Term Description
Air retarder system

A combination of air retarder assemblies installed to provide a continuous retarder to the movement of air through portions of building enclosure assemblies.

Air space

A cavity or unfilled space between two constituent parts in a roof assembly or other enclosure element of a building.

Air-impermeable insulation

An insulation having an air permeance equal to or less than 0.02 L/s-m2 at 75 Pa pressure differential tested according to ASTM E2178 or E283.

Aliphatic polyurethane

An organic polymer containing straight or branched chain arrangements of carbon atoms. As compared to aromatic polyurethanes, coatings based on aliphatic polyurethane binders typically have better weathering characteristics.

Aliphatic polyurethane coating

A polyurethane coating that contains a specific class of isocyanates based on a long straight chain molecular structure; typically used in finish coats that are exposed to the elements. It is noted for its good weather resistance.


The capacity of water solutions to neutralize acids; a property imparted by the solution's content of carbonates, bicarbonates, hydroxides, and occasionally borates, silicates, and phosphates.


Cracking of a surfacing bitumen, asphalt, coating or mastic or coating on a spray polyurethane foam roof system that occurs during the aging process in which the loss of volatile oils and the oxidation brought about by solar radiation produces a pattern or cracks similar to an alligator's hide; the cracks may or may not extend through the surfacing material.

Aluminized steel

Sheet steel with a thin aluminum coating bonded to the surface to enhance weathering characteristics.


A nonrusting, malleable metal sometimes used for metal roofing and flashing.

Ambient temperature

The temperature of the air existing on all sides; air temperature.


(1) The determination of the nature or proportion of one or more constituents of a substance, whether separated or not; (2) a qualitative or quantitative determination of one or more components of a sample cut from an existing roof system.


A metal or material that readily gives up electrons to a cathodic material in the presence of an electrolyte (see "galvanic cell," "galvanic series" and "cathodic"). As a result, the anodic material oxidizes to protect the cathodic material from corrosion.


American National Standards Institute.


(Formerly) American Plywood Association. The full designation in current use is "APA—The Engineered Wood Association."


(Formerly) American Plastics Council. The full designation in current use is "The Plastics Division of the American Chemistry Council (ACC)." "ACC Plastics Division" is the common-use form.


(Formerly) American Plastics Council/Spray Polyurethane Foam Alliance. See "APC."


See "atactic polypropylene."

Application rate

The average quantity (mass, volume or thickness) of material applied per unit area.

Application temperature

The temperature of a material, such as hot asphalt, when applied to the roof.


A person technically qualified and professionally licensed to practice architecture; that is, designing and administering the construction of buildings.

Architectural panel

A metal roof panel; requires a continuous or closely spaced substrate and relies on slope to shed water.

Architectural shingle

See "dimensional shingle."

Area divider

A raised, flashed assembly, typically a single- or double-wood member attached to a wood base plate that is anchored to the deck. It is used to accommodate thermal stresses in a waterproofing system where an expansion joint is not required or to separate large roof areas or roof systems composed of different/incompatible materials; it may be used to facilitate installation of tapered insulation.

Area practices

Design or application techniques particular to a specific geographical region.


Asphalt Roofing Manufacturers Association.