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Building Construction - Moisture/Vapor Barrier
Moisture or water vapor moves into building cavities in three ways:
1. With air currents,
2. By diffusion through materials,
3. By heat transfer. Of these three, air movement accounts for more than 98% of all water vapor movement in building cavities. A vapor retardant and an air barrier serve to reduce this problem, but are not necessarily interchangeable.
Vapor retardant slow the rate of vapor diffusion into the thermal envelope of a structure. Other wetting mechanisms, such as wind-borne rain, capillary wicking of ground moisture, air transport (infiltration), are equally important.
1. With air currents,
2. By diffusion through materials,
3. By heat transfer. Of these three, air movement accounts for more than 98% of all water vapor movement in building cavities. A vapor retardant and an air barrier serve to reduce this problem, but are not necessarily interchangeable.
Vapor retardant slow the rate of vapor diffusion into the thermal envelope of a structure. Other wetting mechanisms, such as wind-borne rain, capillary wicking of ground moisture, air transport (infiltration), are equally important.
Extracted from Wikipedia
