Glossary of Roofing Related Terms

Below is an exhaustive list of terms you may hear while investigating your construction options. Please do not hesitate to contact us for clarification of any terms or processes you'd like explained in greater detail. We would be more than happy to answer any questions you may have.


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

Alligatoring – Shrinkage cracking of the surfacing bitumen on a built-up roof, producing a pattern similar to an alligator’s hide. The cracks may or may not extend through the entire surfacing bitumen thickness.

Alloys, polymeric – A blend of two or more polymers, e.g., a rubber and a plastic to improve a given property, e.g., impact strength.

Asphalt – A dark brown to black cementitious material whose predominating constituents are bitumens that occur in nature or are obtained in petroleum processing.

Asphalt felt – An asphalt-saturated felt.

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.

Asphaltene – A high molecular weight hydrocarbon fraction precipitated from asphalt by a designated paraffinic naphtha solvent at a specified temperature and solvent-asphalt ratio.

Note: The asphaltene fraction should be identified by the temperature and solvent-asphalt ratio used.

Atactic – A chain of molecules in which the position of the side methyl groups is more or less random. (Amorphic; Low Crystallinity)

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Backup plate – A rgid plate to support an end lap to provide uniform compression.

Backnailing – blind (i.e., concealed by overlapping felt) nailing of roofing felts to a substrate in addition to hot-mopping to prevent slippage.

Ballast – Loose aggregate, concrete pavers, or other material designed to prevent wind uplift or flotation of a loose-laid roof system.

Base sheet – A saturated or coated felt placed as the first ply in a multi-ply bituminous roofing membrane.

Batten – Raised rib, in a metal roof, or a separate part or formed portion in a metal roofing panel.

Beaufort scale – A scale in which the force of the wind is indicated by numbers from 0 to 12. No.7 is “near gale” at 52-61 km/h (32-38 m.p.h.). No. 9 is “strong gale” at 76-87 km/h (47-54 m.p.h.).

Bitumen – (1) A class of amorphous, black or dark colored, (solid, semisolid, or viscous) cementitious substances natural or manufactured, composed principally of high molecular weight hydrocarbons, soluble in carbon disulfide, and found in asphalts, tars, pitches, and asphaltites; (2) A generic term used to denote any material composed principally of bitumen; (3) In the roofing industry there are two basic bitumens: asphalt and coal-tar pitch. Before application they are either (a) heated to a liquid state, (b) dissolved in a solvent, or (c) emulsified.

Bituminous emulsion – A suspension of minute globules of bituminous material in water or in an aqueous solution.

Bituminous, adj. – Containing or treated with bitumen. Examples: bituminous concrete, bituminous felts and fabrics, bituminous pavement.

Blanket insulation – Fiberglass insulation in roll form, often installed between metal roof panels and the supporting purlins.

Blister – An enclosed pocket of air-water vapor, trapped between membrane plies or between membrane and substrate.

Blister (Polyurethane Foam) – Undesirable rounded delamination of the surface of a polyurethane foam whose boundaries may be either more or less sharply defined.

Block copolymer – An essentially linear copolymer in which there are repeated sequences of polymeric segments of different chemical structure.

Block or board thermal insulation – Rigid or semi-rigid thermal insulation preformed into rectangular units.

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 nailer for attachment of the membrane or flashing. (2) Wood cross-members installed between rafters or joists to provide support at cross-joints between deck panels. (3) Cohesion or adhesion between similar or dissimilar materials in roll or sheet form that may interfere with the satisfactory and efficient use of the material.

Blocking, wood – Treated wood members designed to help prevent movement of insulation.

Blowing agent – A compounding ingredient used to produce gas by chemical or thermal action, or both, in manufacture of hollow or cellular articles.

Blueberry – A small bubble or blister in the flood coating of a gravel-surfaced membrane.

Bodied solvent adhesive – An adhesive consisting of a solution of the membrane compound in solvent used in the seaming of membranes.

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

Boot – A bellows type covering to exclude dust, dirt, moisture, etc., forming a flexible closure.

Breaking strain – % elongation at which a sheet or other tested component ruptures under tensile force.

Breaking stress – Stress (in force per linear or area units) at which sheet, or other tested component, ruptures under tensile force.

British thermal unit (BTU) – Heat energy required to raise the temperature of one pound of water by 1°F (= 1055 joules).

Brooming – Embedding a ply by using a broom to smooth it out and ensure contact with the adhesive under the ply.

Btuh – Btu per hour.

Building code – Published regulations and ordinances established by a recognized agency describing design loads, procedures, and construction details for structures. Usually applying to designated political jurisdiction (city, county, state, etc.). Building codes control design, construction, and quality of materials, use and occupancy, location and maintenance of buildings and structures within the area for which the code was adopted. (See Model Codes)

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 bitumen, and surfaced with mineral aggregate, bituminous material, or a granule surfaced sheet (abbreviation, BUR).

Bull – Roofer’s term for flashing or plastic cement.

Butyl rubber – A synthetic rubber based on isobutylene and a minor amount of isoprene. It is vulcanizable and features low permeability to gases and water vapor and good resistance to aging, chemicals and weathering.

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Calender – A machine with two or more rolls, operating at selected surface speeds and controlled temperatures, for sheeting, laminating, skim coating (topping) and a friction coating to a controlled thickness or surface characteristic, or both.

Camber – A predetermined curvature designed into a structural member to offset the anticipated deflection under design load.

Canopy – Any overhanging or projecting roof structure with the extreme end usually unsupported.

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

Capflashing – See Flashing.

Capsheet – A granule-surfaced coated felt used as the top ply of a built-up roofing membrane.

Caulk – To seal joints, seams, or voids by filling with a waterproofing compound or material.

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

Cavity Wall – A wall built of hollow masonry units arranged to provide a continuous internal air space.

Centistoke – unit measurement of viscosity-i.e., resistance to flow. 1 cS = 1 x 10-6 m2/s.

Chain scission – Breaking of chemical bonds between carbon atoms by UV photo-oxidation, a reversal of the asphalt-blowing polymerization process that produces long chainlike hydrocarbon chains, resulting in embrittlement and cracking.

Chalk resistance – A measurement of performance for paint systems; the ability to resist a dusty/chalky appearance over time.

Chalking – A powdery residue on the surface of a material resulting from degradation or migration of an ingredient, or both.

Channel mopping – See Strip mopping under Mopping.

