Valley - The internal angle formed by the intersection of two sloping roof planes.

Vapor retarder - Any material used to prevent the passage of water vapor.

Vent - Any outlet for air that protrudes through the roof deck such as a pipe or stack. Any device installed on the roof, gable or soffit for the purpose of ventilating the underside of the roof deck.

Vent sleeve - See collar.

VALVE - A device to stop, start or regulate the flow of liquid or gas through or from piping.

VAPOR- The gaseous form of any substance.

VAPOR RETARDER (BARRIER) - A membrane which is placed between the insulation and the roof deck to retard water vapor in the building from entering the insulation and condensing into liquid water.

VEINING - In roofing, the characteristic lines or "stretch marks" which develop during the aging process of soft bitumens.

VENT PIPE - A vertical pipe of relatively small dimensions which protrudes through a roof to provide for the ventilation of gasses.

VENTILATOR - Device installed on the roof for the purpose of ventilating the interior of the building.

VENTING - The process of installing roof vents in a roof assembly to relieve vapor

Pressure; the process of water in the insulation course of the roof assembly

evaporating and exiting via the roof vents.

VENT STACK - A vertical vent pipe installed for the purpose of providing circulation of air to and from any part of a drainage system.

VENT SYSTEM – In plumbing, a system to provide a flow of air to or from a drainage system or to provide circulation of air within such system to protect traps seals from siphonage and back pressure.

VERMICULITE - An aggregate somewhat similar to perlite that is used as an aggregate in lightweight roof decks and deck fills. It is formed from mica, a hydrous silicate.

VISCOSITY - The internal frictional resistance offered by a fluid to change of shape or to the relative motion or flow of its parts.

VISIBLE LIGHT TRANSMITTANCE – The percentage of visible light (390 to 770) nanometers) within the solar spectrum that is transmitted through glass.

VISUAL MOCK UP – Small scale demonstration of a finished construction product.

VOLTAGE - The driving force behind the flow of electricity somewhat like pressure is in a water pipe.

VOLTMETER - measures the voltage flowing through a circuit. The circuit must be closed to allow the voltage to flow.

VALLEY - A term applied to a depressed angle formed by the meeting of two inclined slopes of a roof.

VAPOR - The gaseous form of any substance.

VAPOR RETARDER (BARRIER) - A membrane which is placed between the insulation and the roof deck to retard water vapor in the building from entering the insulation and condensing into liquid water.

VEINING - The characteristic lines or "stretch marks" which develop during the aging process of soft bitumens.

VENT PIPE - A vertical pipe of relatively small dimensions which protrudes through a roof to provide for the ventilation of gasses.

VENTILATOR - Device installed on the roof for the purpose of ventilating the interior of the building.

VENTING - 1. The process of installing roof vents in a roof assembly to relieve vapor pressure.

2. The process of water in the insulation course of the roof assembly evaporating and exiting via the roof vents.

VERMICULITE - An aggregate somewhat similar to perlite that is used as an aggregate in lightweight roof decks and deck fills. It is formed from mica, a hydrous silicate.

VERTICAL APPLICATION - Roll roofing laid parallel to the slope of a roof.

VISCOSITY - The internal frictional resistance offered by a fluid to change of shape or to the relative motion or flow of its parts.