Lawmasters Inc. bldgGlossary of Roofing Terms for Consumers

 

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


For word origins and even more definitions check out Merriam-Webster’s Online Collegiate® Dictionary & Thesaurus.

 

A

Aggregate: (a) crushed stone, crushed slag or water worn gravel used for surfacing a built-up roof; (b) 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.

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

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

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

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

Dead-Level Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D312, Type I.

Flat Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D312, Type II.

Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D312, Type III.

Special Steep Asphalt: A roofing asphalt conforming to the requirements of ASTM Specification D312, Type IV.

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-saturated felt or an asphalt coated felt.

Asphalt Mastic: A Mixture of asphaltic material and graded mineral aggregate that can be poured when heated but requires mechanical manipulation to apply when cool.

Asphalt, Steam Blown: an asphalt produced by blowing steam through molten asphalt to modify its 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.

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B

Backnailing: The practice of blind-nailing roofing felts to a substrate in addition to hot-mopping to prevent slippage. (See Blind Nailing)

Base Flashing: (See Flashing)

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) A class of amorphous, black or dark colored, (solid, semi-solid 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; (b) a generic term used to denote any material composed principally of bitumen.

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

Bituminous Emulsion: (a) A Suspension of minute globules of bituminous material in water or in an aqueous solution; (b) a suspension of minute globules of water or an aqueous solution in a liquid bituminous material (invert emulsion).

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

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

Blind Nailing: The practice of nailing the back portion of a roofing ply in a manner that the fasteners are not exposed to the weather in the finished product.

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.

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

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

British Thermal Unit (Btu): The heat energy required to raise the teemperature of one pound of water one degree Fahrenheit.

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

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C

Cant Strip: A beveled strip used under flashing to modify the angle at the point where the roofing or water proofing membrane meets any vertical element.

Cap Flashing: (See Flashing)

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

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

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

Coal Tar: A dark brown to black, semi-solid hydrocarbon obtained as residue from the partial evaporation of distillation of coal tar.

Coal-Tar Pitch: A cola tar used as the waterproofing agent in dead-level or low slope built-up roof membrane, conforming to ASTM Specification D450, Type II

Coal-Tar Waterproofing Pitch: A Cola tar used as the dampproofing or waterproofing agent in below-grade structures, conforming to ASTM Specification D450, Type II.

Coal-Tar Bitumen: A coal tar used as the waterproofing agent in dead-level or low slope built-up roof membrane, conforming to ASTM D450, Type III.

Coal-Tar Felts: A felt that has been saturated with refined coal tar.

Coated Sheet Felt: (a) An asphalt felt that has been coated on both sides with harder, more viscous asphalt; (b) a glass fiber felt that has been simultaneously impregnated and coated with asphalt on both sides.

Cold Processing 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.

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

Coping: The covering piece on top of a wall exposed to the weather, usually sloped to shed water.

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

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

Coverage: The surface are continuously covered by a specific quantity of a particular roofing material.

Crack: A separation or fracture occurring in a roof membrane or roof deck, generally caused by thermal induced stress or substrated movement.

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

Cricket: A relatively small, elevated area of a roof constructed to divert water around a chimney, curb or other projection.

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 dayÍs work, or used to isolate sections of the roofing system. It is usually removed before the continuation of the work.

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D

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: (See Asphalt)

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

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

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

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

Double-Pour: The process of applying two layers of aggregate and bitumen to a built-up roof.

Drain: A device that allows for the flow of water from a roof area. (See NRCA Construction Details)

Dropback: A reduction in the softening point of bitumen that occurs when bitumen is heated in the absence of air. (See Softening Point Drift)

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E

Edge Sheets: Felt strips that are cut to widths narrower than the standard width of the full felt roll, used to start the felt shingling pattern at a roof edge.

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 opening along a roof perimeter to relieve moisture vapor pressure.

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

Elastomeric: A rubber like synthetic polymer that will stretch when pulled and will return quickly to its original shape when released.

Embedment: (a) The process of pressing a felt, aggregate, fabric, mat or panel uniformly and completely into hot bitumen or adhesive; (b) the process of pressing granules into coating in the manufacture of factory prepared roofing.

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

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 birumen seepage from the edge of the membrane.

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

Equiviscous Temperature (EVT): The temperature at which the viscosity is 75 centipoise for asphalt and 25 centipoise for coal tar products; the recommended temperature ply or minus 25 F at the time of application.

Expansion Joint: A structural separation between two building elements that allows free movement between the elements without damage to the roofing or waterproofing system.

