Glossary – D

Deck: A structural component of the roof of a building. The deck must be capable of safely supporting the design dead and live loads, including the weight of the roof systems, and the additional live loads required by the governing building codes and provide the substrate to which the roofing or waterproofing system is applied the structural surface of a building to which a roof assembly is installed. Decks are either non-combustible (e.g. corrugated metal, concrete, or gypsum) or combustible (e.g. wood plank or plywood).


Degree Day: A unit that represents one degree of difference from a given point (as 65°) in the mean daily outdoor temperature and is used especially to measure heat requirements. A unit used in estimating the fuel consumption for a building; equal to the number of degrees that the mean temperature, for a 24-hour day, is below the “base temperature”; the base temperature is taken as 65°F (18.3°C) in the U.S.A.


Delta T: The temperature differential between two objects. ∆T


Delamination: A type of failure for composite materials. Repeated cyclic stresses or impacts can cause layers to separate, forming a mica-like structure of separate layers, with significant loss of mechanical toughness.


Dew Point: The temperature at which a vapor (as water) begins or would begin to condense. Dew-Point Temperature: (1) The temperature at which air becomes saturated with water vapor. (2) The temperature at which air has a relative humidity of 100%.


Direct Current (DC): Current flows only in one direction in a circuit.


Dielectric: Insulating material.


Dielectric Constant: Ability of a material to withstand electric stress before breaking down and becoming a conductor. The dielectric strength of air is 1.


Distance/Target Size Value: A numerical value that may be used to determine the measurement area of an infrared imaging radiometer at a given distance. This value may also be used to calculate minimum target size at a given distance.


Diffuse Reflector: A surface that produces a diffuse image of a reflected source.


Doctor of Veterinary Medicine: A professional person qualified and authorized to give medical care
and treat disease, disorder, and injury in non-human animals.


DOE: U.S. Department of Energy, Washington D.C.