Roofing Dictionary

The following is a dictionary of basic roofing terms from the NRCA Roofing and Waterproofing Manual.
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Abrasion resistance: the ability to resist being worn away by contact with another moving, abrasive surface, such as foot traffic, mechanical equipment, wind-blown particles, etc.

Absorption: the ability of a material to accept within its body, quantities of gases or liquid, such as moisture.

Accelerated weathering: the exposure of a specimen to a specified test environment for a specified time with the intent of producing in a shorter time period, effects similar to actual weathering.

Acid etch: in waterproofing, the use of a strong acid to remove the surface of concrete to expose the aggregate.

Acrylic coating: a liquid coating system based on an acrylic resin. Generally, a latex-based coating system that cures by air drying.

Acrylic resin: polymers of acrylic or methacrylic monomers. Often used as a latex base for coating systems.

Active metal (anodic): a metal or material that readily gives up electrons to a cathodic (noble) material. (See anodic). An active metal will corrode in the presence of moisture when in contact with a cathodic metal.

Adhesion: steady or firm attachment.

Adhesive bond break: a material to facilitate independent movement between two units that would otherwise bond together.

Aggregate: (1) crushed stone, crushed slag or water-worn gravel used for surfacing a built-up roof system; (2) any granular material.

Aged R-value: thermal resistance value established by utilizing artificial conditioning procedures for a prescribed time period.

Air leakage: the unintended movement of air from a location where it is intended to be contained to another location.

Alligatoring: the cracking of the surfacing bitumen on a bituminous roof or coating on a SPF roof, producing a pattern of cracks similar to an alligator’s hide; the cracks may not extend completely through the surfacing bitumen or coating.

Aluminized steel: sheet steel with a thin aluminum coating bonded to the surface to enhance weathering characteristics.

Aluminum: a nonrusting, malleable metal sometimes used for metal roofing and flashing.

Anodic: a metal or material that readily gives up electrons to a cathodic material in the presence of an electrolyte (see Galvanic series).

ANSI: American National Standards Institute.

Anticapillary hem: a hem used in a metal panel seam to reduce the potential for water migration.

APA: American Plywood Association.

APC: American Plastics Council.

APP: see Atactic polypropylene.

Application rate: the average quantity (mass, volume or thickness) of material applied per unit area.

Apron flashing: a term used for a flashing located at the juncture of the top of a sloped roof and a vertical wall, chimney or steeper-sloped roof.

APC/SPFA: American Plastics Council/Spray Polyurethane Foam Alliance.

Architectural panel: a metal roof panel, typically a double standing seam or batten seam; usually requires solid decking underneath and relies on slope to shed water.

Architectural shingle: an asphalt shingle that provides a dimensional appearance.

Area divider: a raised, flashed assembly, typically a single- or double-wood member attached to a wood base plate, that is anchored to the roof deck. It is used to accommodate thermal stresses in a roof system where an expansion joint is not required, or to separate large roof areas or separate roof systems comprised of different/incompatible materials, and may be used to facilitate installation of tapered insulation.

ARMA: Asphalt Roofing Manufacturers Association.

Area practices: design or application techniques peculiar to a specific geographical region.

Asbestos: a group of natural, fibrous, impure silicate materials.

ASHRAE: American Society of Heating, Refrigerating and Air-Conditioning Engineers.

Asphalt: a dark brown or black substance found in a natural state or, more commonly, left as a residue after evaporating or otherwise processing crude oil or petroleum. Asphalt may be further refined to conform to various roofing grade specifications:

Dead-level asphalt: a roofing asphalt conforming to the requirements of ASTM Specification D 312, Type I.

Flat asphalt: a roofing asphalt conforming to the requirements of ASTM Specification D 312, Type II.

Steep asphalt: a roofing asphalt conforming to the requirements of ASTM Specification D 312, Type III.

Special steep asphalt: a roofing asphalt conforming to the requirements of ASTM Specification D 312, Type IV.

Asphalt, Air blown: asphalt produced by blowing air through molten asphalt to raise its softening point and modify other properties.

Asphalt emulsion: a mixture of asphalt particles and emulsifying agent, such as bentonite clay and water.

Asphalt felt: an asphalt-saturated and/or asphalt-coated felt (see Felt).

Asphalt primer: see Primer.

Asphalt roof cement: a trowelable mixture of solvent-based bitumen, mineral stabilizers, other fibers and/or fillers. Classified by ASTM Standard D 2822-1 Asphalt Roof Cement, and D 4586-2 Asphalt Roof Cement, Asbestos-Free, Types I and II. Type I is sometimes referred to as “plastic cement,” and is made from asphalt characterized as self-sealing, adhesive
and ductile, and conforming to ASTM Specification D 312, Type I; Specification D 449, Types I or II; or Specification D 946 (see Plastic cement and Flashing cement.) Type II is generally referred to as “vertical-grade flashing cement,” and is made from asphalt characterized by a
high softening point and relatively low ductility, and conforming to the requirement of ASTM Specification D 312, Types II or III; or Specification D 449, Type III. (see Plastic cement and Flashing cement.)

