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| Back-Nailing | The method of fastening the back or upper side of a ply of roofing felt or other component in a roof system so that the fasteners are covered by the following ply. |
| Back-Surfacing | A fine mineral material on the back side of roofing materials such as roll roofing to keep them 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 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; <BR><BR>(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. |
| Butt Joint | Where two separate, adjacent pieces of material abut. |
| Butyl | A hydrocarbon radical, C4H9. Butyl has a rubber-like consistency, is formed from the copolymerization 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. |