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Glossary of Roofing Terms - B

Back Nailing: The technique of fastening the back or top side of a ply of roofing felt, shingle, or other component in a roof system so that the fasteners are covered by the following ply or course and not left exposed to the weather.

Back Surfacing: A fine mineral material applied to the back side of roofing materials such as asphalt shingles or roll roofing to keep the materials from sticking together while packaged.

Back Water Lap: A lap installed in such a way that it obstructs the flow of water.

Bake-out: A method of reducing future VOC emissions from furniture or construction materials in which a building is heated after construction or refurnishing in an attempt to accelerate those emissions before occupancy.

Balanced System: A ventilation system where 50% of the required ventilating area is provided by vents located in the upper portion of the roof with the balance provided by undereave or soffit vents.

Balcony: A railed platform projecting from a wall.

Ballast: A material installed over the top of a roof membrane to help hold it in place. Ballast is loose-laid and usually consists of stones or pavers.

Balustrade: A railing system including a rail or rails and the supporting posts, or balusters.

Bargeboard: A board, often ornamental, which conceals the projecting roof timbers at gable ends.

Bar Joist: Common term for “Open Web Steel Joist” (which see).

Barrel Roof: A curved roof that has the appearance of a section of the side of a barrel.

Base Coat: The first coat in a multi-coat application.

Base Flashing: Those parts of a roof which are attached to the field membrane and seal the system at vertical intersections, such as at roof/wall and roof/curb junctures. (See also Flashing).

Basement: The below-grade and foundational part of a building containing occupiable space.

Base Ply: The primary layer of roofing material in a roof system. (See also Base Sheet).

Base Sheet: An impregnated and/or coated felt attached to the deck, insulation, or cover board and used as the first ply in some built-up and modified bitumen roof systems.

Batt: A roll or sheet of fibrous material used for stuffing or insulation. See Batt Insulation.

Batten: (1) A strip of solid material such as wood, metal, or plastic usually fastened to the structural deck for use in attaching roof system components such as tiles or metal panels; (2) (Also Batten Bar or Batten Strip) A similar strip of solid material which is used to fasten the roof membrane and/or base flashing in place.

Batten Seam: A seam in a metal roof which is formed around a batten.

Batt Insulation: Fibrous insulation manufactured as sheets or rolls. Typically made from fiberglass or stone wool.

Beam: A structural member, such as a joist or a rafter, with the primary function of carrying transverse loads.

Bearing Plate: A steel plate placed under a structural member in order to distribute the force on the member to its support.

Beaufort Scale: (Beaufort Wind Force Scale) A measurement system that relates wind speed to observable conditions.

Bell Roof: A roof with a cross-section similar to that of a bell.

Below Grade Waterproofing: Any of various waterproofing systems applied on below grade walls, such as basement walls, that are intended to resist moisture penetration due to hydrostatic pressure from the surrounding soil, and to last the life of the structure.

Belvedere: Any structure situated so as to provide access to a scenic view. Typically placed on a hilltop or upper portion of a building. 

Bentonite: A highly absorbent clay, which expands when wet, derived from volcanic ash. Often used in below grade waterproofing or in roof coating emulsions.

Bermuda Seam: A metal roof in which the roofing panels are installed perpendicular to the roof slope so that the roof has a step profile.

Bird Bath: Trivial amounts of standing water on a roof that completely evaporate relatively quickly. (See also Ponding).

Bird Screen: A mesh, usually wire, installed across vents or other openings in order to prevent birds from entering a building

Bird Stop: A strip of material such as shaped metal, tile, or foam installed under the first course of a tile roof to prevent birds from nesting under the tiles, as well as to align the first course of tile with the subsequent courses.

Bitumen: A general term for mixtures of high molecular weight hydrocarbons and other substances which occur either naturally or as a product of coal or petroleum processing. In roofing and waterproofing, “bitumen” typically refers to asphalt or coal tar pitch.

Bitumen-Stop: A dam constructed by extending a ply in a built-up roof beyond the other field plies and folding it back onto the top of the system.  Its purpose is to prevent bitumen from leaking down the side of the building or into penetrations within the system.

Blackberry: A small bubble in the flood coat of a built-up roof.

Blanket Insulation: See Batt Insulation.

Bleeder Strip: See Rake-Starter Strip.

Bleeding: The migration of a coloring substance from one material into an adjacent material.

