Roofing Terms

Talk like a Roofer

Check out our glossary of roofing terms so you know what the heck we’re talking about.


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

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.

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

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

Active: will corrode in the presence of moisture or a “noble” metal.

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.

Adhesion: the state in which two surfaces are held together by interracial forces which may consist of molecular forces or interlocking action, or both.

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.

Air Leakage: (as it relates to passive ventilation) negative condition where air leaks into the roof cavity (designed for use as a passive ventilation system) through cracks or openings in the structure in lieu of through the intended intake vents.

Alligatoringthe 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.

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

Aluminum: a non-rusting metal sometimes used for metal roofing and flashing.

Ambient Temperature: the temperature of the air; air temperature.

APP: see Atactic Polypropylene.

Application Rate: the 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 the sloped roof and a vertical wall or steeper-sloped roof.

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: 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 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.)

ARMA: Asphalt Roofing Manufacturers Association

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 lilt

»       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 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 2822-91 Asphalt Roof Cement, and D 4586-92 Asphalt Roof Cement, Asbestos-Free, Types I and 11

»       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 l; Specification D 449, Types I or Il; 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 lil; or Specification D 449, Type lilt (See Plastic Cement and Flashing Cement.)

ASTM: American Society for Testing and Materials

Atactic Polypropylene: a group of high molecular weight polymers formed by the polymerization of propylene.

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

Back-Nailing: (also referred to as Blind-Nailing) the practice of nailing the back portion of a roofing ply, steep roofing unit, or other components in a manner so that the fasteners are covered by the next sequential ply, or course, and are not exposed to the weather in the finished roof system.

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

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

Bar Joist: see Steel Joist

Barrel Vault: a building profile featuring a rounded profile to the roof on the short axis, but with no angle change on a cut along the long axis.

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

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

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

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

Batten Seam: a metal panel profile attached to and formed around a beveled wood or metal batten.

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

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

Bi-Level Drain: see Dual-Level Drain.

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

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

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

Bitumen-Stop: see Envelope and Bleed Sheet.

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

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

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

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

Bleeder Strip: see Rake-Starter.

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

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

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

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

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

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

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

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

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

Brake: hand- or power-activated machinery used to form metal.

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

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

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

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

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

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

Bundle: an individual package of shakes or shingles.

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

Button Punch: a process of indenting two or more thicknesses of metal that are pressed against each other to prevent slippage between the metal.

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

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

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

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


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 nonconductor.

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

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.

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.

C-Channel: a structural framing member.

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.

Centipoisea unit of measure of absolute viscosity. (Note: The viscosity of water is one centipoise. The lower the number, the less the viscosity.)

Centistokea unit of viscosity – the ratio of a liquid’s absolute viscosity to the density of that liquid.

Chalk: a powdery residue on the surface of a material.

Chalk Line: a line made on the roof by snapping a taut string or cord dusted with colored chalk. Used for alignment purposes.

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

Channel Flashing: For steep-slope roof construction) a type of flashing used at roof-to-wall junctures and other roof-to-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 a 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 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™) a synthetic, rubber-like thermoses material, based on high molecular weight polyethylene with suphonyl chloride, usually formulated to produce a self-vulcanizing membrane. Classified by ASTM Standard D 501 9-89.

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.

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. (See Figure 1.)

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

Clipped Glable: a gable cutback at the peak in a hip-roof form. (See Figure 2.)

Closed-Cut Valleya 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 centerline.

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 lil 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 lilt

»       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 lilt

»       Coal Tar Waterproofing Pitch: a coal tar used as the dampproofing or waterproofing agent in belowgrade 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.

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-saturated felt that has also been coated on both sides with harder, more viscous “coating” asphalt; (2) a glass fiber felt that has been simultaneously impregnated and coated with asphalt on both sides.

Coating: a layer of material spread over a surface for protection or decoration. Coatings for SPF are generally liquids, semi-liquids, or mastics; spray, roller, or brush applied; and cured to an elastomericconsistency.

Coefficient of Thermal Expansion: a mathematical formulation used to predict the change in dimension (typically length) of a material as a function of temperature change.

Cohesion: the degree of internal bonding of one substance to itself.

Cold Forming: the process of using press brakes, roll farmers, etc., to shape metal into desired profiles at ambient room temperature.

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.

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

Collector Box: see Conductor Head.

Color Stability: the ability of a material to retain its original color.

Column: a primary structural member used in a vertical position in a building to transfer loads from horizontal structural members (e.g., main roof beams, trusses, or rafters) to the foundation/footing.

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.)

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.

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

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.

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

Copper: a natural weathering metal used in metal roofing; typically used in 16 or 20 ounce per square foot thickness (4.87 or 6.10 kg/sq m).

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.

Counterflashingformed 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.

Cover Plate: a metal strip sometimes installed over the joint between formed metal pieces.

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

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.)

Creep: the permanent deformation of a roofing material or roof system caused by movement of the roof membrane, or compression of a roof insulation board at fastener positions, that results from continuous load or thermal stress or loading. Creep at roof temperature is sometimes called “cold flow.”

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.)

Cross Ventilation: the effect that is provided when air moves through a roof cavity between the vents.

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.

Cure Time: the time required to effect curing. 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-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. (See Figure 4.)

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

Dead Level: essentially horizontal or flat, as in a roof deck or rooftop with no intentional slope to the roof drains. Also referred to as zero (0) slope. (See Slope.)

Dead-Level Asphalt: see Asphalt.

Dead Loads: permanent non-moving loads that result from the weight of a building’s structural and architectural components, mechanical and electrical equipment, and the roof assembly itself. Essentially the same as “dead weight” or “dead weight loads.”

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. Decks are either non-combustible (e.g., corrugated metal, concrete, or gypsum) or combustible (e.g., wood plank or plywood), and provide the substrate to which the roofing or waterproofing system is applied.

Deflection (Bowing, Sagging): the downward displacement of a structural member or system under load.

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

Degree Days: the difference between a reference temperature (usually 65°F [1 8.3°C]) and the mean temperature for the day, times 24 hours, times the number of days in the period. Degree days are used to compare the severity of cold or heat during the heating or cooling season.

Delaminationseparation of the laminated layers of a component or system.

Design Loads: those loads specified in building codes or standards published by federal, state, county, or city agencies, or in owners’ specifications to be used in the design of a building.

Dew Point Temperature: the temperature at which water vapor condenses in cooling air at the existing atmospheric pressure and vapor content. Cooling at or below the dew point will cause condensation.

Diaphragm: see Roof Diaphragm.

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

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

Dimensional Stability: the ability of a material to resist change in length, width, and/or thickness that results from exposure to elevated or freezing temperatures, and moisture, over time.

Dome: a roof that is shaped like a half-circle, or a variation of one.

Domer: a framed projection through the slopping plane of a roof. (See figure 5)

Double Coverage: application of asphalt, slate, or wood roofing such that the lapped portion is at least 2 inches (51mm) wider than the exposed portion, resulting in two layers of roofing material over the deck.

Double Graveling: the process of applying two layers or flood coats of bitumen and aggregate to a built-up roof. Loose aggregate should be swept from the first application prior to the second coating of bitumen and aggregate. Approximately 50% of the second aggregate application will remain adhered in the bitumen flood coat unless physically removed.

Double Lock Standing Seam: a standing seam that utilizes a double, overlapping interlock between two seam panels. (See Standing Seam.)

Downspout: a 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.

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 overchanging component, with an outward projecting lower edge, intended to control the direction of dripping water and help protect underlying building components. A drip edge also can be used to break the continuity of contact between the roof perimeter and wall components to help prevent capillary action.

Dry: (1) to change the physical state of a material by the loss of components through evaporation, absorption, oxidation, or a combination of these effects; (2) the absence of water or moisture.

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

Dry-In or Dry-In Felt: usually the underlayment or the process of applying the underlayment for steep roofing.

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 level and the waterproofing membrane level used to collect and direct the flow of runoff water from a horizontal slip. (See NRCA Waterproofing Detail WP-9.)

Durability: the ability to withstand physical, chemical, or environmental abuse.

Dust Free: a surface is considered dust free when a finger can be lightly run over the surface without picking up any dirt, dust, or chalk on the finger.

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

Eave: a projecting edge of a roof that extends beyond the supporting wall. (See Figure 6.)

