A vapor retarder, also known as a vapor barrier, is a type of building material used to prevent the diffusion of water vapor through walls, ceilings, and roofs. Water vapor can cause significant damage to building materials, leading to structural decay and the growth of mold and mildew. Vapor retarders are designed to control the flow of moisture through a building envelope by reducing the amount of water vapor that can enter or exit the structure.
Vapor retarders can be made from a variety of materials, including foil, plastic, and paper. The effectiveness of a vapor retarder is determined by its perm rating, which measures the amount of water vapor that can pass through the material over a given period of time. The lower the perm rating, the more effective the vapor retarder is at preventing the flow of moisture.
When installing a vapor retarder, it is important to ensure that it is properly sealed and installed in the correct location. A vapor retarder is typically installed on the warm side of the insulation, which is the side that faces the interior of the building. It should be installed in such a way that it forms a continuous barrier, with no gaps or holes that would allow moisture to pass through.
Overall, the use of a vapor retarder is an important consideration for any building project, as it can help to prevent moisture-related damage and improve the overall durability and longevity of the structure.