Dead load: The weight of building components and other loads that do not change over time. Decibel: A measure of the intensity of sound. Deciduous tree: A tree that drops all its leaves in winter. Deflection: The amount by which a given point on a structural member moves when the member is placed under load. Dehumidifier: A machine that removes moisture from the air, usually by condensing it on metal coils that are cooled by a compression cycle. Dewatering: Lowering the level of water in the soil of a building site in order to keep the excavation dry during foundation work. Dew point: The temperature at which water will begin to condense from a given mass of air. Diffraction: The bending of light or sound waves by their being passed over sharp edges, especially a series of edges whose spacing is similar to the wavelength of the light or sound. Direct current: A flow of electricity that is constant in polarity and intensity. Direct gain system: Heating a building by admitting sunlight into the inhabited space. Dome: A structural form consisting of an arch rotated about its vertical axis. A dome is often a hemisphere or some other portion of a sphere. Double-envelope building: A building with two independent, complete enclosures, one inside the other, with an air space between. Double-hung window: A window with two sashes, both of which slide on vertical tracks. Double-skin facade: A building wall with two layers separated by an air space. Downspout: A vertical pipe that conducts water runoff from a roof to the ground. Drainage composite: A thick, highly porous material placed against the outside of a foundation wall so that ground water approaching the wall falls down through the material to drainage pipes at the base of the wall instead of reaching the outside surface of the wall. Drip: Any building feature that causes water to fall clear of the building at that point rather than run along the surface. Dual duct system: An air conditioning system in which parallel ducts carry warm air and cool air. In each room of the building, thermostatically controlled dampers regulate the relative amounts of air from each of the two ducts that are mixed to achieve the desired temperature. Duct: A round or rectangular tube through which air is circulated. Eave: The lowest edge of a sloping roof. Echo: A reflection of sound that occurs long enough after the original sound to sound like a separate sound. Effluent: The supernatant of decomposed sewage. Elastic modulus: The ratio of stress to deformation in a given material; a measure of the stiffness of a material. Emittance: A measure of the ability of a material to radiate heat to another body. Equinox: A position in the earth's orbit where the north and south poles are equidistant from the sun. There are two
Concrete, air-entrained: Concrete that contains microscopic air bubbles. Air-entrained concrete flows more freely when freshly mixed and is much more resistant to freeze-thaw damage than ordinary concrete. Condensate: A liquid created by condensing a gas, such as the liquid water produced when moist air contacts a cold surface. Condensation: The changing of a material from a gaseous state to a liquid state. Condenser: A component of a steam-driven power plant in which spent steam is cooled to return it to a liquid state. Conduction: The passage of heat or electricity through a solid material. Conduit: A plastic or metal tube through which electric wires pass. Constant air volume system (CAV): A heating and/or cooling system in which the rate of air circulation is constant, but the temperature of the air varies. Continuity: In a structure, the property of having structural elements joined rigidly together so that they act as a single unit. Control joint: An intentional, usually straight-line crack in a surface of material that tends to shrink, used to avoid random cracking in the material. Convection: Circulation that is powered by the difference in density between warm and cool air or water. Convective: Using convection as a mode of heat transfer. Convector: A device for heating air by means of steam or hot water that circulates through metal tubing that is exposed to the air. A convector usually has many metallic fins attached to the tubing to increase its surface area. The fin-tube assembly is usually housed in a sheet-metal enclosure with openings for the circulation of air. Cooling, radiational: The cooling of the earth at night by direct radiation of terrestrial heat into the blackness of space. Corbel: A masonry structural device in which each brick or stone projects slightly over the one below it. Crawl space: A continuous access area, not tall enough to stand in, beneath the ground floor of a building. Creep: The long-term shortening of concrete under compressive stress. Cross connection: A faulty plumbing installation that allows sewage or contaminated water to be drawn into water supply pipes if water pressure in the pipes should fail. Crown: A slight upward curvature in the paving of a road; a curvature in a piece of lumber. Curtain board: A noncombustible sheet material that hangs from the ceiling of an industrial building to help restrict the spread of fire through the building. Damper: A metal flap that acts as a valve for air flow in a duct, a fuel-burning appliance, or a fireplace. Damp-proof coating: A thin asphaltic coating applied to the outside of a building foundation wall in order to limit the penetration of moisture through the wall. Daylighting: Lighting the interior of a building with direct or indirect light from the sun. DC: See Direct current.
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