Building Construction
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 retarder and an air barrier serve to reduce this problem, but are not necessarily interchangeable.
Vapor retarders 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.
Read more about this topic: Vapor Barrier
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