Roofing Glossary of Terms

Welcome to our collection of roofing terms. We have compiled a list of common roofing terms and their definitions from across the web as a resource for those who are looking for more information about roofing.

A-C     D-F     G-I     J-K     M-O     P-S     T-V     W-Z


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

Alligatoring: the cracking of the surfacing bitumen on a built-up roof, producing a pattern of cracks similar to an alligator's hide; the cracks may or may not extend through the surfacing bitumen.

Ambient Temperature: temperature of air - - air temperature.

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

Area Divider: a raised, double wood member attached to a properly flashed wood base plate that is anchored to the roof deck. It is used to relieve thermal stresses in a roof system where no expansion joints have been provided.

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

Asphalt: A dark brown to black material in which the predominating constituents are bitumens, which occur in nature or are obtained in petroleum processing.

Asphalt, Air Blown: an asphalt produced by blowing steam through molten asphalt to modify its properties, normally used for highway bitumen.

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

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Backnailing: the practice of blind nailing (in addition to hot mopping) all the plies of a substrate to prevent slippage. (See BLIND NAILING.)

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

Base Flashing: see FLASHING.

Base Ply: the base ply is the first ply when it is a separate ply and not part of a shingled system.

Base Sheet: a saturated or coated felt placed as the first ply in some multi-ply built up roof membranes.

Bentonite: a 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.

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

Bituminous: containing or treated with bitumen. Examples: bituminous concrete, bituminous concretes, bituminous felts and fabrics, bituminous pavement.

Bituminous Grout: a mixture of bituminous material and fine sand that will flow into place without mechanical manipulation when heated.

Blind Nailing: the practice of nailing the back portion of a roofing ply.

Blister: a spongy raised portion of a roof membrane, ranging in area from 1 inch in diameter and of barely detectable height upward. Blisters result from the pressure buildup of gases entrapped in the membrane system. these gases most commonly are air and/or water vapor. Blisters usually involve delamination of the underlying membrane plies.

Bond: the adhesive and cohesive forces holding two roofing components in intimate contact.

Boot: covering of flexible material, which may be preformed to a particular shape, used to seal around a penetration.

Brooming: embedding a ply of roofing material by using a broom to smooth out the ply and ensure contact with the adhesive under the ply.

BTU: (British Thermal Unit) - the heat energy required to raise the temperature of 1 pound of water 1 degree Fahrenheit.

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 a roof assembly, and usually associated with improper installation.

Built-up Roof Membrane: a continuous, semi-flexible roof membrane assembly, consisting of plies of saturated felts, coated felts, fabrics or mats between which alternate layers of bitumen are applied, generally surfaced with mineral aggregate, bituminous materials, or a granule-surfaced roofing sheet. (Abbreviation: BUR.)

Butyl: a 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.

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Cant Strip: a beveled strip of wood or wood fiber that fits into the angle formed by the intersection of a horizontal surface and a vertical surface. The 45-degree slope of the exposed surface of the cant strip provides a gradual angular transition from the horizontal surface to the vertical surface.

Capillary: the action by which the surface of a liquid (where it is in contact with a solid) is elevated or depressed, depending upon the relative attraction of the molecules of the liquid for each other and for those of the solid.

Cap Sheet: a granule-surfaced coated sheet used as the top ply of a built-up roof membrane or flashing.

Caulking: a composition of vehicle and pigment, used at ambient temperatures for filling joints, that remains plastic for an extended time after application.

CPE (PolyChlorinated ethylene): a thermoplastic material, used for single ply roof membranes, composed of high molecular weight polyethylene which has been chlorinated.

Chlorosulfonated Polyethylene (CSPE or CSM) (Hypalon): a synthetic, rubber like thermoset material, based upon high molecular weight polyethylene with suphonyl chloride, usually formulated to produce a self vulcanizing membrane.

Coal Tar Bitumen: a dark brown to black, semi-solid hydrocarbon formed as a residue from the partial evaporation or distillation of coal tar. It is used as the waterproofing agent in dead-level or low-slop built-up roofs. It differs from COAL TAR PITCH in having a lower front-end volatility.

Coal Tar Felt: See TARRED FELT.

