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This glossary is intended to help you understand terms you will encounter as you plan your roofing project
(Please Note: This roofing glossay is not in precise alphabetical order)

	By First Letter A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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	absorption: The ability of a material  to accept within its body quantities of gases or liquid,  such as moisture. adhesion: (1) The degree of attachment between two surfaces held together by interfacial forces—mechanical or chemical or both; (2) the degree of attachment or bonding between application of the same substance; (3) the combined ultimate strength of the molecular forces and the mechanical interlocking achieved between the adhesive and the surface bonded. Adhesion is measured in shear and peel modes. AFA: American Fiberboard Association. ANSI: American National Standards Institute. aliphatic polyurethane coating: A polyurethane coating that contains a specific class of isocyanates based on a long straight chain molecular structure. Normally used in finish coats that are exposed to the elements. It is noted for its good weather resistance. ambient temperature: The temperature of the air existing on all sides; air temperature. application rate: The average quantity (mass, volume or thickness) of material applied per unit area. application temperature: The temperature of a material, such as hot asphalt, when applied to the roof. asphalt shingle: A shingle manufactured by coating a reinforcing material (paper felt or fiberglass mat) with an asphalt-based coating and having mineral granules on the side exposed to the weather. See “shingle.” asbestos: A group of naturally occurring, fibrous impure silicate materials.  This material is often found in older roofing system felts and mastics and poses a serious health risk if disturbed without following proper abatement procedures. ARMA: Asphalt Roofing Manufacturers Association.		adhere: To cause two surfaces to be held together by the combined strength of the molecular forces and the mechanical interlocking achieved between adhesive and the bonded surface. adhesive: A cementing substance that produces a steady and firm attachment or adhesion between two surfaces. aggregate: (1) Crushed stone, crushed slag, water-worn gravel or marble chips used for surfacing a built-up or polymer-modified bitumen roof system; (2) any granular material. AIA: American Institute of Architects. air barrier: The assembly of materials used in building construction to reduce or retard the uncontrolled passage of air into and out of the building. alligatoring: Cracking of a surfacing bitumen, asphalt, coating or mastic or coating on a spray polyurethane foam (SPF) roof system that occurs during the aging process in which the loss of volatile oils and the oxidation brought about by solar radiation produces a pattern or cracks similar to an alligator’s hide; the cracks may or may not extend through the surfacing material. 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. architect: A person technically qualified and professionally licensed to practice architecture; that is, designing and  dministering the construction of buildings. architectural shingle: See “dimensional shingle.” asphalt: A dark brown to black cementitious material in which the predominating constituents are bitumens found in a natural state or more commonly left as a residue after evaporating or otherwise processing crude oil or petroleum. See “bitumen.”
		B ↑ Top
	backnailing: The practice of nailing the concealed portion of a roofing ply, steep roofing unit or other components in a manner such that the fasteners are covered by the next ply, or course, and are not exposed to the weather in the finished roof system. Hot-mopped roofing felts and polymer-modified bitumen sheets may be backnailed to prevent slippage. Also referred to as “blindnailing.” backrolling: Rolling a coating by hand, normally behind the spray or power roller applicator, to ensure better coverage and adhesion. base coat: The first coat of a multicoat system. 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 steep-slope roof system, a strip of wood or metal usually set in or over the structural deck, used to elevate and/or attach a primary roof covering; (4) in a single-ply membrane roof system, a narrow plastic or metal bar that is used to fasten or hold the roof membrane and/or base flashing in place. bitumen: (1) A class of amorphous, black or dark-colored, (solid, semi-solid or viscous) cementitious substances, natural or manufactured, composed principally of highmolecular-weight hydrocarbons, soluble in carbon disulfide, and found in asphalts, tars, pitches and asphaltites; (2) a generic term used to denote any material composed principally of bitumen, typically asphalt or coal tar. blister: (1) A raised portion of a roofing membrane resulting from local internal pressure, such as 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; (2) the similarly formed surface swelling in coated prepared roofing such as asphalt shingles; (3) separation of a coating from a substrate; may be caused by water absorption and the resultant swelling or subsurface corrosion. bond: (1) The adhesive and/or cohesive forces holding two components in positive contact; (2) a surety; typical types are: bid, performance and payment; (3) a guarantee relating to roof system performance. boot: (1) A covering made of flexible material that 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. broadcast: To cast or distribute granular or aggregate surfacing material. 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 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. 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.		ballast: A material, such as minimum nominal #1-1⁄ 2 inch size or #4, or alternatively, #3, #24, #2 or #1—as specified in ASTM D448—smooth river stone, crushed stone, standard precast concrete pavers or interlocking, beveled, doweled or contoured fit lightweight concrete pavers, which employs its mass and the force of gravity to hold a roof membrane system in place. base flashing (membrane base flashing): Plies or strips of roof membrane material used to closeoff 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 and extends up the vertical surface.  See “flashing.” base ply: The bottom or first ply in a built-up or polymermodified bitumen roof system when additional plies are to be subsequently installed. batten seam: A name applied to a common standing seam metal panel profile that may use a square- or rectangular-profile snap-on cap or may be attached to and formed around a beveled wood or metal batten. bituminous: Containing or treated with bitumen, e.g., bituminous concrete, bituminous felts and fabrics, and bituminous pavement. bituminous waterproofing: A waterproofing method available for positive-side waterproofing only; cold or hot bituminous application with reinforcing material. blocking: (1) Sections of wood (which may be preservativetreated) 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; (2) wood cross-members installed between rafters or joists to provide support at cross-joints between deck panels. bonding agent: A chemical substance applied to a suitable substrate to create bond between it and a succeeding layer. See “adhesive.” bridging: (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-size asphalt shingles. brooming: 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. buck: A sheet (membrane, felt, etc.) lap facing upslope allowing water to hit against the edge of it rather than facing downslope to allow water to run over it smoothly. 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. 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.
