This glossary contains many useful terms and definitions that will help you understand much of the work we do at ROOFCORP.

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Back-nailing (also referred to as "Blind-nailing"): the practice of blind nailing the back portion of a roofing ply, steep roofing unit, or other components in a manner so that the fasteners are covered by the next sequential ply, or course, and are not exposed to the weather in the finished roof system.

Ballast: a material, such as aggregate or precast concrete pavers, which employs its mass and the force of gravity to hold (or assist in holding) single-ply roof membranes in place.

Bar joist: (see Steel joist).

Barrel vault: a building profile featuring a rounded profile to the roof on the short axis, but with no angle change on a cut along the long axis.

Barrier board: noncombustible board stock material of low thermal conductivity placed between two elements of a roof assembly.

Base flashing (membrane base flashing): plies or strips of roof membrane material used to close-off and/or seal a roof at the horizontal-to-vertical intersections, such as at a roof-to-wall juncture. Membrane base flashing covers the edge of the field membrane. (see Flashing.) Base ply: the bottom or first ply in a built-up roof membrane when additional plies are to be subsequently installed.

Base sheet: an impregnated, saturated, or coated felt placed as the first ply in some low-slope roof systems.

Batten: (1) cap or cover; (2) in a metal roof, a metal closure set over, or covering the joint between, adjacent metal panels; (3) in a wood roof, a strip of wood usually set in or over the structural deck, used to elevate and/or attach a primary roof covering such as tile; (4) in a single ply membrane roof system, a narrow plastic, wood or metal bar that is used to fasten or hold the roof membrane and/or base flashing in place.

Batten seam: a metal panel profile attached to and formed around a beveled wood or metal batten.

Bentonite: a porous clay formed by the decomposition of volcanic ash that swells 5 to 6 times its original volume in the presence of water.

Bermuda seam: a metal panel profile featuring a step-down profile that runs perpendicular to the slope of the roof.

Bird bath: random, inconsequential amounts of residual water on a roof membrane.

Bitumen: (1) a class of amorphous, black or dark colored, (solid, semi-solid or viscous) cementitious substances, natural or manufactured, composed principally of high molecular weight hydrocarbons, soluble in carbon disulfide, and found in asphalts, tars, pitches and asphaltenes; (2) a generic term used to denote any material composed principally of bitumen, typically asphalt or coal tar. Bitumen-stop: see Envelope or Bleed-sheet.

Bituminous emulsion: a suspension of minute particles of bituminous material in water.

Blackberry (also referred to as "Blueberry" or "Tar-boil"): a small bubble or blister in the flood coat of an aggregate-surfaced built-up roof membrane.

Blanket (batt) insulation: glass fiber or other compressible fibrous insulation, generally available in roll form.

Bleed-sheet: a sheet material used to prevent the migration of bitumen.

Bleeder strip: (see Rake-starter).

Blind-nailing: the use of nails that are not exposed to the weather in the finished roofing system.

Blister: an enclosed pocket of air, which may be mixed with water or solvent vapor, trapped between impermeable layers of felt or membrane, or between the membrane and substrate.

Blocking: sections of wood (which may be preservative treated) built into a roof assembly, usually attached above the deck and below the membrane or flashing, used to stiffen the deck around an opening, act as a stop for insulation, support a curb, or serve as a nailer for attachment of the membrane and/or flashing.

Blowing agent: an expanding agent used to produce a gas by chemical or thermal action, or both, in manufacture of hollow or cellular materials.

BOCA: Building Officials and Code Administrators, International, Inc. Bond: the adhesive and/or cohesive forces holding two components in positive contact.

Boot: (1) a covering made of flexible material, which may be preformed to a particular shape, used to exclude dust, dirt, moisture, etc., from around a penetration; (2) a flexible material used to form a closure, sometimes installed at inside and outside corners.

Brake: hand- or power-activated machinery used to bend metal. Bridging: (1) when membrane or base flashing is unsupported at a juncture; (2) bridging in steep-slope roofing occurs when reroofing over standard-sized asphalt shingles with metric-sized asphalt shingles.

British thermal unit (BTU): the heat energy required to raise the temperature of 1 pound of water degree Fahrenheit (joule). For the metric equivalent, see Joule.

Broadcast: uniformly cast or distribute granular or aggregate surfacing material.

Brooming: to improve the embedding of a ply or membrane by using a broom or squeegee to smooth it out and ensure contact with the adhesive under the ply or membrane.

Buckle: an upward, elongated displacement of a roof membrane frequently occurring over insulation or deck joints. A buckle may be an indication of movement within the roof assembly.

Building code: The minimum construction requirements established generally by national organizations of experts and adopted completely or in altered form by local governing authorities.

Built-up roof (BUR): a continuous, semi-flexible roof membrane, consisting of multiple plies of saturated felts, coated felts, fabrics or mats assembled in place with alternate layers of bitumen, and surfaced with mineral aggregate, bituminous materials, a liquid-applied coating or a granule-surfaced cap sheet.

Bundle: an individual package of shakes or shingles. Bun stock: large solid box-like structure formed during the production of polystyrene insulation; individual board stock pieces are then cut from the bun.

Butt joint: a joint formed by adjacent, separate sections of material, such as where two neighboring pieces of insulation abut.

Button punch: a process of indenting two or more thicknesses of metal that are pressed against each other to prevent slippage between the metal.

Butyl: rubber-like material produced by polymerizing isobutylene.

Butyl coating: an elastomeric coating system derived from polymerized isobutylene. Butyl coatings are characterized by low water vapor permeability.

Butyl rubber: a synthetic elastomer based on isobutylene and a minor amount of isoprene. It can be vulcanized and features low permeability to gases and water vapor.

Butyl tape: a sealant tape sometimes used between metal roof panel seams and/or end laps; also used to seal other types of sheet metal joints, and in various sealant applications.