Eave Height: the vertical dimension from finished grade to the cave.

Eaves-Trough: see Gutter.

Edge Stripping: membrane flashing strips cut to specific widths used to seal/flash perimeter edge metal and the roof membrane.

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: the formulation of crystalline deposits, generally whitish in color, on the surface of stone, brick, concrete, or other masonry surface when moisture moves through and evaporates on the masonry. May also be caused by free alkalies leached from mortar, grout, or adjacent concrete.

Elasticity: the property of matter by virtue of which it tends to return to its original size and shape after removal of a stress or force which caused a deformation.

Elastomernatural or synthetic material which, at room temperature, can be stretched under low stress and, upon immediate release of the stress or force, will return quickly to its approximate original dimensions.

Elastomericthe elastic, rubber-like properties of a material that will stretch when pulled and will return relatively quickly to its original shape when released.

Elastomeric Coating: a coating system which, when fully cured, is capable of being stretched at least twice its original length (100% elongation) and recovering to its original dimensions.

Electrolyte: a liquid, most often a solution, that will conduct current.

Elongation: the ability of a material (e.g., roofing membrane) to be stretched by the application of a force.

Embedment: (1) the process of installing or pressing-in a reinforcement felt, fabric, mat or panel uniformly into bitumen or adhesive; (2) the process of pressing granules into coating during the manufacture of factory-prepared roofing; (3) the process whereby ply sheet, aggregate, or other roofing components settle into hot- or cold-applied bitumen via the force of gravity.

Embrittlementthe loss of flexibility or elasticity of a material. The transition of a flexible material to a brittle state.

Emulsion: a dispersion of fine particles or globules in a liquid. (See Asphalt Emulsion and Bitumen Emulsion.)

End Lap: the distance of overlap where one ply, panel, or piece extends beyond the end of the immediately adjacent underlying ply, panel, or piece. (See Figure 7. )

Envelope (Bitumen-Stop): a continuous edge seal formed at the perimeter and at penetrations by extending the base sheet or one ply of felt beyond the edge of the membrane field plies. After all overlying field plies or insulation are in place, the extended ply is turned back onto the membrane and adhered. The envelope is intended to prevent 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. ECH is typically used in lieu of EPDM when enhanced resistance to animal fat or other oils is needed.

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

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 (1 4°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 D312, Type I, 11, 111, or IV) is as follows:

»       Mop Application: the temperature at which the asphalt’s apparent viscosity is 125 centipoise (0.125 Pass).

»       Mechanical Spreader Application: the temperature at which the asphalt’s apparent viscosity is 75 centipoise (0.075 Pans).

Note: If there are simultaneous mop and mechanical spreader applications, in order to avoid the use of two kettles, the EVE for mechanical spreader application may be used for both application techniques.

Equiviscous Temperature (EVA) for Coal Tar: the recommended EVT for roofing coal tar (ASTM D 450, Type I or lil) is the temperature at which the coal tar’s apparent viscosity is 25 centipoise (0.025 Pans).

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 terpolymerof ethylene, propylene, and a diene. EPDM material is a thermosetting synthetic elastomer.

EVT: Equiviscous Temperature

Exhaust Ventilation: air that is typically vented or exhausted from the roof cavity, typically through vents installed on the upslope portion of the roof. For example, with most steep-slope roof assemblies exhaust vents are typically located at or near the ridge.

Expansion Cleat: a cleat designed to handle thermal movement of the 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 (91 4mm) wide felt in a shingled, four-ply membrane should be approximately 84/~ inches (21 6mm) (See Figure 8); (2) the dimension of sidewall or roofing covering that is not covered or overlapped by the upslope course of component. The typical exposure for a standard-size, 3-tab shingle is 5 inches (127mm), depending upon manufacturer specifications. (See Figure 9.)

Extrusion: a manufacturing process which consists of forcing batched and formulated material (which may be molten) through an orifice called a “die.” The shape and dimensions of the orifice determine the shape and dimensions of the finished product. Extrusion is one method by which some single-ply roofing membranes are manufactured.

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 Corporation (FMRC): (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 large sheets.

Fading: any lightening of initial color.

Fallback: a reduction in the softening point temperature of asphalt that occurs when asphalt is heated for prolonged periods at elevated temperature. (See Softening Point Drift.)

Fascia: a 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 that waterproofs the interior portions of the building.

Fasteners: any of a wide variety of mechanical securement devices and assemblies, including nails, 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 through a combination of mechanical work, moisture, and heat. Roofing felts may be manufactured principally from wood pulp and vegetable fibers (organic felts), asbestos fibers (asbestos felts), glass fibers Fiberglass felts or ply sheet), or polyester fibers.

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

Ferrule: a small metal sleeve placed inside a gutter at the top. A spike is nailed through the gutter into the fascia board to hold the gutter in place. The ferrule acts as a spacer in the gutter to maintain its original shape.

Fiberglass Insulation: blanket or rigid board insulation, composed of glass fibers bound together with a binder, faced or unfaced, used to insulate roofs and walls. Rigid boards usually have an asphalt and kraftpaper facer.

Field of the Roof: the central or main portion of a roof, excluding the perimeter and flashing.

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; the desired effect to take out the 90° angle at the base of a vertical flashing.

Film: a membrane or sheeting having nominal thickness not greater than 10 mils.

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 ability of a building component to act as a barrier to the spread of fire and confine it to the area of origin.

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 half-conical opening formed at a cut edge.

Flaking: detachment of a uniform layer of a coating or surface material, usually related to internal movement, lack of adhesion, or passage of moisture.

Flame Retardant: a substance which is added to a polymer formulation to reduce or retard its tendency to burn.

Flame Spread: Per ASTM E 84, a measure of relative combustibility. The flame spread of a tested material is rated relative to asbestos cement board Flame spread = 0) and red oak flooring Flame spread = 100).

Flammability: the characteristics of a material to burn or support combustion.

Flange: the projecting edge of a rigid or semi-rigid component, such as a metal edge flashing flange, skylight flange, flashing boot, structural member, etc.

Flash Point: the lowest temperature of a liquid at which it gives off vapors sufficient to form an ignitable mixture with air near its surface.

Flashing: components used to weatherproof or seal the 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: as used by the roofing industry, an ASTM D 2822 Type II roof cement that is 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.

Fleece: mats or felts composed of fibers (usually non-woven polyester fibers), often used as a membrane backer.

Flood (Pour) Coat: the surfacing layer of bitumen into which surfacing aggregate is embedded on an aggregate-surfaced built-up roof. A flood coat is generally thicker and heavier than a glaze coat, and is applied at approximately 45-60 pounds per square (2-3 kilograms per meter).

Flood Test: the procedure where a controlled amount of water is temporarily retained over a horizontal surface to determine the effectiveness of the waterproofing.

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

FM: see Factory Mutual Research Corporation.

Force: an action that changes or tends to change the state of rest or motion.

Framed Opening: an opening in a wall or roof of a building, surrounded by structural framing, usually for field installed accessories such as skylights or ventilators.

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

G-90: a typical coating weight for galvanized metal sheet. Equates to 0.90 ounces (26 g) of zinc per sq. ft., measured on both sides.

Gable: a triangular portion of the endwall of a building directly under the sloping roof and above the eave line. (See Figure 10.)

Gable-Shaped Roof: a single-ridge roof that terminates at gable end(s). (See Figure 11.)

Galvalume~: trade name for a coating, used over metal, that is composed of aluminum zinc for corrosion protection.

Galvanic Action: an electroylic reaction between dissimilar metals in the presence of an electrolyte.

Galvanize: to coat with zinc.

Galvanized Steel: steel coated with zinc for corrosion resistance.

Gambrel: a roof that has two pitches on each side. (See Figure 12.)

Gauge: a measurement of rating metal thickness.

Geodesic Dome: a rounded structure made of short, straight, triangular sections that form polygons. (See Figure 13.)

Geotextilea tightly woven fabric used to restrict the flow of fine soil particles and other contaminants while allowing water to pass freely through; used for protection of drainage systems from clogging.

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

Glass Felt: a sheet composed of bonded glass fibers, suitable for impregnation and coating in the manufacture of bituminous roofing and waterproofing materials, and shingles.

Glass Mat: a thin mat composed of glass fibers, woven or non-woven, with or without a binder. This mat may serve as reinforcement for certain roof materials and membranes.

