Barrel Roof: A roof configuration with a partial cylindrical shape to it.

Base Flashing (membrane base flashing): Plies of roof membrane material used to seal a roof at the vertical plane intersections, such as at a roof-wall and roof-curb junctures. (See also Flashing.)

Base Ply: The primary ply of roofing material in a roof system.

Base Sheet: An asphalt-impregnated, or coated felt used as the first ply in some built-up and modified bitumen roof systems.

Batten: (1) A strip of wood usually fastened to the structural deck for use in attaching a primary roof system such as tile; (2) A plastic strip, wood strip, or metal bar which is used to fasten or hold the roof and/or base flashing in place, A.K.A. Termination Bar.

Bermuda Seam: A metal roof that has a step profile.

Bird Bath: Small, inconsequential amounts of water on a roof that quickly evaporate.

Bird Screen: Wire mesh installed over openings in order to prevent birds from entering a building or roof cavity.

Bitumen: Any of various flammable mixtures of hydrocarbons and other substances, occurring naturally or obtained by distillation from coal or petroleum, that are a component of asphalt and tar and are used for surfacing roads and for waterproofing.

Bitumen-Stop: A continuous seal for preventing bitumen from leaking down into or off a building. Is constructed by extending the base sheet or other non-porous ply of felt beyond the edge of the field plies. It is then turned back onto the top of the system and adhered. See also Envelope.

Bituminous Emulsion: Bituminous particles suspended in water or other solution. See also Asphalt Emulsion.

Blackberry: See Tar Boil.

Bleeder Strip: A starter strip placed along rake edges for use in asphalt shingle roofing. See also Rake-Starter.

Blind-Nailing: The use of nails so that they are not exposed to the weather in the finished roofing system. See Back-Nailing

Blister: A pocket of air trapped between layers of felt or membrane. Blisters are usually caused by water or other foreign substances.

Blocking: Pieces of wood built into a roof assembly used to stiffen the deck around an opening, support a curb, or for use as a nailer for attachment of membranes or flashing.

Blown Asphalt: See Air Blown Asphalt.

Blueberry: A small bubble found in the flood coat of an aggregate-surfaced built-up roof. See also Tar Boil.

BOCA: Building Officials and Code Administrators, International, Inc.

BOMA: Building Owners & Managers Association, International

Bond: The force(s) holding two components in positive contact.

Bonding Agent: A chemical agent used to create a bond between two layers.

Boot: A piece of material preformed to protect roof penetrations from dirt, moisture and other foreign and/or damaging substances.

Brake: A piece of equipment used for forming metal.

Bridging: When membrane is unsupported at a juncture.

British Thermal Unit (BTU): The heat energy necessary to raise the temperature of one pound of water one degree Fahrenheit, a joule.

Brooming: Embedding a ply of roofing material into hot bitumen or adhesive by using a broom, squeegee, or other piece of equipment to eliminate voids and help ensure adhesion.

Buckle: A long, tented displacement of a roof membrane. Can occur over insulation and deck joints.

Built-Up Roof Membrane: A roof membrane consisting of layers of bitumen, which serves as the waterproofing component, with plies of reinforcement fabric installed between each layer. The reinforcement material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate, emulsion or a granule-surfaced cap sheet.

Bulb-Tee: A steel reinforcing member used when constructing pre-stressed, poured gypsum decks. When the gypsum is poured, it surrounds the Bult-Tee.

Bundle: An individual package of shingles or shakes.

BUR: An acronym for Built-Up Roof. See Built-Up Roof.

Butadiene: A colorless, highly flammable hydrocarbon, C₄H₆, obtained from petroleum and used in the manufacture of synthetic rubber.

Butyl Tape: A sealant tape used in numerous sealant applications such as sealing sheet metal joints.