Roofing terms

A – B

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

The cracking of surfacing bitumen on a built-up roof. The cracks come from asphalt’s limited tolerance for thermal expansion and contraction, and produce a pattern resembling an alligator’s hide.

Asphalt shingle

A shingle made by coating a reinforcing material — felt or fibrous glass mat — with asphalt, with mineral granules on the side exposed to the weather.

Attic

The open area above the ceiling and under the roof deck of a steep-sloped roof.

Back surfacing

Fine mineral matter applied to the back of shingles to keep them from sticking.

Base flashing

The portion of the flashing attached to or resting on the deck, directing the flow of water onto the roof covering.

Battens

Wood strips, one inch by two inches and four feet long, nailed to the roof, on which the field tile hangs.

Bird stop

A length of formed metal or foam that stops birds nesting in the hollows of tile, and elevates the first course so it sits at the same angle as the courses above.

Blisters

Bubbles that may appear on the surface of asphalt roofing after installation.

Built-up roof

The outer covering of a comparatively flat roof, made of several layers of saturated felt. Each layer is mopped with hot tar or asphalt as it is laid; 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.