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This glossary was designed to help those not directly involved in roofing with their understanding of roofing terminology. Many technical and chemical terms were not included.

Dampproofing: Treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.

Dead Level: Refers to a roof with no slope or pitch.

Dead-Level Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type I. This asphalt is for use in roofs which do not exceed a ¼ in 12 slope (2%).

Dead Loads: Permanent, non-moving loads on a roof resulting from the weight of a building’s components, equipment, and the roof system.

Deck: The structural component of the roof of a building which provides the substrate to which the roofing system is applied.

Decking: See Deck.

Deflection: The downward displacement of a structural member under load.

Degradation: A decline in the appearance, structure, or properties, of a material or substance.

Delamination: Separation of laminated layers of a material or system.

Dew Point Temperature: The temperature at which water vapor turns to liquid in cooling air at the existing atmospheric pressure and vapor content.

Diaphragm: A type of structural roof deck capable of resisting shear that is produced by lateral forces such as wind or seismic loads.

Diffusion: The movement of a substance such as water vapor from regions of high concentration to regions of lower concentration

Dimensional Shingle: A shingle that is textured, or laminated to produce a three-dimensional effect. Also known as Laminated and Architectural Shingles. Please be aware that there are also shingles being produced that can be classified as Dimensional but not as Laminated. These shingles are comprised of a single piece of material rather than two different materials laminated together.

Dimensional Stability: The ability of a material to retain its current properties and to resist a change in size resulting from exposure to temperature changes and moisture.

Dome: A roof with a partial-spherical shape.

Dormer: A framed projection through the sloping plane of a roof.

Double Coverage: Installing roofing so that there is twice the materials used resulting in a double layer of roofing.

Double Graveling: Installing one layer of gravel in a flood coat of hot bitumen, removing the excess gravel and then installing a second layer of gravel in another flood coat of hot bitumen.

Downspout: A conduit for carrying water from a gutter, scupper, drop outlet or other drainage unit from roof to ground level. Also known as a Leader Pipe.

Drain: a device used to carry water off of a roof.

Drip Edge: A steel flashing bent at a 90º angle that is placed along the outer perimeter of steep sloped buildings; used to help direct runoff water away from the building. Drip Edge resembles nosing except that it has an outwardly-angled bottom edge (preferably hemmed). To see the difference between Drip Edge and Nosing, click here.

Dry Bulb Temperature: The temperature of air in degrees Fahrenheit measured by an ordinary thermometer.

Dry Film Thickness: The thickness in mils (thousandths of an inch), of a dried coating or mastic.

Dry-In: (1) The process of installing the underlayment in steep slope roofing; (2) Making a low-slope roof watertight. Does not always mean getting all of the required plies installed.

Dry Rot: Wood rot caused by certain fungi. Dry rot can result from condensation build-up, roof leaks that go untended, or from other problems. Dry rot will not remain localized. It can spread and damage any lumber touching the affected area.

Dual Level Drain: An item that will permit drainage at two different levels.

Dynamic Load: Any moving load on a roof such as people and equipment. Wind can also be considered a Dynamic Load.


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