Glossary of Roofing and Waterproofing Terms

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Back-Nailing: (also referred to as Blind-Nailing) the practice of 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.

Back-Surfacing: fine mineral matter applied to the back side of asphalt shingles and roll roofing to keep them from sticking together while packaged.

Ballast: an anchoring material, such as aggregate, or precast concrete pavers, which employ 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.

Base Flashing (membrane base flashing): plies or strips of roof membrane material used to close-off and/or seal a roof at the roof-to-vertical intersections, such as at a roof-to-wall juncture. Membrane base flashing covers the edge of the field membrane. (Also see Flashing.)

Base Ply: the lowermost ply of roofing in a roof membrane or roof system.

Base Sheet: an impregnated, saturated, or coated felt placed as the first ply in some multi-ply built-up and modified bitumen roof membranes.

Batten: (1) cap or cover; (2) in a metal roof: a metal closure set over, or covering the joint between, adjacent metal panels; (3) wood: 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 membrane roof system: a narrow plastic, wood, or metal bar which 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.

Beautort Scale: a scale in which the force of the wind is indicated on a scale of O to 12, as follows:

Beaufort Scale

Beaufort Number

International Description

Miles per Hour

Meters per Second




less than 1

less than .5

calm; smoke rises vertically


Light air



direction of wind shown by smoke but not by wind vanes


light breeze



wind felt on face; leaves rustle; ordinary vane moved by wind


gentle breeze



leaves and small twigs in constant motion; wind extends light flag


moderate breeze



raises dust and loose paper; small branches are moved


fresh breeze



small trees in leaf begin to sway; crested waveless form on inlet islands


strong breeze



large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty


Moderate (or near) gale



whole trees in motion; inconvenience in walking


Gale (or fresh gale)



breaks twigs off trees; generally impedes progress


strong gale



slight structural damage occurs


Storm (or whole gale)



trees uprooted; considerable damage occurs


violent storm



accompanied by widespread damage





devastation occurs

*The U.S. uses 74 statute mph as the speed criterion for hurricanes.
Reference: 1993 Roofing Materials Guide. Original scale developed in 1805 by British naval officer Sir Francis Beaufort.

Bentonite: a clay, formed from decomposed volcanic ash, with a high content of the mineral montmorillonite; has the capacity of absorbing a considerable amount of water, and swells accordingly.

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

Bi-Level Drain: see Dual-Level Drain.

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

Bird Screen: wire mesh used to prevent birds from entering the building through ventilators, louvers, or other openings. (See Insect Screen.)

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 petroleum asphalts, coal tars and pitches, wood tars and asphalts; (2) a generic term used to denote any material composed principally of bitumen, typically asphalt or coal tar.

Bitumen-Stop: see Envelope and Bleed Sheet.

Bituminous Emulsion: a suspension of minute particles of bituminous material in water or other aqueous solution. (See Asphalt Emulsion.)

Blackberry (sometimes referred to as Blueberry or Tar-Boil): a small bubble or blister in the flood coating of an aggregate-surfaced built-up roof membrane.

Blanket (Bats) Insulation: fiberglass 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 to 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. (author of the BOCA National Building Code).

BOMA: Building Owners & Managers Association, International

Bond: the adhesive and/or cohesive forces holding two components in positive contact.

Bond, Chemical: adhesion between surfaces, usually of similar materials, resulting from a chemical reaction or cross-linking of polymer chains.

Bond, Mechanical: adhesion between surfaces resulting from interracial forces or a physical interlocking.

Bonding Agent: a chemical substance applied to a suitable substrate to create bond between it and a succeeding layer.

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 form metal.

Bridging: (1) when the membrane is unsupported at a juncture; (2) bridging in steep-slope roofing is a method of reroofing over standard-sized asphalt shingles with metric-sized asphalt shingles.

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

Brooming: an action carried out to facilitate embedment of a ply of roofing material into hot bitumen by using a broom, squeegee, or special implement to smooth out the ply and ensure contact with the bitumen or adhesive under the ply.

Buckle: an upward, elongated tenting 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: published regulations and ordinances established by a recognized agency prescribing design loads, procedures, and construction details for structures. Usually applying to designated jurisdictions (city, county, state, etc.). Building codes control design, construction, and quality of materials, use and occupancy, location and maintenance of buildings and structures within the area for which the code has been adopted.

Built-Up Roof Membrane (BUR): a continuous, semi-flexible multi-ply roof membrane, consisting of plies or layers of saturated felts, coated felts, fabrics, or mats between which alternate layers of bitumen are applied. Generally, built-up roof membranes are surfaced with mineral aggregate and bitumen, a liquid-applied coating, or a granule-surfaced cap sheet.

Bundle: an individual package of shakes or shingles.

Bush Hammer: a hammer, originally a hand tool but now usually power driven, having a serrated face containing many pyramid-shaped points; used to provide a roughened surface on concrete.

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 copolymerizing isobutylene with a small amount of isoprene. Butyl may be manufactured in sheets, or blended with other elastomeric materials to make sealants and adhesives.

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 is vulcanizable and features low permeability to gases and water vapor.

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


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