Coal Tar Pitch: A dark brown to black, semi-solid hydrocarbon formed as a residue from the partial evaporation or distillation of coal tar. It is used as the waterproofing agent in dead-level or low-slope built-up roofs. (For specification properties, see ASTM Standard D 450, Types 1 and II.)

Coated Base Sheet: a felt that has been impregnated and saturated with (or felt) asphalt and then coated on both sides with harder, more viscous asphalt to increase its impermeability to moisture; a parting agent is incorporated to prevent the material from sticking to the roll.

Cold Process: a continuous, semi-flexible roof membrane, consisting Roofing: of plies of felts, mats or fabrics that are laminated on a roof with alternate layers of cold-applied roof cement and surfaced with a cold-applied coating.

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

Coping: the covering piece placed on top of a wall that is exposed to the weather. It is usually sloped to shed water.

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

Course: (1) the term used for each application of material that form the waterproofing system or the flashing; (2) one layer of a series of materials applied to a surface (i.e., a five-course wall flashing is composed of three applications of mastic with one ply of felt sandwiched between each layer of mastic.)

Coverage: the surface (in square feet) to be continuously coated by a specific roofing material, with allowance made for a specific lap.

CPE: see chlorinated polyethylene

Crack: a separation or fracture occurring in a roof membrane or roof deck generally caused by thermally induced stress or substrate movement.

Creep: the permanent deformation of a roofing material of roof system caused by the movement of the roof membrane that results from continuous thermal stress or loading.

Cricket: a superimposed construction placed in a roof area to assist drainage.

CSPE: see chlorosulfonated polyethylene

Curb: a raised member used to support roof penetrations, such as skylights, mechanical equipment, hatches, etc. above the level of the roof surface.

Cutback: any bituminous roofing material that has been solvent thinned. Cutbacks are used in cold-process roofing adhesives, flashing cements, and roof coating.

Cutoff: A material seal that is designed to prevent lateral water movement into the edge of a roof system where the membrane terminate at the end of day's work or used to isolate section of the roof system. Cutoffs are usually removed before the continuation of work.

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

Dead Level: the term used to describe an absolutely horizontal roof. Zero slope. (See SLOPE.)

Dead Level Asphalt: a roofing asphalt that has a softening point of 140F (60C) and that conforms to the requirements of ASTM Standard D 312, Type 1.

Dead Loads: non-moving rooftop loads, such as mechanical equipment, air conditioning units, and the roof deck itself.

Deck: the structural surface to which the roofing or waterproofing system (including insulation) is applied.

Degradation: a deleterious change in the chemical structure, physical properties, or appearance of a material due to natural or artificial exposure.

Delamination: separation of the plies in a roof membrane system or separation of laminated layers of insulation.

Dew Point: the temperature at which water vapor starts to condense in cooling air at the existing atmospheric pressure and vapor content.

Drain: a device that allows for the flow of water from a roof area.

Dropback: a reduction in the softening point of bitumen that occurs when bitumen is heated in the absence of air. (See SOFTENING POINT DRIFT.)

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Edge Sheets: felt strips that are cut to widths narrower that the standard width of the full felt roll. They are used to cover joints.

Edge Stripping: application of felt strips cut to narrower widths than the normal width of the full felt roll.

Edge Venting: the practice of providing regularly spaced protected openings along a roof perimeter to relieve moisture vapor pressure.

EIP: Ethylene Interpolymer

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

Elastomeric: the term used to describe the elastic, rubber like properties of a material.

Embedment: (1) the process of pressing a felt, aggregate, fabric, mat, or panel uniformly and completely into hot bitumen or adhesive; (2) the process of placing a material into another material so that it becomes an integral part of the whole material.

Emulsion: the intimate dispersion of an organic material and water achieved by using a chemical or clay emulsifying agent.

End Lap: the distance of overlap where one ply extends beyond the end of the immediately adjacent ply.

Envelope: a continuous felt fold formed by wrapping and securing a portion of a base felt back up and over the felt plies above it. The envelope is intended to prevent bitumen seepage from the edge of the membrane.

