This can be a problem where brick is installed over building paper and vapor permeable sheathing. This can be a problem when there is also a vapor barrier on the exterior. This can be a problem in any below grade space. This can be a problem in any air-conditioned enclosure. Vapor barriers installed on the interior of assemblies prevent assemblies from drying inward. However, they often prevent assemblies from drying. Vapor barriers were originally intended to prevent assemblies from getting wet. Incorrect use of vapor barriers is leading to an increase in moisture related problems. It is frightening indeed that construction practices can be so dramatically influenced by so little research and reassuring indeed that the inherent robustness of most building assemblies has been able to tolerate such foolishness. Rose (1997) regales readers of this history. The history of cold climate vapor barriers itself is a story based more on personalities than physics. Vapor barriers are also a cold climate artifact that have diffused into other climates more from ignorance than need. In the strictest sense air barriers are also vapor barriers when they control the transport of moisture-laden air.Īn excellent discussion about the differences between vapor barriers and air barriers can be found in Quirrouette (1985). This is a type of migration of water vapor. When this air moves from location to location due to an air pressure difference, the vapor moves with it. The confusion arises because air often holds a great deal of moisture in the vapor form. Confusion on the issue of vapor barriers and air barriers is common.
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