Glossary of roofing terms

ACCELERATED WEATHERING The process in which materials are exposed to a controlled environment where various phenomena, such as heat, water, condensation and light are altered to magnify their effects, thereby accelerating the weathering process. The physical properties that result from this exposure are then measured and compared to those of the original, unexposed material.

ADHESIVE A substance which joins two or more materials through chemical bonding.

AGGREGATE (1) Crushed stone, crushed slag, or water-worn gravel used for surfacing a roof; (2) Any granular mineral material. (Also BALLAST.)

ALLIGATORING The cracking of the surfacing asphalt on a built-up roof, producing a pattern of cracks similar to an alligator's hide.

ANCHOR BAR A metal strip used to secure a membrane to a substrate. (Also BATTEN, TERM BAR, TERMINATION BAR.)

APPLICATION RATE The quantity (mass, volume or thickness) of material applied per unit area.

AREA DIVIDER See Control Joint.

ASBESTOS A group of natural, fibrous impure silicate materials.

ASPHALT A dark brown or black substance found in a natural state or, more commonly, left as a residue after evaporating or otherwise processing crude oil or petroleum. Asphalt is then further processed to conform to various roofing grade specifications. (Also BITUMEN.)

ASPHALT, AIR BLOWN An asphalt produced by blowing air through molten asphalt at an elevated temperature to raise its softening point and modify other properties.

ASPHALT FELT An asphalt coated or saturated felt.

ASTM American Society for Testing and Materials.

BACKMOP To mop hot asphalt on the back of a roofing material before embedding it in a mopping of asphalt on the substrate.

BACK-NAILING The practice of blind-nailing roofing felts to a substrate in addition to hot mopping to prevent slippage. (Also BLIND NAILING.)

BACK WATER LAP A lap installed so that water flows against it.

BALLAST An anchoring material, such as rounded river rock, gravel, or pre-cast concrete pavers, which is used to hold single ply roofing membranes in place and to stabilize the roof system from wind uplift forces. (Also AGGREGATE.)

BASE PLY The bottom or first ply in a roofing membrane when additional plies are to be subsequently installed.

BASE SHEET A product specifically intended to be used as a base or first ply in a roofing system.

BATTEN A narrow metal band or plate, usually of galvanized steel or aluminum, which is used to fasten or hold in place a single ply membrane.

BIRD BATH A shallow, insignificant amount of water left on the surface of a roof membrane after a rain.

BITUMEN A generic term for various amorphous, semi-solid
mixtures of hydrocarbons derived from coal or petroleum. (Also ASPHALT, COAL TAR.)

BLIND NAILING The use of nails that are not exposed to the weather in the finished roofing. (Also BACK NAILING.)

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

BLOCKING (1) Wood built into a roofing system above the deck and below the membrane and flashing to (a) stiffen the deck around an opening, (b) act as a stop for insulation, (c) serve as a nailing subsrate for attachment of the membrane or flashing; (2) Wood crossmembers installed between rafters or joists to provide support at cross-joints between deck panels; (3) Adhesion between similar or dissimilar materials in roll or sheet form that may interfere with the satisfactory and efficient use of the material.

BLOWING AGENT An expanding agent used to produce a gas by chemical or thermal action, or both, in manufacture of hollow or cellular materials including closed cell thermal insulations.

BOND The adhesive and cohesive forces holding two roofing components in intimate contact.

BONNET A conical or pyramid-shaped metal counterflashing installed on a pipe or other penetration to counterflash a pitch pocket. (Also UMBRELLA, COOLIE CAP.)

BROOMING Embedding a ply by using a broom or other device to smooth it out and ensure contact with the adhesive under the ply.

BUILT-UP ROOFING (BUR) A continuous, semi-flexible membrane consisting of plies of saturated felts, coated felts, fabrics or mats assembled in place with alternate layers of asphalt, and surfaced with mineral aggregate, bituminous materials, a granule surfaced sheet or some type of liquid coating.