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 used to measure the mass of moisture.

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: aggregate resulting from the natural erosion of rock.

Gravel Stop: a low profile upward-projecting metal edge flashing with a flange along the roof side, usually formed from sheet or extruded metal. Installed along the perimeter of a roof to provide a continuous finished edge for roofing material. Acts as a bitumen-stop during mop application of hot bitumen along a perimeter edge.

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.

Grout (Non-Shrink): a cementitious material used to fill pitch-pans/pockets, prior to the application of a pourable sealer.

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.

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

Hardness: the relative resistance of a material to indentation.

Headlap: the distance of overlap measured from the uppermost ply or course to the point that it laps over the undermost ply or course. (See Figures 14 and 15.)

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 thermoses 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. (See Figure 16.)

Hip Roof: a roof that rises by inclined planes to form one or more hips. (See Figure 17.)

Hoist: a mechanical lifting device.

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

“Hot” or “Hot Stuff”: the roofer’s term for hot bitumen.

Humidity: the amount of moisture contained in the atmosphere. Generally expressed as percent relative humidity (the ratio of the amount of moisture [water vapor] actually present in the air, compared to the maximum amount that the air could contain at the same temperature.)

HVAC: heating, ventilating, and air conditioning equipment.

Hypalon~: a registered trademark of E.l. duPont de Nemours, Inc., for “chlorosulfonated polyethylene” (CSPE). (See Chlorosulfonated Polyethylene.)

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.

Impact Resistance: the ability of a roofing material to resist damage (e.g., puncturing) from falling objects, application equipment, foot traffic, etc. The impact resistance of the roofing assembly is a function of all of its components, not just the membrane itself.

Impregnate: to coat, saturate, and/or surround the fibers of a reinforcing mat or fabric with an enveloping liquid material, (e.g., bitumen, elastomeric compound, etc.).

Incline: the slope of a roof expressed either in percent or in the number of vertical units of rise per horizontal units of run. (See Slope.)

Infrared Thermography: a practice of roof system analysis where an infrared camera is used to measure the temperature differential of a roof surface to locate areas of underlying wet or moist insulation. (See Thermal Image.)

Inorganic: any chemical or compound that is derived from minerals, does not contain carbon, and is not classified as organic; being or composed of materials other than hydrocarbons and their derivatives; not of plant or animal origin.

Insect Screen: wire mesh used to prevent insects from entering the building through ventilators, louvers, or other openings.

Insulation: any of a variety of materials designed to reduce the flow of heat, either from or into a building. (See also Thermal Insulation.)

Intake Ventilation: the fresh air that is drawn into a passive ventilation system through vents typically installed in the soffit or eave of a roof.

Interlaymenta felt, metal, or membrane sheet material used between courses of steep-slope roofing to improve the weather- and water-shedding characteristics of the primary roof covering during times ofwinddriven rain and snow. Typically used with wood shakes.

Interlocking Shingles: individual shingles that mechanically attach to each other to provide wind resistance.

Internal Pressure: pressure inside a building that is a function of ventilating equipment, wind velocity, and the number and location of openings and air leaks.

Inverted Roof Membrane Assembly (IRMA™): a patented, proprietary variation of the “Protected Membrane Roof Assembly” in which Styrofoam Brand Insulation and ballast are placed over the roof membrane. IRMA™ and Styrofoam are registered trademarks of the Dow Chemical Company.

Isocyanatea highly reactive organic chemical containing one or more isocyanate (-N=C=O) groups. A basic component in SPF based systems and some polyurethane coating systems.


Joist: any of the small timbers, metal or wood beams arranged parallel from wall to wall to support a floor, ceiling, or roof of a building.

k-Factor: thermal conductivity for a unit thickness of material. Expressed at Btu~ln/Hr.Ft2~°F. R-value is equal to the thickness of the thermal material divided by the k-factor (R=x/k where x = thickness).

Knee Cap: a metal cover trim that fits over a panel rib after it has been cut and bent.

Laminate: to bond two or more layers of a material together to make a finished product.

Laminated Shingles: see Dimensional Shingles or Architectural Shingles.

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.

Latex: a colloidal dispersion of a polymer or elastomer in water which coagulates into a film upon evaporation of the water.

Lead: a soft workable metal used for miscellaneous flashings.

Leader Head: see Conductor Head.

Leeward: the opposite direction from which the wind is blowing. The side sheltered from the wind.

Lift: the sprayed polyurethane foam that results from a pass. It usually is associated with a certain pass thickness and has a bottom layer, center mass, and top skin in its makeup.

Light Reflectance: the percentage of light that is not absorbed by the surface of a material.

Live Loads: temporary loads that the roof structure must be designed to support, as required by governing building codes. Live loads are generally moving and/or dynamic or environmental, (e.g., people, installation equipment, wind, snow, ice or rain, etc.).

Load Deflection: see Deflection.

Loose-laid Membranes: membranes that are not attached to the substrate except at the perimeter of the roof and at penetrations. Typically, loose-laid membranes are held in place with ballast, such as water-worn stone, gravel, pavers, etc.

Low Temperature Flexibility: the ability of a membrane or other material to remain flexible (resist cracking when flexed), after it has been cooled to a low temperature.

Mansard: a decorative steep-sloped roof on the perimeter of a building.

Mansard Roof: a steeper roof that terminates into a flat roof at its high point. (See Figure 18.)

Masonry: anything constructed of such materials as bricks, stone, concrete blocks, ceramic blocks, or concrete.

Mastic: see Asphalt Roof Cement.

Mat: a thin layer of woven, non-woven, or knitted fiber that serves as reinforcement to the material or membrane.

Material Safety Data Sheets (MSDS): a written description of the chemicals in a product, and pertinent other data including such things as safe handling and emergency procedures. In accordance with OSHA regulations, it is the manufacturer’s responsibility to produce an MSDS and the employer’s responsibility to communicate its contents to employees.

Mechanically-Fastened Membranes: generally used to describe membranes that have been attached at defined intervals to the substrate. Mechanical fastening may be performed with various fasteners and/or other mechanical devices, such as plates or battens.

Membrane: a flexible or semi-flexible material, which functions as the waterproofing component in a roofing or waterproofing assembly, and whose primary function is the exclusion of water.

Metal Film: a layer of foil made from a single metallic substance, or from an alloy, that is laminated to a membrane during manufacture. The metal foil serves as the weathering surface of the membrane or flashing material.

Metal Flashing: accessory components fabricated from sheet metal and used to weatherproof terminating roof covering edges. Frequently used as through-wall flashing, cap flashing (coping), counterflashing, stepflashing, etc. (See Flashing.)

Metallic Waterproofing: a compound modified through the inclusion of one or more polymers (e.g. atactic polypropylene, styrene butadiene sytrene, etc.); (2) composite sheets consisting of a polymer modified bitumen often reinforced and sometimes surfaced with various types of mats, films, foils, and mineral granules.

Meter: unit of length measurement in the metric system, equal to 39.37 inches.

Mica Dust: crystallized complex silicate minerals that are pulverized into dust form for use as a release agent. (See Talc.)

Migration: the absorption of oil or vehicle from a compound into an adjacent porous surface.

Mill: a unit of measure, one mil is equal to 0.001 inches or 25.400 microns, often used to indicate the thickness of a roofing membrane.

Mildew: a superficial coating or discoloring of an organic material due to fungal growth, especially under damp conditions.

Millimeter: a unit of measure equal to one thousandth (0.001) of a meter, or 0.03937 inches.

Mineral Fiber: inorganic fibers of glass, asbestos, or rock (mineral wool).

Mineral Granules: see Granules.

Mineral Stabilizer: a fine, water-insoluble inorganic material, used in a mixture with solid or semi-solidhit’~minous materials.

Mineral-Surfaced Roofing: roofing materials whose surface or top layer consists of mineral granules.

Mineral-Surfaced Sheet: a roofing sheet that is coated on one or both sides with asphalt and surfaced with mineral granules.

Miter: the joint produced by joining two diagonally cut pieces.

Model Codes: a compilation of standards or codes established to provide uniformity in regulations pertaining to building construction. Examples: ICBO – International Conference of Building Officials; BOCA – Building Officials and Code Administrators; SBC – Standard Building Code.