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	camber: 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 buildings components, such as parapets or columns. See “flashing” and “coping.” cellular concrete: A poured-in-place roof deck material composed of Portland cement, water, a foaming agent or pregenerated foam and air. It’s oven-dry density is about 24 to 32 pounds per cubic foot. chalk: A powdery residue on the surface of a material. chalking: The formation of a friable powder on the surface caused by the disintegration of the binding medium by weather factors. cleat: A continuous metal strip, or angled piece, used to secure metal components. See “clip.”. clip: A noncontinuous metal component or angle piece used to secure a metal panel to a substrate or two or more metal components together. See “cleat.” coal tar: A dark brown- to black-colored, semisolid hydrocarbon produced by the distillation of coal. 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 D450, Type I. coated base sheet: A coated felt intended to be used as a base ply in a built-up or polymer-modified bitumen roof membrane. coated felt (sheet): (1) An asphalt felt that has been coated on both sides with harder, more viscous asphalt;  (2) a fiberglass felt that has been simultaneously impregnated and coated with asphalt on both sides. cold rolled: The process of forming steel into sheets, panels or shapes on a series of rollers at room temperature. combing ridge: A term used to describe an installation of finishing slate shingles or wood roofing at the ridge of a roof whereby the shingles on one side project beyond to the apex of the ridge. conductor head: An enlargement or catch basin at the top of a downspout or leader to receive rainwater from a gutter or scupper. coping: The covering piece on top of a wall exposed to the weather, usually made of metal, masonry or stone. cornice: The decorative horizontal molding or projected roof overhang. 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). coverage: The surface area uniformly covered by a specific quantity of a particular material at a specific thickness. crazing: Fine, random cracks forming a network on the surface of a membrane, coating or film. 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. 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.		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  epending 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. 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. cementitious-wood fiber deck: Treated wood fibers bonded together with Portland cement or other resinousor cementitious-type binder that are compressed and molded to form a structural material. Examples of product trade names are Tectum and Insul-rock. chimney: Stone, masonry, prefabricated metal or woodframed structure containing one or more flues projecting through and above a roof chlorinated polyethylene (CPE): A thermoplastic material used for single-ply roof membranes composed of highmolecular- weight polyethylene that has been chlorinated with a process that yields a flexible rubber-like material.  CPE can be vulcanized but usually is used in a nonvulcanized state. chlorosulfonated polyethylene (CSPE or CSM): Probably best known by the DuPont trade name Hypalon,® a synthetic, rubber-like thermoset material, based on highmolecular-weight polyethylene with sulphonyl chloride, usually formulated to produce a self-vulcanizing membrane.  Membranes in vulcanized and nonvulcanized forms are used; classified by ASTM D5019. coal-tar roof cement: A trowelable mixture of processed coal-tar base, solvents, mineral fillers and/or fibers. Classified by ASTM D4022, “Coal Tar Roof Cement, Asbestos Containing.” coating: A fluid material applied in the field as a film to the roof surface to provide weather protection to the original roof substrate. cold-applied: Designed for or capable of being applied without heating as contrasted to hot-applied. Coldapplied materials are furnished in liquid state, whereas hot-applied materials are furnished as solids that must be heated to liquefy before application. composite board roof insulation: Rigid board insulation generally composted of perlite or wood fiberboard factorybonded to polyisocyanurate or polystyrene. compressive strength: The property of a material that relates to its ability to resist compression loads. control joint: A groove that 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. cool roof: A roof system that uses products made of highly reflective and emissive materials for its top surface. Cool roof surfaces can remain at markedly lower temperatures when exposed to solar heat in service than surfaces of roofs constructed with traditional non-reflective roofing products. 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 insulations are glassfaced siliconized gypsum board, fiberglass board, perlite board, wood fiberboard or mineral fiberboard. Cover boards are also recommended between polyisocyanurate insulation and single-ply membranes to protect the polyisocyanurate. 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.