Asphalt shingle: a shingle manufactured by coating a reinforcing material (felt or fibrous glass mat) with asphalt and having mineral granules on the side exposed to the weather. (see Shingle)

Asphaltene: a high molecular weight hydrocarbon fraction precipitated from asphalt by a designated solvent (paraffinic naphtha) at a specified temperature and solvent-asphalt ratio.

ASTM: American Society for Testing and Materials.

Atactic polypropylene: a group of high molecular weight polymers formed by the polymerization of propylene.
The NRCA Roofing and Waterproofing Manual—Fifth Edition 974 Glossary

Attic: the cavity or open space above the ceiling and immediately under the roof deck of a steep-sloped roof.

Roofing Dictionary

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. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 975

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. The NRCA Roofing and Waterproofing Manual—Fifth Edition 976 Glossary

Roofing Dictionary


Calender: (1) to press between rollers or plates in order to smooth and glaze or to thin into sheets; (2) a machine for calendering.

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

Canopy: any overhanging or projecting roof structure, typically over entrances or doors.

Cant: in SPF-based roofing, a beveling of foam at horizontal/vertical joints to increase strength and promote water run off.

Cant strip: a beveled strip used under flashings 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 wall flashing; (2) a flashing used to cover the top of various buildings 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 modified bitumen roof membranes and/or flashings.

Capacitance meter: a device used to locate moisture or wet materials within a roof system by measuring the ratio of the change to the potential difference between two conducting elements separated by a non-conductor.

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.

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

Cathodic: A metal or material that readily attracts electrons from an anodic material in the presence of an electrolyte (see Galvanic Series).

Caulk: a composition of vehicle and pigment used at ambient temperatures for filling/sealing joints or junctures, that remains elastic for an extended period of time after application.

Caulking: (1) the physical process of sealing a joint or juncture; (2) sealing and making weather-tight the joints, seams or voids between adjacent surfaces by filling with a sealant.

Cavitation: the formation of a partial vacuum or cavity in a liquid.

Cavity wall: an exterior wall usually of masonry, consisting of an outer and inner withe separated by a continuous air space, but connected together by wire or sheet-metal tiles.

C-channel: a structural framing member.

Cellular glass insulation: A rigid closed-cell insulation board made from crushed glass and hydrogen sulfide gas.

Cementitious waterproofing: heavy cement-based compounds and various additives that are mixed and packaged for use in a dry form; the packaged mixture is then mixed with water and liquid bonding agents to a workable concrete-like consistency.

Centipoise: a unit of measure of absolute viscosity. (The viscosity of water is one centipoise. The lower the number, the less viscous the material.)

Centistoke: a unit of viscosity; the ratio of a liquid’s absolute viscosity to the density of that liquid.

CERL: Construction Engineering Research Laboratory.

Chalk: a powdery residue on the surface of a material.
The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 977

Chalk line: a line made on the roof or other flat surface by snapping a taut string or cord dusted with colored chalk.

Chalking: the formation of a powdery surface condition from the disintegration of a binder or elastomer.

Channel flashing: in steep-slope roof construction, a type of flashing used at roof-to-wall junctures and other rooftop-vertical plane intersections where an internal gutter is needed to handle runoff. Commonly used with profile tile.

Chemical resistance: the ability to withstand contact with specified chemicals without a significant change in properties.

Chimney: stone, masonry, prefabricated metal or wood-framed structure, containing one or more flues, projecting through and above the roof.

Chlorinated polyethylene (CPE): a thermoplastic material, used for single-ply roof membranes, composed of high molecular weight polyethylene that has been chlorinated with a process that yields a flexible rubber-like material.

Chlorosulfonated polyethylene (CSPE or CSM): probably best known by the DuPont trade name Hypalon™, a synthetic, rubber-like thermoset material, based on high molecular weight polyethylene with sulphonyl chloride, usually formulated to produce a self-vulcanizing membrane. Classified by ASTM Standard D 5019.

Cladding: a material used as the exterior wall enclosure of a building.

Cleat: a continuous metal strip, or angled piece, used to secure metal components (also see Clip).

Clerestory: an upward extension of enclosed space created by carrying a setback vertical, wall (typically glazed) up and through the roof slope. Two intersecting shed roofs on different planes.

Clip: A non-continuous metal component or angle piece used to secure two or more metal components together. (see Cleat.)

Clipped gable: a gable cutback near the peak in a hip-roof form.

Closed-cut valley: a method of valley application in which shingles from one side of the valley extend across the valley while shingles from the other side are trimmed back approximately 2 inches (51 mm) from the valley

Closure strip: a metal or resilient strip, such as neoprene foam, used to close openings created by joining metal panels or sheets and flashings.

Coal tar: a dark brown to black colored, semi-solid hydrocarbon produced by the distillation of coal. Coal tar pitch is further refined to conform to the following roofing grade specifications:

Coal tar pitch: a coal tar used as the waterproofing agent in dead-level or low-slope built-up roof membranes and membrane waterproofing systems, conforming to ASTM Specification D 450, Type I.

Coal tar waterproofing pitch: a coal tar used as the dampproofing or waterproofing agent in below-grade structures, conforming to ASTM Specification D 450, Type II.

