Glossary

Construction Dictionary and Glossary of Construction Terms

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D

Term	Definition
Dead Load	Load on a building element contributed by the weight of the building materials.
Decibel (dB)	Adopted for convenience in representing vastly different sound pressures. The sound pressure level (SPL) in decibels is 10 times the logarithm to the base 10 of the squared ratio of the sound pressure to a reference pressure of 20 micropascals. This reference pressure is considered the lowest value at 100 Hz that the ear can detect. For every 10 dB increase or decrease in SPL, a sound is generally judged to be about twice or half as loud as before the change.
Decoupling	Separation of elements to reduce or eliminate the transfer of sound, heat or physical loads from one element to the other.
Deflection	Displacement that occurs when a load is applied to a member or assembly. The dead load of the member or assembly itself causes some deflection as may occur in roofs or floors at mid-span. Under applied wind loads maximum deflection occurs at mid-height in partitions and walls.
Deflection Limitation	Maximum allowable deflection is dictated by the bending limit of the finish material under the required design load (e.g., usually 5 psf for interior partitions). Often expressed as ratio of span (L) divided by criterion factor (120, 180, 240, 360). For example, in a 108 or 120" high wall, allowable deflection under L/240 criterion equals 120"/240 or 1/2" maximum. Selection of limiting heights and spans are frequently based on minimum code requirements and accepted industry practice as follows: (a) L/120 for gypsum panel surfaces and veneer plaster finish surfaces, (b) L/240 for conventional lath and plaster surfaces, (c) L/360 for mechanically attached marble or heavy stone to walls; however, support for its own weight should be from the floor or separate supports. Although some building codes permit these deflections, more conservative criteria are frequently advised so that applied loads are not visible or aesthetically unacceptable.
Deformation	Change in shape of a body brought about by the application of a force internal or external. Internal forces may result from temperature, humidity or chemical changes. External forces from applied loads can also cause deformation.
Design Load	Combination of weight (dead load) and other applied forces (live loads) for which a building or part of a building is designed. Based on the worst possible combination of loads.
Dew Point	The temperature at which air becomes saturated with moisture and below which condensation occurs.
Door Buck	Structural element of a door opening. May be the same element as the frame if frame is structural, as in the case of heavy steel frames.
Double-Hung Window	Window sash that slides vertically and is offset in a double track.
Drip	Interruption or offset in an exterior horizontal surface, such as a soffit, immediately adjacent to the fascia. Designed to prevent the migration of water back along the surface.
Drywall	Generic term for interior surfacing material, such as gypsum panels, applied to framing using dry construction methods, e.g., mechanical fasteners or adhesive. See SHEETROCK brand Gypsum Panels.