		D ↑ Top
	dead load: 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 system, and the additional live loads required by the governing building codes and provide the substrate to which the roof or waterproofing system is applied. Decks are either noncombustible, (e.g., corrugated metal, concrete or gypsum) or combustible (e.g., wood plank or plywood). diffusion: (1) The movement of water vapor from regions of high concentration (high water vapor pressure) toward regions of lower concentration; (2) spreading of a constituent in a gas, liquid or solid tending to make the composition of all parts uniform; (3) the spontaneous movement of atoms or molecules to new sites within a material. dimensional stability: The degree to which a material maintains its original dimensions when subjected to changes in temperature and humidity. 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; also called a conductor or leader. drag load: The external force, for example, from the weight of ice and snow, applied to a steep-slope roof system component forcing the component downslope. 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. dynamic load: Any load that is nonstatic, such as a wind load or moving live load.		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. 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. differential movement: In roofing and waterproofing, dimensional changes in dissimilar interfacing materials characterized by different and incompatible rates of change of dimensions, such as membranes and flashing materials, resulting from a temperature change or change in loading. See “thermal movement.” dormer: A structure projecting from a sloping roof usually housing a window or ventilating louver. 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.” drainage mat: A fabric composite or a nondegradable plastic configured to allow drainage of water, typically with adhered filter fabric to prevent growth medium and fines from blocking the drainage path. drainage course: A separate layer of material that provides a location for moisture to move laterally through a protected-membrane roof system. A drainage course relieves hydrostatic pressure from a material’s surface and the associated weight of water. dry-in (or dry-in felt): Usually the underlayment or the process of applying the underlayment for steep-slope roofing. In low-slope roofing, it is usually called a temporary roof.
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	eave: The lower edge of a sloping roof; that part of a roof which projects beyond the wall. ECH: Polyepichlorohydrin, commonly referred to as epichlorohydrin. See “epichlorohydrin.” elasticity: The property of a body that causes it to tend to return to its original shape after deformation (such 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. electro-galvanized: A method of application of corrosion- resistant zinc coatings for fasteners. 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. epoxy: A class of synthetic, thermosetting resins that produce tough, hard, chemical-resistant coatings and adhesives. ethylene propylene diene terpolymer (EPDM): A terpolymer of ethylene, propylene and diene with the residual unsaturated portion of the diene in the side chain to provide for vulcanization. It is a thermosetting synthetic elastomer. EPDM is an acronym for “ethylene propylene diene M-class rubber,” which is a name assigned to this material within the classification established in ASTM D1418. 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. expansion joint: A structural separation between two building elements that allows free movement between the elements without damage to the roof or waterproofing system.		edge venting: The practice of providing regularly spaced or continuously protected (louvered or otherwise shielded) 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. elongation: The ratio of the extension of a material to the length of the material prior to stretching. Usually, elongation is expressed as a percentage of the original length. embedment: (1) The process of pressing/positioning a felt, aggregate, fabric, mat or panel into hot bitumen or adhesive to ensure contact at all points; (2) the process of pressing/positioning granules into coating in the manufacture of factory-prepared roofing, such as shingles. emissivity: (1) Infrared emissivity is a measure of the ability of a surface to shed some of its absorbed heat (in the form of infrared radiation) away from the surface; emissivity is expressed as a percentage or a decimal factor; (2) the ratio of radiant energy emitted from a surface under measurement to that emitted from a black body (the perfect emitter and absorber) at the same temperature. EPDM: Ethylene propylene diene M-class rubber, also called ethylene propylene diene terpolymer. See “ethylene propylene diene terpolymer.” epichlorohydrin (ECH): A synthetic rubber including two epichlorohydrin-based elastomers. It is similar to and compatible with EPDM. erosion: (1) Weathering, wearing away or degradation; (2) wearing away of a coating by chalking or the abrasive action of water or windborne particles or grit. ethylene interpolymers (EIPs): A group of thermoplastic compounds generally based on PVC polymers from which certain single-ply roofing membranes can be formulated. expanded polystyrene (EPS): A type of plastic foam insulation product having predominately closed-cell structure manufactured from expanded polystyrene beads in a molding process; boards or blocks are formed. See “insulation.” expansion: The increase in length or volume of a material or body caused by temperature, moisture or other environmental conditions.
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	fabric: (1) A woven cloth or material of organic or inorganic filaments, threads or yarns used for reinforcement in certain membranes and flashings; (2) geotextile membranes used as a protective or separating layer in roof and waterproofing systems. 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 (fiberglass felts or ply sheets) or polyester fibers. filler: A relatively inert ingredient added to modify physical characteristics. See “stabilizer.” fillet: A heavy bead of waterproofing compound or sealant material generally installed at the point where vertical and horizontal surfaces meet to obtain a more gradual transition through the 90-degree angle at the base of a vertical flashing. fire-retardant-treated (FRT) plywood: Plywood that 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. flange: The projecting edge of a rigid or semirigid component, such as an edge metal flashing flange. flash point: The lowest temperature at which vapors above a combustible substance ignite in air when exposed to an ignition source. flashing: Components used to weatherproof or seal roof system edges at perimeters, penetrations, walls, expansion joints, valleys, 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. fleece: Mats or felts composed of fibers, sometimes used as a membrane backer friabilty: The tendency of material or product to crumble or break into small pieces easily. freeze-thaw resistance: Resistance to cycles of freezing and thawing that could affect applications, appearance or performance.		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 a low-slope roof system. fastener: Any of a wide variety of mechanical securement devices and assemblies, including nails, staples, screws, cleats, clips and bolts, that may be used to secure various components of a roof assembly. fiberboard: Insulation composed principally of cellulose fibers usually derived from paper, paperboard stock or wood, with or without binders. See “insulation.” fiberglass base sheet: A fiberglass-reinforced base sheet for built-up roof system construction, impregnated and coated with asphalt and surfaced with mineral matter; classified by ASTM D4601 as Type I or Type II. filter fabric: A tightly woven fabric, typically polyester or polyethylene/polypropylene, used to restrict the flow of fine particles and other contaminants while allowing water to pass freely through. It is used to protect drainage systems from clogging. 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. 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.” flood (pour) coat: The surfacing layer of bitumen into which surfacing aggregate is embedded on an aggregate-surfaced built-up roof. FM Approvals: Commonly referred to as FM, a research and testing business unit of FM Global (a commercial and industrial property insurer) that classifies roofing components and assemblies for their fire, traffic, impact (hail), weathering and  ind-uplift resistance.