Coal tar bitumen: a proprietary trade name for Type III coal tar used as the dampproofing or waterproofing agent in dead-level or low-slope built-up roof membranes and membrane waterproofing systems, conforming
to ASTM D 450, Type III.

Coal tar felt: a felt that has been saturated or impregnated with refined coal tar.

Coal tar roof cement: a trowelable mixture of processed coal tar base, solvents, mineral fillers and/or fibers. Classified by ASTM Standard D 4022, “Coal Tar Roof Cement, Asbestos Container.”

Coarse orange peel surface texture: a surface showing a texture where nodules and valleys are approximately the same size and shape. This surface is acceptable for receiving a protective coating because of the roundness of the nodules and valleys. The NRCA Roofing and Waterproofing Manual—Fifth Edition 978 Glossary

Coated base sheet: a coated felt intended to be used as a base ply in a built-up or modified bitumen roof membrane.

Coated fabric: fabrics that have been impregnated and/or coated with a plastic like material in the form of a solution, dispersion hot-melt or powder. The term also applies to materials resulting from the application of a preformed film to a fabric by means of calendering.

Coated felt (Sheet): (1) an asphalt felt that has been coated on both sides with harder, more viscous asphalt; (2) a glass fiber felt that has been simultaneously impregnated and coated with asphalt on both sides.

Coating: a layer of liquid material applied to a surface for protection or appearance.

Cobwebbing: a phenomenon observed during spray application characterized by the formation of web-like threads along with the usual droplets leaving the spray gun nozzle.

Code: a collection of laws (regulations, ordinances or statutory requirements) adopted by governmental authority. (see Building code and Model code.)

Coefficient of thermal expansion: the coefficient of change in dimension of a material per unit of dimension per degree change in temperature.

Cohesion: the molecular forces of attraction by which the body of a material is held together.

Coil coating: the application of a finish to a coil of metal using a continuous mechanical coating process.

Cold forming: the process of shaping metal into desired profiles without the application of heat.

Cold rolled: the process of forming steel into sheets, panels, or shapes on a series of rollers at room temperature.

Cold roof assembly: a roof assembly configured with the insulation below the deck, not typically in contact with
the deck, allowing for a ventilation space. The temperature of the roof assembly remains close to the outside air temperature.

Color stability: the ability of a material to retain its original color after exposure to weather.

Column: in structures, a relatively long, slender structural compression member such as a post, pillar or strut; usually vertical which acts in (or near) the direction of its longitudinal axis.

Combing ridge: a term used to describe an installation of finishing slate or wood at the ridge of a roof whereby the slates on one side project beyond to the apex of the ridge.

Combustible: capable of burning.

Combustion: a chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light either as glow or flames; the process of burning.

Compatible materials: two or more substances that can be mixed, blended, or attached without separating, reacting, or affecting the materials adversely.

Composition shingle: a unit of asphalt shingle roofing.

Composite board roof insulation: rigid board insulation generally comprised of perlite or wood fiberboard factory bonded to polyisocyanurate or polystyrene.

Compounded thermoplastics: a category of roofing membranes made by blending thermoplastic resins with plasticizers, various modifiers, stabilizers, flame retardants, UV absorbers, fungicides and other proprietary substances
alloyed with proprietary organic polymers.

Compressive strength: the property of a material that relates to its ability to resist compression loads. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 979

Concealed-nail method: a method roofing application in which all nails are driven into the underlying course of roofing and covered by a subsequent, overlapping course.

Concealed plate: see Cover plate.

Condense: to make denser or more compact, as when a material (e.g., water vapor) changes from its gas phase to its liquid phase.

Condensate: the liquid resulting from the condensation of a gas.

Condensation: the conversion of water vapor or other gas to liquid phase as the temperature drops; the act or process of condensing.

Conditioning: the storage of a material specimen under specified temperature, humidity, etc. for a specified time prior to testing.

Conductance, Thermal: the thermal transmission in unit time through unit area of a particular body or assembly having defined surfaces, when unit average temperature difference is established between the surfaces.
C=Btu/h•ft2•°F (C=W/m2•K).

Conductor head: an enlargement or catch basin at the top of a downspout or leader to receive rainwater from a gutter or scupper.

Construction joint: (1) a joint where two successive placements of concrete meet; (2) a separation provided in a building which allows its component parts to move with respect to each other.

Contact cements: adhesives used to adhere or bond various roofing components. These adhesives adhere mated components immediately on contact of surfaces to which the adhesive has been applied.

Contamination: the process of making a material or surface unclean or unsuited for its intended purpose, usually by the addition or attachment of undesirable foreign substances.

Control joint: a groove which is formed, sawed, or tooled in a concrete or masonry structure to regulate the location and amount of cracking and separation resulting from the dimensional change of different parts of the structure, thereby avoiding the development of high stresses.

Coping: the covering piece on top of a wall exposed to the weather, usually made of metal, masonry, or stone and sloped to carry off water.

Copolymer: the product of polymerization of two or more substances (as two different isomers) together.

Copolymerization: a chemical reaction that results in the bonding of two or more dissimilar monomers to produce large, long-chain molecules that are copolymers.

