Glossary of Roofing and Waterproofing Terms
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Dampproofing: treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.

Dead Level: essentially horizontal or flat, as in a roof deck or rooftop with no intentional slope to the roof drains. Also referred to as zero (0) slope. (See Slope.)

Dead-Level Asphalt: see Asphalt.

Dead Loads: permanent non-moving loads that result from the weight of a building's structural and architectural components, mechanical and electrical equipment, and the roof assembly itself. Essentially the same as "dead weight" or "dead weight loads."

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. Decks are either non-combustible (e.g., corrugated metal, concrete, or gypsum) or combustible (e.g., wood plank or plywood), and provide the substrate to which the roofing or waterproofing system is applied.

Deflection (Bowing, Sagging): the downward displacement of a structural member or system under load.

Degradation: a deleterious change in the chemical structure, physical properties, or appearance of a material due to natural or artificial exposure (e.g., exposure to radiation, moisture, heat, freezing, wind, ozone, oxygen, etc.).

Degree Days: the difference between a reference temperature (usually 65°F [1 8.3°C]) and the mean temperature for the day, times 24 hours, times the number of days in the period. Degree days are used to compare the severity of cold or heat during the heating or cooling season.

Delamination: separation of the laminated layers of a component or system.

Design Loads: those loads specified in building codes or standards published by federal, state, county, or city agencies, or in owners' specifications to be used in the design of a building.

Dew Point Temperature: the temperature at which water vapor condenses in cooling air at the existing atmospheric pressure and vapor content. Cooling at or below the dew point will cause condensation.

Diaphragm: see Roof Diaphragm.

Diffusion: the movement of water vapor from regions of high concentration (high water vapor pressure) toward regions of lower

Dimensional Shingle: a shingle that is textured, overlayed, or laminated and designed to produce a three-dimensional effect. (Also see Laminated Shingles and Architectural Shingles).

Dimensional Stability: the ability of a material to resist change in length, width, and/or thickness that results from exposure to elevated or freezing temperatures, and moisture, over time.

DOE: Department of Energy

Dome: a roof that is shaped like a half-circle, or a variation of one.

Domer: a framed projection through the slopping plane of a roof. (See figure 5)

Double Coverage: application of asphalt, slate, or wood roofing such that the lapped portion is at least 2 inches (51mm) wider than the exposed portion, resulting in two layers of roofing material over the deck.

Double Graveling: the process of applying two layers or flood coats of bitumen and aggregate to a built-up roof. Loose aggregate should be swept from the first application prior to the second coating of bitumen and aggregate. Approximately 50% of the second aggregate application will remain adhered in the bitumen flood coat unless physically removed.

Double Lock Standing Seam: a standing seam that utilizes a double, overlapping interlock between two seam panels. (See Standing Seam.)

Downspout: a 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 overchanging component, with an outward projecting lower edge, intended to control the direction of dripping water and help protect underlying building components. A drip edge also can be used to break the continuity of contact between the roof perimeter and wall components to help prevent capillary action.

Dry: (1) to change the physical state of a material by the loss of components through evaporation, absorption, oxidation, or a combination of these effects; (2) the absence of water or moisture.

Dry Bulb Temperature: the temperature of air as measured by an ordinary thermometer. Units are F (C).

Dry Film Thickness: the thickness, expressed in mils, of an applied and cured coating or mastic. For comparison, see Wet Film Thickness.

Dry-In or Dry-In Felt: usually the underlayment or the process of applying the underlayment for steep roofing.

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 level and the waterproofing membrane level used to collect and direct the flow of runoff water from a horizontal slip. (See NRCA Waterproofing Detail WP-9.)

Durability: the ability to withstand physical, chemical, or environmental abuse.

Dust Free: a surface is considered dust free when a finger can be lightly run over the surface without picking up any dirt, dust, or chalk on the finger.

Dynamic Load: any load which is nonstatic, such as a wind load or a moving live load.