Roofing Terminology
(Click on a letter to learn more)
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Vapor Migration
The movement of water vapor from a region of high vapor pressure to a region of lower vapor pressure.
Vapor Pressure Gradient
A graph, analogous to a temperature gradient, indicating the changes in water vapor pressure at various cross sectional planes through a roof or wall system.
Vapor Retarder
A material designed to restrict the passage of water vapor through a wall or roof. In the roofing industry, a vapor retarder should have a perm rating of 0.5 or less.
Vent
An opening designed to convey water vapor or other gas from inside a building or a building component to the atmosphere, thereby relieving vapor pressure.
Vermiculite
An aggregate used in lightweight insulation concrete, formed by the heating and consequent expansion of a micaceous mineral.
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