Chlorinated polyethylene (CPE) – Family of polymers produced by chemical reaction of chlorine on the linear backbone chain of polyethylene. The resultant rubbery thermoplastic elastomers presently contain 2545% chlorine by weight and 0-25% crystallinity. CPE can be vulcanized but is usually used in a nonvulcanized form.

Chlorosulfonated polyethylene (CSPE) –  Family of polymers that are produced by polyethylene reacting with chlorine and sulfur dioxide. Present polymers contain 25-43% chlorine and 1.0-1.4% sulfur. They are used in both vulcanized and nonvulcanized forms. Most membranes based on CSPE are nonvulcanized. ASTM designation for this polymer is CSM. Best known by the DuPont Tradename “Hypalon”.

Closure strip – A resilient strip such as neoprene, flat on one side and formed to the contour of ribbed sheets on the other, used to close openings created by joining metal sheets and flashings.

Coefficient of thermal expansion – The change in length per unit of length for a unit change in temperature. (Thus the coefficient per °F must be multiplied by 1.8 for the coefficient per oC.)

Coal tar – A dark brown to black cementitious material produced by the destructive distillation of coal.

Coal tar felt – A felt saturated with refined coal tar.

Coal tar pitch – Dark brown to black, solid cementitious material obtained as residue in the partial evaporation or distillation of coal tar.

Coated fabric – Fabrics impregnated and/or coated with a plastic material in the form of a solution, dispersion hot melt, or powder. (The term also applies to materials resulting from the application of a preformed film to a fabric by means of calendering.) Coated sheet (or 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.

Coating weight – Weight of coating on surface (both sides), usually expressed in ounces per sq. ft. or grams per sq. meter.

Coil coating – The application of an organic finish to a coil of metal using a continuous process. Cold flow – Slow deformation, undergravitational force, at or below roomtemperature. (See Creep) 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.

Condensation – The conversion of water vapor or other gas to liquid as the temperature drops or atmospheric pressure rises. (See also Dew Point) Condensation polymerization – Polymerization in which monomers are linked together with the splitting off of water or other simple molecules.

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=(W/ m2•K) C=(Btu/h•ft2•°F).

Conductivity (Thermal) – The time rate of transfer of heat by conduction through a unit thickness across unit area for unit difference of temperature.

Conductivity, thermal – The thermal transmission, by conduction only, in unit time through unit area between two isothermal surfaces of an infinite slab of a homogeneous material of unit thickness, in a direction perpendicular to the surface, when unit temperature difference is established between the surfaces. k=(W/m•K) k=(Btu/h•ft2•°F).

Coping – A covering on top of a wall exposed to the weather, usually sloped to carry off water. Copolymer – A mixed polymer, the product of polymerization of two or more substances at the same time.

Counterflashing – Formed metal or elastomeric sheeting secured on or into a wall, curb, pipe, rooftop unit, or other surface, to shield 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.

Covering – The exterior roof and wall covering for a metal building system.

Cream Time – This is the time, measured in seconds at a given temperature, when the “A” and “B” components of a polyurethane foam compound will begin to expand after being mixed through the spray gun.

Creep – The dimensional change with time of a material under load, following the initial instantaneous elastic deformation. Creep at room temperature is sometimes called cold flow.

Creep modulus – The ratio of initial applied stress to creep strain.

Creep strain – The total strain, at any given time, produced by the applied stress during a creep test.

NOTE:  The term creep, as used in this method, reflects current plastics engineering usage. Plastics have a wide spectrum of retardation times and the elastic portions of strain cannot be separated in practice from nonelastic.

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.

Cross-linking – A general term referring to the formation of chemical bonds between polymeric chains to yield an insoluble, three dimensional polymeric structure. Cross-linking of rubbers is vulcanization, qv.

Curb – A raised member used to support roof penetrations such as skylights, hatches, etc.

Cure – To change the properties of a polymeric system into a more stable, usable condition by the use of heat, radiation, or reaction with chemical additives.

NOTE:  Cure may be accomplished, for example, by removal of solvent or cross-linking.

Curing – See Vulcanizations.

Curled felt – BUR membrane defect characterized by a continuous, open longitudinal seal with top felt rolled back from underlying felt.

Cutback – Solvent-thinned bitumen used in cold process roofing adhesives, flashing cements, and roof coatings.

Cutoff – A detail designed to prevent lateral water movement into the insulation where the membrane terminates at the end of a day’s work, or used to isolate sections of the roofing system, usually removed before the continuation of the work.

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Dampproofing – Treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.

Dead-level – Absolutely horizontal, or zero slope. (See Slope)

Dead level asphalt – A roofing asphalt conforming to the requirements of Specification D312, Type I.

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

Degree-days – The difference between a reference temperature (usually 18°C [65°F]) and the mean temperature for the day times 24 hours times the number of days in the period. Degree-days are used to compare the severity of cold or heat during the heating or cooling season.

Delamination – Separation of the plies in a membrane or separation of insulation layers after lamination.

Denier – A unit used in the textile industry to indicate the fineness of continuous filaments. Fineness in deniers equals the mass in grams of 9,000 meter length of the filament.

Depth of measurement – The maximum thickness of a roof system upon which a given moisture survey method is effective.

Design loads – The “live load” (i.e. superimposed loads) that a structure is designed to resist (with appropriate safety factor) plus “dead load” (i.e., weight of permanent loads).

Dew point – The temperature at which water vapor starts to condense in cooling air at the existing atmospheric pressure and vapor content.

Double pour – Doubling of flood-coat, graveling-in operation, to provide additional waterproofing integrity for a BUR membrane.

Downspout – A conduit used to carry water from the gutter of a building to the ground or storm drain.

Dry (n.) – A material that contains no more water than one would find at its equilibrium moisture content.

Duckboard – A boardwalk or slatted flooring laid on a wet, muddy or cold surface.

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Eave – The line along the sidewall formed by the intersection of the planes of the roof and wall.

Eave height – The vertical dimension from finished floor to the eave.

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 insulation. (It is of doubtful efficacy.)

Efflorescence – A deposit or encrustation of soluble salts, generally white and most commonly consisting of calcium sulfate, that may form on the surface of stone, brick, concrete, or mortar when moisture moves through and evaporates on the masonry. Often caused by free alkalies leached from mortar, grout, or adjacent concrete.

Elasticity – The property of matter by virtue of which it regains its original size and shape after removal of stress.

Elastomer – A macromolecular material that returns rapidly to its approximate initial dimensions and shape after subsequent release of stress.