EPDM: Ethylene Propylene Diene Monomer (commonly referred to as a "rubber roof")

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

Equilibrium Moisture Content (EMC): (1) the moisture content of material stabilized at a given temperature and relative humidity, expressed as percent moisture by weight; (2) the typical moisture content of a material in any given geographical area.

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

Expansion Joint: a structural separation between two building elements designed to minimize the effect of the stresses and movements of a building's components and to prevent these stresses from splitting or ridging the roof membrane.

Exposure: (1)the transverse dimension of a roofing element not overlapped by an adjacent element in any roof system. The exposure of any ply in a membrane may be computed by dividing the felt width minus 2 inches by the number of shingled plies; thus, the exposure of a 36-inch-wide felt in a shingled, four-ply membrane should be 8 1/2 inches; (2) the time during which a portion of a roofing element is exposed to the weather.

Extrusion: a manufacturing process which consists of forcing batched and formulated material through an orifice.

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Fabric: a woven cloth of organic or inorganic filaments, threads, or yarns.

Factory Mutual: an organization that classifies roof assemblies for their fire characteristics and wind-uplift resistance for insurance companies in the United States.

Felt: a fabric manufactured from vegetable fibers (organic felts), asbestos fibers (asbestos felts), or glass fibers (glass fiber felts). The manufacturer process involves mechanically interlocking the fibers of the particular felt material in the presence of moisture and heat.

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

Fine Mineral Surfacing: a water soluble, inorganic material, more than 50 percent of which passes through the No. 35 sieve, that may be used on the surface of roofing material.

Fishmouth: Membrane defect consisting of an opening in the edge lap of a felt in a built up membrance; a consequence of an edge wrinkle.

Flashing: components used to weatherproof or seal the roof system edges at the perimeters, penetrations, walls and other places where the roof covering is interrupted or terminated.

Flashing Cement: a trowelable mixture of cutback bitumen and mineral stabilizers, including asbestos or other inorganic fibers.

Flat Asphalt: a roofing asphalt that has a softening point of approximately 170F (77C) and that conforms to the requirements of ASTM Standard D 312, Type II.

Flood Coat: the top layer of bitumen into which the aggregate is embedded on an aggregate-surfaced built up roof.

Fluid Applied Elastomer: as elastomeric material, which is fluid at ambient temperature, that dries or cures after application to form a continuous membrane.

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Glass Fiber Felt: A felt sheet in which glass fibers are bonded into the felt sheen with resin. Glass fiber felts are suitable for impregnation and coating. They are used in the manufacture and coating of bituminous waterproofing material, roof membranes, and shingles.

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

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

Gravel: coarse, granular aggregate, containing pieces approximately 5/8 inch to 1/2 inch in size and suitable for use in aggregate on built up roofs.

Gravel Stop:
a flange devices, frequently metallic, designed to provide a continuous finished edge for roofing materials and to prevent loose aggregate form washing off of the roof.

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Heat Welding: method of melting or fusing together the overlapping edges of separate sheets of thermoplastics and polymer modified bitumens.

Headlap: the minimum distance, measured at 90 degrees to the eaves along the face of a shingle or felt, form the upper edge of the shingle or felt to the nearest exposed surface.

an area where a liquid applied material is missing.

"Hot Stuff"or "Hot": the roofer's term for hot bitumen

Hygroscopic: the term used to describe a material which attract, absorbs and retains atmospheric moisture.

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

Infrared Thermography: a practice of roof analysis where an infrared camera is used to measure the temperature differential of a roof surface to locate areas of underlying moisture.

Inorganic: being or composed of matter other than hydrocarbons and their derivatives, or matter hat is not of plant or animal origin.

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

Inverted Roof Membrane Assembly (IRMA): a patented, proprietary variation of the "Protected Membrane Roof Assembly" in which Stryofoam Brand insulation and ballast are placed over the roof membrane. IRMA and Stryofoam are registered trademarks of the Dow Chemical Corporation.

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Lap: that part of a roof or flashing that overlaps or covers any portion of the same or another type of adjacent component.

Lead: a soft workable metal used for miscellaneous flashings.

Life cycle costing: a method of economic analysis that takes into account expected costs over the useful life of an asset.

