as the United States and Canada, they are now a part of building codes. This makes having a home inspection in an older home important to ensure that your home is up to code and protected.