Embedment – (1) the process of pressing a felt, aggregate, fabric, mat, or panel uniformly and completely into hot bitumen or adhesive to ensure intimate contact at all points; (2) the process of pressing granules into coating in the manufacture of factory prepared roofing, such as shingles.

Emulsion – A dispersion of fine particles or globules of a liquid in a liquid. Asphalt emulsions consist of asphalt globules, an emulsifying agent such as bentonite clay and water.

Endlap – The overlap where one panel or felt nests on top of the end of the underlying panel or felt.

Envelope – A continuous edge seal formed by extending one ply of felt beyond the edge of the assembly. After other plies or insulation are in place, the extended ply is turned back and adhered.

EIP (Elastoplastic) – pertaining to polymeric materials, including thermoplastic and elastomeric categories.

EPDM – A synthetic elastomer based on ethylene, propylene, and a small amount of a non-conjugated diene to provide sites for vulcanization. EPDM features excellent heat, ozone and weathering resistance, and low temperature flexibility.

Epichlorohydrin rubber – A synthetic rubber that includes two epichlorohydrin-based elastomers of saturated high molecular weight, aliphatic polyethers with chloro-methyl side chains. The two types include a homopolymer (CO) and a copolymer of epichlorohydrin and ethylene oxide (ECO). These rubbers are vulcanized with a variety of reagents that react difunctionally with the chloromethyl group, including diamines, urea, thioureas, 2-mercaptoimidazoline, and ammonium salts. This rubber offers excellent oil resistance.

Equilibrium moisture content – (1) Moisture content of a 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.

EVA – Family of copolymers of ethylene and vinyl acetate used for adhesives and thermoplastic modifiers. They possess a wide range of melt indexes.

EVT (Equiviscous Temperature) – Temperature at which the viscosity of an asphalt is appropriate for application. Viscosity units are generally expressed in centipoise or centistokes. Tolerance on EVT is usually ± 1400 (± 25oF).

Exotherm – Heat generated in a chemical reaction.

Expansion joint – A structural separation between two building elements that allows free movement (expansion or contraction) between elements without damage to the roofing or waterproofing system.

Exposure – (1) The transverse dimension of a roofing element not overlapped by an adjacent element in any roofing system. The exposure overlapped by an adjacent element in any roofing system. The exposure of any ply in a membrane may be computed by dividing the felt width minus 51 mm (2 in.), by the number of shingled plies; thus, the exposure of 914 mm (36 in.) wide felt in a shingled, four ply membrane should be 216 mm (8-1/2 in.); (2) The time during which a portion of a roofing element is exposed to the weather.

Extra steep asphalt – See Super Steep Asphalt.

Extractables – Components or substances removable from a solid or liquid mixture by means of an appropriate solvent.

Extruder – A machine with a driven screw that forces ductile or semi-soft solids through a die opening of appropriate shape to produce continuous film, strip, or tubing.

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Fabric – A woven cloth of organic or inorganic filaments, threads, or yarns.

Fabric reinforcement – A fabric, scrim, etc., used to add structural strength to a 2 or more ply polymeric sheet. Such sheeting is referred to as “supported”.

Fabrication – (1) The manufacturing process performed in a plant to convert raw material into finished metal building components. The main operations are cold-forming, cutting, punching, welding, cleaning, and painting; (2) the creation of large panels of rubber from smaller calendar width sheets as in EPDM.

Fallback – Reduction in bitumen softening point, sometimes caused by refluxing or overheating in a relatively closed container.

Fascia – A decorative trim or panel projecting from the face of a wall, serving as a weather closure at gable and endwall.

Felt – A flexible sheet manufactured by the interlocking of fibers through a combination of mechanical work, moisture, and heat, without spinning, weaving, or knitting. Roofing felts are manufactured from vegetable fibers (organic felts), glass fibers (glass fiber felts) or polyester fibers (synthetic fiber mats).

Felt mill ream – The mass in pounds of 480 ft2 of dry, unsaturated felt, also termed “point weight.”

Fiber glass insulation – Blanket insulation, composed of glass fibers bound together with a thermoset binder, faced or unfaced, used over or under purlins to insulate roofs and walls, semi-rigid boards, usually with a facer.

Field – The “job site,” “building site,” or general market area.

Fill – As used in textile technology refers to the threads or yarns in a fabric running at right angles to the warp. Also called filler threads.

Filler strip – See Closure Strip.

Film – Sheeting having nominal thickness not greater than (0.25 mm) 10 mils.

Fin – A sharp, raised edge capable of damaging a roof membrane.

Fine mineral surfacing – Water insoluble inorganic material, more than 50% of which passes the 500 micrometer (No. 35) sieve, used on the surface of roofing.

Fishmouth – (1) A half cylindrical or half conical opening formed by an edge wrinkle or failure to embed a roofing felt; (2) In shingles, a half conical opening formed at a cut edge.

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 counter-flashing shields the upper edges of the base flashing.

Flashing cement – A trowelable mixture of cutback bitumen, mineral stabilizers and fibers.

Flash point – Temperature at which a test flame ignites vapor above a liquid surface.

Flat asphalt – A roofing asphalt conforming to the requirements of Specification D312, Type II.

Fleece – Term used to describe mats or felts of usually nonwoven fibers.

Flood coat – The top layer of bitumen used to hold the aggregate on an aggregate surfaced roofing membrane.

Fluid-applied elastomer – An elastomeric material, fluid at ambient temperature, that dries or cures after application to form a continuous membrane. Such systems normally do not incorporate reinforcement.

Fluorocarbon films – Substituted ethylene polymers, featuring outstanding formability, heat resistance, color retention, and resistance to solvents and chalking.

Framed opening – Frame work (headers and jambs) and flashing which surround an opening in the wall or roof of a building; usually for field-installed accessories such as overhead doors or powered roof exhausters.

“Free carbon” in tars – The hydrocarbon fraction precipitated from a tar by dilution with carbon disulfide.

Friability – The tendency of a material or product to crumble or break into small pieces easily.

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Gable roof – A ridged roof that terminates in gables.

Galvalume – Trade name for steel coated with aluminum-zinc alloy for corrosion protection.

Galvanic cell – A cell in which chemical change is the source of electrical energy. It usually consists of two dissimilar conductors in contact with each other and an electrolyte.

Galvanized steel – Steel coated with zinc for corrosion resistance.

Glass felt – Glass fibers bonded into a sheet with resin and suitable for impregnation in the manufacture of bituminous waterproofing, roofing membranes, and shingles.

Glass mat – A thin mat of glass fibers with or without a binder.

