Glossary of Roofing and Waterproofing Terms

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Water Absorption: the amount of water absorbed by a material after immersion for a prescribed period of time. May be expressed as a percentage of the original weight of the material.

Water Cure: a method of curing a material, such as concrete, by applying a fine mist of water over the surface to control the rate of moisture evaporation from the material.

Water Cutoff: see Cutoff.

Water Stop: a diaphragm used across a joint as a sealant, usually to prevent the passage of water.

Water Table: the level within the ground below which the soil is saturated with water.

Water Vapor Transmission: a measure of the rate of transmission of water vapor through a material under controlled laboratory conditions of temperature and humidity. Customary units are grains/h~ft2. (See ASTM Standard E 96.)

Waterproof: the quality of a membrane, membrane material, or other component to prevent water entry.

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

Wear Course: the top layer of surfacing that carries pedestrian or vehicular traffic. Sometimes referred to as wearing surface.

Wear Surface: see Wear Course.

Weather Infiltration: the negative condition where rain or snow penetrate the roof. The condition is typically wind-driven.

Weatherometer: an instrument used to subject material specimens to accelerated weathering conditions.

Weep Holes: small openings whose purpose is to permit drainage of water that accumulates inside a building component (e.g., a brick wall, skylight frame, etc.).

Weld: to join pieces of metal together by heat fusion.

Wet: a condition where free water is present in a substance.

Wet Bulb Temperature: the temperature of air as registered by a thermometer whose bulb is covered by a water wetted wick. Units are F.

Wet Film Thickness: the thickness, expressed in mils, of a coating or mastic as applied but not cured. For comparison, see Dry Film Thickness.

Wicking: the process of moisture movement by capillary action, as contrasted to movement of water vapor.

Wind Clip: a steep-slope roofing attachment device that fits over the butt end of tile, slate, and stone to help secure individual roofing units from wind-uplift.

Wind Load: force exerted by the wind on a structure or part of a structure.

Wind Uplift: the force caused by the deflection of wind at roof edges, roof peaks or obstructions, causing a drop in air pressure immediately above the roof surface. This force is then transmitted to the roof surface. Uplift may also occur because of the introduction of air pressure underneath the membrane and roof edges, where it can cause the membrane to balloon and pull away from the deck.

Windward: being in or facing the direction toward which the wind is blowing. The side exposed to the prevailing wind.

Wire Tie System: a scheme of attachment for steep-slope roofing units (e.g., tile, slate, and stone) utilizing fasteners (nails and/or screws) in conjunction with wire to make up a concealed fastening system.

Work Slab: see Mud Slab.

Woven Valley: a method of valley construction in which shingles or roofing from both sides of the valley extend across the valley and are woven together by overlapping alternate courses as they are applied.

Wythe: a masonry wall, one masonry unit, a minimum of two inches thick.

Z section: a member formed from coiled steel stock in the shape of a "Z."

Zinc: a metal that has application considerations including high expansion-contraction rates and low-temperature restrictions.


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