Modified Bitumen: (1) a bitumen modified through the inclusion of one or more polymers (e.g., atacticpolypropylene, styrene butadiene styrene, etc.); (2) composite sheets consisting of a polymer modified bitumen often reinforced and sometimes surfaced with various types of mats, films, foils, and mineral granules.

Moisture Contour Map: a map used to graphically define the location of moisture within a roof assembly after a moisture scan has been performed.

Moisture Relief Vent: a venting device installed through the roofing membrane to relieve moisture vapor pressure from within the roofing system.

Moisture Scan: the use of a mechanical device (capitance, infrared, or nuclear) to detect the presence of moisture within a roof assembly. (See Non-Destructive Testing.)

Mole Run: a meandering buckle or ridging in a roof membrane not associated with insulation or deck joints.

Monolithic: formed from or composed of a single material; seamless.

Monomer: a simple molecule that is capable of combining with a number of like or unlike molecules to form a polymer.

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, are coated with adhesive or bitumen, and are then turned over and applied to the substrate.

Mopping: the application of hot bitumen, with a roofer’s hand mop or mechanical applicator, to the substrate or to the felts of a bituminous membrane.

»       Solid Mopping: a continuous mopping of a surface.

»       Spot Mopping: a mopping pattern in which hot bitumen is applied in roughly circular areas, leaving a grid of unmapped, perpendicular bands on the roof.

»       Sprinkle Mopping: a random mopping pattern in which heated bitumen beads are strewn onto the substrate with a brush or mop.

»       Strip Mopping: a mopping pattern in which hot bitumen is applied in parallel bands.

Multiple Coat: two or more layers of coating applied to a substrate.

Nailer(commonly referred to as Blocking) a piece or pieces of dimensional lumber and/or plywood secured to the structural deck or walls, which provide a receiving medium for the fasteners used to attach membrane or flashing. Generally, it is recommended that nailers be the same thickness as the adjacent insulation, and may be treated with a non-oil-borne preservative, and be of sufficient width to fully support the horizontal flashing flange of a metal flashing (where used).

Nailing: the application of nails. May be: (1) exposed nailing of roofing wherein nail heads are exposed to the weather; (2) concealed nailing of roofing wherein nail heads are concealed from the weather by an overlapping material.

Negative Side Waterproofing: an application wherein the waterproofing system and the source of hydrostatic pressure are on opposite sides of the structural element.

Neoprene: a synthetic rubber (polychloroprene) used in liquid-applied and sheet-applied elastomeric roof membranes or flashings.

Nesting: 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.

Net Free Vent Area: the area, measured in square inches, open to unrestricted air flow and commonly used as a yardstick to measure relative vent performance.

Night Seal (or Night Tie-Of0: a material and/or method used to temporarily seal a membrane edge during construction to protect the roofing assembly in place from water penetration. Usually removed when roofing application is resumed.

Nineteen-lach Selvage (Double-Coverage or Split-Sheet): a prepared roofing sheet with a 17 inch (430mm) granule surfaced exposure and a non-granule surfaced 19 inch (485mm) selvage edge. This material is sometimes referred to as SIS, double-coverage, or according to ASTM Standard D 371-89, Standard Specification for Asphalt Roll Roofing (Organic Felt) Surfaced with Mineral Granules, Wide Selvage.

Ninety-Pound: a prepared organic felt roll roofing with a granule surfacing that has a mass of approximately 90 pounds per 100 square feet, (4400 g/m2).

No-Cutout Shingles: shingles consisting of a single solid strip with no cutouts.

Non-Breathing Membrane: a membrane that does not allow significant amounts of water vapor or air to pass through; which has a perm rating 1.0 or less per ASTM E 96, Procedure E.

Non-Destructive Testing (NOT): a method to evaluate the disposition, strength, or composition of materials without damaging the object under test. Typically used to evaluate moisture content in roofing assemblies, the three common test methods are electrical capacitance, infrared thermography, and nuclear back-scatter.

Non-Flammable: liquid having no measurable flash point.

Non-Friable: a material that, when dry, cannot be crumbled, pulverized or reduced to powder by hand pressure.

Non-Oxidizing: a material which resists oxidation in exterior exposures or accelerated weathering.

Non-Traffic Bearing: for waterproofing purposes, a membrane system requiring some form of protection barrier and wearing surface.

Non-Volatile Content: that portion of a material that does not evaporate under normal ambient conditions.

Non-Vulcanized Membrane: a membrane manufactured from thermoplastic compounds that retains its thermoplastic properties throughout the service life of the membrane.

Nonwovena term used to describe the random arrangement of reinforcing fibers (glass, polyester, etc.) in a mat or scrim.

NRCA: National Roofing Contractors Association

NTRMA: National Tile Roofing Manufacturers Association

Nuclear Testing (Nuclear Back-Scatter): a device that contains a radioactive source to emit high velocity neutrons into a roof system. Reflecting neutrons are measured by a gauge that is used to detect moisture.

Nylon: generic name for a family of polyamide polymers, used as a scrim in some fabric-reinforced sheeting.


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.

Open Valley: a method of valley construction in which the steep-slope roofing on both sides are trimmed along each side of the valley, exposing the valley flashing.

Orange Peel Surface Texture: the surface shows a fine texture and is compared to the exterior skin of an orange. This surface is considered acceptable for receiving a protective coating. The theoretical coverage rate cannot be used without adding a minimum 10% additional material to adequately cover the orange peel texture.

Organic: being or composed of hydrocarbons or their derivatives originating from plant or animal matter.

Organic Felt: an asphalt roofing base material manufactured from cellulose fibers.

Organic Shingle: an asphalt shingle reinforced with material manufactured from cellulose fibers.

Osmosis: the diffusion of fluids through a semi-permeable membrane or porous partition.

Overspray: undesirable depositions of airborne spray loss.

Overspray Surface Texture: the surface shows a linear coarse textured pattern and/or a pebbled surface. This surface is generally downwind of the sprayed polyurethane path and is unacceptable for proper coating coverage and protection, if severe. The minimum percentage of additional material to be added will vary from 25% to 50% depending upon the type of surface texture.

Ozone Resistance: the ability of a material to resist the deteriorating effects of ozone exposure.

Pallet: a platform (typically wooden) used for storing and shipping materials.

Pan: the bottom flat part of a roofing panel which is between the ribs of the panel.

Pan Former: power roll-forming equipment that produces a metal roofing panel from a flat sheet.

Parapet Wall: that part of a perimeter wall immediately adjacent to the roof which extends above the roof.

Parge: in masonry construction, a coat of cement mortar on the face of rough masonry, the earth side of foundation and basement walls, or the like.

Partially-Attached: a roofing assembly in which the membrane has been “spot affixed” to a substrate, usually with an adhesive or a mechanical device.

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.

Peel Strength: the average force (or force per unit width) required to peel a membrane or other material from the substrate to which it has been bonded.

Penetration: (1) any object passing through the roof; (2) the consistency (hardness) 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.

Percent Elongation: in tensile testing, the increase in the gauge length of a specimen measured at or after fracture of the specimen within the gauge length. Usually expressed as a percentage of the original gauge length.

Perlitean aggregate used in lightweight insulating concrete and in preformed perlitic insulation boards, formed by heating and expanding siliceous volcanic glass.

Perm: a unit of water vapor transmission defined as 1 grain of water vapor per square foot per hour per inch of mercury pressure difference (1 inch of mercury = 0.49 psi). The formula for perm is: P = Grains of Water Vapor/Square Foot.Hour~lnch Mercury (P = grain~in/ft2.h~in Hg [P = ng/(Pa~s~m)]).

Permeability: (1) the capacity of a porous material to conduct or transmit fluids; (2) the amount of a fluid moving through a barrier in a unit time, unit area, and unit pressure gradient not normalized for, but directly related to, thickness.

Permeancethe rate of water vapor transmission per unit area at a steady state through a material, membrane or assembly, expressed in Grain/Square Foot.Hour~lnch Mercury (grain/ft2.h~in Hg [ng/Pa~a~m2]).

Phased Application: the installation of separate roof system or waterproofing system component(s) during two or more separate time intervals. Application of surfacings at different time intervals are typically not considered phased application. (See Surfacing.)

Picture Framing: a square or rectangular pattern of buckles or ridges in a roof covering generally coinciding with insulation or deck joints; generally, a function of movement of the substrate.