Copper: a natural weathering metal used in metal roofing or flashing; typically used in 16 ounce per square foot (0.56 mm) and 20 ounce per square foot (0.69 mm) thicknesses.

Core cut or core sample: (1) a sample from a low-slope roof system taken for the purpose of obtaining primarily qualitative information about its construction. Typically, core cut analysis can verify or reveal the type of membrane surfacing; the type of membrane; the approximate number of plies; the type, thickness and condition of the insulation (if any); and the type of deck used as a substrate for the roof system. (2) for in SPF-based roof systems, core cuts are used to obtain both quantitative and qualitative information, such as the thickness of the foam, the thickness and adhesion of the coating, thickness of individual passes and adhesion between passes and the adhesion of the foam to its substrate.

Cornice: the decorative horizontal molding or projected roof overhang.

Counter batten: vertical wood strips installed on sloped roofs over which horizontal battens are secured. The primary roof covering is attached or secured to these horizontal battens. The NRCA Roofing and Waterproofing Manual—Fifth Edition 980 Glossary

Counterflashing: formed metal or elastomeric sheeting secured on or into a wall, curb, pipe, rooftop unit or other surface, to cover and protect the upper edge of a base flashing and its associated fasteners.

Course: (1) the term used for a row of roofing material that forms the roofing, waterproofing or flashing system; (2) one layer of a series of materials applied to a surface (e.g., a five-course wall flashing is composed of three applications of roof cement with one ply of felt or fabric sandwiched between two layers of roof cement).

Cover board: an insulation board used over closed cell plastic foam insulation (e.g., polyisocyanurate) to prevent blistering when used in conjunction with hot bituminous membranes. Suitable cover board insulation are glassfaced siliconized gypsum board, glass-fiber board, perlite board, wood-fiber board or mineral-fiber board. Cover boards are also recommended between polyisocyanurate insulation and single ply membranes to protect the polyisocyanurate.

Cover plate: a metal strip sometimes installed over or under the joint between formed metal pieces.

Coverage: the surface area uniformly covered by a specific quantity of a particular material at a specific thickness.

CPA: copolymer alloy.

Crack: a nonlinear separation or fracture occurring in a material.

Cream time: time in seconds (at a given temperature) when the A and B components of polyurethane foam will begin to expand after being mixed. Recognizable as a change in color of the materials.

Cricket: a relatively small area of a roof constructed to divert water from a horizontal intersection of the roof with a chimney, wall, expansion joint or other projection. (see Saddle.)

Cross-linking: the formation of chemical bonds between polymeric chains. Cross-linking of rubber is referred to as vulcanization or “curing.”

CRREL: Cold Regions Research and Engineering Laboratory.

Crystalline waterproofing: a compound of cement, quartz or silica sand, and other active chemicals that are mixed and packaged for use in a dry powder form; the packaged mixture is then mixed with water and applied to a concrete surface where it penetrates into the pores of concrete.

CSPE: chlorosulfonated polyethylene.

Cupola: a relatively small roofed structure, generally set on the ridge or peak of a main roof area for ventilation or aesthetic purposes.

Curb: (1) a raised member used to support roof penetrations, such as skylights, mechanical equipment, hatches, etc. above the level of the roof surface; (2) a raised roof perimeter relatively low in height.

Cure: a process whereby a material is caused to form permanent molecular linkages by exposure to chemicals, heat, pressure and/or weathering.

Cure time: the time required for a material to reach its desirable long-term physical characteristics.

Cured concrete: concrete that has attained its intended design performance properties.

Curing agent: an additive in a coating or adhesive that results in increased chemical activity between the components with an increase or decrease in rate of cure.

Curing compound: a liquid that is sprayed or otherwise applied to newly placed concrete which retards the loss of water during curing.

Cutback:solvent-thinned bitumen used in cold-process roofing adhesives, roof cements and roof coatings. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 981

Cutoff: a permanent detail designed to prevent lateral water movement in an insulation system and used to isolate sections of a roofing system.

(Note: A cutoff is different from a tie-in, which may be a temporary or permanent seal.) (see Tie-In.)

Cutout: the open portions of a strip shingle between the tabs. Sometimes referred to as a keyway.

Roofing Dictionary


Dampproofing: treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.

Dead level: absolutely horizontal or zero slope. (see Slope.)

Dead-level asphalt: see Asphalt.

Dead loads: the weight of a structure itself, including the weight of fixtures or equipment permanently attached to it.

Deck: a structural component of the roof of a building. The deck must be capable of safely supporting the design dead and live loads, including the weight of the roof systems, and the additional live loads required by the governing building codes and provide the substrate to which the roofing or waterproofing system is applied the structural surface of a building to which a roof assembly is installed. Decks are either non-combustible (e.g., corrugated metal, concrete, or gypsum) or combustible (e.g., wood plank or plywood).

Deflection (bowing, sagging): (1) the deformation of a structural member as a result of loads acting on it; (2) any displacement in a body from its static position, or from an established direction or plane, as a result of forces acting on the body.