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

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

Live Loads: temporary loads that the roof structure must be designed to support, (e.g., people, installation equipment, rain, snow, ice, etc.)

Loose laid membranes: membranes that are not attached to the substrate except at the perimeter. Typically held in place with ballast.

Low Temperature Flexibility: the ability of a membrane to remain flexible after it has been cooled to a low temperature.

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Manufacturer's Bond: a security company's guarantee that it will stand behind a manufacturer's liability to finance membrane repairs occasioned by ordinary wear within a period generally limited to 5, 10, 15, or 20 years.


Mechanically Fastened Membranes: membranes attached at defined intervals to the substrate.

Membrane: a flexible or semi-flexible roof covering or waterproofing layer, whose primary function is the exclusion of water.

Metal Flashing: see FLASHING; metal flashing is frequently used as through wall flashing, cap flashing, counterflashing or gravel stops.

a superficial coating or discoloring of an organic material due to fungal growth.

Mineral Fiber Felt:
a felt with mineral wool as its principal component.

Mineral Granules: opaque, natural, or synthetically colored aggregate commonly used to surface cap sheets, granule-surfaced sheets, and roofing shingles.

Mineral Stabilizer: a fine, water-insoluble inorganic material, used in a mixture with solid or semi solid bituminous materials

Mineral Surfaced Roofing: built up roofing material whose top ply consists of granule surfaced sheet.

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

Modified Bitumen: composite sheets consisting of a polymer (e.g., atactic polypropylene (APP), or styrene butadiene styrene (SBS)) often reinforced and sometimes surfaced with various types of mats, films, foils and mineral granules.

Moisture Relief Vent: venting device through the roofing membrane to relieve moisture vapor pressure from within the roof assembly.

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

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 and are then turned over and applied to the substrate.

Mopping: an application of hot bitumen applied to the substrate or to the felts of a built up roof membrane with a mop or mechanical applicator.

..Solid Mopping: a continuous mopping of a surface, leaving no unmopped areas.

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

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

Mud Cracking: surface cracking of surface material resembling dried cracked earthen mud.

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Nailing: (1) in the Exposed Nail Method, nail heads are exposed to the weather; (2) in the Concealed Nail Method, nail heads are concealed from the weather.

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

Night Seal: method used to temporarily seal a membrane edge during construction to protect the roof assembly from water penetration.

Nineteen-Inch Selvage: a prepared roofing sheet with a 17-inch granule surfaced edge. This material is sometimes referred to as SIS or as Wide-Selvage Asphalt Roll Roofing Material Surfaced with Mineral Granules.

Ninety-Pound: a prepared organic felt roll with granule surfacing what has a mass of approximately 90 pounds per 100 square feet.

Nitrile Rubber:
a membrane whose predominant resinous ingredient is a synthetic rubber made by the polymerization of acrylonitrile with butadiene.

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

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

Nuclear Testing: a device that contains a radioactive source to emit high velocity neutrons into a roof system. Reflected neutrons are measured to ascertain presence of moisture.

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Orange Peel: a surface condition that shows a fine texture resembling the texture of an orange.

Organic: being or composed of hydrocarbons or their derivatives, or matter of plant, or animal origin.

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Parapet Wall: perimeter wall, which extends above the roof.

Peel Strength: average force required to peel a membrane from the substrate to which it has been bonded.

Penetration: any object passing through the roof.

Perlite: an aggregate used in lightweight insulation concrete and in preformed perlitic insulation board, formed by heating and expanding siliceous volcanic.

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 = 0.491 psi). The formula for perm is: P = GRAINS OF WATER VAPOR/SQUARE FOOT * HOUR * INCH MERCURY

Permeance: an index of a material's resistance to water vapor transmission. (See PERM.)

Phase Application: the installation of a roof system or waterproofing system during two or more separate time intervals.

Phenolic: a rigid closed-cell foam product with an orange or light red foam core, sandwiched between various types of facers. Problems have been reported with board shrinkage, and corrosion of adjacent metal roof assembly components. (Contact IRC staff for further information and details.)

Picture Framing: a rectangular pattern of ridges in a roof membrane over insulation or deck joints.