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	galvanized steel: Steel coated with zinc for corrosion  esistance. 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. gambrel: (1) A roof that has two pitches on each side of a central ridge where the upper roof areas have less slope than the lower roof areas; (2) a roof with two inclines on each slope. glaze coat: (1) The top layer of asphalt on a smoothsurfaced 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. 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. gypsum deck: A mixture of calcined gypsum binder and wood chips or other aggregate; when mixed with water, sets to a conglomerate mass; used for poured gypsum roof decks.		glass felt: Glass fibers bonded into a sheet with resin and suitable for impregnation with asphalt in the manufacture of bituminous waterproofing, roof membranes and shingles. granules: Opaque, natural or synthetically colored aggregate commonly used to surface cap sheets, shingles and other granule-surfaced roof coverings; also referred to as mineral or ceramic granules. gusset: (1) Used at the bottom of a steep-slope roof system valley, a large flat metal piece(s) wider than the valley to help prevent buildup at the base of the valley either from debris or ice-dam formations. (2) A plate used to connect two or more members or to reinforce a joint. 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. 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.
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	head lap: (1) The distance of overlap measured from the uppermost ply or course to the point where it laps over the undermost ply or course; (2) the head lap area. Heat welding: A 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. hem: The edge created by folding metal back on itself.		heat-fused: To be installed by heating the underside of the sheet with a propane torch or other heating device, melting the polymer-modified bitumen on the bottomside and adhering the sheet in the molten material. hip: The sloping line along the outer angle formed by the meeting of two sloping sides of a roof with eaves that meet at a right angle. hip roof: A roof that rises by inclined planes from all four sides of a building to form hips at the intersection of adjacent roof slopes.
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	IBC: International Building Code. A model building code published by the International Code Council (ICC); applies to all construction except detached one- and twofamily dwellings and townhouses. ice dam: A mass of ice formed at the transition from a warm to a cold roof surface, frequently formed by refreezing meltwater at the overhang of a steep roof causing ice and water to back up under roofing materials. IRC: International Residential Code; a model building code published by the International Code Council (ICC); applies to detached one- and two-family dwellings and townhouses.		incline: The slope of a roof expressed in percent or in units of vertical rise per units of horizontal run. insulation: Any of a variety of materials designed to reduce the flow of heat from or into a building. See “thermal insulation.” interlocking shingles: Individual shingles that mechanically attach to one another to provide enhanced wind resistance without reliance on sealing strips. isocyanate: A highly reactive organic chemical containing one or more isocyanate groups. A basic component in spray polyurethane foam (SPF) systems and some polyurethane coating systems.
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	joist: Any of the small timbers, metal or wood beams arranged parallel to one another and spanning from wall to wall to support a floor, ceiling or roof of a building.		joule: A unit of energy or work in the SI system; equals the work done by a force of 1 newton, which acts over a distance of 1 meter in the direction of the force.
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	kick-out: A lower downspout section used to direct water away from a wall.		kick-out flashing (diverter): A metal flashing detail installed at the eave end of a roof-to-wall transition designed to direct runoff  way from the wall or wall cladding.
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	lap: That part of a roofing, waterproofing or flashing component that overlaps or covers any portion of the same or another type of adjacent component. lap cement: An asphalt-based roof cement formulated to adhere overlapping plies or asphalt roll roofing. lap seam: Occurs where overlapping materials are seamed, sealed or otherwise bonded. liquid-applied built-up roof: A continuous, semi-flexible roof membrane consisting of multiple plies of felts, mats or fabrics laminated together with alternate layers of roof cements and surfaced with a liquid-applied coating with or without aggregate surfacing.		leaching: (1) The action of removing soluble constituents from a solid into a solution; (2) the dissolving out of soluble substances when water seeps through a roof system. leeward: The direction opposite that from which the wind is blowing. The side sheltered from the wind. For comparison, see “windward.” lightweight concrete: (1) Concrete with a density of less than 115 lb/ft3; (2) Poured deck fill composed of a combination of two or more of the following: gypsum, vermiculite, perlite, wood fibers and air-entrained concrete. low-slope roofs: A category of roofs that generally includes weatherproof membrane types of roof systems installed on slopes at or less than 3:12.
