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Vacuum breaker: A device in a water supply line that introduces air into the line if water pressure is lost, so as to pre vent contaminated water from being drawn into the line.
Vapor barrier: See Vapor retarder.
Vapor pressure: The partial pressure exerted by water vapor in the air.
Vapor retarder: A sheet material or coating that is highly resistant to the passage of water vapor, used to prevent water from condensing inside a wall or ceiling. Often called, incorrectly, a vapor barrier.
Variable air volume system (VAV): A heating and cooling system for a building that regulates temperature by varying the amount of conditioned air that is delivered to each space or zone.
Vasomotor regulation: The human body’s expansion or contraction of blood vessels as a means to regulate body temperature.
Vault: A structural device consisting of an arch translated along an axis perpendicular to its plane, or a combination of such forms.
VAV: See Variable air volume system.
Vent, plumbing: A pipe that opens a system of waste piping to the air so that it remains always at atmospheric pressure and avoids trap siphoning.
Ventilation, infiltration: Renewing the air in a building by means of air passing through cracks and holes in the building enclosure.
Ventilation, mechanical: Renewing the air in a building with electrically powered fans that introduce a %age of out door air as they recirculate indoor air.
Ventilation, natural: Renewing the air in a building using only the forces of wind and /or convection.
Vernal equinox: The day in late March when the north-south axis of the earth lies perpendicular to the sun’s rays. Day and night have the same length on the vernal and autumnal equinoxes.
Visual task: The focus of one’s attention in a luminous environment.
Voussoir: A wedge-shaped component of an arch.
Waffle slab: A two-way concrete joist system, which resembles a waffle when viewed from beneath.
Wainscot: An interior wall facing that starts from the floor or baseboard but does not extend to the ceiling.
Warm-air heating system: A system that uses air as a medium to transport heat to the interior of a building.
Wash: A slope on a top surface that causes it to shed water.
Water hammer: A loud knocking sound in water supply pipes caused by the instantaneous deceleration to zero of water in the pipes.
Water, hard: Water that is rich in calcium ions.
Water softener: A device that replaces calcium ions in water with sodium ions.
Weatherstripping: Linear gaskets, pads, metal strips, brushes, or other devices designed to reduce air leakage through cracks around doors and windows.
Weep hole: An opening in the exterior of a wall or window frame that drains to the exterior any water that may accumulate within.
Well: A hole drilled or dug into the ground for the purpose of obtaining water.
Whispering gallery: A concave surface or surfaces that focus sound in such a way that faint sounds can be heard over comparatively long distances.
Wind tunnel: A laboratory device that houses a scale model and simulates the flow of wind around buildings or other objects with a small-scale flow of air around the model.
Wired glass: Glass sheet material formed around a wire mesh that serves to hold the glass together if it should break during a fire.
Working drawings: The technical drawings from which a building is built.
Wythe: A vertical layer of a masonry wall that is one brick, one block, or one stone thick.
Yield point: The stress at which a material begins to distort permanently.