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Check out the roofing dictionary, definitions for common words associated with roofing, commercial / industrial roofing, roof membranes, roof failures and roof materials.

Alligatoring: the cracking of the surfacing bitumen on a bituminous roof or coating on a SPF roof. The cracks may not extend completely through the surfacing bitumen or coating. These cracks are the result of the limited tolerance of asphalt to thermal expansion or contraction. The pattern of cracks resembles an alligator's hide.

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

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

Asphalt: A brownish-black solid or semisolid mixture of bitumens obtained from native deposits or as a petroleum by-product, used in paving, roofing, and water-proofing.

ASTM: American Society for Testing and Materials.

Bitumen: a generic term for an amorphous, semi-solid mixture of complex hydrocarbons derived from an organic source. Two used in the roofing industry are asphalt and coal tar.

Blister: an enclosed pocket of air, which may be mixed with water or solvent vapor, trapped between impermeable layers of felt or membrane, or between the membrane and substrate. The NRCA Roofing and Waterproofing Manual-Fifth Edition Glossary 975. Blisters usually involve delamination of the underlying membrane plies.

Built-up roof (BUR): a continuous, semi-flexible roof membrane, consisting of multiple plies of saturated felts, coated felts, fabrics or mats assembled in place with alternate layers of bitumen, and surfaced with mineral aggregate, bituminous materials, a liquid-applied coating or a granule-surfaced cap sheet.

Cant strip: a beveled strip used under flashings to modify the angle at the point where the roofing or waterproofing membrane meets any vertical element.

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

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

Coal tar: a dark brown to black colored, semi-solid hydrocarbon produced by the distillation of coal.

Coal tar pitch: a coal tar used as the waterproofing agent in dead-level or low-slope built-up roof membranes and membrane waterproofing systems, conforming to ASTM Specification D 450, Type I. Coarse orange peel surface texture: a surface showing a texture where nodules and valleys are approximately the same size and shape. This surface is acceptable for receiving a protective coating because of the roundness of the nodules and valleys. The NRCA Roofing and Waterproofing Manual-Fifth Edition 978 Glossary

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

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

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

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

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

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

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

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

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

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

DOE: U.S. Department of Energy.

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

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

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

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

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

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

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

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

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

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

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

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

Factory Mutual Research (FMR): commonly referred to as "FM," a research and testing organization that classifies roofing components and assemblies for their fire, traffic, impact (hail), weathering, and wind-uplift resistance for four major insurance companies in the United States. Fastener: any of a wide variety of mechanical securement devices and assemblies, including nails, staples, screws, cleats, clips and bolts, which may be used to secure various components of a roof assembly.

Felt: a flexible sheet manufactured by the interlocking of fibers with a binder or through a combination of mechanical work, moisture and heat. Felts are manufactured principally from wood pulp and vegetable fibers (organic felts), asbestos fibers (asbestos felts), glass fibers (glass fiber felts or ply sheets), or polyester fibers.

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

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).

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

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

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

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

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

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

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

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

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.

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

Infrared thermography: The process of displaying variations of apparent temperatures (variation of temperature or emissivity or both) over the surface of an object by measuring variations in infrared radiance.

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

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.

Liquid-applied: application of bituminous cements, adhesives or coatings installed at ambient or slightly elevated temperatures.

Liquid-applied built-up roof: a continuous, semi-flexible roof membrane, consisting of multiple plies of felts, mats or fabrics laminated together with alternate layers of roof cements and surfaced with a liquid -applied coating with or without aggregate surfacing.

Low-slope roofs: a category of roofs that generally include weatherproof membrane types of roof systems installed on slopes at or less than 3:12 (14 degrees).

Mastic: a thick adhesive material used as a cementing agent for holding waterproofing membrane in place. (see Asphalt roof cement).

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

Membrane: a flexible or semi-flexible roof covering or waterproofing whose primary function is to exclude water.

Metal: any of various opaque, fusible, ductile and typically lustrous substances that are good conductors of electricity and heat. The NRCA Roofing and Waterproofing Manual-Fifth Edition Glossary 991. Modified bitumen: (1) a bitumen modified by including one or more polymers (e.g., atactic polypropylene, styrene butadiene styrene, etc.); (2) composite sheets consisting of a polymer modified bitumen often reinforced with various types of mats or films and sometimes surfaced with films, foils or mineral granules.

Moisture scan: the use of a mechanical device (capacitance, infrared, or nuclear) to detect the presence of moisture within a roof assembly. (see Non-destructive testing.)

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

Mud cracking: surface cracking resembling a dried mud flat.

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

NRCA: National Roofing Contractors Association. Orange peel surface texture: in SPF roofing, a condition of the foam in which 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.

Overspray: undesirable depositions of airborne spray.

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

Parapet wall: the part of a perimeter wall that extends above the roof.