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	mansard: A decorative steep-sloped roof on the perimeter of a building. material safety data sheet (MSDS): A written description of the chemicals in a material or product and other pertinent data, including such things as safe handling and emergency procedures. In accordance with OSHA regulations, it is the manufacturer’s responsibility to produce MSDSs and the employer’s responsibility to communicate their contents to employees. mineral fiber: Insulation composed principally of fibers manufactured from rock, slag or glass, with or without binders. modified bitumen: See “polymer-modified bitumen.” mopping: The application of hot bitumen with a mop or mechanical applicator to the substrate or plies of a bituminous membrane.		mastic: A thick adhesive material used as a cementing agent for holding waterproofing membrane in place. mechanically fastened membrane: Generally used to describe a membrane that has been attached to the substrate at defined intervals. membrane: A flexible or semiflexible roof covering or waterproofing whose primary function is to exclude water. mil: A unit of measure, one mil is equal to 0.001 inches; often used to indicate the thickness of a roof membrane. mineral-surfaced roofing: Roofing materials with a surface or top layer consisting of a granule-surfaced sheet. mop and flop: An application procedure in which roofing elements (insulation boards, felt plies, cap sheets, etc.) are initially placed upside down adjacent to their ultimate locations; coated with adhesive or bitumen; and turned over and adhered to the substrate.
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	NBP: Acrylonitrile butadiene polymer blend. One proprietary NBP membrane is commonly referred to as nitrile-butadiene copolymer. nesting: (1) The installation of new metal roof deck directly on top of existing metal roof deck; (2) a method of reroofing with new asphalt shingles over existing shingles in which the top edge of the new shingle is butted against the bottom edge of the existing shingle; also known as “butt-and-run method.” neoprene: A synthetic rubber (polychloroprene) used in liquid- or sheet-applied elastomeric roof membranes or flashings.		nailer: (Sometimes referred to as “blocking”); a piece or pieces of dimensional lumber and/or plywood secured to a structural deck or walls that provides a receiving medium for the fasteners used to attach membrane or flashing. See “blocking (1).” NFPA: National Fire Protection Association; an international nonprofit organization. Its mission is to reduce the worldwide burden of fire and other hazards on the quality of life by providing and advocating consensus codes and standards, research, training and education. NFPA publishes the NFPA 70, “National Electrical Code” (NEC). NRCA: National Roofing Contractors Association.
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	open time: The period of time after an adhesive has been applied and allowed to dry during which an effective bond can be achieved by joining the two surfaces. OSHA: Occupational Safety and Health Administration; a government agency in the U.S. Department of Labor. Its mission is to maintain a safe and healthy work environment. overflow drainage: Component(s) in a roof or waterproofing drainage system used to protect it against damage from a water load imposed by blocked or partially blocked primary drainage system; e.g., overflow scupper, overflow interior drain.		oriented strand board (OSB): A mat-formed panel product with oriented layers resulting in directional properties. OSB is comprised primarily of wood strands bonded with exterior adhesive formulations under heat and pressure. Design capacities are referenced to the primary and secondary structural axes, which typically correspond to the manufacturing machine and cross-machine directions, respectively. The primary direction is often referred to as the strength direction. overburden: Any material installed on top of a waterproofing assembly.
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	pan: The bottom flat part of a roofing panel that is between the ribs of the panel. pass: (1) A layer of material, usually applied by the spray method, that is allowed to reach cure before another layer (“pass”) is applied; (2) a term used to explain a spray motion of the foam gun in the application of the spray polyurethane foam (SPF) material. The speed of the pass controls the thickness of the SPF. perforated felt: Bitumen-saturated felt perforated with closely spaced small holes to allow air and moisture to escape during application of built-up roofing; depending on the type of material or specific use, can be classified in accordance with  STM D226, D2626 or D4897 requirements. permeability: (1) The time rate of vapor transmission through unit area of flat material of unit thickness (values in reference sources are quoted for unit thicknesses) induced by unit vapor pressure difference between two specific surfaces under specified temperature and humidity conditions. The English (inch•pound) unit of measurement for permeability is (grains•in.)/(h•ft2•in. Hg), which is commonly referred to as “perm•inch” units; (2) The property of a porous material that permits a fluid (or gas) to pass through it; commonly refers to water vapor permeability of a sheet material or assembly and is defined as water vapor permeance per unit thickness. plastic cement: A roofing industry generic term used to describe asphalt roof cement that is a trowelable mixture of solvent-based bitumen, mineral stabilizers, and other fibers and/or fillers; generally it is intended for use on relatively low slopes, not vertical surfaces. See “asphalt roof cement” and “flashing cement.” polyisobutylene (PIB): A product formed by the polymerization of isobutylene; may be compounded for use as a roof membrane material. polyisocyanurate foam board: A thermal insulation composed of polyisocyanurate foam with adhered facers; commonly called iso or isoboard; classified in accordance with ASTM C1289. polyurethane coating: A one- or two-part solvent-based coating that contains polyisocyanate monomer and a hydroxyl containing resin, that