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| Roofing Terms & Definitions 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. Alligatoring is not always indicative of roof failure or leakage. Aluminum paint - an oil based coating mixed with aluminum particles, used for protecting asphalt roofs from UV rays & preserving a roofs life. Asphalt - a black bitumen material used in roofing in hot & cold form , also called tar. Asphalt Felt #30 - an asphalt-saturated felt or an asphalt coated felt, primarily used as the base layer on sloped roofs. Backnailing - the practice of blind-nailing roofing felts to a substrate in addition to hot- mopping to prevent slippage. Base Ply - the lowermost ply of roofing material in a roof membrane assembly. Base Sheet - a saturated or coated felt placed as the first ply in some multi-ply built-up roof membranes. Bitumen - a class of amorphous, black or dark colored, cementitious substance, natural or manufactured, found in asphalts, tars, and pitches. Blister - An enclosed pocket of air mixed with water or solvent vapor, trapped between impermeable layers of felt, or between the felt and substrate. Blocking - wood built into a roofing system above the deck and below the membrane and flashing to stiffen the deck around an opening, act as a stop for insulation, or to serve as a nailer for attachment of the membrane or flashing. Bull - Name given to plastic cement in some areas. Cant Strip - a beveled strip used under flashing to modify the angle at the point where the roofing or waterproofing membrane meets any vertical element. Cap Flashing - (See Flashing.) Cap Sheet - a granule-surfaced coated sheet used as the top ply of a built-up roof membrane or flashing. Coal Tar - a dark brown to black, semi-solid hydrocarbon obtained as residue from the partial evaporation or distillation of coal tar. Coal tar can be a substitute for asphalt, although rarely is used due to it's caustic and hazardous nature. Cold-Process Roofing - a continuous, semi-flexible roof membrane, consisting 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. Coping - the covering piece on top of a wall exposed to the weather, usually sloped to shed water. Counter flashing - the metal that laps down over the wall or step flashings, terminating and sealing the juncture where roof meets wall or vertical surface. Course - 1) the term used for each application of material that forms the waterproofing system or the flashing; 2) one layer of 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). Cricket - Wooden structure built at the high side of a chimney or wall to divert water. Crickets can also be installed on flat roofs with tapered insulation to help eliminate ponding. Deck - the structural surface to which the roofing or waterproofing system (including insulation) is applied. See Substrate. Delamination - separation of the plies in a roof membrane system or separation of laminated layers of insulation. Drain - a device that allows for the flow of water from a roof area. Drip edge - a metal flashing installed at the low point of roof slope where water runs off, typically consisting of 2 sides, the nailer flange and the exposed face. Drying-In - The application of roofing felt to the roof deck. Eave - The lower projecting portion of a roof overhang. Elastomeric - a rubber like synthetic polymer that will stretch when pulled and will return quickly to its original shape when released, primarily used for waterproofing walls & vertical surfaces. Expansion Joint - a structural separation between two building elements that allow free movement between the elements without damage to the roofing or waterproofing system. Factory Mutual (FM) - an organization the classifies roof assemblies for their fire characteristics and wind up-lift resistance for insurance companies in the United States. Fascia - The wood trim covering the rafters and rafter ends, just beneath the drip edge metal. Felt - a flexible sheet manufactured by the interlocking of fibers through a combination of mechanical work, moisture and heat. Felts are manufactured principally from organic fibers or glass fibers; other fibers may be present in each type. Flashing - the system used to seal membrane edges at walls, expansion joints, drains, gravel stops, and other places where the membrane is interrupted or terminated. Base flashing covers the edge of the membrane. Cap flashing or counter flashing shields the upper edges of the base flashing. Flashing Cement - a trowelable mixture of cutback bitumen and mineral stabilizers, often used for repairs & filling pitch pans. Flood Coat - the top layer of bitumen into which the aggregate (Gravel) is embedded on an aggregate-surfaced built-up roof Furring - the fastening of thin strips of wood to fascia board at the roofs perimeter. The purpose of furring strip is to prevent water from running directly off the drip edge onto the fascia, which can cause rot. Galvanize - to plate with zinc, originally by electric shock galvanic action, providing protection from rust. Glass felt - glass fibers bonded into a sheet with resin and suitable for impregnation in the manufacture of bituminous waterproofing