Glass transition – The reversible change in an amorphous polymer or in amorphous regions of a partially crystalline polymer from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one

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 membrane, when application of additional felts, or the flood coat and aggregate surfacing are delayed.

Gloss – Subjective term describing the relative amount and nature of mirror-like reflection from a surface

Grain – Weight unit equal to 1/7000 Ib, used in measuring atmospheric water vapor content.

Granule – See Mineral Granules.

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

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

Green building technology – Utilizing technology to reduce impact on the earth. Includes recyclability, reduction in carbon dioxide, ozone or other atmospheric pollutants, and reduction of urban heat islands.

Grout – Mixture of cement, sand, and water used to fill cracks and cavities. Often used under base plates or leveling plates to obtain uniform bearing surfaces.

Gutter – A channel member installed at the eave of the roof for the purpose of carrying water from the roof to the drains or down spouts.

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Haunch – The deepened portion of a column or rafter, designed to accommodate the higher bending moments at such points. (Usually occurs at connection of column and rafter.)

Header – A horizontal framing structural member of a door, window, or other framed opening.

Headlap – The minimum distances measured at 90 degrees to the eave along the face of a shingle or felt as applied to a roof, from the upper edge of the shingle or felt, to the nearest exposed surface.

Heat capacity – The amount of energy required to raise the temperature of a unit substance 1°F (or 1°C).

Heat seaming – The process of joining two or more thermoplastic films or sheets by heating areas in contact with each other to the temperature at which fusion occurs. The process is usually aided by a controlled pressure. In dielectric seaming, the heat is induced within films by means of radio frequency waves.

Heat transfer – The transmission of thermal energy from a location of higher temperature to a location of lower temperature. This can occur by conduction, convection or radiation.

Hip roof – A roof which rises by inclined planes from all four sides on the building. The line where two adjacent sloping sides of a roof meet is called the Hip.

Homopolymer – A natural or synthetic high polymer derived from a single monomer.

Holiday – An area where a liquid applied material is missing, a void.

Hot-dip metallic coating – Adherent protective coating applied by immersing steel in a molten bath of coating material.

Hood – Cover, usually light gage metal, over piping or other rooftop equipment.

“Hot stuff” or “hot” – A roofer’s term for hot bitumen.

Humidity – The amount of moisture contained in the atmosphere. Generally expressed percent relative humidity. (The ratio of the vapor pressure to the saturation pressure for given conditions times 100.)

Humidity test – A test involving exposure of specimens at controlled levels of humidity and temperature.

Hydrocarbons – An organic chemical compound containing mainly the elements carbon and hydrogen. Aliphatic hydrocarbons are straight chain compounds of carbon and hydrogen. Aromatic hydrocarbons are carbon-hydrogen compounds based on the cyclic or benzene ring. They may be gaseous (CH4, ethylene, butadiene), liquid (hexene, benzene), or solid (Natural rubber, napthalene, cispolybutadiene).

Hygroscopic – Attracting, absorbing, and retaining atmospheric moisture.

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

Inorganic, adj – Comprising matter other than hydrocarbons and their derivatives, or matter not of plant or animal origin.

Insulation – See Thermal Insulation.

Internal pressure – Pressure inside a building, a function of wind velocity, building height, and number and location of openings.

lsocyanate – A highly reactive chemical grouping composed of a nitrogen atom bonded to a carbon atom bonded to an oxygen atom; =N=C=O; a chemical compound, usually organic, containing one or more isocyanate groups.

Isoboard – Abridgement of polyisocyanurate foam insulation board.

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Joist –  Any of the small timbers or metal beams arranged parallel from wall to wall to support a floor, ceiling or roof of a building.

Kesternich test – Simulates acid rain conditions by subjecting samples to a sulfur dioxide atmosphere as well as condensing moisture.

Kick-out (Elbow) – (Turn-Out) A lower downspout section used to direct water away from a wall.

Laitance –  An accumulation of finer particles on the surface of fresh concrete due to an upward movement of water (as when excessive mixing water is used).

Lap – Dimension by which a felt covers an underlying felt in BUR membrane. “Edge” lap indicates the transverse cover; “End” lap indicates the cover at the end of the roll. These terms also apply to single-ply membranes.

Lapped joint – A joint made by placing one surface to be joined partly over another surface and bonding the overlapping portions.

Layer (Plywood) – A layer is a single veneer ply or two or more plies laminated with parallel grain direction. Two or more plies laminated with grain direction parallel is a “parallel laminated layer”.

Leno fabric – An open fabric in which two warp yarns wrap around each fill yarn in order to prevent the warp or fill yarns from sliding over each other.

Live load – Live load means all loads including snow, exerted on a roof except dead, wind, and lateral loads.

Loose-laid membrane – A unadhered roofing membrane anchored to the substrate only at the edges and penetrations through the roof and ballasted against wind uplift by loose aggregate or payers.

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Macromolecule – A large molecule in which there is a large number of one or several relatively simple chemical units, each consisting of several atoms bonded together.

Masonry – Anything constructed of materials such as bricks, concrete blocks, ceramic blocks, and concrete.

Mastic – Caulking or sealant normally used in sealing roof panel laps.

Membrane – A flexible or semi-flexible roof covering or waterproofing whose primary function is the exclusion of water.

Memory – Tendency of a material to regain a previous configuration–notably, the tendency of glass-fiber felts not to lie flat on their substrate after unrolling; the retraction of single-ply roll goods which were stretched during production or winding.

Mer – The repeating structural unit of any high polymer.

Mesh – The square opening of a sieve.

Metal flashing – See Flashing–frequently used as through-wall cap, or counterflashing.

Mineral Fiber – Inorganic fibers of glass, asbestos or mineral wool (slag).

Mineral Granules – Natural or synthetic aggregate, ranging in size from 500•m (1•m = 10-6m) to 1/4 in. diameter, used to surface BUR or modified bitumen cap sheets, asphalt shingles, and some cold process membranes.

Model Codes – Codes established to provide uniformity in regulations pertaining to building construction. Examples: Uniform Building Code published by lCBO National Building Code by BOCA Standard Building Code by SBCCI International Building Code (New)

Modulus of elasticity – The ratio of stress (nominal) to corresponding strain below the proportional limit of a material, expressed in force per unit area based on the minimum initial cross sectional area.

Moisture conduction – Migration by wicking as contrasted to vapor movement.

Moisture contour map – A map with lines connecting continuous levels of moisture. When drawn by computer the wettest areas are often indicated by darkest symbols and the driest areas left blank.

