Aggregate: A surfacing material or ballast for a roof system. Aggregate can be rock, stone, crushed stone or slag, water-worn gravel, crushed lava rock or marble chips. Used in Single Ply systems for EDPM roofing. EPDM roofing is a continuous, semi-flexible roof membrane consisting of piles of saturated felts, coated felts, fabrics or mats between which alternate layers of bitumen are applied, generally surfaced with mineral aggregate, bituminous materials, or a granule surfaced roofing sheet.

Algae discoloration: A type of roof discoloration caused by algae, also called fungus growth.

Alligatoring:   Alligatoring is term used to describe the cracking of surfacing bitumen on a built-up roof. These cracks are the result of the limited tolerance of asphalt to thermal expansion or contraction, and produce a pattern that resembles an alligator's hide.