Pinhole: a tiny hole in a coating, film, foil, membrane, or laminate.

Pipe Boot: prefabricated flashing piece used to flash around circular pipe penetrations.

Pitch: see Coal Tar, Incline, and Roof Slope.

Pitch-Pocket (Pitch-Pan): a flanged, open bottomed enclosure made of sheet metal or other material, placed around a penetration through the roof, filled with grout and bituminous or polymeric sealants to seal the area around the penetration.

Pittsburgh Lock Seam: a method of interlocking metal, usually at a slope change.

Plastic Cement: a roofing industry generic term used to describe Type I asphalt roof cement that is a trowelable mixture of solvent-based bitumen, mineral stabilizers, other fibers and/or fillers. Generally, intended for use on relatively low slopes – not vertical surfaces. (Also see Asphalt Roof Cement and Flashing Cement.)

Plastic Film: a flexible sheet made by the extrusion of thermoplastic resins.

Plasticizer: a material, frequently solvent-like, incorporated in a plastic or a rubber to increase its ease of workability, flexibility, or extensibility.

Plastomerica plastic-like polymer consisting of any of various complex organic compounds produced by polymerization, and capable of being molded, extruded, or cast into various shapes or films.

Pliability: the material property of being flexible or moldable.

Ply: a layer of felt, ply sheet, or reinforcement in a roof membrane or roof system.

Polyester: a polymeric resin which is generally cross-linked or cured and made into a variety of plastic materials and products. Polyester fibers are widely used as the reinforcing medium in reinforced membranes. (See Polyester Fiber.)

Polyester Fiber: a synthetic fiber usually formed by extrusion. Scrims made of polyester fiber are used for fabric reinforcement.

Polymer: a natural or synthetic chemical compound of high molecular weight, or a mixture of such compounds, formed when monomers (small individual molecules) are combined to form large long-chain molecules.

Polymer Modified Bitumen: See Modified Bitumen.

Polypropylene: a tough, lightweight plastic made by the polymerization of high-purity propylene gas.

Polyvinyl Chloride (PVC): a synthetic thermoplastic polymer prepared from vinylchloride. 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.

Pondingthe excessive accumulation of water at low-lying areas on a roof.

Pop Rivet: a relatively small headed pin with an expandable head for joining relatively light gauge metal.

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 rainfall, during ambient drying conditions.

Positive Side Waterproofing: an application where the waterproofing systems and the source of the hydrostatic pressure are on the same side of the structural element.

Pourable Sealer: a type of sealant often supplied in two parts, and used at difficult-to-flash penetrations, typically in conjunction with pitch-pockets to form a seal.

Pre-Tinning: coating a metal with solder or tin alloy, prior to soldering or brazing it.

Press Brake: a machine used in cold-forming sheet metal or strips of metal into desired profiles.

Prestressed Concrete: concrete in which the reinforcing cables, wires, or rods in the concrete are tensioned before there is load on the member, holding the concrete in compression for greater strength.

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 which 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.

Protected Membrane Roof (PMR): an insulated and ballasted roofing assembly, in which the insulation and ballast are applied on top of the membrane (sometimes referred to as an “inverted roof assembly”).

Puncture Resistance: extent to which a material is able to withstand the action of a sharp object without perforation.

Purlinhorizontal secondary structural member that transfers loads from the primary structural framing.

PVC: Polyvinyl Chloride.

R-Value: the resistance to heat transfer of a material. Insulators have relatively high R values. Units are °F.Ft2.Hr/Btu.

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.

Rafter: one of a series of sloped structural members, that extend from the ridge or hip to the downslopeperimeter or cave, designed to support the roof deck and its associated loads. (See Figure 19.)

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 regret.

Rake: the sloped edge of a roof at or adjacent to the first or last rafter. (See Figure 20.)

Rake-Starter (Bleeder Strip): starter-strip used along rake edges in conjunction with asphalt shingle roofing.

Re-Cover: the addition of a new roof membrane or steep-slope roof covering over a major portion of an existing roof assembly. This process does not involve removal of the existing roofing.

Reflectivity: see Light Reflectance.

Reglet: a sheet metal receiver for the attachment of counterflashing. (A regret may be inset into a raggle, embedded behind cladding, or be surface mounted.)

Reinforced Membrane: a roofing 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 scams, nylon, or polyethylene sheeting.

Relative Humidity: the ratio of the weight of moisture in a given volume of air-vapor mixture to the saturated (maximum) weight of water vapor at the same temperature, expressed as a percentage. For example, if the weight of the moist air is 1 pound and if the air could hold 2 pounds of water vapor at the same temperature, the relative humidity (RH) is 50 percent.

Release Tape (or Strip): a plastic film or paper strip that is applied to the back of self-sealing shingles and other materials. The strip prevents the material from sticking together in the roll or bundle. With asphalt shingles, the strip need not be removed for application of the shingles.

Replacement: the practice of removing an existing roof system down to the roof deck and replacing it with a new roofing system.

Reroofing: the process of re-covering, or tearing-off and replacing an existing roof system.

Resin: component B in SPF. This component contains a catalyst, blowing agent, fire retardants, surfactants and polyol. It is mixed with the A component to form polyurethane.

Resistance, Thermal: the average temperature difference between two defined surfaces of a particular body or assembly when unit thermal transmission in unit time through unit area is established between the surfaces. R=°F.h~s~ft2/Btu (R=K.m2NV).

Ridge: highest point on the roof, represented by a horizontal line where two roof areas intersect, running the length of the area. (See Figure 21.)

Ridge Cap: a material or covering applied over the ridge of a roof.

Ridge Course: the last or top course of roofing materials, such as tile, roll roofing, shingles, etc., that covers the ridge and overlaps the intersecting field roofing.

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. Most ridge vents are either premanufactured metal or flexible, shingle-over type.

Ridging: see Buckle.

Roll Goods: a general term applied to rolls of roofing felt, ply sheet, etc., which are typically furnished in rolls.

Roll Roofing: smooth-surfaced or mineral-surfaced, coated, prepared felts.

Roof Assembly: an assembly of interacting roof components (includes the roof deck, vapor retarder [if present], insulation, and roof covering).-

Roof or Roofer’s Cement: see Asphalt Roof Cement or Coal Tar Roof Cement.

Roof Covering: the exterior roof cover or skin of the roof assembly, consisting of membrane, panels, sheets, shingles, tiles, etc.

Roof Curb: raised frame used to mount mechanical units (such as air conditioning or exhaust fans), skylights, etc.

Roof Diaphragm: a structural roof deck that is capable of resisting shear that is produced by lateral forces, such as wind or seismic loads.

Roof Jack: a metal bracket used to support toe-boards on steep-slope roofs. (Also see Flashing Collar.)

Roof Overhang: a roof extension beyond the exterior wall of a building.

Roof Seamer: machine that crimps neighboring metal roof panels together, or that welds laps of membrane sheets together using heat, solvent, or dielectric energy.

Roof Slope: the angle a roof surface makes with the horizontal, expressed as a ratio of the units of vertical rise to the units of horizontal length (sometimes referred to as run). For English units of measurement, when dimensions are given in inches, slope may be expressed as a ratio of rise to run, such as 4:12, or as a percent.

Roof System: a system of interacting roof components, generally consisting of membrane or primary roof covering and insulation (not including the roof deck) designed to weatherproof and, sometimes, to improve the building’s thermal resistance.

Roofer: craftsman who applies roofing materials.

Rosin Paper (specifically Rosin-Sized Sheathing Paper): a non-asphaltic paper used as a sheathing paper or slip sheet in some roof systems.

Rubber: a polymeric material which, at room temperature, is capable of recovering substantially in shape and size after removal of a force. May be natural or synthetic.

Run: horizontal dimension of a slope.

  Saddle: a relatively small raised substrate or structure constructed to channel or direct surface water to drains or off the roof. A saddle may be located between drains or in a valley, and is often constructed like a small hip roof or like a pyramid with a diamond-shaped base. (See Cricket.)

Sag: undesirable excessive flow in material after application to a surface.

Saturated Felt: a felt that has been partially saturated with low softening point bitumen.

Screeding: the process of striking off excess concrete to bring the top surface of the concrete to the proper finish and elevation.

Screen Wall: a nonstructural wall erected around units or curbs on a roof. Typically the framing consists of girts with a wood or metal covering attached to the frame.

