Valley gutter—A channel used to carry off water from the "V" of a roof. This condition is usually created when two buildings are joined side by side.

Vapor barrier—(More precisely, vapor retarder). A layer of material used to appreciably reduce the flow of water vapor into thermal insulation from the high vapor pressure side.

Vapor migration—The movement of water vapor from a region of high vapor pressure to a region of lower vapor pressure.

Vapor pressure—The pressure exerted by a vapor that is in equilibrium with its solid or liquid form.

Vapor retarder—A material that provides a resistance to the transmission of water vapor under specified conditions.

Vent—An opening designed to convey water vapor or other gas from inside a building or a building component to the atmosphere.

Ventilator—An accessory usually used on the roof that allows air to pass through.

Vermiculite—An aggregate used in lightweight insulating concrete, formed by heating and expanding a micaceous mineral.

Viscoelastic—Characterized by changing mechanical behavior, from nearly elastic at low temperature to plastic, like a viscous fluid, at high temperature.

Vulcanizate—A term used to denote the product of the vulcanization of a rubber compound without reference to shape or form.

Vulcanization—An irreversible process during which a rubber compound, through a change in its chemical structure, e.g., cross-linking, becomes less plastic and more resistant to swelling by organic liquids, and elastic properties are conferred, improved, or extended over a greater range of temperature.