Glossary of Roofing Terms

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

Algae discoloration: a type of roof discoloration caused by algae, commonly called fungus growth.

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, or air temperature.

American method: application of giant individual shingles with the long dimension parallel to the rake. Shingles are applied with a 3/4-inch space between adjacent shingles in a course.

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.
ASTM: American Society for Testing and Materials. A voluntary organization concerned with development of consensus standards, testing procedures and specifications.

Asphalt: a dark brown to black material in which the predominating constituents are bitumen’s, which occur in nature or are obtained in petroleum processing…
Asphalt, air blown: asphalt produced by blowing steam through molten asphalt to modify its properties, normally used for highway bitumen.

Asphalt plastic roofing cement: asphalt-based cement used to bond roofing materials. Also known as flashing cement or mastic; should conform to ASTM D-4586.

A tactic polypropylene: a group of high molecular weight polymers formed by the polymerization of propylene.

Back nailing: the practice of blind nailing (in addition to hot mopping) all the plies of a substrate to prevent slippage, see Blind nailing.
Back surfacing: fine mineral matter applied to the back side of shingles to keep them from sticking.

Balanced system: a ventilation system where 50% of the required ventilating area is provided by vents located in the upper portion of the roof with the balance provided by under eave or soffit vents.

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: 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.

Brands: airborne burning embers released from a fire.

Bridging: a method of reroofing with metric-sized shingles.

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: a flat or low-sloped roof consisting of multiple layers of asphalt and ply sheets.

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.)
Bundle: a package of shingles. There are 3, 4 or 5 bundles per square.

Butt edge: the lower edge of the shingle tabs.

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.

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, see Flashing.
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.

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

Cement: see Asphalt plastic roofing cement.

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

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

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

Class “A”: the highest fire-resistance rating for roofing as per ASTM E-108. Indicates roofing is able to withstand severe exposure to fire originating from sources outside the building.

Class “B”: fire-resistance rating that indicates roofing materials are able to withstand moderate exposure to fire originating from sources outside the building.

Class “C”: fire-resistance rating that indicates roofing materials are able to withstand light exposure to fire originating from sources outside the building.

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.

Collar: pre-formed flange placed over a vent pipe to seal the roof around the vent pipe opening. Also called a vent sleeve.

Condensation: the conversion of water vapor or other gas to liquid as the temperature drops or the atmospheric pressure rises.

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.

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 result 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.

Damper: An adjustable plate for controlling draft.

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, also called zero slopes, 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.

Dormer: a framed window unit projecting through the sloping plane of a roof.

Double coverage: application of asphalt roofing such that the lapped portion is at least two inches wider than the exposed portion, resulting in two layers of roofing material over the deck.

Downspout: a pipe for draining water from roof gutters. Also called a leader.

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

Drip edge: a non-corrosive, non-staining material used along the eaves and rakes to allow water run-off to drip clear of underlying construction.

Dropback: a reduction in the softening point of bitumen that occurs when bitumen is heated in the absence of air.

Dutch lap method: application of giant individual shingles with the long dimension parallel to the eaves. Shingles are applied to overlap adjacent shingles in each course as well as the course below.

Eaves: the horizontal, lower edge of a sloped roof.

Eaves flashing: additional layer of roofing material applied at the eaves to help prevent damage from water back-up.

Edging strips: boards nailed along eaves and rakes after cutting back existing wood shingles to provide secure edges for reroofing with asphalt shingles.

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.

Ell: an extension of a building at right angles to its length.

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 see page 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.
Exposed nail method: application of roll roofing in which all nails are driven into the cemented, overlapping course of roofing. Nails are exposed to the weather.

Exposure I grade plywood: type of plywood approved by the American Plywood Association for exterior use.

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.

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.

Feathering strips: tapered wood filler strips placed along the butts of old wood shingles to create a level surface when reroofing over existing wood shingle roofs, also called horse feathers.

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.
Fiber glass mat: an asphalt roofing base material manufactured from glass fibers.

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.

Fish mouth: Membrane defect consisting of an opening in the edge lap of a felt in a built up membrane; 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 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.
Free-tab shingles: shingles that do not contain factory-applied strips or spots of self-sealing adhesive.

Gable: the upper portion of a sidewall that comes to a triangular point at the ridge of a sloping roof.

Gable roof: a type of roof containing sloping planes of the same pitch on each side of the ridge. It contains a gable at each end.

Gambrel roof: a type of roof containing two sloping planes of different pitch on each side of the ridge. The lower plane has a steeper slope than the upper. It contains a gable at each end.

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.

Granules: ceramic-coated colored crushed rock that is applied to the exposed surface of asphalt roofing products.

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

Gutter: the trough that channels water from the eaves to the downspouts.

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

Head lap: 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.

HEX shingles: shingles that have the appearance of a hexagon after installation.

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

Hip: the inclined external angle formed by the intersection of two sloping roof planes; runs from the ridge to the eaves.

Hip roof: a type of roof containing sloping planes of the same pitch on each of four sides; contains no gables.

Hip shingles: shingles used to cover the inclined external angle formed by the intersection of two sloping roof planes.

Horse feathers: see Feathering strips.

“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.

Ice dam: condition formed at the lower roof edge by the thawing and re-freezing of melted snow on the overhang; can force water up and under shingles, causing leaks.

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.

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

Inverted Roof Membrane Assembly (IRMA): the 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 Corporation.

Laminated shingles: strip shingles containing more than one layer of tabs to create extra thickness; also called three-dimensional shingles.

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 slope application: Method of installing asphalt shingles on roof slopes between two and four inches per foot.

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

Louver: A slanted opening for ventilation.

Mansard roof: a type of roof containing two sloping planes of different pitch on each of four sides. The lower plane has a much steeper pitch than the upper, often approaching vertical; contains no gables.

