Term Description

(1) An instance of a membrane or base flashing unsupported at a juncture; (2) occurs in steep-slope roofing when the nesting method is not used in re-covering, such as roofing over standard-size asphalt shingles with metric-sized asphalt shingles.

British thermal unit (Btu)

The heat energy required to raise the temperature of one pound of water 1 degree Fahrenheit.


To cast or distribute granular or aggregate surfacing material.


Embedding 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.


See "British thermal unit."


(Of runoff) to run into a sheet (membrane, felt, etc.) lap facing upslope.


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 and adopted completely or in altered form by local governing authorities. Building code controls design, construction, quality of materials, use and occupancy, location, and maintenance of buildings and structures within the area for which the code was adopted.

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.

Butt edge

The lower, exposed edge of a shingle, tile or shake.

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

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 rubber is manufactured into various sheet goods, blended with other rubber materials and is often used to make sealant.

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.


A structural framing member.


A manufacturing process by which some polymeric membranes and other sheets are produced.

California valley

See ‚"no-cut valley.‚"


A slight convexity, arching or curvature (as of a beam, roof deck or road).

Cant strip

A beveled strip used to modify the angle at the point where the roofing or waterproofing membrane meets any vertical element.

Cap flashing

(1) Usually composed of metal, used to cover or shield the upper edges of the membrane base flashing or wall flashing; (2) a flashing used to cover the top of various building components, such as parapets or columns. See "flashing" and "coping."

Cap sheet

A sheet, often granule-surfaced, used as the top ply of some built-up or polymer-modified bitumen roof membranes and/or flashings.

Capillary action

(1) The action by which the surface of a liquid where it is in contact with a solid is elevated or depressed depending on the relative attraction of the molecules of the liquid for each other and for those of the solid; (2) the siphoning of liquid into a joint or void between two adjacent surfaces.


An ingredient that initiates a chemical reaction or increases the rate of a chemical reaction when combined with another chemical.


A metal or material that readily attracts electrons from an anodic material in the presence of an electrolyte. See "galvanic series."


A composition of vehicle and pigment used at ambient temperatures for filling/sealing joints or junctures; remains elastic for an extended period of time after application.