Degradation: a deleterious change in the chemical structure, physical properties or appearance of a material from natural or artificial exposure (e.g., exposure to radiation, moisture, heat, freezing, wind, ozone, oxygen, etc.).

Degree days: a unit used in estimating the fuel consumption for a building; equal to the number of degrees that the mean temperature, for a 24-hour day, is below the “base temperature”; the base temperature is taken as 65° F (18.3° C) in the U.S.A.

Delamination: separation of the laminated layers of a component or system.

Design loads: the total load on a structural system for the most severe combination of loads and forces which it is designed to sustain.

Dew-point temperature: the temperature at which air becomes saturated with water vapor. The temperature at which air has a relative humidity of 100%.

Diaphragm: a floor slab, metal wall panel, roof panel, or the like, having a sufficiently large in-plane shear stiffness and sufficient strength to transmit horizontal forces to resisting systems.

Diffusion: the movement of water vapor from regions of high concentration (high water vapor pressure) toward regions of lower concentration.

Dimensional shingle: a shingle that is textured, overlayed, or laminated and designed to produce a three-dimensional effect. (also see Laminated shingle and Architectural shingle.)

Dimensional stability: the degree to which a material maintains its original dimensions when subjected to changes in temperature and humidity.

DOE: U.S. Department of Energy.

Dormer: a structure projecting from a sloping roof usually housing a window or ventilating louver.

Double coverage: application of asphalt, slate, or wood roofing such that the lapped portion is at least 2 inches (50 mm) wider than the exposed portion, resulting in two layers of roofing material over the deck.

Double lock standing seam: in a metal roof panel or metal cap, a standing seam that uses a double overlapping interlock between two metal panels. (see Standing seam.) The NRCA Roofing and Waterproofing Manual—Fifth Edition 982 Glossary

Double pour: to apply two layers or flood coats of bitumen and aggregate to a built-up roof.

Downspout: a vertical pipe or conduit used to carry runoff water from a scupper, conductor head or gutter of a building to a lower roof level or to the ground or storm water runoff system.

Drag load: the external force (e.g., from the weight of ice and snow) applied to a steep-slope roof system component forcing the component downslope.

Drain: an outlet or other device used to collect and direct the flow of runoff water from a roof area.

Drip edge: a metal flashing or other overhanging component with an outward projecting lower edge, intended to control the direction of dripping water and help protect underlying building components.

Dry: free or relatively free from a liquid, especially water; (2) to remove water or moisture.

Dry bulb temperature: the temperature of air as measured by an ordinary thermometer.

Dry film thickness: the thickness, expressed in mils, of an applied and cured coating or mastic. For comparison, see Wet film thickness.

Drying time: the time required for the loss of volatile components so that the material will no longer be adversely affected by weather conditions such as dew, rain, or freezing.

Dual level drain: in waterproofing, an outlet or other device with provisions for drainage at both the wearing surface and waterproofing membrane levels used to collect and direct the flow of runoff water from a horizontal slab.

Dynamic load: any load which is nonstatic, such as a wind load or moving live load.


Eave: the lower edge of a sloping roof that part of a roof which projects beyond the wall.

Eave height: the vertical dimension from finished grade to the eave.

Eave-trough: see Gutter.

ECH: polyepichlorohydrin, commonly referred to as epichlorohydrin. (see Epichlorohydrin.)

Edge stripping: membrane flashing strips cut to specific widths used to seal/flash perimeter edge metal and the roof membrane application of felt strips cut to narrower widths than the normal felt-roll width to cover a joint between metal perimeter flashing and built-up roofing.

Edge venting: the practice of providing regularly spaced or continuously protected (e.g., louvered) openings along a roof edge or perimeter, used as part of a ventilation system to dissipate heat and moisture vapor.

Efflorescence: an encrustation of soluble salts, commonly white, deposited on the surface of stone, brick, plaster, or mortar; usually caused by free alkalies leached from mortar or adjacent concrete as moisture moves through it.

EIP: ethylene interpolymer.

Elasticity: the property of a body that causes it to tend to return to its original shape after deformation (as stretching, compression or torsion).

Elastomer: a macromolecular material that returns rapidly to its approximate initial dimensions and shape after substantial deformation by a weak stress and subsequent release of that stress.

Elastomeric coating: a coating that is capable of being stretched at least twice its original length (100 percent elongation) and recovering to its original dimensions.

Elongation: the ratio of the extension of a material to the length of the material prior to stretching. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 983

Embedment: (1) the process of pressing/positioning a felt, aggregate, fabric, mat, or panel into hot bitumen or adhesive to ensure intimate contact at all points; (2) the process of pressing/positioning granules into coating in the manufacture of factory-prepared roofing, such as shingles.

Embrittlement: the loss of flexibility or elasticity of a material.

Emulsion: A mixture of bitumen and water, with uniform dispersion of the bitumen or water globules, usually stabilized by an emulsifying agent or system.

End lap: the distance of overlap where one ply, pane, or piece extends beyond the end of the immediately adjacent underlying ply, panel, or piece.

Envelope (Bitumen-stop): a continuous membrane edge seal formed at the perimeter and at penetrations by folding the base sheet or ply over the plies above and securing it to the top of the membrane. The envelope prevents bitumen seepage from the edge of the membrane.