BULL A slang term for asphalt roofing cement..

BUTT JOINT A joint or seam formed by joining separate sections of membrane atthe edges without overlap (i.e., edge to edge). Once the edges have been joined, the seam is usually covered and sealed with a narrow strip of membrane material or compatible tape.

BUTYL A rubber material produced by copolymerizing isobutylene with a small amount of isoprene. Butyl is variously manufactured into sheet goods, blended with other rubber materials, and is often used to make sealants and adhesives.

CALENDERING A manufacturing process by which polymeric membranes and sheeting are produced. The finished material is formed by passing it between the nips of a series of large counter-rotating steel rollers which produces a film or sheet of uniform thickness. The device used forthis purpose is a calender.

CAMBER A slight convex curve of a surface, such as in a pre-stressed concrete deck.

CANT STRIP A beveled strip used under flashings of bituminous systems to modify the angle at the point where the roofing or waterproofing membrane meets any vertical element.

CAP FLASHING See COUNTERFLASHING.

CAP SHEET A granule surfaced, coated felt used as the top ply of a roofing membrane.

CELLULAR GLASS INSULATION A rigid roof insulation board composed of heat-fused, closed glass cells blown with hydrogen sulfide.

CHLORINATED POLYETHYLENE (CPE) A thermoplastic material, used for single ply membranes, which is composed of high molecular weight polyethylene which has been chlorinated,  a process which yields a flexible rubber-like material.

CHLOROSULFONATED POLYETHYLENE (CSPE) A synthetic, rubber-like thermoset material, based on high molecular weight polyethylene with pendant sulphonyl chloride groups, usually formulated to produce a self*vulcanizing membrane.

COAL TAR FELT A felt that has been saturated with refined coal tar.

COAL TAR PITCH A dark brown to black, solid material obtained as a residue in the partial evaporation or distillation of coal tar.

COATED FELT (1) An asphalt felt that has been coated on both sides with harder, more viscous asphalt; (2) A glass fiber felt that has been simultaneously impregnated and coated with asphalt on both sides.

COEFFICIENT OF THERMAL EXPANSION The change in dimension of a material as a function of temperature. It is usually reported in inches per inch per øF or millimeters per millimeter per øC.

COLD PROCESS ROOFING A continuous, semi-flexible membrane consisting of plies of felts, mats, or fabrics laminated on a roof with alternate layers of roof cement and surfaced with a cold-applied coating.

COMPOSITE BOARD A roof insulation board composed of two different types of insulating materials bonded together to form one integral product.

COMPRESSIVE STRENGTH The ability of roofing materials and components to resist deformation or other damage caused by the weight or compression of either "live" or "dead loads." High compressive strength may be especially important in insulation boards.

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

CONDUCTANCE, THERMAL The thermal transmission in unit time through unit area of a particular body or assembly having defined surfaces, when unit average temperature difference is established between the surfaces. (C = BTU/hr.ff2.øF) [C=W/m2oK]

CONTACT CEMENTS Adhesives which may be used to adhere or bond together various roofing components. The adhesive is applied to the surfaces to be joined in a liquid state, and then allowed to dry before the surfaces are mated. The bond is formed immediately as the surfaces touch.

CONTROL JOINT A raised, flashed assembly (typically a single- or double-wood member attached to a wood base plate) that is anchored to the roof deck. It is used to relieve thermal stresses in a roof system where an expansion joint is not required, or to separate large roof areas (sometimes between expansion joints), and may be used to facilitate installation of tapered insulation.

COPING A covering on top of a wall exposed to the weather, usually sloped to carry off water.

CORE A small sample removed from a roof assembly, usually in conjunction with moisture surveys or investigations.

COUNTERFLASHING Formed metal, elastomeric sheeting or other material secured on or into a wall, curb, pipe, roof-top unit, or other surface, to cover and protect the upper edge of a base flashing and its associated fasteners.

COVERAGE The surface area to be continuously covered by a specific quantity of a particular material.