reacts during cure to form elastomeric coating. ponding: The excessive accumulation of water at lowlying areas on a roof that remains after 48 hours after precipitation under conditions conducive to drying. positive drainage: The drainage condition in which consideration has been made during design for all loading deflections of the deck and additional roof slope has been provided to ensure drainage of the roof area within 48 hours of precipitation. primer: (1) A thin, liquid-applied solvent-based bitumen that may be applied to a surface to improve the adhesion of subsequent applications of bitumen; (2) a material that is sometimes used in the process of seaming single-ply membranes to prepare the surfaces and increase the strength (in shear and peel) of the field splice; (3) a thin liquidapplied material that may be applied to the surface of spray polyurethane foam (SPF) to improve the adhesion of subsequent application of SPF protective coatings.		parapet wall: The part of a perimeter wall that extends above a roof. pedestal: A support or base for rooftop components such as pavers, pipes and small rooftop units. penetration: (1) Any construction (e.g., pipes, conduits, HVAC supports) passing through a roof; (2) the consistency of a bituminous material expressed as the distance, in tenths of a millimeter (0.1 mm), that a standard needle penetrates vertically into a sample of material under specified conditions of loading, time and temperature (ASTM D5 is the test method used for bituminous materials). A cone is sometimes used for special purposes instead of a needle. perlite: An aggregate used in lightweight insulating concrete and preformed perlitic insulation boards, formed by heating and expanding siliceous volcanic glass. pitch-pocket (pitch-pan): A flanged, open-bottomed enclosure made of sheet metal or other material placed around a penetration through the roof, properly stripped in to the roof membrane and filled with grout and bituminous or polymeric sealants to seal the area around the penetration. plank deck: A wood deck of planks usually 15⁄ 8 inches to 31⁄ 2 inches thick and 6 inches to 8 inches wide laid on the flat tongued-and-grooved or splinted edges and spiked together. pliability: The material property of being flexible or moldable. ply: A layer of felt or ply sheet in a built-up roof membrane or roof system. polyisocyanurate foam: A cellular, unfaced, preformed rigid thermal insulation produced by the polymerization of polyisocyanates in the presence of polyhydroxyl compounds, catalysts, cell stabilizers, and blowing agents; classified in accordance with ASTM C591. polymer-modified bitumen: (1) A bitumen modified by including one or more polymers (e.g., atactic polypropylene, styrene butadiene styrene); (2) composite sheets consisting of a polymer-modified bitumen often reinforced with various types of mats or films and sometimes surfaced with films, foils or mineral granules. polyvinyl chloride (PVC): A synthetic thermoplastic polymer prepared from vinyl chloride. PVC can be compounded into flexible and rigid forms through the use of plasticizers, stabilizers, fillers and other modifiers. Rigid forms are used in pipes; flexible forms are used in the manufacture of sheeting and roof membrane materials. prestressed concrete: Concrete in which the reinforcing cables, wires or rods are tensioned before there is load on the structural member, holding the concrete in compression for greater strength. protected membrane roof (PMR): An insulated and ballasted roof assembly in which the insulation and ballast are applied on top of the membrane (sometimes referred to as an inverted roof assembly). puncture resistance: The ability of a material to withstand the action of a penetrating or puncturing object. PVC: See “polyvinyl chloride (PVC).”
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	raggle: A groove or slot often cut in a masonry wall or other vertical surface adjoining a roof for inserting an inset flashing component such as a reglet. rake: The sloped edge of a roof at or adjacent to the first or last rafter. receiver: A component in a two-piece counterflashing that may be surface-mounted to a wall, inset into a raggle or embedded behind cladding. It is used for ease of installation and future maintenance and repair or replacement. See “reglet.” reinforced membrane: A roof or waterproofing membrane that has been strengthened by the addition or incorporation of one or more reinforcing materials, including woven or nonwoven glass fibers, polyester mats or scrims, nylon or polyethylene sheeting. ridge cap: A material or covering applied over the ridge of a roof. roof assembly: An assembly of interacting roof components including the roof deck, vapor retarder (if present), insulation and membrane or primary roof covering designed to weatherproof. rosin paper (specifically rosin-sized sheathing paper): A nonasphaltic paper used as a sheathing paper or slip sheet in some roof systems.		R-value: See “thermal resistance (R)” racking: A method of asphalt shingle application also referred to as the “straight-up method,” whereby shingle courses are applied vertically up the roof rather than laterally or across and up; requires placing a part of a shingle under product already in place every other course, which may result in a less than recommended number of nails being used for fastening. reflectivity: Defined as the reflectance of an opaque, optically flat surface or coating of thickness sufficient to be a completely opaque. Reflectivity is a property of a material, while “reflectance” is a property of a sample of the material. reglet: A sheet-metal receiver for the attachment of counterflashing. A reglet may be surface-mounted, inset into a raggle or embedded behind cladding. ridge: Highest point on a roof, represented by a horizontal line where two roof areas intersect, running the length of the area. ridge vent: A ventilator located at the ridge that allows the escape of warm and/or moist air from the attic area or rafter cavity. roof curb: Raised frame used to mount mechanical units such as air conditioning units, exhaust fans, skylights, etc., on a roof. run: Horizontal dimension of a slope.