EPDM: Ethylene propylene diene monomer (see also Ethylene propylene diene terpolymer.)

Epichlorohydrin (ECH): a synthetic rubber including two epichlorohydrin based elastomers. It is similar to and compatible with EPDM.

Epoxy: a class of synthetic, thermosetting resins that produce tough, hard, chemical-resistant coatings and adhesives.

Equilibrium moisture content (EMC): (1) the moisture content of a material stabilized at a given temperature and relative humidity, expressed as percent moisture by weight.

Equiviscous temperature (EVT): the temperature at which a bitumen attains the proper viscosity for built-up membrane application.

Equiviscous temperature (EVT) application range: the recommended bitumen application temperature range. The range is approximately 25° F (14° C) above or below the EVT, thus giving a range of approximately 50° F
(28° C). The EVT range temperature is measured in the mop cart or mechanical spreader just prior to application of the bitumen to the substrate.
Equiviscous temperature (EVT) for asphalt: the recommended EVT for roofing asphalt (ASTM D 312, Type I, II, III or IV) is as follows:

Mop application: the temperature at which the asphalt’s apparent viscosity is 125 centipoise (0.125 Pa•s).

Mechanical spreader application: the temperature at which the asphalt’s apparent viscosity is 75 centipoise (0.075 Pa•s).

Note: In order to avoid the use of two kettles if there are simultaneous mop and mechanical spreader applications, the EVT for mechanical spreader application can be used for both application techniques.

Equiviscous temperature (EVT) for coal tar: the recommended EVT for roofing coal tar (ASTM D 450, Type I or III) is the temperature at which the coal tar’s apparent viscosity is 25 centipoise (0.025 Pa•s).

Ethylene interpolymers (EIP): a group of thermoplastic compounds generally based on PVC polymers from which certain single-ply roofing membranes can be formulated.

Ethylene propylene diene terpolymer (EPDM): designated nomenclature of ASTM for a terpolymer of ethylene, propylene and diene. EPDM material is a thermosetting synthetic elastomer.

EVT: Equiviscous temperature.

Exhaust ventilation: air that is vented or exhausted from the roof cavity, typically through vents installed on the up slope portion of the roof.
For example, with most steep-slope roof assemblies, exhaust vents are typically located at or near the ridge. The NRCA Roofing and Waterproofing Manual—Fifth Edition 984 Glossary

Exotherm: heat generated by a chemical reaction.

Expansion cleat: a cleat designed to accommodate thermal movement of metal roof panels.

Expansion joint: a structural separation between two building elements that allows free movement between the elements without damage to the roofing or waterproofing system.

Exposed-nail method: a method of asphalt roll roofing application in which all nails are driven into the adhered, overlapping course of roofing. Nails are exposed to the weather.

Exposure: (1) the traverse dimension of a roofing element or component not overlapped by an adjacent element or component in a roof covering. For example, the exposure of any ply in a built-up roof membrane may be computed by dividing the felt width, minus 2 inches (51 mm), by the number of shingled plies; thus, the exposure of 36 inch (914 mm) wide felt in a shingled, four-ply membrane should be approximately 81/2 inches (216 mm) (See Figure 8); (2) the dimension of sidewall or roofing covering that is not covered or overlapped by the up slope course of component. The typical exposure for a standard-sized, three-tab shingle is 5 inches (127 mm), depending on manufacturer specifications.

Extrusion: a process in which heated or unheated material is forced through a shaping orifice (a die) in one continuously formed shape, as in film, sheet, rod or tubing.

Eyebrow: a dormer, usually of small size, whose roof line over the upright face is typically an arched curve, turning into a reverse curve to meet the horizontal at either end. Also, a small shed roof projecting from the gable end of the larger, main roof area.


Fabric: a woven cloth or material of organic or inorganic filaments, threads, or yarns used for reinforcement in certain membranes and flashings.

Factory Mutual Research (FMR): commonly referred to as “FM,” a research and testing organization that classifies roofing components and assemblies for their fire, traffic, impact (hail), weathering, and wind-uplift resistance for four major insurance companies in the United States.

Factory seam: a splice/seam made by the manufacturer during the assembly of sections of materials into larger sheets/panels.

Fading: any lightening of initial color.

Fallback: a reduction in bitumen softening point, sometimes caused by refluxing or overheating in a relatively closed container. (see Softening Point Drift.)

Fascia: (1) in steep-slope roofing, a board that is nailed to the ends of a roof rafter; sometimes supports a gutter; (2) in low-slope roofing, the vertical or steeply sloped roof or trim located at the perimeter of a building. Typically, it is a border for the low-slope roof system.

Fastener: any of a wide variety of mechanical securement devices and assemblies, including nails, staples, screws, cleats, clips and bolts, which may be used to secure various components of a roof assembly.

Feathering strips: tapered wood filler strips placed along the butt ends of old wood shingles to create a relatively smooth surface when reroofing over existing wood shingle roofs. Referred to in some regions of the country as
“horse feathers,” or leveling strips.

Felt: a flexible sheet manufactured by the interlocking of fibers with a binder or through a combination of mechanical work, moisture and heat.

