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).
Degradation: a deleterious change in the chemical structure, physical properties or appearance of a material from natural or artificial exposure (e.g. exposure to radiation, moisture, hear, freezing, wind, ozone, oxygen, etc).
Delamination: separation of the laminated layers of a component or system.
Double coverage: application of asphalt, slate, or wood roofing such that the lapped portion is at least 2 inches (50 mm) wider than the exposed portion, resulting in two layers of roofing material over the deck.
Double pour: to apply two layers or flood coats of bitumen and aggregate to a built-up roof.
Downspout: a vertical pipe or conduit used to carry runoff water from a scupper, conductor head or gutter of a building to a lower roof level or to the ground or storm water runoff system.
Drain: an outlet or other device used to collect and direct the flow of runoff water from a roof area.
Drip edge: a metal flashing or other overhanging component with an outward projecting lower edge, intended to control the direction of dripping water and help protect underlying building components.
Dry film thickness: the thickness, expressed in mils, of an applied and cured coating or mastic. For comparison, see Wet film thickness.
Drying time: the time required for the loss of volatile components so that the material will no longer be adversely affected by weather conditions such as dew, rain, or freezing.
Dual level drain: in waterproofing, an outlet or other device with provisions for drainage at both the wearing surface and waterproofing membrane levels used to collect and direct the flow of runoff water from a horizontal slab.