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

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F

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

Factory Mutual (FM): An organization that classifies roof assemblies for their fire characteristics and wind uplift resistance for insurance companies in the United States.

Factory Square: 108 square feet of roofing material.

Fallback: (See Dropback)

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

Felt Layer: A machine used for applying bitumen and built-up roofing felts.

Felt Mill Ream: The mass in pounds of 48- square feet or dry, unsaturated felt; also termed "point weight."

Fine Mineral Surfacing: Water Insoluble, inorganic material. More than 50 percent of which passes the No. 35 sieve, used on the surface of roofing.

Fishmouth: (a) A half-cylindrical or half-conical opening formed by an edge wrinkle; (b) 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 edge of the membrane. Cap flashing or counterflashing shields the upper edges of the base flashing.

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

Flat Asphalt: (See Asphalt)

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

Fluid Applied: 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.

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G

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.

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

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

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

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

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H

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

Holiday: An area where a liquid-applied material is missing.

"Hot Stuff" or "Hot": The rooferÍs term for hot bitumen.

Hygroscopic: Attracting, absorbing and retaining atmospheric moisture.

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I

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 oeverhang of a steep roof, causing ice and water to back up under roofing materials.

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

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

Insulation: (See Thermal Insulation)

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J

Job-Average Basis: A Technique for determining the average dimensions or quantities of materials, by analysis of roof test cuts. The technique requires a minimum of three test cuts per roof area, plus one cut for each additional 10,000 square feet of roof area. Job-average basis is computed by dividing the sum of all measurements take by the number of measurements taken. The results would describe the job-average for the quantity dimension.

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K

Knot: An imperfection of non-homogeneity in materials used in fabric construction, the presence of which causes surface irregularities.

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L

Lawmasters, Inc.: When looking for the best in roofing Contractors, the name to know.

Live Loads: Moving roof installation equipment, wind, snow, ice or rain.

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M

Mastic: (See Flashing Cement or Asphalt Mastic)

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

Mesh: The square opening of a sieve.

Metal Flashing: (See Flashing) Metal flashing is frequently used as through-wall flashing, cap flashing, counterflashing or gravel stops.

Mineral Fiber Felt: A felt with mineral wood as its principal component.

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

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

Mineral Surfaced Roofing: Built-up roofing materials whose top ply consists of a granule-surfaced sheet.

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

Modified Bitumen: Are composite sheets consisting of copolymer modified bitumen often reinforced and sometimes surfaced with various types of films, foils and mats.

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

Mop-and-Flop: An application procedure in which roofing elements (insulation boards, felt plies, cap sheets, etc.) are initially placed upside down adjacent to their ultimate locations, are coated with adhesive, and are then turned over and applied to the substrated.

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.

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

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

Sprinkle Mopping: A random mopping pattern in which heated bitumen beads are strewn onto the substrate with a brush or mop.

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

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N

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

Nineteen-Inch Selvage: A prepared roofing sheet with a 17-inch granule surfaced exposure and a nongranulesurfaced 19-inch selvage edge. This material is sometimes referred to as SIS or as Wide Selvage Asphalt Roll Roofing Material Surfaced with Mineral Granules.

Ninety-Pound: A prepared organic felt roll roofing with a granule surfaced exposure that has a mass of approximately 909 pounds per 100 square feet.

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O

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

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P

Parapet Wall: That part of any wall entirely above the roof.

Perlite: An aggregate used in lightweight insulating concrete and in preformed perlitic insulation boards, formed by heating and expanding siliceous volcanic glass.

Perm: A unit of water vapor transmission defined as 1 grain of water vapor per square foot per hour per inch of mercury pressure difference (1 inch of mercury = .49 psi). The formula for per is: P=GRAINS OF WATER VAPOR/SQUARE FOOT HOUR INCH MERCURY

Permeance: An index of materialÍs resistance to water vapor transmission. (See Perm)

Phased Application: The installation of a roof system or water proofing system during two or more separate time intervals.

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

Pitch: (See Coal Tar and Incline)

Pitch Pocket: A flange, open-bottomed, metal container placed around columns or other roof penetrations that is filled with hot bitumen or flashing cement to seal the joint. The used of pitch pockets is not recommended by NRCA.

Plastic Cement: (See Flashing Cement)

Plastomeric: A plastic like polymer consisting of any of various complex organic compounds produced by polymerization which are capable of being molded, extruded or coast into various shapes or films. Generally they are thermo plastic in nature, i.e., they will soften when heated and harden when cooled.