CRICKET A relatively small, elevated area of a roof constructed to divert water from a horizontal intersection of the roof with a chimney, wall, expansion joint, or other projection.

CURB A masonry, metal or wood edge extending above the roof deck at openings for roof-mounted equipment.

CUT BACK Solvent-thinned asphalt used in cold-proces
roofing adhesives, flashing cements and roof coatings.

CUTOFF A detail designed to prevent lateral water movement into the roofing system where the membrane terminates at the end of a day's work, or used to isolate sections of the roofing system.

DEAD LEVEL Absolutely horizontal, or zero slope.

DEAD LEVEL ASPHALT A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type I.

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

DEW POINT The temperature at which an air mixture is saturated with water vapor. If the temperature is at or below the dew point, condensation will occur.

DIMENSIONAL STABILITY The change in length and/or width of a material that results from exposure to the elements over time.

DIPPER A device used to dip and pour hot asphalt.

DOUBLE POUR To apply two layers of aggregate and asphalt to a bituminous roof.

DRY FELT A felt which has not been saturated with asphalt.

EDGE STRIPPING Application of felt strips cut to narrower widths than the normal felt-roll width to cover a joint between flashing and built-up roofing.

EDGE VENTING The practice of providing regularly spaced protected openings at a roof perimeter to relieve water vapor pressure in the roofing system.

ELASTOMERIC MEMBRANES A broad group of sheet materials which possess elastomeric or elastic rubber-like properties. Elastomeric materials and membranes may be manufactured from a variety of polymers.

ELONGATION The ability of a roofing membrane material to be stretched or elongated by the application of a force.

EMBEDMENT The process of pressing a felt, aggregate, fabric, mat, or panel uniformly and completely into hot asphalt or adhesive to ensure intimate contact at all points. (Also BROOMING.)

EMBRITTLEMENT The loss of flexibility, elasticity, or ductility of a material. The transition of a flexible material to a brittle material.

EMULSION An intimate mixture of asphalt and water, with uniform dispersion of the asphalt or water globules, usually stabilized by an emulsifying agent or system.

ENVELOPE A continuous membrane edge seal formed at the perimeter and at penetrations by folding the base sheet or ply over the plies above and securing it to the top of the membrane. The envelope prevents asphalt seepage from the edge of the merebrane.

EQUILIBRIUM MOISTURE CONTENT (1)The moisture content
of a material stabilized at a given temperature and relative humidity, expressed as a percent moisture by weight; (2) The typical moisture content of a material in any given geographical area.

EQUIVISCOUS TEMPERATURE (EVT) The temperature at which the viscosity of an asphalt is 125 cST (125 mm2/s) [75 cST (75mm2/s) for machine applications]; the recommended asphalt temperature _+25øF (_+14øC) at the time of application to the substrate.

ETHYLENE PROPYLENE DIENE TERPOLYMER (EPDM) An elastomeric material synthesized from ethylene, propylene, and small amounts of diene monomer. EPDM is widely used in single ply roofing membranes.

EXPANDED POLYSTYRENE (EPS) A roof insulation board formed from expanded beads of a plastic polVmer molded into blocks and then cut to size.

EXPANSION JOINT A structural separation between two building elements that allows free movement between the elements without damage to the building or roofing system.

EXPANSION JOINT COVER A building element which waterproofs and seals an expansion joint in a structure. Typically made from elastomeric materials and/or metal.

EXPOSURE (1) The transverse dimension of a roofing element not overlapped by an adjacent element in any roofing system;
(2) The time during which a portion of a roofing element is exposed to the weather.

EXTRUDED POLYSTYRENE A roof insulation board formed from a polystyrene polymer with integral closed cells, by a continuous extrusion process.

FACTORY MUTUAL (FM) A group of insurance companies which insures large industrial and commercial properties in the U.S. and Canada. Factory Mutual Research Corporation tests and classifies roof assemblies and components based on their fire characteristics, and resistance to wind uplift and hail damage.

