Valley: A trough or gutter formed by the angle of two sloped roof sections intersecting at less than 180 degrees (when viewed from outside of the building). The opposite of a hip. Valleys are channels for water run-off and are usually subjected to greater hydrodynamic forces than other sloped roof areas.

Valley Flashing: The (typically) sheet metal material used to line a roof valley.

Valley Gutter: A specially-formed roof component installed in a roof valley to carry water down the roof while withstanding the greater hydrodynamic forces a valley normally experiences.

Valley Jack: A rafter that is attached to the ridge at one end and a valley rafter at the other. Shorter than a common rafter.

Valley Rafter: The rafter that follows and supports the line of a roof valley, connecting the ridge to the wall plate where two sloped roof sections intersect.

Valley Roof: A roof that has at least one valley.

Vane: See Weather Vane.

Vapor Barrier:  Vapor Retarder. A material, such as a waterproof coating or a sheet membrane, installed to prevent or reduce the movement of water vapor into a building component, such as a roof assembly, in order to prevent interstitial condensation.

Vapor Flow: The movement of water vapor from areas of high water content to areas of low water content as a function of temperature and relative humidity.

Vapor Migration: See Vapor Flow.

Vapor Pressure: Or equilibrium vapor pressure. The pressure at which a liquid and its vapor are in equilibrium at a specific temperature; the pressure of the vapor resulting from evaporation of a liquid in contact with the liquid in an enclosed area.

Vapor Retarder: See Vapor Barrier.

Variance: Authorization from the responsible authority permitting construction that deviates from the rules set out in the governing code.

Veneer: 1. Masonry Veneer: A non-structural facing layer of (usually) brick. 2. Wood Veneer: A thin layer of wood glued to a substrate such as particle board to give the appearance of solid wood. One of the thin layers of wood which are glued together to create plywood, each with the grain at a right angle to the next to improve structural strength and stability.  

Veneer Tie: A strip of metal used to hold a masonry veneer to the wall that it covers.

Vent: An opening or device designed to transfer air, heat, water vapor, or exhaust gases from an enclosed structure into the atmosphere. Also see Intake Ventilation.

Vent Cap: A piece that protects the open end of a vent stack from precipitation or debris while still permitting air flow.

Ventilation: The process of intentionally allowing or forcing air to enter and exit an enclosed space.

Ventilator: A device that forces the intake and expulsion of air in an enclosed space.

Vent Pipe: A pipe that serves as a vent.

Vent Sleeve: A pre-formed flashing unit designed to fit around a vent pipe.

Vent Stack: A plumbing vent that typically penetrates the roof.

Verge: The projecting edge of the roofing material (such as tiles) above a gable.

Vergeboard: See Bargeboard.

Verge Trim: Roof component which protects and secures the verge of a roof.

Verge of Popcorn Texture: The roughest surface texture of a spray polyurethane foam roof that is considered acceptable for receiving the protective waterproof coating. Extra coating material is required for proper coverage and this texture is therefore considered undesirable.

Vermiculite: A hydrous phyllosilicate mineral which undergoes significant expansion when heated. Vermiculite is used as an aggregate in some lightweight insulating concretes and as a loose-fill insulation.

Vibration Isolator: A support for rooftop equipment designed to reduce the amount of vibration transmitted from the equipment to the building structure.

Viscosity: The measure of a fluid’s resistance to flow.

Viscous: Highly resistant to flow.

Visor Roof: See Pent Roof.

Visual Inspection: Inspection by sight alone, without the use of any testing devices.

Vitrified Brick: Glazed brick that is impervious to water penetration.

VOC: Volatile Organic Compounds.

Void: An empty space or break in continuity. In a built-up roof, an area between two felts that has no bitumen.

Volatile: Describing something which easily vaporizes or evaporates quickly.

Volatile Organic Compounds: Organic chemicals having a high vapor pressure at room temperature, causing them to easily transform from liquid or solid into vapor at an ordinary temperature and pressure.

Vulcanization: A chemical process that improves the strength and resiliency of natural or synthetic rubber by combining the material with sulfur or similar additives under heat and pressure.