Penetration: (1) any construction (e.g., pipes, conduits, HVAC supports) passing through the roof; (2) the consistency of a bituminous material expressed as the distance, in tenths of a millimeter (0.1 mm), that a standard needle penetrates vertically into a sample of material under specified conditions of loading, time, and temperature.

Pinhole: a tiny hole in a coating, film, foil, membrane or laminate comparable in size to one made by a pin.

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

Pitch: see Coal tar.

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.

Pliability: the material property of being flexible or moldable.

Ply: a layer of felt or ply sheet in a built-up roof membrane or roof system.

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.

Pond: a surface which is incompletely drained. The NRCA Roofing and Waterproofing Manual-Fifth Edition 996 Glossary.

Ponding: the excessive accumulation of water at low-lying areas on a roof that remains after the 48 hours after the end rainfall under conditions conducive to drying.

Popcorn surface texture: in SPF roofing, the condition in which the foam surface shows a coarse texture where valleys form sharp angles. This surface is unacceptable for proper coating and protection.

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 following rainfall during conditions conducive to drying.

PVC: polyvinyl chloride.

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

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 scrims, nylon, or polyethylene sheeting.

Relative humidity (RH): the ratio of the pressure of water vapor present in a given volume of air to the pressure of fully saturated water vapor at the same temperature, expressed as a percentage.

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.

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

Ridge vent: a ventilator located at the ridge that allows the escape of warm and/or moist air from the attic area or rafter cavity.

Roof: (1) the cover of a building; (2) to cover with a roof.

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

Roof jack: a metal or wood bracket used to support toe-boards on steep-slope roofs. (also see Flashing Collar.)

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 an angle.

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

Rubber: a material that is capable of recovering from large deformations quickly and forcibly.

Run: horizontal dimension of a slope.

Saddle: a small tapered/sloped roof area structure that helps to channel surface water to drains. Frequently located in a valley. A saddle is often constructed like a small hip roof or pyramid with a diamond-shaped base.

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

SBS: see Styrene butadiene styrene.

Sealant: (1) a material that has the adhesive and cohesive properties to form a seal; (2) a mixture of polymers, fillers, and pigments used to fill and seal joints where moderate movements is expected; unlike caulking, it cures to a resilient solid.

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

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

Shelf life: the maximum time a packaged material can be stored under specified conditions and still meet the performance requirements specified.

Single-lock standing seam: a standing seam that uses 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 thermoset or thermoplastic membrane.

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

Skylight: an opening in a roof that is glazed with a transparent or translucent material; used to admit diffused light to the space below.

Slope: the angle of incline, usually expressed as a ratio of rise to run, or as an angle. (See Roof Slope.) The NRCA Roofing and Waterproofing Manual-Fifth Edition Glossary 1001

Smooth surface texture: in SPF roofing, the condition of the foam in which the surface shows spray undulation and is ideal for receiving a protective coating.

Smooth-surfaced roof: a roof membrane without mineral granule or aggregate surfacing.

Specification: a precise statement of a set of requirements to be satisfied by a material, product, system, or service.

SPF: spray polyurethane foam.

SPF compound: a term used to describe the raw materials (isocyanate and resin) used to make polyurethane foam.

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.

Spud: to remove the roofing aggregate and most of the bituminous top coating by scraping and chipping.

Square: a unit used in measuring roof area equivalent to 100 square feet (9.29 m2) of roof area.

Standing seam: in metal roofing, a type of seam between adjacent sheets of material made by turning up the edges of two adjacent metal panels and then folding or interlocking them in a variety of ways.

Steep-slope roofs: a category of roofing that generally include water-shedding types of roof coverings installed on slopes exceeding 3:12 (14 degrees). The NRCA Roofing and Waterproofing Manual-Fifth Edition Glossary 1003

Styrene butadiene styrene copolymer (SBS): high molecular weight polymers that have both thermoset 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).

SPF surface textures: smooth orange peel, coarse orange peel, verge of popcorn, popcorn, treebark, and oversprayed. The NRCA Roofing and Waterproofing Manual-Fifth Edition 1004 Glossary

Tensile strength: the strength of a material under tension as distinct from torsion, compression or shear.

Thermal expansion: the increase in the dimension or volume of a body due to temperature variations.

Thermoplastic: a material that softens when heated and hardens 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 class of polymers that, when cured using heat, chemical, or other means, changes into a substantially infusible and insoluble material.

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

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

Volatile: a relative term expressing the tendency to form vapor. The NRCA Roofing and Waterproofing Manual-Fifth Edition 1008 Glossary Volatile organic compounds (VOC): means any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participate in atmospheric photochemical reactions.

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.

Weatherproof: the ability of a membrane or roof covering to prevent the passage of water with a limited amount of hydrostatic pressure.

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.


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