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.

Masonry primer: an asphalt-based primer used to prepare masonry surfaces for bonding with other asphalt products.

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, counter flashing or gravel stops.

Mildew: 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 semisolid bituminous materials

Mineral surfaced roofing: built up roofing material whose top ply consists of a 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., a tactic 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
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.

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.

Natural ventilation: a ventilation system utilizing ventilators installed in openings in the attic and properly positioned to take advantage of natural air flow to draw hot summer or moist winter air out and replace it with fresh outside air.

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 old shingles in which the top edge of the new shingle is butted against the bottom edge of the existing shingle tab.

Net free area: Area unobstructed by screens, louvers or other materials.

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.

No-cutout shingles: shingles consisting of a single, solid tab with no cutouts.

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

Non-veneer panel: any wood based panel that does not contain veneer and carries an APA span rating, such as wafer board or oriented strand board.

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

Normal slope application: method of installing asphalt shingles on roof slopes between 4 inches and 21 inches per foot.

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.

Open valley: method of valley construction in which shingles on both sides of the valley are trimmed along a chalk line snapped on each side of the valley. Shingles do not extend across the valley. Valley flashing is exposed.

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.

Overhang: That portion of the roof structure that extends beyond the exterior walls of a building.

Pallets: wooden platforms used for storing and shipping bundles of shingles.

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 roofing

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.

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.

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

Pitch: the degree of roof incline expressed as the ratio of the rise, in feet, to the span, in feet.

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: 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 ” 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.

Ply: the number of layers of roofing: i.e. one-ply, two-ply.

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.

Primer: 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.

Quick-setting cement:
Asphalt-based cement that adheres tabs of strip shingle to the course below; also adheres roll roofing laps applied by the concealed nail method.

the resistance to heat transfer of a material.

Racking: roofing application method in which shingle courses are applied vertically up the roof rather than across and up. Not a recommended procedure.

Rafter: the supporting framing member immediately beneath the deck, sloping from the ridge to the wall plate.

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

Random-tab shingles: shingles on which tabs vary in size and exposure.
Reflectivity: the ability of the surface of a material to reflect the infrared energy of a light source.

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

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.

Release tape: a plastic or paper strip that is applied to the back of self-sealing shingles. This strip prevents the shingles from sticking together in the bundles, and need not be removed for application.

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

Ridge: the uppermost, horizontal external angle formed by the intersection of two sloping roof planes.

Ridging: upward “tenting” displacement of a roof membrane, frequently occurring over insulation joints, deck joints and base sheet edges; generally associated with improper application.

Ridge shingles: shingles used to cover the horizontal external angle formed by the intersection of two sloping roof planes.

Rise: the vertical distance from the eaves line to the ridge.

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.

Run: the horizontal distance from the eaves to a point directly under the ridge.

Saturant: asphalt used to impregnate an organic felt base material.

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

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.

Self-sealing cement: a thermal-sealing tab cement built into the shingle to firmly cement the shingles together automatically after they have been applied properly and exposed to warm sun temperatures. In warm seasons, the seal will be complete in a matter of days. In colder seasons, sealing time depends on the temperature and amount of direct sunlight hitting the shingles. Hand sealing with plastic cement should be done to ensure sealing in winter.

Self-sealing shingles: shingles containing factory-applied strips or spots of self-sealing adhesive.

Self-sealing strip or spot: factory-applied adhesive that bonds shingle courses together when exposed to the heat of the sun after application.

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.

Shading: slight differences in shingle color that may occur as a result of normal manufacturing operations.

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

Sheathing: exterior grade boards used as a roof deck material.

Shed roof: a roof containing only one sloping plane; has no hips, ridges, valleys or gables.

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.

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

Single coverage: asphalt roofing that provides one layer of roofing material over the deck.

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.

Soffit: The finished underside of the eaves.

Soil stack: a vent pipe that penetrates the roof.

see Dropback soil stack: a sanitation pipe that penetrates the roof – used to vent plumbing fixtures; as called 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).
Span: the horizontal distance from eaves to eaves.

Specialty eaves flashing membrane: a self-adhering, waterproofing shingle underlayment designed to protect against water infiltration due to ice dams or wind driven rain.

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.

Square-tab shingles: shingles on which tabs are all the same size and exposure.

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 occurring at an upturned rib.

Starter strip: asphalt roofing applied at the eaves that provide protection by filling in the spaces under the cutouts and joints of the first course of shingles.

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.

Steep slope application: method of installing asphalt shingles on roof slopes greater than 21 inches per foot.

Step flashing: flashing application method used where a vertical surface meets a sloping roof plane.

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 shingles: asphalt shingles that are approximately three times as long as they are wide.

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.

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.

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 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.

Tab: the exposed portion of strip shingles defined by cutouts.

Talc: see Back surfacing.

Taping: see Stripping.

Tar: a brown or black bituminous material, liquid or semisolid in consistency, in which the predominating constituents are bitumen 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.

Telegraphing: a shingle distortion that may occur when a new roof is applied over an uneven surface.

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 retardants, 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.

Three-tab shingle: the most popular type of asphalt shingle usually 12″ x 36″ in size with three tabs.

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 Membrane.
Top lap: that portion of the roofing covered by the succeeding course after installation.

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

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

Valley: the internal angle formed by the intersection of two sloping roof planes to provide water runoff.

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.

Vent sleeve: see Collar.

Ventilators: devices that eject stale air and circulate fresh air (i.e., ridge, roof, gable, under-eave, foundation or rafter vents and vented soffit panels.)

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

Water cutoff: see Cut off.

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

Woven valley: method of valley construction in which shingles from both sides of the valley extend across the valley and are woven together by overlapping alternate courses as they are applied. The valley flashing is not exposed.