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Abrasion resistance - the ability to resist being worn away by contact with another moving, abrasive surface, such as foot traffic, mechanical equipment, wind-blown particles, etc.

Absorption - the ability of a material to accept within its body, quantities of gases or liquid, such as moisture.

Accelerated weathering - the exposure of a specimen to a specified test environment for a specified time with the intent of producing in a shorter time period, effects similar to actual weathering.

Acid etch - in waterproofing, the use of a strong acid to remove the surface of concrete to expose the aggregate.

Acrylic coating - a liquid coating system based on an acrylic resin. Generally, a latex-based coating system that cures by air drying.

Acrylic resin - polymers of acrylic or methacrylic monomers. Often used as a latex base for coating systems.

Active metal (anodic) - a metal or material that readily gives up electrons to a cathodic (noble) material. (See anodic). An active metal will corrode in the presence of moisture when in contact with a cathodic metal.

Adhesion - steady or firm attachment.

Adhesive bond break - a material to facilitate independent movement between two units that would otherwise bond together.

Aged R-value - thermal resistance value established by utilizing artificial conditioning procedures for a prescribed time period.

Aggregate - (1) crushed stone, crushed slag or water-worn gravel used for surfacing a built-up roof system; (2) any granular material.

Air leakage - the unintended movement of air from a location where it is intended to be contained to another location.

Aluminized steel - sheet steel with a thin aluminum coating bonded to the surface to enhance weathering characteristics.

Aluminum - a nonrusting, malleable metal sometimes used for metal roofing and flashing.

Anodic - a metal or material that readily gives up electrons to a cathodic material in the presence of an electrolyte (see Galvanic series).

ANSI - American National Standards Institute.

Anticapillary hem - a hem used in a metal panel seam to reduce the potential for water migration.

APA - American Plywood Association.

APC - American Plastics Council.

APC/SPFA - American Plastics Council/Spray Polyurethane Foam Alliance.

APP - see Atactic polypropylene.

Application rate - the average quantity (mass, volume or thickness) of material applied per unit area.

Apron flashing - a term used for a flashing located at the juncture of the top of a sloped roof and a vertical wall, chimney or steeper-sloped roof.

Architectural panel - a metal roof panel, typically a double standing seam or batten seam; usually requires solid decking underneath and relies on slope to shed water.

Architectural shingle - an asphalt shingle that provides a dimensional appearance.

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

Area practices - design or application techniques peculiar to a specific geographical region.

ARMA - Asphalt Roofing Manufacturers Association.

Asbestos - a group of natural, fibrous, impure silicate materials.

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