Mole run – A meandering ridge in a membrane not associated with insulation or deck joints.

Monomer – A simple molecule which is capable of combining with a number of like or unlike molecules to form a polymer.

Mop-and-flop – A procedure in which roof components (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 adhered to the substrate.

Mopping – Application of hot bitumen with a mop or mechanical applicator to the substrate or to the plies of a built-up or modified-bitumen roof. There are four types of mopping: (1) solid–a continuous coating; (2) spot–bitumen is applied in roughly circular areas, generally about 460 mm (18 in.) in diameter, leaving a grid of unmopped, perpendicular area, (3) strip– bitumen is applied in parallel bands, generally 200 mm (8 in.) wide and 300 mm (12 in) apart; (4) sprinkle–bitumen is shaken on the substrate from a broom or mop in a random pattern.

Mud cracking – Surface cracking resembling a dried mud flat.

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Nail-type concrete anchor – A hammer-driven fastener with spiral or annular rings that provides pullout strength.

Nailer – Wood member bolted or otherwise anchored to a nonnailable deck or wall to provide nailing anchorage of membrane or flashing.

Nailing – (1) Exposed nailing of roofing wherein nail heads are bare to the weather; (2) Concealed nailing of roofing wherein nail heads are concealed from the weather. (See also Blind Nailing) Needle punched – A mechanical entanglement of dry laid (usually cross-lapped, carded staple fiber) webs where barbed needles achieve, in multiple punches, mechanical bonding.

Neoprene – Synthetic rubber (polychloroprene) used in liquid or sheet-applied elastomeric roofing membranes or flashing.

Neutral sealants – Acid-free and amine-free sealants.

Nitrile rubber – A family of copolymers of butadiene and acrylonitrile that can be vulcanized into tough oil resistant compounds. Blends with PVC are used where ozone and weathering are important requirements in addition to its inherent oil and fuel resistance.

Nondestructive testing (NDT) – Methods for evaluating the strength or composition of materials without damaging the object under test.

Nonwoven fabric – A structure produced by bonding or interlocking of fibers (or both) by mechanical, thermal or solvent means (or combinations thereof).

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Off-ratio mix – When the mixture of isocyanate and resin does not conform to the manufacturer’s recommended mixing ratio. The acceptable ratio for most systems is when the two components are combined in equal volumes.

Olefin – An unsaturated open-chain hydrocarbon containing at least one double bond: ethylene or propylene.

Olefin plastics – Plastics based on polymers made by the polymerization of olefins or copolymerization of olefins with other monomers, the olefins being at least 50 mass %.

One-on-one – See Phased Application.

Organic, adj. – Composed of hydrocarbons or their derivatives, or matter of plant or animal origin.

Organic coating – Coatings that are generally inert or inhibited. May be temporary (e.g., slushing oils) or permanent (paints, varnishes, enamels, etc.).

Organic content – Usually synonymous with volatile solids in an ashing test; e.g., a discrepancy between volatile solids and organic content can be caused by small traces of some inorganic materials , such as calcium carbonate, that lose weight at temperatures used in determining volatile solids.

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Panel clip – Independent clip used to attach roof panels to substructure.

Panel creep – Tendency of the transverse dimension of a roof panel to gain in modularity due to spring-out or storage-distortion.

Parapet – Portion of wall above the roof line.

Pascal – SI unit of measure for force per unit area (N/m2).

Pea gravel – Small gravel with a diameter approaching that of a pea. Size roughly defined by ASTM D448, Number 7 or smaller.

Peak – The uppermost point of a gable.

Penetration – The consistency of a bituminous material expressed as the distance in tenths of a millimetre (0.1 mm) that a standard needle or cone vertically penetrates a sample of material under specified conditions of loading, time, and temperature.

Percent elongation – In tensile testing, the increase in the gauge length, measured after fracture of the specimen within the gauge length.

Percent water by volume – =(Volumse of Water in Sample/Volume of Sample)x100

Percent water by weight – =(Sample Weight Wet-Sample Weight Dry/Sample Weight Dry)x100

Perlite – An aggregate used in lightweight insulating concrete and in preformed perlite insulating board, formed by heating and expanding siliceous volcanic glass.

Perm – (vapor transmission) Unit to measure water vapor transmission – one grain of water vapor per square foot per hour per inch of mercury pressure difference. 1 Perm = 1 grain/h•ft2•in. Hg = 5.74 x 10-11 kg/Pa•s•m2.

Permeability – (1) The capacity of a porous medium to conduct or transmit fluids; (2) The amount of liquid moving through a barrier in a unit time, unit area and unit pressure gradient not normalized for but directly related to thickness; (3) The product of vapor permeance and thickness (for thin films, ASTM E96 – over 3.2 mm (1/8 in.), ASTM C355). Usually reported in perm inches or grain/h•ft2•in. Hg per inch of thickness. 1 perm inch = 1.46 x 10-12 kg/Pa•s•m.

Permeance – The rate of water vapor transmission per unit area at a steady state through a membrane or assembly, expressed in ng/Pa•s•m2 (grain/ft2•h•in. Hg).

Petroleum pitch – A dark brown to black, predominantly aromatic, solid cementitious material obtained by the processing of petroleum, petroleum fractions, or petroleum residuals.

Phased application – The installation of a roofing or waterproofing system during two or more separate time intervals; a roofing system not installed in a continuous operation.

Phenolic plastics – Plastics based on resins made by the condensation of phenols, such as phenol and cresol, with aldehydes.

Picture framing – A rectangular pattern of ridges in a membrane over insulation or deck joints.

Pig spout – A sheet metal flashing designed to direct the flow of water out through the face of the gutter rather than through a downspout.

Pinhole – A tiny hole in a film, foil, or laminate comparable in size to one made by a pin.

Pitch – See Incline; Coal Tar Pitch; or Petroleum Pitch.

Pitch pocket – A flanged, open bottomed container placed around a column or other roof penetration and filled with hot bitumen, flashing cement or pourable sealer.

Plastic – A material that contains as an essential ingredient one or more organic polymeric substances of large molecular weight. It is solid in its finished state and at some stage in its manufacture or processing into finished articles can be shaped by flow.

Plastic cement – See Flashing Cement.

Plasticizer – Material, frequently solvent-like, incorporated in a plastic or a rubber to increase its ease of workability, flexibility, or extensibility. Adding the plasticizer may lower the melt viscosity, the temperature of the second order transition, or the elastic modulus of the polymer.

