V

Valley: The internal intersection of two sloping roof planes that runs from the eaves to the ridge. This intersection collects the greatest volume of water run-off.

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.

Vent: An opening or device used to permit air or vapors to exit an enclosed structure.

Ventilator: A device that circulates fresh air and expels stale air.

Vermiculite: One off a group of micaceous hydrated silicate minerals related to the chlorites and used in lightweight insulating concrete.

Viscosity: The resistance of a material to heat flow.

Viscous: Having a fairly high resistance to heat flow.

Void: An open space or a break in continuity; a gap.

Volatile: That which readily vaporizes; evaporates quickly.

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.

W

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 Cure: To control the rate of cure of materials such as concrete by spraying a fine mist of water on the surface.

Waterproof: Being resistant to moisture infiltration.

Waterproofing: The treatment of a surface or structure in order to prevent the passage of water under hydrostatic pressure.

Weather: To undergo degradation in quality and appearance which is caused by exposure to the sun, wind, rain, etc.

Weep Holes: Small holes used to permit moisture to drain that has gathered inside a building component.

Weld: To join multiple metal or PVC components together by heat fusion.

Wet Bulb Temperature: Air temperature in F as measured by a thermometer with a bulb covered by a damp wick.

Wet Film Thickness: The thickness of an uncured material such as a coating.

Wick: To convey liquid by capillary action.

Wind Clip: A clip that slips over the ends of tile, slate and other steep slope roofing materials in order to help prevent wind uplift damage.

Wind Load: The force that wind puts on structures.

Wind Uplift: (1) The upward displacement of a section of a roof system or component caused by movement of air from a location of higher air pressure, such as inside a building, to an area of lower air pressure, such as the surface of a roof during a windy day. Strong wind across the surface of a roof, especially at corners and along perimeters, creates low air pressure above the surface of the roof. Nature will automatically try to compensate for this by moving air from an area of higher pressure such as inside a building. If all penetrations and perimeters are not properly sealed, then "blow-off" can occur. (2) Displacement or blow-off of shingles or other roofing caused by the wind.

Wire Tie: A system for attaching heavy steep slope roofing materials such as slate r tile by using wire fasteners in addition to or in place of nails.

Woven Valley: A valley construction whereby the valley has a woven look which is effected by overlapping alternate courses of shingles from both sides of the valley.

Z

Z Bar or Z Section: A piece of steel formed in the shape of a "Z."

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.

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