Glossary: D


DamperA movable vane used to vary the volume of air passing through a duct, inlet, or outlet.
Damping CapacityThe ability of a material to absorb vibrational energy.
DarbyA tool used to level concrete in a form after it has been screeded.
Dead LoadLoad on a building element contributed by the weight of the building materials.
Decibel (dB)A unit for measuring sound energy or power. Adopted for convenience in representing vastly different sound pressures.
DeciduousDescribing trees that shed their leaves annually, as opposed to evergreen.
DecouplingSeparation of elements to reduce or eliminate the transfer of sound, heat or physical loads from one element to the other.
DeedA written instrument that is used to transfer real property from one party to another.
DeflectionDisplacement 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 LimitationMaximum 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).
DeformationChange 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.
Degree DaysThe number of degrees that the mean temperature for any day at a particular locatoin is below 65 degrees Fahrenheit.
DehumidificationThe removal of water vapor from the air.
DehumidifierA cooling, absorption, or adsorption device used for removing moisture from the air.
DehydrationThe removal of water vapor from any substance.
DelaminationThe separation of the plies in a laminate or plies from a base material.
Density(1) With regards to materials, a measurement that compares the amount of matter an object has relative to its volume.(2) In city or site planning, a measure of the number of people, families, etc. that occupy a specified area.
DesiccantAny absorbent, adsorbent, liquid, or solid that removes water or water vapor from a material.
DesiccationThe process of evaporating or removing water vapor from a material.
Design LoadCombination 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 PointThe temperature at which air becomes saturated (100 percent relative humidity) with moisture and below which condensation occurs. 
DewateringPumping subsurface water from an excavation to maintain dry and stable working conditions.
DiaphragmA horizontal roof or floor structural element designed to resist lateral loads and transmit them to shear walls (vertical resisting elements).
Dielectric StrengthThe maximum voltage a dielectric (nonconductor) can withstand without fracture.
DiffuserA circular, square, or rectangular air distributing outlet, usually in the ceiling, that has members to discharge supply air in several directions, mixing the supply air with the secondary air in the room.
Dimensional LumberLumber from 2 inches (50.8 mm) up to, but not including, 5 inches (127 mm) thick and 2 inches (50.8 mm) or greater in width.
Direct Current (DC)Electricity that flows in one direction.
Door BuckStructural 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 GlazingTwo parallel sheets of glass with an air space in between.
Double TeesT-shaped precast floor and roof units that span long distances unsupported.
Double-Hung WindowWindow sash that slides vertically and is offset in a double track.
Drainage(1) In buildings and infrastructure, the system by which excess water is collected, comducted, and dispersed.(2) In landscaping, the capacity of soil to receive and transmit water.
Dressed LumberLumber having one or more sides planed smooth.
DripInterruption 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.
Drip LineAn imaginary line on the ground described by the outermost branches of a tree.
DrivewayA vehicular path generally leading from a public street to a structure on private property.
Dry-Press ProcessThe process used to make bricks when the clay contains 10 percent or less moisture.
DrypackA stiff granular grout.
DrywallGeneric 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.
DuctA hollow tube through which air is circulated.
DuctileCapable of being stretched or deformed without fracturing (plastic deformation).
DuctilityA measure of the capability of a material to be stretched or deformed without breaking.
Dwelling UnitAn independent living area which includes its own private cooking and bathing facilities.
Dynamic LoadAny load that is nonstatic.