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	saddle: A small tapered/sloped roof area structure that helps to channel surface water to drains; frequently located in a valley. A saddle is often constructed like a small hip roof or pyramid with a diamond-shaped base. SBS: See “styrene butadiene styrene copolymer (SBS).” scrim: A woven, nonwoven or knitted fabric composed of continuous strands of material used for reinforcing or strengthening membranes. self-adhering membrane: A membrane that can adhere to a substrate and to itself at overlaps without the use of an additional adhesive. The undersurface of a selfadhering membrane is protected by a release paper or film, which prevents the membrane from bonding to itself during shipping and handling. service life: (1) The period of time a building component or system will function successfully without replacement or excessive repair assuming reasonable or expected periodic maintenance is performed; (2) the number of years of service a material, system or structure will provide before rehabilitation or replacement is required. shingle: (1) A small unit of prepared roofing designed for installation with similar units in overlapping rows or courses on inclines normally exceeding 3:12 slope; (2) to cover with shingles; (3) to apply any sheet material in succeeding overlapping rows like shingles. single-ply membranes: Roof membranes that are fieldapplied using just one layer of membrane material (either homogeneous or composite) rather than multiple layers. single-ply roofing: A roof system in which the principal roof covering is a single-layer flexible thermoset or thermoplastic membrane. slippage: Relative lateral movement of adjacent components of a roof membrane. It occurs mainly in roofing membranes on a slope, sometimes exposing the lower plies or even the base sheet to the weather. snow guard: A series of devices attached to the roof in a pattern that attempts to hold snow in place, thus preventing sudden snow or ice slides from the roof; any device intended to prevent snow from sliding off a roof. soffit vent: A manufactured or custom built air inlet source located at the downslope eave or in the soffit of a roof assembly. solvent welding: A process where a liquid solvent is used to chemically weld or join together two or more layers of certain membrane materials (usually thermoplastic). splice plate: A metal plate placed underneath the joint between two pieces of metal. splice-tape: Cured or uncured synthetic rubber tape used for splicing membrane materials squeegee: (1) A blade of leather or rubber set on a handle and used for spreading, pushing or wiping liquid material on, across or off a surface; (2) to smooth, wipe or treat with a squeegee. steep-slope roofs: A category of roofing that generally includes water-shedding types of roof coverings installed on slopes exceeding 3:12. step flashing: Individual pieces of sheet-metal material used to flash walls, around chimneys, dormers and such projections along the slope of a roof. Individual pieces are overlapped and stepped up the vertical surface. substrate: The surface upon which a roofing or waterproofing membrane is applied (e.g., in roofing, the structural deck or rigid board insulation). sump: An intentional depression around a roof drain or scupper that promotes drainage.		saturated felt: A felt that has been immersed in hot bitumen; the felt adsorbs as much bitumen as it can retain under the processing conditions but remains porous and contains voids. scupper: A drainage device in the form of an outlet through a wall, parapet wall or raised roof edge typically lined with a sheet-metal sleeve. seam: A joint formed by mating two separate sections of material. Seams can be made or sealed in a variety of ways, including adhesive bonding, hot-air welding, solvent welding, using adhesive tape and sealant. self-flashing: The ability of a material to be applied around a penetration or at a roof transition without the need for other flashing materials. shear strength: The resistance to forces that cause or tend to cause two contiguous parts of a body to slide relative to each other in a direction parallel to their contact plane. shelf life: The maximum time interval during which a material may be stored and remain in a usable condition according to the material manufacturer; usually related to storage conditions. shrinkage: A decrease in one or more dimensions of an object or material. side lap: The continuous longitudinal overlap of neighboring like materials. slag: A hard aggregate that is left as a residue from blast furnaces; may be used as a surfacing material on certain (typically bituminous) roof membrane systems. slate: A hard, brittle metamorphic rock consisting mainly of clay minerals used extensively as dimensional stone for steep roofing and in granular form as surfacing on some other roofing materials. smooth-surfaced roof: A membrane roof system that includes a weathering surface without mineral granule or aggregate surfacing. snow load: The live load due to the weight of snow on a roof (expressed in lb/ft2) included in design calculations. soffit: The exposed undersurface of any exterior overhanging section of a roof eave. soil stack: A sanitation pipe that penetrates the roof; used to vent plumbing fixtures. span: The distance between supports or beams, girders or trusses. splice: Bonding or joining of overlapping materials. See “seam.” square: (1) A unit used in measuring roof area equivalent to 100 square feet; (2) a quantity of material sufficient to cover 100 square feet of a roof deck. standing seam: In metal roofing, a type of seam between adjacent sheets of material made by turning up the edges of two adjacent metal panels and then folding or interlocking them in a variety of ways. starter course: The first layer of roofing, applied along a line adjacent to the downslope perimeter of the roof area; with steep-slope water-shedding roof coverings, the starter course is covered by the first course. strip flashing: Membrane flashing strips used for sealing or flashing metal flashing flanges into the roof membrane. styrene butadiene styrene copolymer (SBS): High molecular weight copolymer with thermoset and thermoplastic properties (thermoplastic elastomer), formed by the block copolymerization of styrene and butadiene monomers; used as the modifying compound in SBS polymer-modified asphalt roofing membranes to impart rubberlike qualities to the asphalt.