Plasticizers – May be monomeric liquids (phthalate esters), low molecular weight liquid polymers (polyesters) or rubbery high polymers (EVA). The most important use of plasticizers is with PVC where the choice of plasticizer dictates under what conditions the membrane may be used.

Plastisols – Mixtures of resins and plasticizers that can be cast or converted to continuous films by the application of heat.

Ply – A layer of felt in a roofing membrane; a four-ply membrane should have at least four plies of felt at any vertical cross section cut through the membrane.

Ply (Plywood) – A single veneer lamina in a glued plywood panel.

Plywood – A flat panel built up of sheets of wood veneer called plies, united under pressure by a bonding agent to create a panel with an adhesive bond between plies as strong as or stronger than, the wood. Plywood is constructed of an odd number of layers with grain of adjacent layers perpendicular. Layers may consist of a single ply or two or more plies laminated with parallel grain direction. Outer layers and all odd numbered layers generally have the grain direction oriented parallel to the long dimension of the panel.

Pointing – (1) Troweling mortar into a joint after masonry units are laid. (2) Final treatment of joints in cut stonework. Mortar or a putty-like filler is forced into the joint after the stone is set.

Polyester fiber – Generic name for a manufactured fiber in which the fiber-forming substance is any long chain synthetic polymer composed of an ester of a dihydric alcohol and terephthalic acid. Scrims made of polyester fiber are used for fabric reinforcement.

Polyisobutylene – The polymerization product of isobutylene varying in consistency from a viscous liquid to a rubberlike solid, with corresponding variation in molecular weight from 1,000 to 400,000. Polyisocyanurate – Thermoset polymer formed by polymerization of isocyanate; rigid foam insulation meeting ASTM C1289; a thermal insulation similar in appearance to polyurethane foam, but with improved fine resistance or rating.

Polymer – A macromolecular material formed by the chemical combination of monomers having either the same or different chemical composition. Plastics, rubbers, and textile fibers are all high molecular weight polymers.

Polyols – A polyhydric alcohol, i.e., one containing three or more hydroxyl groups.

Polypropylene (C3H5)n – A synthetic thermoplastic polymer, with a molecular weight of 40,000 or more.

Polyvinyl Chloride (PVC) – A synthetic thermoplastic polymer prepared from vinylchloride. PVC can be compounded into flexible and rigid forms through the use of plasticizers, stabilizers, filler, and other modifiers; rigid forms used in pipes; flexible forms used in manufacture of sheeting.

Pond – A roof area that retains water instead of draining after rainfall.

Ponding – Water in low or irregular roof areas that remains longer than 48 hours after the cessation of rainfall.

Pot Life – The working time once a product has been reacted (catalyzed).

Pre-painted coil – Coil steel which receives a paint coating prior to the forming operation.

Press brake – A machine used in cold-forming metal sheet or strip into desired cross-section.

Prestressed concrete – Concrete in which the reinforcing cables, wires, or rods in the concrete are tensioned before there is load on the member, holding the concrete in compression for greater strength.

Preventive maintenance – The regular, scheduled, inspection for and the repair of normal, expected breakdown of materials and equipment. Prime coat – First liquid coat applied in a multiple coat system.

Primer (bituminous) – A thin liquid bitumen applied to a surface to improve the adhesion of heavier applications of bitumen and to absorb dust.

Protected membrane roof (PMR) – Roof assembly with insulation on top of membrane instead of vice versa, as in conventional roof assembly (also known as inverted or upsidedown roof assembly).

Puncture resistance – Index of a material’s ability to withstand the action of a sharp object without perforation.

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R-Factor – Resistance to heat flow. The summation of individual thermal resistances in an assembly.

Racking – To stretch or strain by force, such as by the thermal or wind action.

Raggle – See Reglet.

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

Rake angle – Angle fastened to purlins at rake for attachment of endwall panels.

Rake trim – A flashing designed to close the opening between the goof and endwall panels.

Re-covering – The process of covering an existing roof system with a new roof.

Reentrant corner – An inside corner of a surface, where stress concentrations may occur.

Reglet – A groove in a wall or other surface adjoining a roof surface for 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 mass per unit volume (or partial pressure) of water vapor in an air-vapor mixture to the saturated mass per unit volume (or partial pressure) of the water vapor at the same temperature, expressed as a percentage.

Relative saturation –  =(Volume of Water in Sample/Maximum volume of water sample could hold) x100

Remedial roofing – The repair of selected isolated portions of the roof system to return the roof to uniform condition. This normally involves the removal of wet materials along with correction of the original cause of the problem.

Reroofing – The removal of all roof system components down to the structural deck followed by installation of a completely new roofing system.

Resistance, thermal – See Thermal Resistance.

Retrofit – the modification of an existing building or facility to include new systems or components.

Ridge – Highest point on the roof of the building, a horizontal line running the length of the building.

Ridge cap – A transition of the roofing materials along the ridge of a roof. Sometimes called ridge roll or ridge flashing.

Ridging – An upward, tenting displacement of a membrane, frequently over an insulation joint.

Roll goods – A general term applied to rubber and plastic sheeting, usually furnished in rolls.

Roll roofing – Coated felts, either smooth or mineral surfaced.

Roof cement – See Flashing Cement.

Roof covering – The exposed exterior roof skin.

Roof curb – An accessory used to mount and level units (such as air conditioning and exhaust fans) on the sloped portion of the building roof.

Roof jack – An accessory used to cover pipes (such as vents or flues) that penetrate the roof panel.

Roof overhang – A roof extension beyond the endwall/sidewall of a building.

Roof seamer – Machine that crimps panels together or that welds laps of E/P systems using heat, solvent or dielectric energy.

Roof slope – The angle a roof surface makes with the horizontal, measured in the number of inches of vertical rise in a horizontal length of 12 inches. (Or as a ratio such as 1:48, or as a per cent.) Roofing system – An assembly of interacting components designed to weatherproof, and normally to insulate, a building’s top surface.

Rubber – A material capable of quickly recovering from large deformations, normally insoluble in boiling solvent such as benzene, methyl ethyl ketone, and ethanol toluene azeotrope. A rubber in its modified state retracts within 1 mm to less than 1.5 times its original length after being stretched to twice its length.

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Sacrificial protection – Reducing the extent of corrosion of a metal in an electrolyte by coupling it to another metal that is electrochemically more active in the environment, i.e., galvanic protection.

Saddle – A small structure that helps to channel surface water to drains. Frequently located in a valley, a saddle is often constructed like a small hip roof or like a pyramid with a diamond-shaped base (also see Cricket).

