WALKWAYS: High-traffic and high-service areas on a rooftop, particularly those with vents, hatches, and heavy-duty air conditioning units, that have been reinforced with extra coating and granules to prevent damage to the polyurethane foam system.
WATER ABSORPTION: The percentage increase in the weight of a specimen after immersion in water for a specified time. For SPFs, water absorption is reported as a volume percentage in accordance with ASTM D 2842.
WATER-BLOWN FOAM: A spray polyurethane foam formulation of any density that uses water as the predominant (reactive) blowing agent.
WATER-RESISTANT BARRIER (WRB): Materials or a combination of materials that are primarily designed to be used to keep liquid water from entering the building enclosure. Water-resistive barriers are combined with flashing and other materials to ensure that there is a shingled assembly to direct liquid water which passes on the cladding system to the exterior. Also known as a weather-resistive barrier.
WATER VAPOR PERMEABILITY: See PERMEABILITY; WATER VAPOR.
WATER VAPOR PERMEANCE: See PERMEANCE; WATER VAPOR.
WATER VAPOR TRANSMISSION: The migration of water vapor.
WATER VAPOR TRANSMISSION RATE: The rate at which water vapor will diffuse through a unit area of material. Units are usually grains/ft2•hr.
WEATHER-RESISTIVE BARRIER: See WATER-RESISTANT BARRIER.
WET-BULB TEMPERATURE: The temperature of air as registered by a thermometer whose bulb is covered by a water wetted wick. Units are °C or °F.
WET-FILM GAUGE: A gauge for measuring the thickness of wet coating as applied to a flat smooth surface.
WET-FILM THICKNESS: The thickness, expressed in mm or mils, of a coating or mastic as applied, but not cured. Compare to DRY-FILM THICKNESS. (See also DRY-FILM THICKNESS; MIL.)
WINDSCREEN: A device to minimize the effects of wind on coating or polyurethane foam application.
WIND UPLIFT: The force caused by the obstructions causing a drop in air pressure deflection of wind at roof edges, roof peaks, or immediately above the roof surface.
WRB: See WATER-RESISTANT BARRIER.WUFI: A computer-based, one-dimensional model to simulate transient heat and moisture transfer through building assemblies, developed by the Fraunhofer Institute in Holtzkirchen, Germany. WUFI can be used to predict condensation, moisture accumulation, and mold growth potential in building assemblies. WUFI is an acronym for the German phrase Wärme Und Feuchte Instationär (translation: transient heat and moisture).
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