Pitch Pocket: a flange, open bottomed, metal container placed around columns or other roof penetration that is filled with hot bitumen and/or flashing cement to seal the joint.

Plastic Cement: see FLASHING CEMENT

Ply: a layer of felt in a built up roof membrane system. A four-ply membrane system has four plies felt. The dimension of the exposed surface (the "exposure") of any ply may be computed by dividing the felt width (minus 2 inches) by the number of plies; thus, the exposed surface of a 36 inch wide felt in a four ply membrane should be 8 1/2 inches. (See EXPOSURE.)

Pond: a roof surface that is incompletely drained.

Positive Drainage: the drainage condition in which consideration has been made for all loading deflection of the deck, and additional roof slop has been provided to ensure complete drainage of the roof area within 24 hours of rainfall.

Pourable Sealer: a type of sealant often supplied in two parts and is typically used to fill pitch pans.

Protected Membrane Roof (PMR): an insulated and ballasted roof assembly, in which the membrane is covered by the insulation and ballasted (sometimes referred to as an "inverted roof assembly").

Psychometric Chart: a diagram relating to the properties of humid air with temperature.

a thin, liquid bitumen applied to a surface to improve the adhesion of subsequent application of bitumen.

PVC: Polyvinyl Chloride – Usually associated with a thermoplastic single ply roof membrane system.

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R-Value: the resistance to heat transfer of a material.

Rake: the sloped edge of a roof at the first or last rafter.

Reflectivity: the ability of the surface of a material to reflect the infra red energy of a light source.

Reglet: a groove in a wall or other surface adjoining a roof surface for use in the attachment of counterflashing.

Reinforced Membrane: a roofing or waterproofing membrane reinforced with felts, mats, fabrics, or chopped fibers.

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 pound of water vapor at a given temperature, the relative humidity (RH) is 50 percent.

Reroofing: the practice or applying new roofing material over existing roofing materials.

Ridging: an upward, "tenting" displacement of a roof membrane, frequently occurring over insulation joints, deck joints and base sheet edges. Generally associated with improper application. (See picture framing)

Roll Roofing: the term applied to smooth surfaced or mineral surfaced coated felts.

Roof Assembly: an assembly of interacting roof components (including the roof deck) designed to weatherproof and, normally, to insulate a building's top surface.

Roof System: a system of interacting roof components (NOT including the roof deck) designated to weatherproof and, normally, to insulate a building's top surface.

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

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

SBS: See Styrene Butadiene Styrene

Screen: an apparatus with apertures for separating sizes of material.

Seal: (1) a narrow closure strip made of bituminous materials; (2) to secure a roof from the entry of moisture.

Sealant: a mixture of polymers, fillers, and pigments used to fill and seal joints where moderate movement is expected; it cures to a resilient solid.

Self –Adhering Membrane:
a membrane that can adhere to a substrate and to itself without use of adhesives. The undersurface is protected by a release paper.

Selvage: an edge or edging that differs from the main part of (1) a fabric, or (2) granule-surfaced roll roofing material.

Selvage Joint: a lapped joint designed form mineral surfaced cap sheets. The mineral surfacing is omitted over a small portion of the longitudinal edge of the sheet below in order to obtain better adhesion of the lapped cap sheet surface with the bituminous adhesive.

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

Shingle: (1) a small unit of prepared roofing material designed to be installed with similar units in overlapping rows on inclines normally exceeding 25 percent; (2) to cover with shingles; (3) to apply any sheet material in overlapping rows like shingles.

Shingling: (1) the procedure of laying parallel felts so that one longitudinal edge of each felt overlaps and the other longitudinal edge underlaps, an adjacent felt. (See PLY.) Normally, felts are shingled on a slope so that the water flows over rather than against each lap; (2) the application of shingles to a sloped roof.

Sieve: an apparatus with apertures for separating sizes of material.

Slag: a hard, air-cooled aggregate that is left as residue from blast furnaces. It is used as a surfacing aggregate and should be surface dry and free of sand, clay, or other foreign substances at the time of application.