Sandwich panel – A panel assembly used as covering; consists of an insulating core material with inner and outer skins.

Scarf – To scrap or abrade a surface to remove degraded or wet polyurethane foam. Scupper – Channel through parapet, designed for peripheral drainage of the roof, usually a safety overflow to limit accumulation of ponded rainwater caused by clogged drains.

Scrim – A woven, open mesh reinforcing fabric made from continuous filament yarn. Used in the reinforcement of polymeric sheeting.

Sealant – Any material used to close up cracks or joints to protect against leaks. Lap sealant is applied to exposed lap edges in E/P systems.

Sealing washer – A metal-backed rubber washer assembled on a screw to prevent water from migrating through the screw hole.

Seam strength – Strength of a seam of material measured either in shear or peel modes, reported either in absolute units, e.g., pounds per inch of width--or as a percent of the sheeting strength.

Self-drilling screw – A fastener that drills and taps its own hole, used as a fastener for attaching panels to purlins and girts.

Self-tapping screw – A fastener that forms receiving threads when turned into a previously drilled hole. It is for attaching panels to purlins and girts and for connecting trim and flashing.

Selvage – An edge or edging which differs from the main part of: (1) a fabric, or (2) granule surfaced roll roofing.

Service life – Anticipated useful life of a building, building component or building subsystem (e.g., roof system).

Shark fin – Curled felt projecting upward through the flood coat and aggregate of a BUR membrane.

Shear – The force tending to make two contacting parts slide upon each other in opposite directions parallel to their plane of contact.

Sheeting – A form of plastic or rubber in which the thickness is very small in proportion to length and width and in which the polymer compound is present as a continuous phase throughout, with or without fabric.

Shelf life – Maximum safe time to store a fluid construction material before use.

Shingle – (1) A small unit of prepared roofing designed for installation with similar units on overlapping rows on inclines normally exceeding 25%; (2) To cover with shingles, and (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 also 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.

SI – The international symbol for the metric unit (Le Systeme International d’Unites).

Sidelap – The continuous overlap of closures along the side of a panel.

Sieve – An apparatus with square apertures for separating sizes of material.

Sill – The bottom horizontal framing member of an opening such as a window or door.

Single slope – A sloping roof with one surface. The slope is from one wall to the opposite wall of rectangular building.

Siphon break – A small groove to arrest the capillary action of two adjacent surfaces.

Skylight – A roof accessory to admit light, normally mounted on a curbed, framed opening.

Slab – A semi-finished steel product, intermediate between ingot and plate, with the width at least twice the thickness.

Slippage – Relative lateral movement of adjacent felts (or sheets) in a roof membrane. It occurs mainly in roofing membranes on a slope, sometimes exposing the lower plies or even the base sheet to the weather.

Slope – Tangent of the angle between the roof surface and the horizontal plane, expressed as a percentage, or in inches of rise per foot of horizontal distance. (See also Incline) Smooth surfaced roof – A roof membrane without mineral aggregate surfacing.

Soffit – The underside covering of any exterior overhanging section of a roof, gable or sidewall.

Softening point – Temperature at which a bitumen becomes soft enough to flow as determined by an arbitrary, closely defined method.

Softening point drift – Change in softening point during storage or application. (See also Fallback) Solid mopping – See Mopping.

Sprinkle mopping – See Mopping.

Spud – To remove the roofing aggregate and most of the bituminous top coating by scraping and chipping.

Spudder – Heavy steel implement with a dull, bevel-edged blade for removing embedded aggregate from a BUR membrane surface.

Spunbonded – A generic name for nonwoven fabrics formed directly from polymer chips, spun into continuous filaments which are laid down and bonded continuously, without an intermediate step. Spunlaced – A hydroentangled nonwoven fabric whereby a dry laid staple fabric is mechanically bonded by water jet which entangles the individual fibers.

Square – A roof area of 9.29 m2 (100 ft2), or enough material to cover 9.29 m2 of deck.

Stack vent – A vertical outlet designed to relieve pressure exerted by water vapor between a membrane and the vapor retarder or deck.

Stainless steel – An alloy of steel which contains a high percentage of chrominum. Also may contain nickel or copper. Has excellent resistance to corrosion.

Standing seam – Watertight seam type featuring an upturned rib, which may also be structural. It is made by turning up the edges of two adjacent metal panels and then folding them over in one of a variety of ways.

Standing water test – Evaluations in which test panels are submerged in aqueous solutions and alternately dried in air.

Starting platform – A movable platform used to support a seaming machine as it begins to roll-seal a metal seam.

Steep asphalt – A relatively viscous roofing asphalt conforming to the requirements of Specification D312, Type Ill.

Strain – Deformation under stress.

Strawberry – See Blueberry.

Stress – (1) A measure of the load on a structural member in terms of force per unit area (Mpa) (kips per sq. in.); (2) The force acting across a unit area in solid material in resisting the separation, compacting or sliding that tends to be induced by external forces. Also the ratio of applied load to the initial cross sectional area, or the maximum stress in the outer fibers due to an applied flexural load.

Stress concentration – A condition in which stress is highly localized, usually induced by an abrupt change in the shape of a member or at a substrate joint (e.g., between insulation joints) Stress relaxation – The time-dependent change in the stress resulting from application of a constant total strain to a specimen at a constant temperature. The stress-relaxation at a given elapsed time is equal to the maximum stress resulting when the strain is applied minus the stress at the given time.

Strikethrough – A term used in the manufacture of fabric reinforced polymeric sheeting to indicate that two layers of polymer have made bonding contact through the reinforcing scrim.

Strippable films – Added protection sometimes applied to continuous strip in coil coating process. Applied after prime and topcoats to resist damage prior to and during erection.

Stripping – Strip flashing: (1) The technique of sealing a joint between metal and bituminous membrane with one or two plies of felt or fabric and hot- or cold-applied bitumen; (2) The technique of taping joints between insulation boards or deck panels.

Substantial Completion – The stage in the progress of the work when it is sufficiently complete for the owner to occupy or utilize the work for its intended use.

Substrate – Surface upon which a roof component is placed (structural deck or insulation).

Super-steep asphalt – A high viscosity roofing asphalt conforming to the requirements of Specification D312, Type IV.

Supported sheeting – See Fabric Reinforcement.

Surface cure – Curing or vulcanization which occurs in a thin layer on the surface of a manufactured polymeric sheet or other items.