materials, roof membranes, and shingles. Granules - The rock like material used on the surface of shingles or rolled roofing such as #90 or modified bitumen. (See Mineral Granules) Gravel - course, granular aggregate, with pieces larger than sand grains, resulting from the natural erosion of rock. Gutter - a trough or channel along or under eaves of a roof, to carry off rain water. Incline - the slope of a roof expressed either in percent or in the number of vertical units of rise per horizontal unit of run. For example, a 5”:12” incline is a slope of 5” of vertical drop for every 12” horizontally, or 22 degrees. (also see pitch chart.) Insulation - a rigid board composed of wood, glass or cardboard fibers, or polyisocyanurate foam, applied to the roof deck to reduce the transferring of heat outdoor temperature and sun light. Lead stacks - Sleeve & base fashioned from a lead sheet to seal penetrations where plumbing vent pipes exit through the roof. Mastic - (See Flashing Cement.) Membrane - a flexible or semi-flexible roof covering or waterproofing layer, whose primary function is the exclusion of water. Mineral Granules - opaque, natural, or synthetically colored aggregate commonly used to surface cap sheets, granule-surfaced sheets, and roofing shingles. (See Granules) Mineral-Surfaced Roofing - built-up roofing material whose top ply consists of a granule- surfaced sheet. Modified Bitumen - composite sheets consisting of copolymer modified bitumen often reinforced and sometimes surfaced with various types of films, foils and mats. Most modified bitumens are partially composed of recycled tires, plastics & rubber. Mopping - the application of hot bitumen with a mop or mechanical applicator to the substrate or to the felts of a built-up roof membrane. Ninety-Pound (#90) - a prepared organic felt roll roofing with a granule surfaced exposure that has a mass of approximately 90 pounds per 100 square feet. Overflow scupper - additional scupper of approximately equal size to an active scupper that serves as an emergency overflow in case primary drains are clogged with debris. Parapet Wall - the part of any wall entirely above the roof. Perlite - an aggregate used in lightweight insulating concrete and in preformed perlitic insulation boards. Pitch - (See Coal Tar and Incline.) Pitch Pan - a flanged, open-bottomed metal container placed around columns, legs or other roof penetrations that is filled with hot bitumen or flashing cement to seal the joint. Support legs for air conditioning units are sealed with pitch pans, as are electrical conduit penetrations. 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 of felt. Pond - a roof surface that is incompletely drained. Primer - thin bitumen applied to a surface to improve the adhesion of subsequent applications of bitumen, serving a similar purpose as a primer coat of paint would. Rake - The end of a gable slope, the outer edge of the first or last rafter. Re-covering - the process of covering an existing roofing system with a new roofing system. Replacement - the practice of removing an existing roof system and replacing it with a new roofing system. Re-roofing - the process of re-covering or replacing an existing roofing system. (See Re- covering and Replacement.) Scupper - an opening in a building to allow water to run off the roof. Seventy Five Pound (#75) - an asphalt impregnated fiberglass sheet, primarily used as the base layer in flat roofs. Shingle - a small unit of prepared roofing material designed for installation with similar units in overlapping rows on inclines of 2”:12” (9.5 degrees) or greater. Slope - the angle or pitch of a roof. Spalling - the act of concrete splitting or breaking up in layers, usually due to water penetration. Square - Unit of measure. One square is 100 square feet, equivalent to 10'X10' area. Substrate - the surface upon which the roofing or waterproofing membrane is applied (i.e., plywood, tongue & groove, concrete, corrugated steel). Sump - an intentional depression around a drain. Tapered Insulation - insulation boards that have a slight bevel, laid out in increasing & decreasing thickness in order to create a gradual slope to assist drainage and alleviate ponding. (Illustration 4) Tie-In - The joining of roofing from separate roof areas. Tile - a thin, usually rectangular piece of stone , concrete, or unglazed fired clay, used for roofing. Tin cap - small round metal discs used in conjunction with nails as a fastener for the base ply of roofing. Underwriters Laboratories (UL) - an organization that classifies roof assemblies for their fire characteristics and wind up-lift resistance. Valley - The junction of two roof slopes that come together forming a V shape, with a channel to disperse water. Vapor Retarder - a material designed to restrict the passage of water vapor through a roof or wall. 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. Waterproofing - treatment of a surface or structure to prevent the passage of water under hydrostatic pressure. Waterproofing is usually performed to cement and stucco walls by sealing cracks with caulking and elastomeric paint. |
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