Felts are manufactured principally from wood pulp and vegetable fibers (organic felts), asbestos fibers (asbestos felts), glass fibers (glass fiber felts or ply sheets), or polyester fibers.

Felt machine (Felt Layer):a mechanical device used for applying bitumen and roofing felt or ply sheet simultaneously.

Ferrule: a metal sleeve placed inside a gutter at the top. A spike or screw is nailed/screwed through the gutter face and ferrule into the fascia board to hold the gutter in place. The ferrule acts as a spacer in the gutter to maintain its original shape.
The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 985

Field seam: a splice or seam made in the field (not factory) where overlapping sheets are joined together using an adhesive, splicing tape, or heat- or solvent-welding.

Filler: a relatively inert ingredient added to modify physical characteristics.

Fillet: a heavy bead of waterproofing compound or sealant material generally installed at the point where vertical and horizontal surfaces meet; to reduce the desired effect to take out the 90° angle at the base of a vertical flashing.

Film: sheeting having a nominal thickness not greater than 10 mils (0.25 mm).

Film thickness: the thickness of a membrane or coating. Wet film thickness is the thickness of a coating as applied; dry film thickness is the thickness after curing. Film thickness is usually expressed in mils (thousandths of an inch).

Fin: a term used to describe a deck surface condition. A sharp raised edge (generally in concrete) capable of damaging a roof membrane or vapor retarder.

Fine mineral-surfacing: water-insoluble, inorganic material, more than 50 percent of which passes through a No. 35 sieve. Used on the surface of various roofing materials and membranes to prevent sticking.

Fire resistance: the property of a material or assembly to withstand fire or give protection from it.

Fire retardant treated (FRT) plywood: plywood which has been impregnated, under pressure, with mineral salts; in the event of fire, the burning wood and salts emit noncombustible gases and water vapor instead of the usual flammable vapors.

Fishmouth: (also referred to as an edge wrinkle) (1) a half-cylindrical or half-conical shaped opening or void in a lapped edge or seam, usually caused by wrinkling or shifting of ply sheets during installation; (2) in shingles, a halfconical opening formed at a cut edge.

Flaking: in protective coatings, the detachment of small pieces of the coating film.

Flammable: subject to easy ignition and rapid flaming combustion.

Flame retardant: a chemical used to impart flame resistance.

Flame spread: the propagation of a flame away from its source of ignition.

Flammability: those characteristics of a material that pertain to its relative ease of ignition and ability to sustain combustion.

Flange: the projecting edge of a rigid or semi-rigid component, such as a metal edge flashing flange.

Flash point: the lowest temperature at which vapors above a volatile combustible substance ignite in air when exposed to a flame.

Flashing: components used to weatherproof or seal roof system edges at perimeters, penetrations, walls, expansion joints, valley, drains and other places where the roof covering is interrupted or terminated. For example, membrane base flashing covers the edge of the field membrane, and cap flashings or counterflashings shield the upper edges of the base flashing.

Flashing cement: a trowelable mixture of solvent-based bitumen and mineral stabilizers that may include asbestos or other inorganic or organic fibers. Generally, flashing cement is characterized as vertical-grade, which indicates it is intended for use on vertical surfaces. (see Asphalt Roof Cement and Plastic Cement.)

Flashing collar: (sometimes referred to as a roof jack or flashing boot) an accessory flashing used to cover and/or seal soil pipe vents and other penetrations through the roof.

Flat lock: a method of interlocking metal panels in which one panel edge is folded back on top of itself and the other panel is folded under, after which the two panels are hooked together. The NRCA Roofing and Waterproofing Manual—Fifth Edition 986 Glossary

Fleece: mats or felts composed of fibers, sometimes used as a membrane backer.

Flood (pour) coat: the surfacing layer of bitumen into which surfacing aggregate is embedded on an aggregatesurfaced built-up roof.

Flood test: the procedure in which a controlled amount of water is temporarily retained over a horizontal surface to determine the effectiveness of the waterproofing system.

Fluid-applied elastomer: a liquid elastomeric material that cures after application to form a continuous waterproofing membrane.

Fly-in: method of application for roll materials by which the dry sheet is set into the bitumen or adhesive applied to the roof surface.

FM: see Factory Mutual Research (FMR).

Foam stop: the roof edge treatment upon which SPF is terminated.

Force: a strength or energy exerted or brought to bear; cause of motion or change.

FPL: Forest Products Laboratory.

Froth pack: a term used to describe small, disposable aerosol cans that contain SPF components. Two component froth packs are available to do small repairs for sprayed polyurethane foam-based roofs.


G-90: a designation for galvanized metal sheet, indicating 0.90 ounces (26 g) of zinc per square foot, measured on both sides.

Gable: the vertical triangular portion of the end of a building having a double-sloping roof, from the level of the eaves to the ridge of the roof.

Gable roof: a single-ridge roof that terminates at gable end(s).

Galvalume: trade name for a metal alloy coating that is composed of aluminum, zinc and silicone.

Galvanic action: an electrochemical action that generates electrical current between two metals of dissimilar electrode potential.

