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.
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.
Attic: The open area above the ceiling and under the roof deck of a steep-sloped roof.
Asphalt shingle: a shingle manufactured by coating a reinforcing material (felt or fibrous glass mat) with asphalt and having mineral granules on the side exposed to the weather.
Back surfacing: Fine mineral matter applied to the back side of shingles to keep them from sticking.
Base flashing: That portion of the flashing attached to or resting on the deck to direct the flow of water onto the roof covering.
Battens: 1"x2"x4' wood strips nailed to the roof, upon which the field tile hangs.
Bird stop: In addition to preventing birds from nesting in the hollows of the tile, this length of formed metal or foam elevates the first course of tile so that it is positioned at the same angle as subsequent courses.
Blisters: Bubbles that may appear on the surface of asphalt roofing after installation.
Built-up roof: An outer covering of a comparatively flat roof, consisting of several layers of saturated felt. As laid, each layer is mopped with hot tar or asphalt. The top layer is finished with a mineral or rock covering and a special coating.
Bundle: A package of shingles. There are 3, 4 or 5 bundles per square.
Butt edge: The lower edge of the shingle tabs.