Scrim: a woven, nonwoven, or knitted fabric, composed of continuous strands of material used for reinforcing or strengthening membranes. Scrim may be incorporated into a membrane by the laminating or coating process.

Scuttle: a hatch that provides access to the roof from the interior of the building.

Seal: (1) a generic term for a function that prevents or controls the passage of water; (2) to secure a roof or structure from the entry of moisture.

Sealant: a single- or multi-component polymeric or bituminous-based material used to weatherproof many types of construction joints where moderate movement is expected. The material comes in various grades: pourable, self-leveling, non-sag, gun grade, and cured or uncured tapes.

Sealer: a coating designed to prevent absorption of finish coats into porous surfaces; a coating designed to prevent bleeding.

Sealing Washer: a rubber or neoprene washer, sometimes metal-backed, typically assembled on a fastener to prevent water from migrating into and through the fastener hole.

Seam: a joint formed by mating two separate sections of material. Seams may be made or sealed in a variety of ways, including adhesive bonding, hot-air welding, solvent welding, using adhesive tape, sealant, etc.

Seam Strength: the force or stress required to separate or rupture a seam in the membrane material.

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 self-adhering membrane is protected by a release paper or film, which prevents the membrane from bonding to itself during shipping and handling.

Self-Drilling Screw: a fastener that drills and taps its own hole during application.

Self-Sealing Shingle: an asphalt shingle containing factory-applied strip or spots of heat sensitive adhesive intended to adhere the overlying shingle once installed on the roof and warmed by the sun.

Self-Tapping Screw: a fastener that forms receiving threads when turned into a previously drilled hole.

Self-Vulcanized Membrane: a membrane manufactured from compounds that are thermoplastic during manufacture and installation, but whose polymers eventually cross-link and cure during exposure.

Selvage: (1) an edge or edging that differs from the main part of a fabric, granule-surfaced roll roofing or cap sheet, or other material; (2) a specially defined edge of the material (lined for demarcation), which is designed for some special purpose, such as overlapping or seaming.

Selvage Edge: an edge designed for certain sheet good materials, e.g., mineral-surfaced sheets. With mineral surfaced sheets, the surfacing is omitted over a portion of the longitudinal edge of the sheet (e.g., mineral surface cap sheet) in order to obtain better adhesion of the overlapping sheet.

Service Temperature Limits: the minimum or maximum temperature at which a coating, SPF, or other material will perform satisfactorily.

Shading: slight differences in surfacing color, such as shingle granule coloring, that may occur as a result of manufacturing operations.

Shark Fin: an upward-curled felt side lap or end lap.

Shear Strength: (in roofing) the stress required to disrupt a seam or bonded joint or attachment by forcing the substrate material to slide out from the overlying material or vice versa.

Shed Roof: a roof containing only one sloping plane. Has no hips, ridges, or valleys. (See Figure 22.)

Sheet Metal Flashing: see Metal Flashing.

Shelf Life: the period of time within which a material such as coating or SPF components remain suitable for use.

Shingle: (1) individual unit of prepared roofing material designed for installation with similar units in overlapping rows or courses on inclines normally exceeding 3:12 slope (25%); (2) to cover with shingles; (3) to apply any roofing material in succeeding overlapping rows or courses similar to shingles.

Shingling: (1) the application of shingles; (2) the procedure of applying shingles or laying parallel felts so that one longitudinal edge of each felt overlaps and the other longitudinal edge of the adjacent shingle or felts underlaps. Felts are normally shingled from a downslope portion of the roof to the upslope portion of the roof area so that runoff water flows over rather than against each felt lap. Felts are also applied in shingle fashion on relatively low slopes.

Shrinkage: a reduction in size.

Shrinkage Crack: in waterproofing, a separation in a material, like a concrete substrate, caused by the inability of the material to resist a reduction in size which occurs during its hardening process, curing process, or both.

Side Lap: the continuous longitudinal overlap of neighboring like materials. (See Figures 23 and 24.)

Side Lap Fastener: a fastener used to connect adjacent panels together at the side lap.

Side Lap-Ganging: pattern or application for roofing materials, as related to the amount of cover or side overlap of adjacent like materials.

Siding: the exterior wall finish material applied to a light frame wood structure.

Sieve: an apparatus with uniform sized openings for separating sizes of material.

Silicone-based Water Repellants: any of the organopolysiloxanes (silicone derivative) applied to masonry materials for dampproofing or repelling water.

Sill: the bottom horizontal framing member of an opening, such as below a window or door.

Sill Flashing: a flashing of the bottom horizontal framing member of an opening, such as below a window or door.

Single Coverage: roofing material that provides one layer over the substrate to which it is applied.

Single-Lock Standing Seam: a standing seam that utilizes one overlapping interlock between two seam panels, in contrast with the double interlocking used in a double standing seam.

Single-Ply Membranes: roofing membranes that are field applied using just one layer of membrane material (either homogeneous or composite) rather than multiple layers.

Single-Ply Roofing: a roofing system in which the principal roof covering is a single layer flexible membrane, often of thermoses, thermoplastic, or polymer modified bituminous compounds.

Single-Ply System: generally, there are six types of single-ply roofing systems:

1) Fully-adhered

2) Loose-laid

3) Mechanically-fastened

4) Partially-adhered

5) Protected membrane roof

6) Self-adhering

Skinning: the formation of a dense film on the surface of a liquid coating or mastic.

Skylight: a roof accessory, set over an opening in the roof, designed to admit light. Normally transparent, and mounted on a raised framed curb.

Slag: a hard, air-cooled aggregate that is left as a residue from blast furnaces, which 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.

Slating Hook: a steep-slope roofing attachment device, shaped like a hook, that can be used for fastening roofing slate.

Slip Sheet: sheet material, such as reinforced kraft paper, rosin-sized paper, polyester scrim, or polyethylene sheeting, placed between two components of a roof assembly (such as between membrane and insulation or deck) to ensure that no adhesion occurs between them, and to prevent possible damage from chemical incompatibility, wearing, or abrasion of the membrane.

Slope: the angle of incline, usually expressed as a ratio of rise to run, or as a percent. (See Roof Slope.)

Smooth Surface Texture: the surface shows spray undulation and is ideal for receiving a protective coating. Even though the surface texture is classified as smooth, the theoretical coverage rate cannot be used without adding a minimum of 5% additional material to adequately cover the undulation.

Smooth Surfaced Roof: a roof membrane without mineral granule or aggregate surfacing.

Snap-On Cap: a separate cap that snaps on over the vertical legs of some single standing or batten seam metal roof systems.

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.

Snow Load: a load imposed on buildings or other structures due to snowfall. (Categorized as live or environmental load.)

Soffit: the enclosed underside of any exterior overhanging section of a roof cave.

Soffit Vent: a premanufactured or custom built air inlet source located at the downslope eave or in the soffit of a roof assembly.

Softening Point: the temperature at which bitumen becomes soft enough to flow, as determined by a closely defined method (ASTM Standard test method D 36 or D 3461).

Softening Point Drift: a change in the softening point of bitumen. (See Fallback.)

Soil Stack: a sanitation pipe that penetrates the roof; used to vent plumbing fixtures.

Solder: a lead/tin mixture that is melted and used to bond two pieces of some metals together.

Solid Mopping: see Mopping.

Solvent: liquid used to dissolve or disperse film-forming constituents, and which evaporates during drying and does not become a part of the dried film.

Solvent Cleaners: used to clean some single-ply roofing membranes prior to splicing, typically including heptane, hexane, white gasoline, and unleaded gasoline.

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).

Spalling: a condition in which the outer layer or layers of masonry or concrete material begin to break off or flake away.

Special Steep Asphalt: Type IV Asphalt. (See Asphalt.)

Specification: a statement of requirements for a given job or project. Usually describes products, materials, and processes to be used. A specification may also contain terms of the contract.

SPI/SPFD: The Society of the Plastics Industry/Sprayed Polyurethane Foam Division

Splash Block: a small masonry or polymeric block laid on the ground or lower roof below the opening of a downspout used to help prevent soil erosion and aggregate scour in front of the downspout.

Splice: bonding or joining of overlapping materials. (See Seam.)

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.

Split: a rupture (generally linear) or tear in a material or membrane resulting from tensile forces.

