Backnailing: The practice of blind-nailing roofing felts to a substrate in addition to hot mopping to prevent slippage.  (See "Blind Nailing").

Back-Surfacing: A fine mineral material on the back side of roofing materials such as roll roofing to keep the membrane from sticking together while packaged.

Ballast: A material installed over the top of a roof membrane to help hold it in place. Ballasts are loose laid and can consist of aggregate, or concrete pavers.

Bar Joist: See "Steel Joist"

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

Base Flashing: The system used to seal membrane edges at walls, expansion joints and other places where the membrane intersects vertical surfaces. Base flashings are most commonly fabricated of membrane or sheet metal.

Base Ply: The lowermost ply of roofing material in a roof membrane assembly.

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. Sometimes referred to as a termination Bar.

Bermuda Seam: A metal roof configuration that has a stepped 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 of a building. 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 in place. See also "Envelope".

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

Blackberry: A small bubble or blister in the flood coating of a gravel-surfaced roof membrane.

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

Blind-Nailing: The installation of nails in such a manner so that they are not exposed to the weather in the finished roofing system. See "Back-Nailing"

Blister: A pocket of air mixed with water or solvent vapor, trapped between impermeable layers of felt or between the felt and substrate. Blisters are usually caused by moisture or other foreign substances entrapped within or beneath the roof membrane.

Blocking: Wood built into a roof assembly used to stiffen the deck around an opening, act as a stop for insulation, or for use as a nailer for attachment of membrane or flashing.

Blown Asphalt: A bitumen produced by blowing air through molten asphalt at an elevated temperature to raise it’s softening point and modify other properties.

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

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

BOMA: Building Owners & Managers Association, International

Bond: The adhesive and cohesive forces holding two components in positive contact.

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

Boot: A preformed cylinder used to flash pipe penetrations. May be constructed of metal or an elastomeric membrane.

Brake: (1) A piece of equipment used for forming metal. (2) A straight bend in a metal sheet.

Bridging: A section of membrane that is unsupported by a structural substrate.

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 (BUR): A roof membrane composed of multiple plies of roofing felt or membrane adhered in alternate applications of bitumen.

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. Also used to add elastic properties to modified asphalt.

Butt Joint: A joint in which two separate, adjacent pieces of material are abutted.

Butyl: A hydrocarbon radical, C4H9. Butyl has a rubber-like consistency, is formed from the co polymerization of isobutylene and isoprene and is used primarily in sealants and adhesives.

Butyl Rubber: A butyl-based, synthetic elastomer.

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


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