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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 MIGRATION- The natural movement of water vapor from regions of higher vapor pressure to regions of lower vapor pressure.

VAPOR PRESSURE- The pressure at which a liquid and its vapor are in equilibrium at a definite temperature.

VAPOR RETARDER- A material used to restrict the passage of water vapor through a roof assembly.

VEINING- The characteristic lines or "stretch marks" which develop during the aging process of soft bitumens. Veneer- Any of the thin layers of wood glued together to make plywood.

VENT- An opening or device used to permit air or vapors to exit an enclosed structure.

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

VENTILATION SHORT CIRCUIT- The disruption of air flow in an intake-exhaust ventilation system. For instance, if vents such as turbine vents or gable vents are placed in between the intake vents and exhaust vents (such as soffit and ridge vents) then the draw created by the stack effect will be disrupted and the ventilation system will be much less effective.

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, OR 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.

VULCANIZE- To improve the strength, resiliency, and freedom from stickiness and odor of rubber, for example, by combining with sulfur or other additives in the presence of heat and pressure.

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WALKWAYS- Designated areas for foot traffic on roofs.

WATER ABSORPTION- The increase in weight of a test specimen expressed as a percentage of its dry weight after being immersed in water for a specified time at a given temperature.

WATER GUARD- A turned up edge on valley metal or continuous wall flashing; used to prevent water migration under the roof system.

WARM WALL- The finished wall inside of a structure, used in roofing to determine how to install waterproof underlayments at eaves.

WARRANTY- The written promise to the owner of roofing materials for material related problems.

WATER STOP- A device designed to protect the exposed edge of a partially installed BURM from water entrance.

WATERPROOFING- The process where a building component is made totally resistant to the passage of water and/or water vapor.

WATER VAPOR- Moisture existing as a gas in air.

WEEP HOLE- A hole that allows for drainage of entrapped water from masonry structures.

WELD- The joining of components together by fusing. In thermoplastics, refers to bonding together of the membrane using heat or solvents.

WIND UPLIFT- The upward force exerted by wind traveling across a roof.

WRINKLE- A raised pattern of ridges running in a random fashion in a BUR.

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ZINC- A bluish-white, lustrous metallic element that is brittle at room temperature but malleable with heating. It is used to form a wide variety of alloys including brass, bronze, various solders, and nickel silver, in galvanizing iron and other metals, for electric fuses, anodes, and meter cases, and in roofing, gutters, flashings, edge metals and also for various household objects. Atomic number 30; atomic weight 65.37; melting point 419.4 °C; boiling point 907 °C; specific gravity 7.133 (25 °C); valence 2.

ZONOLITE- A lightweight, insulating concrete composed of portland cement, water, and vermiculite aggregate.