FACTORY SEAM A splice made by the manufacturer during the assembling of narrow width material into large sheets.

FACTORY SQUARE Quantity of sheet material required to complete 100 sq ft of roofing.

FALLBACK A reduction in asphalt softening point, sometimes caused by refiuxing or overheating in a relatively closed container.

FELT A flexible sheet manufactured by the interlocking of fibers with a binder or through a combination of mechanical work, moisture and heat. Felts are manufactured principally from vegetable fibers (organic felts), asbestos fibers (asbestos felts), glass fibers (glass fiber felts) or polyester fibers; other fibers may be present in each type.

FELT LAYER A machine used for applying asphalt and built-up roofing felts.

FIBERBOARD A rigid roof insulation board composed principally of wood and cane fibers integrally treated with binders.

FIELD SEAM See SEAM.

FINGER BLISTERS Finger-shaped blisters or wrinkles in the plies of a roofing or waterproofing membrane.

FISHMOUTH A half-cylindrical or half-conical-shaped opening or void in a lapped edge or seam of a membrane, usually caused by wrinkling, or discontinuities in the lap.

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 edges of the membrane. Cap or countedlashing shields the upper edges of the base flashing.

FLASHING CEMENT A trowelable mixture of cutback asphalt and mineral stabilizers possibly including 'asbestos or other inorganic fibers.

FLAT ASPHALT A roofing asphalt conforming to the requirements of ASTM Specification D 312, Type II.

FLOOD COAT The top layer of asphalt used to hold the aggregate on an aggregate-surfaced, bituminous membrane.

FLUID-APPLIED ELASTOMER An elastomeric material, fluid at ambient temperatures, that dries or cures after application to form a continuous membrane. Such systems normally do not incorporate reinforcements.

FLUX (1) A bituminous material used as a feed stock for further processing and as a material to soften other bituminous materials; (2) To remeltthe coating asphalt on the back of an asphalt or modified bitumen cap sheet during application.

GLASS FELT A glass mat that has been impregnated and/or coated with asphalt to create a roofing product.

GLASS MAT A thin mat of glass fibers with or without a binder.

GLAZE COAT A thin layer of asphalt (usually 10-15 pounds per 100 sq. ft.) applied to a bituminous membrane system.

GRANULES See MINERAL GRANULES.

GRAVEL Coarse, granular aggregate, with pieces larger than sand grains, resulting from the natural erosion of rock.

GRAVEL IN To spread aggregate on the surface of the roofing membrane.

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

HEADLAP In a bituminous assembly, the overlap between the lower edge of the top exposed ply and the upper edge of the bottom ply, which provides a margin which ensures that the membrane is actually a two, three, or four ply membrane.

HEAT AGING Controlled exposure to elevated temperatures over time.

HEAT WELDING A process or method of melting and sealing or fusing together the overlapping edges of separate sections of thermoplastic or uncured elastomeric roofing membranes by the application of heat and pressure.

HOLIDAY An area where a liquid-applied material is missing. An absence of adhesive. (Also V01D, SKIP.)

"HOT STUFF" OR "HOT" A roofer's term for hot asphalt. (Also ASPHALT, BITUMEN, COAL TAR PITCH.)

ICE DAM A mass of ice formed at the transition from a warm to a cold roof surface. Frequently formed by refreezing meltwater at the overhang of a steep roof, an ice dam may cause ice and water to back up under shingles or other roofing materials.

INCLINE The slope of a roof expressed in percent or in the number of vertical units of rise per horizontal unit of run. (Also SLOPE.)

INORGANIC Composed of matter other than hydrocarbons and their derivatives, or matter that is not of plant or animal origin.

INSULATION See THERMAL INSULATION.

INVERTED ROOF MEMBRANE ASSEMBLY (IRMA) A patented variation of the "Protected Membrane Roof Assembly" in which STYROFOAM Brand insulation and ballast are placed over the membrane. (Also PRMA,)

ISOCYANURATE See POLYISOCYANURATE INSULATION.

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