Surfactants – Surface active agents that reduce surface tension when dissolved in water or water solutions, or reduce interfacial tension between two liquids, or between a liquid and a solid.

Susceptibility – When not otherwise qualified, the degree of change in viscosity with temperature.

Tack-free – A film is considered tack-free when the finger, with a slight pressure, will not leave a mark. The surface will not be sticky.

Tapered edge strip – A tapered insulation strip used to elevate the roofing at the perimeter and at penetrations of the roof.

Tar boils – Bubbles of moisture vapor encased in a thin film of bitumen, also known as blueberry, blackberry, etc.

Tear strength – The maximum force required to tear a specified specimen, the force acting substantially parallel to the major axis of the test specimen. Measured in both initiated and uninitiated modes. Obtained value is dependent on specimen geometry, rate of extension, and type of fabric reinforcement. Values are reported in stress, e.g., pounds, or stress per unit of thickness, e.g., pounds per inch.

Tearoff – Removal of a failed roof system down to the structural deck surface.

Tee joint – the condition created by the overlapping intersection of three or four sheets in the membrane.

End Lap Side Lap “Tee” Joint Tensile strength – (1) The maximum tensile stress per unit of original cross sectional area applied during stretching of a specimen to break; units: SI-metric – Megapascal or kilopascal, customary – pound per square inch; (2) The longitudinal pulling stress a material can bear without tearing apart; (3) The ratio of maximum load to original cross-sectional area. Also called ultimate strength.

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Tensile test – A test in which a specimen is subjected to increasing longitudinal pulling stress until fracture occurs.

Therm – A unit of heat commonly used by utilities, equivalent to 100,000 BTU = 1.05 x 108 joules.

Thermal block – A spacer of low thermal conductance material, designed to prevent formation of a thermal bridge.

Thermal bridge – Interruption of a layer of thermal insulation by a material of high thermal conductivity (e.g. metal).

Thermal conductance (C) – The rate of heat flow through a material whose surfaces have stated a temperature differential Btu•in./h•ft4°F(W/m2•°C).

Thermal conductivity (k) – The rate of heat flow through a stated thickness of material with a stated temperature differential Btu/h.ft2•°F (W/m2•°C).

Thermal insulation – A material designed to reduce the conductive heat flow.

Thermal resistance (R) – Resistance to heat flow. The reciprocal of conductance (C).

Thermal shock – Stress-producing phenomenon resulting from sudden temperature drops in a roof membrane – when, for example, a rain shower follows brilliant sunshine.

Thermogram – A visible light record of the display of an infrared camera system via a Polaroid print, 35 mm film, or videotape.

Thermography – A technique for producing heat pictures from the invisible radiant energy emitted from stationary or moving objects at any distance and without in any way influencing the temperature of the objects under view. The electronic generation and display of a visible image of an infrared spectrum.

Thermoplastic – Capable of being repeatedly softened by increase of temperature and hardened by decrease in temperature. The thermoplastic form allows for easier seaming both in the factory and in the field.

Thermoplastic elastomers – Polymers capable of remelt, but exhibiting elastomeric properties; related to elasticized polyolefins. They have a limited upper temperature service range.

Thermoplastic resin – A material with a linear macromolecular structure that will repeatedly soften when heated and harden when cooled.

Thermoset – A material that will undergo (or has undergone) a chemical reaction by the action of heat, catalysts, ultraviolet light, etc., leading to a relatively infusible state.

Through-wall flashing – A water-resistant membrane or material assembly extending totally through a wall and its cavities, positioned to direct any water within the wall to the exterior.

Toggle bolt – A two-piece assembly consisting of a threaded bolt and an expanding clip that can fit through a drilled bolt hole, then spring outward to provide anchorage from the blind side.

Trim – The light gauge metal used in the finish of a building, especially around openings and at intersections of surfaces. Often referred to as flashing.

Tuck pointing – The filling in with fresh mortar of cutout or defective mortar joints in masonry.

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U-Factor – The heat flow across an entire assembly e.g., from air within a building to outside air; the inverse of R-Factor.

Ultimate elongation – The elongation of a stretched specimen at the time of break. Usually reported as percent of the original length. Also called breaking strain.

Unsupported sheeting – A polymer sheeting one or more plies thick without a reinforcing fabric layer or scrim.

Uplift – Wind load on a building which causes a load in the upward direction. (See Suction)

Valley gutter – A channel used to carry off water at the intersection of two sloping roof planes.

Vapor barrier – See Vapor Retarder.

Vapor migration – The flow of water vapor from a region of high vapor pressure to a region of lower vapor pressure.

Vapor pressure – The pressure exerted by a vapor that is in equilibrium with its solid or liquid form.

Vapor retarder – A material that resists the flow of water vapor.

Vent – Opening designed to convey water vapor or other gas from inside a building or a building component to the atmosphere.

Ventilator – An accessory usually used on the roof that allows air to pass through. Vermiculite – An aggregate used in lightweight insulating concrete, formed by heating and expanding a micaceous mineral.

Viscoelastic – Characterized by changing mechanical behavior, from nearly elastic at low temperature to plastic, like a viscous fluid, at high temperature.

Viscosity – Index of a fluid’s internal resistance to flow, measures in centistokes (cSt) for bitumens. (Water has a viscosity of roughly 1 cSt, light cooking oil 100 cSt.) Vulcanization – An irreversible process during which a rubber compound, through a change in its chemical structure, e.g., cross-linking, becomes less plastic and more resistant to swelling by organic liquids, and elastic properties are conferred, improved, or extended over a greater range of temperature.

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Warp – In textiles, the lengthwise yarns in a woven fabric.

Water vapor transmission – (WVT) – Water vapor flow normal to two parallel surfaces of a material, through a unit area, under the conditions of a specified test such as ASTM E96. Customary units are g/h•m2 (grains/h•ft2). 1 grain/h•ft2 = 0.697 g/h•m2.

Waterproofing – Treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.

Weatherometer – An instrument used to subject specimens to accelerated weathering conditions, e.g., rich UV source and water spray.

Wicking – The process of moisture movement by capillary action as contrasted to movement of water vapor.

Yield strength – (1) The longitudinal stress a material can bear before plastic deformation (i.e., elongation under constant stress); (2) The stress at which a material exhibits a specified reduction in the constant stress/strain ratio is the elastic range.

Yield strength – The stress at which a material exhibits a specified deviation from proportionality of stress and strain.

Source: U.S. Army Corps of Engineers,Engineering and Support Center, Huntsville