Term Description
Aromatic polyurethane

An organic polymer usually containing one or more benzene ring structures. As compared to aliphatic polyurethanes, coatings based on aromatic polyurethane binders usually have tougher physical properties.


A group of natural, fibrous impure silicate materials.

Asbestos felt

See ‚"felt.‚"


American Society of Civil Engineering.


American Society of Home Inspectors.


American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc.


A dark brown to black cementitious material in which the predominating constituents are bitumens that occur in nature or are obtained in petroleum processing. See "bitumen." Asphalt may be further refined to conform to various roofing grade specifications:
asphalt, dead-level: A roofing asphalt conforming to the requirements of ASTM D312, Type I.

asphalt, flat: A roofing asphalt conforming to the requirements of ASTM D312, Type II.

asphalt, steep: A roofing asphalt conforming to the requirements of ASTM D312, Type III.

asphalt, special steep: A roofing asphalt conforming to the requirements of ASTM D312, Type IV.

asphalt, waterproofing: A waterproofing asphalt conforming to the requirements of ASTM D449, Types I, II and III.

Asphalt core board

An asphaltic panel that may be used as a cover board layer beneath built-up and polymer-modified bitumen roof membranes. It is a semi-rigid, multi-ply panel constructed of a core of water-insoluble mineral filler with bituminous binder sandwiched between two reinforcing facings.

Asphalt emulsion

A mixture of asphalt particles and emulsifying agent, such as bentonite clay or soap, and water.

Asphalt felt

An asphalt-saturated and/or asphalt-coated felt. See "felt."

Asphalt primer

See "primer."

Asphalt roof cement

A trowelable mixture of asphalt, solvents, mineral stabilizers, fillers or fibers, or both. See Specifications D2822 and D4586. Also, see "plastic cement" and "flashing cement."

Asphalt shingle

A shingle manufactured by coating a reinforcing material (paper felt or fiberglass mat) with an asphalt-based coating and having mineral granules on the side exposed to the weather. See "shingle."

Asphalt, air-blown

Asphalt produced by blowing air through molten asphalt at an elevated temperature to raise its softening point and modify other properties.

ASTM International

The full designation in current use of the largest voluntary standards development organizations in the world formerly known as the American Society for Testing and Materials.

Atactic polypropylene

High-molecular-weight polymer formed by the polymerization of propylene and characterized by random arrangement of the side methyl groups around the chain backbone.

Atmospheric discoloration

Discoloration that may occur because of atmospheric contaminants such as sulfur-containing gases.


The cavity or open space above the ceiling and immediately under the roof deck of a steep-slope roof.


American Wood Protection Association; formerly American Wood Preservers Association.

B-component (B-side)

One component of a two-component polymer system; for polyurethane foam and coatings, the resin component.


The practice of nailing the concealed portion of a roofing ply, steep roofing unit or other components in a manner such that the fasteners are covered by the next ply, or course, and are not exposed to the weather in the finished roof system. Hot-mopped roofing felts and polymer-modified bitumen sheets may be backnailed to prevent slippage. Also referred to as "blindnailing."


Rolling a coating by hand, typically behind the spray or power roller applicator, to ensure better coverage and adhesion.

Backup plate

A rigid plate to support an end lap to provide uniform compression.


A material, such as minimum nominal #1-1/2 inch size or #4, or alternatively, #3, #24, #2 or #1—as specified in ASTM D448—smooth river stone, crushed stone, standard precast concrete pavers or interlocking, beveled, doweled or contoured fit lightweight concrete pavers, that employs its mass and the force of gravity to hold a roof membrane system in place.

Bar joist

See "steel joist."