Blind Nailing: The use of fasteners such that they are not visible or exposed to the weather in the finished system. See also Back Nailing.

Blind Rivet: Also called pop rivet. A mechanical fastener with an expandable shank used when only one side of the material to be fastened is accessible. Typically used for securing light-gauge metal components such as flashing or gutters.   

Blister: A pocket of air and/or water vapor trapped between layers of felt or membrane. Blisters typically develop from lamination voids within the system and grow due to thermal expansion and contraction of the gasses within them.

Blocking: Wood components built into a roof assembly and used to strengthen the deck around an opening, to support a curb, or for use as a nailer for the attachment of membranes or flashing.

Bloom: See Efflorescence.

Blower Door: A test equipment assembly used to measure the air-tightness of buildings or ductwork, and to identify locations of air leakage. 

Blowing Agent: A substance used to produce a cellular structure in a variety of materials that harden after application.

Blown Asphalt: See Air Blown Asphalt.

Blueberry: See Blackberry.

BOCA: Building Officials and Code Administrators International, Inc.

BOMA: Building Owners and Managers Association International

Bond: 1) The force or forces holding two components in positive contact. 2) As a surety, a legally binding promise by one party to assume the obligations of a second party should the second party fail to fulfill a contractual obligation to a third party.

Bonding Agent: A chemical substance used to create a bond between two surfaces.

Boot: A piece of flexible pre-formed material installed in order to seal the roof at a penetration.

Borescope: An optical inspection device used to view the inside of a structure through a hole.

Box Gutter: A gutter, usually rectangular, designed to be installed between two parallel surfaces, as between the edge of a roof and a parapet wall. Also called an internal gutter.

Brake: A device used to bend, shape, or form metal.

Brand: An airborne ember produced by a fire.

Breaking Strain: Percent elongation at which a specimen fails due to tensile force.

Bridging: 1. A characteristic of unsupported areas of membrane at junctures between roof components. 2. In asphalt shingle roofing, a re-roofing technique that typically involves installing metric-sized shingles over standard-sized shingles in a manner that allows the new course of shingles to overlay two courses of the existing shingles.

British Thermal Unit (BTU): Approximately, the quantity of heat energy required to raise the temperature of one pound of water one degree Fahrenheit. Approximately 1055 joules.

Brooming: The use of a broom or squeegee to embed a ply of roofing material into hot bitumen or adhesive, eliminating voids and ensuring adhesion.

Buck: A lap in which the down-slope component laps the up-slope component, causing the edge of the material to obstruct the flow of water. This type of lap is said to “buck water”. See also “Back Water Lap”. 

Buckle: Or Buckling. A tented displacement of a roof membrane, typically at insulation and deck joints.

Building Code: A set of rules specifying the minimum acceptable standards for safety in building construction.

Building Envelope: Also referred to as "building shell" or “building enclosure”. The exterior surface which physically separates the interior and exterior environments of a building. It includes the walls, windows, roof, and foundation floor.

Building Inspector: Government official employed to assure compliance with the building and related codes that are in force in the jurisdiction.

Building Paper: A heavy-duty and water-resistant paper used as a vapor barrier and to provide weatherproofing at the sheathing in frame construction.

Built-Up Roof: Often called “BUR”. A flat or low-sloped roof comprising multiple layers of bitumen and reinforcement plies.

Built-Up Roof Membrane: A roof membrane comprising multiple layers of bitumen, which serves as the waterproofing component, with plies of reinforcement fabric installed between each layer. The reinforcement material typically consists of bitumen-saturated or coated cellulose, fiberglass, or polyester felt. A protective surfacing is normally applied consisting of aggregate, emulsion coating, or cap sheet.

Bulb-Tee: A type of steel reinforcing member used in the construction of pre-stressed, poured gypsum decks.

Bulkhead: A structure above the roof of a building which encloses a stairwell or other opening.

Bundle: An individual package of shingles or shakes.

BUR: An acronym for Built-Up Roof.

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

Butt Edge: The lower edge of a shingle.

Butt Joint: A joint between two separate, adjacent pieces of material, such as insulation boards.

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

Butyl Rubber: A butyl-based synthetic elastomer.

Butyl Tape: A butyl-based sealant tape.

By-product: A product, other than the principal product, generated as a consequence of an industrial process or chemical reaction.