D

DEAD LEVEL: Absolutely horizontal or zero slope. 

DEAD LOADS: The weight imposed on a structural roofing system, including the waterproofing system, roof-mounted equipment, roof structural members, and anything hung from the roof structure. 

DECK: The structural surface to which a roofing or waterproofing system is applied. Spray polyurethane foam may be applied to decks on the exterior side as an insulated roofing system or to the interior side as an insulation system.

DEFLECTION: The deviation of a structural element from its original shape or plane due to physical loading, temperature gradients, or movement of its support. 

DEGRADATION: The deterioration of a substance caused by contact with its environment. 

DELAMINATION: The separation of layers within a material or materials. May result in BLISTER formation. (See BLISTER.)

DESICCANT: A substance that attracts water molecules from the surrounding environment through absorption. Typically used to dry compressed air or to dry makeup air entering chemical storage containers.

DEW POINT: The temperature at which a vapor begins to condense. 

DIFFUSION: The process in which there is movement of a substance from an area of high concentration of that substance to an area of lower concentration, typically through or across a membrane (for example, water vapor diffusing from a humid bathroom into the bathroom walls, resulting in moisture in the wall assembly). 

DIISOCYANATE: An organic chemical compound having two reactive isocyanate (-N=C=O) groups used in the production of polyurethane foams and polyurethane coatings. 

DIMENSIONAL STABILITY: The ability of a material to retain its original size and shape. For polyurethane foam, dimensional stability is determined over time under conditions of controlled temperature and humidity. Measured as a percentage of the original dimension. 

DISCOLORATION: Any change from the initial color. (See also COLOR STABILITY.) 

DRAFTSTOP: A material, device, or construction installed to restrict the movement of air and smoke within the open spaces of concealed areas of building components, such as crawlspaces, floor/ceiling assemblies, roof/ceiling assemblies, and attics.

DRAINAGE: See POSITIVE DRAINAGE.

DRIP EDGE: A projecting piece of material shaped to throw off water and prevent water from running down the face of the wall or another surface. 

DRY-BULB TEMPERATURE (DBT): The temperature of air as measured by an ordinary thermometer. (See also AMBIENT TEMPERATURE; WET BULB TEMPERATURE.) 

DRYING TIME: The time required for the loss of volatile components so that the material will become tack-free and no longer be adversely affected by weather conditions, such as dew, rain, or freezing. Also, contrasted with CURE TIME. (See also CURE TIME.)


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