Galvanic series: a list of metals and alloys arranged according to their relative electrolytic potentials in a given environment.

Galvanize: to coat steel or iron with zinc.

Galvanized steel: steel coated with zinc for corrosion resistance.

Gambrel: a roof that has two pitches on each side, where the upper roof area has less slope than the lower roof areas.

Gauge: a metal thickness measurement.

Geocomposite: a prefabricated water drainage material used to relieve hydrostatic pressure against waterproofing and promote drainage.

Geotextile:a tightly woven fabric used to restrict the flow of fine soil particles and other contaminants while allowing water to pass freely through; used to protect drainage systems from clogging.

Girt: a horizontal beam that supports wall cladding between columns.

Glass fiber insulation: blanket or rigid board insulation, composed of glass fibers bound together with a binder, faced or unfaced, used to insulate roofs and walls. The NRCA Roofing and Waterproofing Manual—Fifth Edition
Glossary 987

Glass felt: glass fibers bonded into a sheet with resin and suitable for impregnation with asphalt in the manufacture of bituminous waterproofing, roofing membranes and shingles.

Glass mat: a thin mat of glass fibers with or without a binder.

Glaze coat: (1) the top layer of asphalt on a smooth-surfaced built-up roof membrane; (2) a thin protective coating of bitumen applied to the lower plies or top ply of a built-up roof membrane when application of additional felts or the flood coat and aggregate surfacing are delayed. (also see Flood coat.)

Gloss: the shine, sheen or luster of a dried film.

Grain: a unit of measure in the English System of units; 7,000 grains equals 1 lb.; used as a measure of the weight of moisture in air.

Granule: (also referred to as mineral or ceramic granule) opaque, natural or synthetically colored aggregate commonly used to surface cap sheets, shingles, and other granule-surfaced roof coverings.

Gravel: coarse granular aggregate resulting from the natural erosion of rock.

Gravel stop: a flanged device, frequently metallic, designed to prevent loose aggregate from washing off the roof and to provide a continuous finished edge for the roofing.

Groundwater level: at a particular site, the level, below which the subsoil and rock masses of the earth are fully saturated with water.

Grout: a mixture of cement, sand, and water used to fill cracks and cavities in masonry.

Gusset: used at the bottom of a steep-slope roof system valley, a large flat metal piece(s) wider than the valley to help prevent build-up at the base of the valley, either from debris or ice dam formations.

Gutter: a channeled component installed along the downslope perimeter of a roof to convey runoff water from the roof to the drain leaders or downspouts.

Gypsum board panels: cementitious board stock with noncombustible core primarily comprised of gypsum that is commonly used as a barrier board thermal barrier or cover board in a roof assembly.


Hand-tabbing: method of spot applying asphalt-based adhesive to shingles for securement and wind resistance.

Headlap: the distance of overlap measured from the uppermost ply or course to the point where it laps over the undermost ply or course.

Heat flow: the quantity of heat transferred to or from a system in a unit of time.

Heat seaming: the process of joining thermoplastic films, membranes, or sheets by heating and then applying pressure to bring both materials in contact with each other. (see Heat welding.)

Heat transfer: the transmission of thermal energy from a location of higher temperature to a location of lower temperature. This can occur by conduction, convection or radiation.

Heat welding: method of melting and fusing together the overlapping edges of separate sheets or sections of polymer modified bitumen, thermoplastics or some uncured thermoset roofing membranes by the application of heat (in the form of hot air or open flame) and pressure. (see Heat seaming.)

Hem: the edge created by folding metal back on itself.

Hip: the inclined external angle formed by the intersection of two sloping roof planes.

Hip roof: a roof that rises by inclined planes to form one or more hips.

Hoist: a mechanical lifting device.
The NRCA Roofing and Waterproofing Manual—Fifth Edition 988 Glossary

Holiday: an area where a liquid-applied material is missing or absent.

Honeycomb: voids left in concrete resulting from failure of the mortar to effectively fill the spaces among coarse aggregate particles.

Hot or Hot stuff: a roofing worker’s term for hot bitumen.

Hue: the subjective perception of color such as red, yellow, green, blue, purple or some combination; white, black or gray possess no hue.

Humidity: the condition of the atmosphere with respect to water vapor. See relative humidity.

HVAC: heating, ventilating, and air conditioning equipment.

Hybrid roof covering: combination of two or more separate and distinct roof membranes; e.g., three ply smooth BUR and a modified bitumen cap.

Hydration: the chemical reaction by which a substance (such as Portland cement) combines with water, giving off heat to form a crystalline structure in its setting and hardening.

Hydrocarbon: an organic chemical compound primarily containing the elements carbon and hydrogen.

Hydrostatic pressure: the pressure equivalent to that exerted on a surface by a column of water of a given height.

Hydrostatic pressure relief system: a system of perimeter and/or under slab drains used to regulate the hydrostatic pressure in the earth surrounding a below-grade structure.

Hygroscopic: attracting, absorbing and retaining atmospheric moisture.

Hypalon™: a registered trademark of E.I. du Pont de Nemours & Co., for ”chlorosulfonated polyethylene” (CSPE). (see Chlorosulfonated polyethylene.)