Roof Online’s Glossary of Roofing Terms
Words that Start with the Letter “W”
Last updated March 3, 2020
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Wagon Roof: See Barrel Roof.
Walkway Pads: Durable pieces of material that can resist physical damage that are installed on top of the roof covering to form walkways in high foot traffic areas on a roof, such as from an access point (like a hatch) to items (like HVAC units) which require regular maintenance.
Wall Dormer: A dormer whose face is an unbroken continuation of the face of the wall below.
Wall Plate: A horizontal structural member at the top of a wall that supports the members, such as the rafters, that support the roof.
Warp: In weaving, the lengthwise yarns that are held in place on a frame while the weft yarns are inserted through them crosswise during the weaving process.
Warranty: A written, legally-binding guarantee or promise issued by a manufacturer or roofing contractor to the end consumer of roofing materials or services that the materials or installed system will perform as expected under the stated conditions. A warranty is generally an element of the roofing contract, expires after a stated period of time, and requires the roofing manufacturer or roofing contractor to repair or replace, at no charge, a roof system or the part of a roof system which does not perform as promised.
Wash: The slope of the upper surface of a building element such as wall coping or a window sill designed to shed water away from the building.
Water Absorption: A physical property of a material, indicating the amount of water that will be absorbed by the material when immersed in water. Typically expressed as the weight increase of the material, as a percentage of its dry weight, after the material has been immersed in water for a specified time at a given temperature.
Water Cure: A technique for controlling the rate of cure of a material, such as concrete, by applying water in the form of a fine mist to the surface to regulate moisture evaporation from the material.
Water Cut-off: See Overnight Tie-in.
Water Cut-off Mastic: A mastic intended to be used as a sealing agent between various membranes and substrates and typically applied at membrane terminations using a compression-type seal.
Waterproof: Impervious to water.
Waterproofing: 1. The process of making a surface or structure impervious or resistant to water. 2. The material applied during this process.
Water Resistant: Able to withstand light or temporary exposure to water but not impervious to water.
Water Stop: Material installed over a joint in a concrete structure to prevent water from entering the joint.
Water Testing: A method of identifying leaks in the building envelope through the controlled application of water to the surface of a building component. Also see Flood Testing.
Water Trough: The part of a roof valley that channels the water running down it.
Water Vapor: The gaseous phase of water.
Water Vapor Transmission Rate: A measure of the passage of water vapor through a material under specific conditions of temperature and humidity.
WBT: Wet Bulb Temperature.
Wear Course: Or wearing course. The top layer of a surfacing application designed to withstand foot or vehicle traffic.
Weather: The exposed part of an installed wood shingle.
Weather Block: Mortar used to fill openings in tile roofs to prevent infiltration by water or debris.
Weathering: The degradation in quality and appearance which is caused by normal exposure to the atmosphere, sunlight, and living things.
Web: The interior members of a truss.
Weft: See Warp.
Weld: To join metal or thermoplastic components together by heat fusion.
Wet Bulb Temperature: The temperature of the air as measured by a thermometer with a bulb covered by a damp wick.
Wet Film Thickness: The thickness of a coating after it is applied but before it cures.
Wicking: The movement of a liquid by capillary action.
Wind Clip: A device that secures the butt end of an individual piece of a steep-slope roof covering such as tile or slate to prevent wind uplift damage.
Wind Load: A type of structural load. The force exerted on a structure by wind.
Wind Scour: The erosion of the protective surfacing on a roof due to the action of the wind. Usually occurs in the corner of a roof, where wind vortices form.
Wind Uplift: The force that acts on a roof assembly due to the drop in air pressure above the surface of the roof when wind blowing across the roof is deflected upward by the side of the building or other obstruction. Air pressure below the roof tends to increase at the same time due to air infiltration into the building through openings such as doors, windows, or cracks, creating a pressure differential that forces the roof membrane upwards.
Windward: Facing the prevailing wind.
Withe: A continuous vertical section of a masonry wall, one unit wide.
Woven Valley: A method of installing asphalt shingles in a roof valley in which the shingles from each side of the valley extend across the valley and are woven together by having the shingles from one side overlap the shingles from the other side in alternating courses. In a woven valley, the valley flashing is not exposed and the shingles form the surface of the water trough.