Wayne's Roofing

	This glossary contains many useful terms and definitions. For easier browsing you can view our Photo Glossary, which has photographs of common roofing sites and problems, or you can browse the entire glossary by our alphabetical listing. A \| B \| C \| D \| E \| F \| G \| H \| I \| J-L \| M \| N \| O-P \| R S \| T \| U-V \| W-Z

	Accelerated Weathering: the process in which materials are exposed to a controlled environment where various exposures such as heat, water, condensation, or light are altered to magnify their effects, thereby accelerating the weathering process. The material’s physical properties are measured after this process and compared to the original properties of the unexposed material, or to the properties of the material that has been exposed to natural weathering. Adhere: to cause two surfaces to be held together by adhesion, typically with asphalt or roofing cements in built-up roofing and with contact cements in some single-ply membranes. Aggregate: rock, stone, crushed stone, crushed slag, water worn gravel or marble chips used for surfacing and/or ballasting a roof system. Aging: the effect on materials that are exposed to an environment for an interval of time. Alligatoring: the cracking of the surfacing bitumen on a built-up roof, producing a pattern of cracks similar to an alligator’s hide; the cracks may or may not extend through the surfacing bitumen. Application Rate: the quantity (mass, volume, or thickness) of material applied per unit area. 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 relieve thermal stresses in a roof system where an expansion joint is not required, or to separate large roof areas (sometimes between expansion joints), and may be used to facilitate installation of tapered insulation. (See NRCA Construction Details.) Asbestos: a group of natural, fibrous, impure silicate materials used to reinforce some roofing products. 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: produced by blowing air through molten asphalt held at an elevated temperature, to raise the asphalt’s softening point and modify other properties. Asphalt Emulsion: a mixture of asphalt particles and an emulsifying agent such as bentonite clay and water. These components are combined by using a chemical or a clay emulsifying agent and mixing or blending machinery. Asphalt Felt: an asphalt-saturated and/or an asphalt-coated felt. (See Felt.) Asphalt Roof Cement: a trowelable mixture of solvent-based bitumen, mineral stabilizers, other fibers and/or fillers. Classified by ASTM Standard D 2822-91 Asphalt Roof Cement, and D 4586-92 Asphalt Roof Cement, Asbestos-Free, Types I and II. Type I is generally 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.) 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
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Back-Nailing: (also referred to as Blind-Nailing) the practice of nailing the back portion of a roofing ply, steep roofing unit, or other components in a manner so that the fasteners are covered by the next sequential ply, or course, and are not exposed to the weather in the finished roof system.

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

Ballast: an anchoring material, such as aggregate, or precast concrete pavers, which employ the force of gravity to hold (or assist in holding) single-ply roof membranes in place.

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

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

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

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

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

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

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

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

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

Blanket (Batt) Insulation: fiberglass or other compressible fibrous insulation, generally available in roll form.

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

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

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

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

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

BOMA: Building Owners & Managers Association, International

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

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

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

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

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

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

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

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

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

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

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

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

Butyl: rubber-like material produced by copolymerizing isobutylene with a small amount of isoprene. Butyl may be manufactured in sheets, or blended with other elastomeric materials to make sealants and adhesives.

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

Butyl Rubber: a synthetic elastomer based on isobutylene and a minor amount of isoprene. It is vulcanizable and features low permeability to gases and water vapor.

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

Calender: a machine with two or more counter-rotating steel rollers used for laminating sheeting or skim coating (topping) to a controlled thickness or surface characteristic, or both.

Calendering: a manufacturing process by which some polymeric membranes and other sheetings are produced.

Camber: a slight convex curve of a surface, such as in a prestressed concrete deck.

Canopy: any overhanging or projecting roof structure, typically over entrances or doors. Sometimes the extreme end is unsupported.

Cant: a beveling of foam at a right angle joint for strength and water run off.

Cant Strip: a beveled or triangular-shaped strip of wood, wood fiber, perlite, or other material designed to serve as a gradual transitional plane between the horizontal surface of a roof deck or rigid insulation and a vertical surface.

Cap Flashing: usually composed of metal, used to cover or shield the upper edges of the membrane base flashing, wall flashing, or primary flashing. (See Flashing and Coping.)

Cap Sheet: a granule-surface coated sheet used as the top ply of some built-up or modified bitumen roof membranes and/or flashing.

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: the action that causes movement of liquids by surface tension when in contact with two adjacent surfaces such as panel side laps.