Slip Sheet: a sheet material placed between two components of a roof assembly to ensure that no adhesion occurs between them, and/or to prevent possible damage from chemical incompatibility, wearing or abrasion of the membrane. Often associated with PVC membranes.

Slippage: the relative lateral movement of adjacent components of a built up roof membrane. It occurs mainly in roof membranes on a slope, sometimes exposing the lower plies to the weather.

Slope: the tangent of the angle between the roof surface and the horizontal. It is measured in inches per foot. The Asphalt Roofing Manufacturers Association (ARMA) ranks slopes as follows:

..Level Slope: up to 1/2 inch per foot

..Low Slope: 1/2 inch per foot to 1 1/2 inches per foot

Steep Slope: over 1 1/2 inches per foot

Smooth Surfaced Roof: a built up roof membrane surfaced with a layer of hot mopped asphalt, cold applied asphalt clay emulsion, cold applied asphalt cutback, or sometimes with an unmopped inorganic felt.

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

Softening Point Drift: a change in the softening point of bitumen during storage or application. (See Dropback)

Soil Stack: a sanitation pipe that penetrates the roof – used to vent plumbing fixtures. (Stink Stacks)

Solid Mopping: see Mopping

Solvent Welding: a process where a liquid solvent is used to chemically weld or join together two or more layers of certain membranes (usually thermoplastics).

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.

Sprinkle Mopping: see Mopping

Square: the term used to describe 100 square feet of roof area.

Stack Vent: a vertical outlet in a built up roof system designed to relieve any pressure exerted by moisture vapor between the roof membrane and the vapor retarder or deck.

Standing Seam: a metal roof system that consists of an overlapping or interlocking seam that occurs at an upturned rib.

Steep Asphalt: a roofing asphalt that has a softening point of approximately 190F (88C) and that conforms to the requirements of ASTM Standard D 312, Type III.

Strawberry: a small bubble or blister in the flood coating of gravel surfaced roof membrane.

Stress Crack: external or internal cracks within a material caused by long-term stress.

Strip Mopping: see MOPPING

Stripping: (1) the technique of sealing a joint between metal and Strip Flashing the built up roof membrane with one or two plies of felt and hot applied or cold applied bitumen; (2) the technique of taping joints between insulation boards on deck panels.

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

Substrate: the surface upon which the roofing or waterproofing membrane is applies (i.e. the structural deck or insulation).

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.

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

Taping: see STRIPPING.

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.

Tarred Felt: a felt that has been saturated with refined coal tar.

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

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

Test Cut: a sample of the roof membrane, usually 4 inches x 40 inches in size, that is cut from a roof membrane to:
* Determine the weight of the average interply bitumen poundage
* Diagnose the condition of the existing membrane (e.g., to detect leaks or blisters).

Thermal Conductance (C): a unit of heat flow that is used for specific thickness of material or for materials of combination construction, such as laminated insulation.

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.

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

Thermal Resistance: an index of material applied to reduce the flow of heat.

Thermal Shock: the stress producing phenomenon resulting from sudden temperature changes in a roof membrane. (For example, when a rain shower follows brilliant, hot sunshine.)

Thermoplastic: materials that soften when heated and harden when cooled.

Thermoplastic Olefin Membrane (TPO): a blend of polypropylene and ethylene-propylene polymers. Colorant, flame retarants, UV absorbers, and other proprietary substances, which may be blended with the TPO to achieve the desired physical properties.

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.

Through Wall Flashing: a water resistant membrane or material assembly extending through a wall and its cavities, positioned to direct any water entering the top of the wall exterior.

Tie-Off: a seal used to terminate a roofing application at to the adjacent roofing system.

TPO: See Thermoplastic Olefin.

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

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Underwriters Laboratories: an organization that classifies roof assemblies for their fire characteristics and wind uplift resistance for insurance companies in the United States.

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

Vapor Pressure Gradient: a graph, analogous to a temperature gradient, indicating the changes in water vapor pressure at various cross sectional planes through a roof or wall system.

Vapor Retarder: a material designed to restrict the passage of water vapor through a wall or roof. In the roofing industry, a vapor retarder should have a perm rating of 0.5 or less.

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

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

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Water Cutoff: see CUTOFFS.

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