Warp—In textiles, the lengthwise yarns in a woven fabric.

Water vapor transmission—(WVT)—Water vapor flow normal to two parallel surfaces of a material, through a unit area, under the conditions of a specified test such as ASTM E96. Customary units are grains/h«ft2.

Waterproofing—Treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.

Weatherometer—An instrument which is used to subject specimens to accelerated weathering conditions, e.g., rich U.V. source and water spray.

Web—That portion of a structural member between the flanges.

Web member—A secondary structural member interposed between the top and bottom chords of a truss.

Wet—A condition where free water is present in a substance.

Wet storage staining—Corrosion products which develop as a result of moisture and limited access to air when coated steels are in contact with one another.

Wicking—The process of moisture movement by capillary action as contrasted to movement of water vapor.

Wide flange structural shape (W-shape)—A hot rolled section having parallel flange surfaces.

Wind load—A load caused by the wind blowing from any horizontal direction.

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