Split Sheet: see Nineteen-lnch Selvage.

Split Slab: a term used to describe two separate concrete slabs. The first is placed as a slab-on-grade or suspended slab, and covered with waterproofing and a drainage system. The second slab, also referred to as a topping slab, is then placed over the underlying slab and waterproofing.

Spot Mopping: see Mopping.

Sprayed Polyurethane Foam (SPF): a foamed plastic material, formed by spraying two components, PMDI ([A] component) and a resin ([B] component) to form a rigid, fully adhered, water-resistant, and insulating membrane.

Spread Coating: a manufacturing process in which membranes are formed using a liquid compound, prepared in mixers and then fed to individual coalers. The mixture is spread onto a supporting reinforcement base layer. After coating, the material passes through a channel causing it to change from a paste to a solid membrane, in sheet form.

Square: 100 square feet (9.29 m2) of roof area.

Square-Tab Shingles: shingles with tabs that are all the same size and exposure.

Stainless Steel: an alloy of steel that contains a high percentage of chromium. Also may contain nickel or copper. Generally, has very good resistance to corrosion.

Standing Seam: a metal roof system that consists of an overlapping or interlocking seam that occurs at an upturned rib. The standing seam may be made by turning up the edges of two adjacent metal panels and overlapping them, 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 watershedding roof coverings, the starter course is covered by the first course.

Starter Sheets: (1) felt, ply sheet, or membrane strips that are made or cut to widths narrower than the standard width of the roll, used to start the shingling pattern at an edge of the roof; (2) particular width sheets designed for perimeters in some mechanically attached and fully adhered single-ply systems.

Starter Strip: roll roofing or shingle strips applied along the downslope eave line, before application of the first course of roofing, intended to fill spaces between cutouts and joints of the first course.

Static Load: any load, as on a structure, that does not change in magnitude or position with time.

Steel Joist (open web steel joist): normally used as a horizontal supporting member between beams or other structural members, suitable for the support of some roof decks.

Steep Asphalt: Type lil Asphalt. (See Asphalt.)

Steep-Slope Roof: a roof of suitable slope to accept the application of water shedding roofing materials.

Steep-Slope Roofing: a category of roofing that includes water shedding types of roof coverings installed on slopes exceeding 3:12 or 25%.

Steeple: a tower or spire, usually located on a church.

Step Flashing: individual pieces of 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.

Stiffener Rib: small intermediate bends in a metal pan used to strengthen the panel.

Strapping (felts): a method of installing roofing rolls or sheet good materials parallel with the slope of the roof.

Straw Nail: a long-shanked nail. Sometimes used for fastening over tile at hips and ridges.

Stress: the internal resistance of a material to a force, measured as a force per unit area.

Stress-Crack: external or internal cracks within a material caused by long-term stress. Environmental factors, such as contact with corrosive material, usually accelerate stress-cracking.

Strike-Through: a term used in the manufacture of fabric-reinforced polymeric sheeting to indicate that two layers of polymer have made bonding contact through the scrim or reinforcement.

Strip Mopping: see Mopping.

Strip Shingles: asphalt shingles that are manufactured in strips, approximately three times as lone as they are

Strippable Films: (for metal) added protection of plastic films sometimes applied to coated or finished metals after the coil coating process. Applied after prime and top coats to resist damage to the finish prior to and during shipping, fabrication, and installation.

Stripping or Strip-Flashing: membrane flashing strips used for sealing or flashing metal flashing flanges into the roof membrane.

Stripping In: application of membrane stripping ply or plies.

Structural Panel: a panel designed to be applied over open framing in which a structural deck is not required.

Styrene Butadiene Rubber: high molecular weight polymers having rubber-like properties, formed by the random copolymerization of styrene and butadiene monomers.

Styrene Butadiene Styrene Copolymer (SBS): high molecular weight polymers that have both thermoses and thermoplastic properties, formed by the block copolymerization of styrene and butadiene monomers. These polymers are used as the modifying compound in SBS polymer modified asphalt roofing membranes to impart rubber-like qualities to the asphalt.

Substrate: the surface upon which the roofing or waterproofing membrane is applied (e.g., in roofing, the structural deck or insulation).

Sump: an intentional depression around a roof drain or scupper that serves to promote drainage.

Superimposed Loads: loads that are added to existing loads. For example, a large stack of insulation boards placed on top of a structural steel deck.

Surface Conductance: a unit of heat flow or heat exchange between a material and the air around it. Ventilation over a surface will decrease the thickness of the air film and reduce the thermal effect (increase the heat flow).

Surface Cure: curing or vulcanization that occurs in a thin layer on the surface of a manufactured polymeric sheet or other items.

Surface Dryness: surface dryness can be evaluated qualitatively by taping an 18 inch by 18 inch (0.46 m by 0.46 m) clear 4 mil polyethylene sheet to a concrete surface, and observing the moisture that may collect on the underside of the polyethylene sheet. Additional details of this procedure may be found in ASTM D 4263.

Surface Erosion: the wearing away of a surface due to abrasion, dissolution, or weathering.

Surface Texture: the resulting surface from the final pass of SPF. The following terms are used to describe the types of SPF surfaces: smooth surface texture, orange peel surface texture, coarse orange peel surface texture, verge of popcorn texture, popcorn surface texture, treebark surface texture, and oversprayed surface texture.

Surfacing: the top layer or layers of a roof covering, specified or designed to protect the underlying roofing from direct exposure to the weather.

Surfactant: short for “surface active agent.” Used to alter the surface tension of liquids. An ingredient in SPF formulations to aid in mixing and controlling cell size.

Synthetic Rubber: any of several elastic substances resembling natural rubber, prepared by the polymerization of butadiene, isoprene, and other unsaturated hydrocarbons. Synthetic rubber is widely used in the fabrication of single-ply roofing membranes.


Tab: the exposed portion of strip shingles defined by cutouts. (See Figure 25.)

Talc: whitish powder applied at the factory to the surface of some roofing materials (e.g., vulcanized EPDM membranes), used as a release agent to prevent adhesion of the membrane to itself.

Tapered Edge Strip: a tapered insulation strip used to (1) elevate and slope the roof at the perimeter and at curbs, and (2) provide a gradual transition from one layer of insulation to another.

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.

Tar: a brown or black bituminous material, liquid or semi-solid 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.

Tar Boils: bubbles of moisture vapor encased in a thin film of bitumen, also known as “blackberries.”

Tarred Felt: see Coal Tar Felt.

Tear-Off and Reroof: the removal of all roof system components down to the structural deck, followed by installation of a completely new roof system.

Tear Resistance: the load required to tear a material, when the stress is concentrated on a small area of the material by the introduction of a prescribed flaw or notch. Expressed in psi (pounds force) per inch width or kN/m (kilonewton per meter width).

Tear Strength: the maximum force required to tear a specimen.

Tensile Fatigue Resistance: the ability of a given membrane material to resist “fatigue” and/or other damage (such as loss of elasticity) caused by the alternate stretching and relaxing of the material over a period of time.

Tensile Strength: the maximum force (longitudinal pulling stress) a material can bear without tearing or breaking apart.

Tensile Test: a test in which a specimen is subjected to increasing longitudinal pulling stress until fracture occurs.

Termination: the treatment or method of anchoring and/or sealing the free edges of the membrane in a roofing or waterproofing system.

Terra Cotta: low-fired clay, either glazed or unglazed.

Test Cut: a sample of the roof, which may contain all components or just the membrane, usually used to diagnose the condition of the existing membrane, evaluate the type and number of plies or number of membranes, or rates of application such as determine the weight of the average interply bitumen mappings.

Thatch Roof: the covering of a roof usually made of straw, reed, or natural foliage (palms) bound together to shed water.

Therm: a unit of heat equivalent to 100,000 BTUs (105.6-106). Commonly used by utilities in quoting prices or costs.

Thermal Barrier: a material applied over polyurethane foam designed to slow the temperature rise of the foam during a fire and delay its involvement in the fire. Thermal barriers for use with SPF must have a time rating of not less than 15 minutes.

Thermal Block: a compression-resistant insulation block installed between the structural steel and the panel to maintain insulation value.