Catalyst: an ingredient in a coating of SPF which initiates a chemical reaction or increases the rate of a chemical reaction.

Cathodic: with regard to metal and galvanic response, cathodic metals are lower in the galvanic series. (May be protected by the more anodic metals.)

Caulk: a material (usually a composition of vehicle and pigment) used for filling/sealing joints or junctures, where no elastomeric properties are required. (See Sealant.)

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

Cavitation: the vaporization of a liquid under the suction force of a pump, usually due to inadequate flow to a pump. The vaporization can create voids within the pump supply line. In SPF spray pumps, cavitation will result in off-ration foam.

Cavity Wall: a wall built or arranged to provide an air space within the wall (with or without insulating material), in which the inner and outer materials are tied together by structural framing.

Chalking: the degradation or migration of an ingredient, in paints, coatings, or other materials.

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

Chlorosulfonated Polyethylene (CSPE or CSM): (probably best known by the DuPont trade name Hypalon TM ) a synthetic, rubber-like thermoset material, based on high molecular weight polyethylene with suphonyl chloride, usually formulated to produce a self-vulcanizing membrane. Classified by ASTM Standard D 5019-89.

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

Cleat: a metal strip, plate or metal angle piece, either continuous or individual (clip), used to secure two or more components together.

Clip: an individual (discrete) cleat. (See Cleat.)

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 obtained as residue from the partial evaporation or distillation of coal tars. Coal tar pitch is further refined to conform to the following roofing grade specifications:

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, conforming to ASTM D 450, Type III.

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

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 Felt: a felt that has been saturated 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.

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 theoretical covering rate cannot be used without adding a mini-mum of 25% additional material.

Coated Base Sheet: a felt that has previously been saturated (filled or impregnated) with asphalt and later coated with harder, more viscous asphalt, which greatly increases its impermeability to moisture.

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.

Cold Process Built-Up Roof: a continuous, semi-flexible roof membrane, consisting of a ply or plies of felts, mats or other reinforcement fabrics that are laminated together with alternate layers of liquid-applied (usually asphalt-solvent based) roof cements or adhesives installed at ambient or a slightly elevated temperature.

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

Combustible: capable 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.

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. Some of the membranes listed in this generic category are CPA, EIP, NBP, and TPA.

Compressive Strength: the ability of materials and components to resist deformation or other damage caused by the weight of compression of either live or dead loads.

Concealed-Nail Method: a method of asphalt roll roofing application in which all nails are driven into the underlying course of roofing and covered by an adhered, overlapping course.

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

Condensation: the conversion of water vapor or other gas to liquid state as the temperature drops or atmospheric pressure rises. (Also see Dew Point.)

Conditioning: the exposure of a material to the influence of a prescribed atmosphere for a stipulated period of time or until a stipulated relation is reached between material and atmosphere.

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/hft 2 °F.

Conductor Head: a transition component between a through-wall scupper and downspout to collect and direct run-off water.

Construction Joint: a formed or assembled joint at a predetermined location where two successive placements of concrete meet.

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.

Coping: the covering piece on top of a wall which is exposed to the weather, usually made of metal, masonry, or stone. It is preferably sloped to shed water back onto the roof.

Copolymer: the product of polymerization of two or more substances at the same time; a mixed polymer.

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

Course: (1) the term used for each row of shingles 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 each layer of roof cement.)

Cove: see Fillet.

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

CPA: Copolymer Alloy.

CPE: Chlorinated Polyethylene.

Crack: a non-linear separation or fracture occurring in a material. May be generally caused by induced stress, dimensional instability, or substrate movement. Some cracks may be more of a linear separation or fracture. (See Split.)

Cricket: an elevated roof substrate or structure, constructed to divert water around a chimney, curb, away from a wall, expansion joint, or other projection/penetration. (See Saddle.)

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.

CSI: Construction Specifications Institute

CSM: ASTM designation for chlorosulfonated polyethylene. (See CSPE.)

CSPE: chlorosulfonated polyethylene.

Cupola: a relatively small roofed structure, generally set on the ridge or peak of a main roof area. (See Figure 3.)

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.

Cutback: solvent-thinned bitumen used in cold-applied (process) roofing adhesives, roof cements, and roof coatings.

Cutoff: a permanent detail designed to seal and 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-off, which may be a temporary or permanent seal.) (See Tie-Off.)

Cutout: the open portions of a strip shingle between the tabs.

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