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	tapered insulation: A system of precut or premolded insulation boards or a poured insulation fill designed to provide slope to the roof deck before installing the roof membrane. tar: A brown or black bituminous material, liquid or semisolid in consistency in which the predominating constituents are bitumens obtained as condensates in the processing of coal, petroleum, oil-shale, wood or other organic materials. textural slate roof system: A term used to designate a slate roof system with a range of slate thicknesses mixed throughout; usually uses slates with rougher texture than standard slate with uneven tails or butts. thermoplastic: A material that softens when heated and hardens when cooled. This process can be repeated provided the material is not heated above the point at which decomposition occurs. thermoplastic olefin membrane (TPO): A blend of polypropylene and ethylene-propylene polymers, colorant, flame retardants, ultraviolet radiation absorbers and other proprietary substances that may be blended with the TPO to achieve the desired physical properties. The membrane may or may not be reinforced. tie-in: In roofing and waterproofing, the transitional seal used to terminate a roofing or waterproofing application at the top or bottom of flashings or by forming a watertight seal with the substrate, membrane, or adjacent roof or waterproofing system. tuckpointing: The process of removing deteriorated mortar from an existing masonry joint and troweling new mortar or other filler into the joint.		taping: (1) The technique of connecting joints between insulation boards or deck panels with tape; (2) the technique of using self-adhering tape-like materials to seam or splice single-ply membranes. termination: The treatment or method of anchoring and/or sealing the free edges of a membrane in a roof or waterproofing system. thermal barrier: In torched membrane applications over combustible substrates, an above-deck barrier incorporated into a roof system before torching as a fire-safety practice. Acceptable thermal barriers include: minimum 3⁄ 4- inch-thick perlite board insulation, minimum 3⁄ 4-inchthick fiberglass or mineral wool board insulation, or minimum 1⁄ 4-inch-thick glass-faced gypsum board. thermoplastic elastomer: A material having the general properties of an elastomer and capable of being repeatedly softened by heat and hardened to shape by cooling without significant degradation of the polymer system; typically more thermally and pressure-sensitive and more sensitive to solvents than thermoset elastomers. through-wall flashing: A water-resistant membrane or material assembly extending totally through a wall and its cavities positioned to direct water within the wall to the exterior, usually through weep holes. torch-applied (torch-down): Method used in the installation of polymer modified bitumen membranes characterized by using open flame propane torch equipment. TPO: thermoplastic olefin.
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	UL label: An identification label or seal affixed to a roofing product or package with the authorization of Underwriters Laboratories Inc. The presence of the label indicates the product has met certain performance criteria.		underlayment: An asphalt-saturated felt or other sheet material (may be self-adhering) installed between a roof deck and roof covering, usually used in a steep-slope roof construction. Underlayment is primarily used to separate a roof covering from the roof deck, shed water and provide secondary weather protection for the roof area of the building.
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	valley: The internal angle formed by the intersection of two sloping roof planes. veneer: (1) A single wythe of masonry for facing purposes that may not be structurally connected; (2) any of the thin layers of wood glued together to form plywood. vapor barrier: See “vapor retarder.”		vapor retarder: Layer(s) of material or a laminate used to appreciably reduce the flow of water vapor into a roof assembly. viscosity: The resistance of a material to flow under stress. For bitumen, viscosity measurements are reported in centipoise (cP or cPs) at a specific temperature; as viscosity increases, flow rate decreases.
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	walkways: (1) High traffic and high-service-frequency areas on a rooftop, particularly those leading and adjacent to vents, hatches and heavy duty air-conditioning units; (2) materials or accessories such as traffic mats or pavers installed on rooftop surfaces to provide wearing surfaces for traffic and/or protect a roof system from damage resulting from rooftop traffic. water and ice-dam protection membrane: A continuous membrane installed under steep-slope roofing materials in areas subject to ice damming or wind-driven rain that prohibits water that gets through the roof covering from getting into the structure; ice- and water-protection membranes classified by ASTM D1970 must also seal around fasteners. waterproofing membrane: The part of a waterproofing system that has the primary function of excluding water; it does not include accessories such as drainage materials or protection boards. See “membrane.” weatherproof: The ability of a membrane or roof covering to prevent the passage of water with a limited amount of hydrostatic pressure. wicking: The process of moisture movement by capillary action. wind uplift: The force caused by the deflection of wind at roof edges, roof peaks or obstructions causing a drop in air pressure immediately above the roof surface.		water-shedding: The ability of individual, overlapping components to resist the passage of water without hydrostatic pressure. water-shedding roof system: A roof system that depends on gravity for quick drainage via water shedding to prevent water entry into or through the system. waterproofing: Treatment of a surface or structure to prevent the passage of water under hydrostatic pressure. waterproofing assembly: An assembly of interacting waterproofing components including the deck, membrane and protection/drainage/insulation course. waterproofing system: A system of interacting waterproofing components consisting at a minimum of a membrane but may also include protection, drainage and insulation courses, as well as waterstops, expansion and control joints, various flashings and counterflashings, and overburden such as pavers, cast concrete and wire mesh or rebars. It does not include the substrate. weld: To join pieces of material together by heat fusion. woven valley: A method of valley construction in which shingles or roofing from both sides of the valley extend across the valley and are woven together by overlapping alternate courses as they are applied.
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	yield: In spray polyurethane foam (SPF) roofing, the volume of foam per unit weight normally expressed as board feet per pound or board feet per 1,000 pounds.
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	zinc: A soft, self-healing metal that reacts with the environment to produce a soft blue-gray zinc carbonate patina that protects the underlying metal from corrosion. Zinc is commonly used as sacrificial (galvanized) coating for a base metal such as sheet steel and iron, in various metal alloys and in oxide form as a white pigment.