Thermal Conductance (C): a unit of heat flow that is used for specific thicknesses of material or for materials of combination or composite construction, such as laminated insulation. The formula for thermal conductance is:

Thermal Conductivity (k): the heat energy that will be transmitted by conduction through 1 square foot of 1 inch thick homogeneous material in one hour when there is a difference of 1 degree Fahrenheit perpendicularly across the two surfaces of the material. The formula for thermal conductivity is: k = Btu/Square FooVlnch /Hour/Degree Fahrenheit

Thermal Image: a visual representation of temperature distribution over a surface area. The image is displayed on a screen, presenting the response to infrared light waves.

Thermal Insulation: a material applied to reduce the flow of heat.

Thermal Movement: changes in dimension of a material as a result of temperature changes.

Thermal Resistance (R): an index of a material’s resistance to heat flow; it is the reciprocal of thermal conductivity (k) or thermal conductance (C). The formula for thermal resistance is:

Thermal Shock: the stress-producing phenomenon resulting from sudden temperature changes in a roof membrane when, for example, a cold rain shower follows brilliant hot sunshine, which may result in sudden cooling or rapid contraction of the membrane.

Thermal Stress: stress introduced by uniform or non-uniform temperature change in a structure or material that is contained against expansion or contraction.

Thermogram: a visible light record of the display of an infrared camera system via a Polaroid print, 35mm film, video tape, or computer generated image.

Thermography: a technique for producing heat “pictures” from the radiant energy emitted from stationary or moving objects without in any way influencing the temperatures of the objects under view. The electronic generation and display of a visible image of an infrared spectrum.

Thermoplastic: materials that soften when heated and harden when cooled. This process can be repeated provided that 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, UV absorbers, and other proprietary substances which may be blended with the TPO to achieve the desired physical properties. The membrane may or may not be reinforced.

Thermoset: a material that solidifies or “sets” irreversibly when heated. This property is usually associated with cross-linking of the molecules induced by heat or radiation.

Thinner: a liquid used to reduce the viscosity of coatings or mastic. Thinners evaporate during the curing process. Thinners may be used as solvents for clean-up of equipment.

Thread Count: the number of threads per inch in each direction, with the warp mentioned first, and the fill second, (e.g., a thread count of 20 x 10 means 20 threads per inch [25.4mm] in the warp and 10 threads per inch [25.4mm] in the fill direction).

Through-Wall Flashing: a water-resistant material, which may be metal or membrane, extending through a wall and its cavities, positioned to direct water entering the top of the wall or cavity to the exterior, usually through weep holes.

Tie-Off: (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 roofing or waterproofing system.

Toggle Bolt: a two-piece assembly consisting of a threaded bolt and an expanding clip that can fit through a drilled hole. The clip can spring outward to provide anchorage from the blind side.

Tongue and Groove Planks: one of the oldest types of dimensional structural wood used as roof decking. The sides are cut with convex and concave grooves so adjacent planks may join in alignment with each other to form a uniform roof deck.

TPO: Thermoplastic Olefin.

Traffic Bearing: in waterproofing, a membrane formulated to withstand a predetermined amount of pedestrian or vehicular use with separate protection and a wear course.

Transverse Seam: the joint between the top of one metal roof panel and the bottom of the next panel, which runs perpendicular to the roof slope.

Tuckpointing: the process of removing deteriorated mortar from an existing masonry joint and trowelingnew mortar or other filler into the joint.

Two-Part System: a coating of SPF formed by the mixing and (usually) the reaction of two different materials.

U-Value: overall thermal conductance. U-value is equal to the inverse of the sum of the R-value in a system (U = 1/R total). Units are Btu/Ft2.Hr.°F.

Ultimate Elongation: the amount a material stretches during tensile testing before it ruptures. Usually expressed as a percentage of the original length.

Ultraviolet (UV): (1) situated beyond the visible spectrum, just beyond the violet end, having wavelengths shorter than wavelengths of visible light and longer than those of X-rays; (2) relating to, producing, or employing ultraviolet radiation.

Underlayment: an asphalt-saturated felt or other sheet material (may be self-adhering) installed between the roof deck and the roof system, usually used in a steep-slope roof construction. Underlayment is primarily used to separate the roof covering from the roof deck, to shed water, and to provide secondary weather protection for the roof area of the building.

Uplift: see Wind Uplift.

Valley: the internal angle formed by the intersection of two sloping roof planes.

Vapor Migration: the movement of water vapor from a region of high vapor pressure to a region of lower vapor pressure.

Vapor Pressure: the pressure at any given temperature exerted by a vapor that is in equilibrium with its liquid or solid form.

Vapor Retarder: material installed to impede or restrict the passage of water vapor through a roof assembly.

Veneer: (1) a single wythe of masonry for facing purposes, may not be structurally connected; (2) any of the thin layers of wood glued together to form plywood.

Vent: an opening designed to convey air, heat, water vapor or other gas from inside a building or a building component to the atmosphere.

Ventilation Short Circuit: (as it relates to a passive ventilation system where the system is designed for air flow between intake and exhaust vents) a ventilation short circuit occurs when air is introduced into the ventilation system from an area higher than the intake vent thereby minimizing or defeating the effectiveness of the intake vent. One example can be a gable vent in a soffit-to-ridge ventilation system. Air intake from the gable vent can short circuit the stack-effect draw of air through the soffit vents, and interrupt the thorough venting of the roof cavity.

Ventilator: an accessory that is designed to allow for the passage of air.

Vermiculite: an aggregate used in lightweight insulating concrete, formed by the heating and consequent expansion of a micaceous material.

Viscosity: the resistance of a material to flow under stress. For bitumen, measured in centipoise. (See Viscous.)

Viscous: resistant to flow under stress. Viscous materials are usually cohesive, and have a sticky consistency.

Void: an open space or break in consistency.

Volatile: descriptive of a substance which passes off easily as a gas or vapor, evaporating quickly.

Volatile Organic Compounds (VOC): organic materials which evaporate at normal temperatures and pressures; organic materials which have vapor pressures greater than 0.1 mm Hg at one atmosphere.

Vulcanization: any of various processes by which natural or synthetic rubber or other polymeric materials may be cured or otherwise treated (i.e., exposed to chemicals, heat, or pressure) to render them non-thermoplastic, and which improve their elastic and physical properties.

Water Absorption: the amount of water absorbed by a material after immersion for a prescribed period of time. May be expressed as a percentage of the original weight of the material.

Water Cure: a method of curing a material, such as concrete, by applying a fine mist of water over the surface to control the rate of moisture evaporation from the material.

Water Cutoff: see Cutoff.

Water Stop: a diaphragm used across a joint as a sealant, usually to prevent the passage of water.

Water Table: the level within the ground below which the soil is saturated with water.

Water Vapor Transmission: a measure of the rate of transmission of water vapor through a material under controlled laboratory conditions of temperature and humidity. Customary units are grains/h~ft2. (See ASTM Standard E 96.)

Waterproof: the quality of a membrane, membrane material, or other component to prevent water entry.

Waterproofing: treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.

Wear Course: the top layer of surfacing that carries pedestrian or vehicular traffic. Sometimes referred to as wearing surface.

Weather Infiltration: the negative condition where rain or snow penetrate the roof. The condition is typically wind-driven.

Weep Holes: small openings whose purpose is to permit drainage of water that accumulates inside a building component (e.g., a brick wall, skylight frame, etc.).

Weld: to join pieces of metal together by heat fusion.

Wet: a condition where free water is present in a substance.

Wet Film Thickness: the thickness, expressed in mils, of a coating or mastic as applied but not cured. For comparison, see Dry Film Thickness.

Wicking: the process of moisture movement by capillary action, as contrasted to movement of water vapor.

Wind Clip: a steep-slope roofing attachment device that fits over the butt end of tile, slate, and stone to help secure individual roofing units from wind-uplift.

Wind Load: force exerted by the wind on a structure or part of a structure.

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. This force is then transmitted to the roof surface. Uplift may also occur because of the introduction of air pressure underneath the membrane and roof edges, where it can cause the membrane to balloon and pull away from the deck.

Windward: being in or facing the direction toward which the wind is blowing. The side exposed to the prevailing wind.

Wire Tie System: a scheme of attachment for steep-slope roofing units (e.g., tile, slate, and stone) utilizing fasteners (nails and/or screws) in conjunction with wire to make up a concealed fastening system.

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.

Wythe: a masonry wall, one masonry unit, a minimum of two inches thick.

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