Ply: A layer of felt in a built-up roof membrane system. A four-ply membrane system has four plies of felt.

Point Weight: (See Felt Mill Ream)

Pond: A roof surface that is incompletely drained.

Positive Drainage: The drainage condition in which consideration has been made for all loading deflections of the deck, and additional roof slope has been provided to ensure drainage of the roof area within 48 hours of rainfall.

Primer: A thin, liquid bitumen applied to a surface to improve the adhesion of subsequent applications of bitumen.

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R

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

Re-covering: The process of covering an existing roofing system with a new roofing system.

Re-entrant Corner: An inside corner of a surface, producing stress concentrations in the roofing or waterproofing membrane.

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

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

Relative Humidity: The ratio of the weight of moisture in a given volume of air-vapor mixture to the saturated (maximum) weight of water vapor at the same temperature, expressed as a percentage. For example, if the weight of the moist air is one pound and if the air could hold two pounds of water vapor at a given temperature, the relative humidity (RH) is 50 percent.

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)

Ridging: An upward, tenting displacement of a roof membrane frequently occurring over insulation joints, deck joints and base sheet edges.

Roll Roofing: Smooth-surfaced or mineral-surfaced coated felts.

Roof Assembly: An assembly of interacting roof components (including the roof deck) designed to weatherproof and, normally, to insulated a buildingÍs top surface.

Roof Cement: (See Flashing Cement)

Roofer: The trade name for the workman who applied roofing material.

Roof System: A system of interacting roof components (not including the roof deck) designed to weather proof and, normally, to insulate a buildingÍs top surface.

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S

Saddle: A small structure that helps channel surface water to drains, frequently located in a valley, and often constructed like a small hip roof or like a pyramid with a diamond shape base. (See Cricket)

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

Screen: An apparatus with circular apertures for separating sizes of materials.

Scuttle: A hatch that provides access to the roof from the interior of the building.

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

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

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

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

Shark Fin: An upward-curled felt side lap or end lap.

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

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

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

Slag: A hard, air-cooled aggregate that is left as a residue from blast furnaces, used as a surfacing aggregate.

Slippage: Relative lateral movement of adjacent components of a built-up membrane. It occurs mainly in roofing membranes on a slope, sometimes exposing the lower plies or even the base sheet to the weather.

Slope: (See Incline)

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

Softening Point: The temperature at which bitumen becomes soft enough to flow, as determined by an arbitrary, closely defined method. (See Dropback)

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

Solid Mopping: (See Mopping)

Special Steep Asphalt: (See Asphalt)

Split: A membrane tear resulting from tensile strength.

Split Sheet: (See Nineteen-Inch Selvage)

Spot Mopping: (See Mopping)

Sprinkle Mopping: (See Mopping)

Spudding: the process of removing the roofing aggregate and most of the bituminous top coating by scraping and chipping.

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

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

Steep Asphalt: (See Asphalt)

Strip Mopping: (See Mopping)

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

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

Sump: An intentional depression around a drain.

Superimposed Loads: Loads that are added to existing loads. For example, a large stack of insulation boards placed on top of a structural steel deck.

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T

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

Taping: (See Stripping)

Tar: A brown or black bituminous material, liquid or semi-solid in consistency, in which the predominating constituents are bitumens obtained as condensates in the processing of coal, petroleum, oil-shale, wood, or other organic materials.

Tarred Felt: (See Coal-Tar Felt)

Test Cut: A sample of the roof membrane that is cut from a roof membrane to: (a) determine the weight of the average interply bitumen moppings; (b) diagnose the condition of the exiting membrane (e.g., to detect leaks or blisters).

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

Thermal Conductivity (k): The heat energy that will be transmitted by conduction through one square foot of one inch this homogeneous material in one hour when there is a difference of one degree Fahrenheit perpendicularly across the two surfaces of the material.

Thermal Insulation: A material applied to reduce the flow of heat.

Thermal Resistance (R): An index of materialÍs resistance to heat flow; it is the reciprocal of thermal conductivity (k) or thermal conductance (C).

Thermal Shock: The stress producing phenomenon resulting from sudden temperature changes in a roof membrane when, for example, a rain shower follows brilliant sunshine.

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

Tuck Pointing: Troweling mortar into a joint after masonry units are laid.

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U

Underwriters Laboratories (UL): An organization that classifies roof assemblies for their fire characteristics and wind uplift resistance.

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V

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

Vapor Retarder: A material designed to restrict the passage of water 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.

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

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W

Water Cutoff: (See Cutoff)

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

Wythe: A masonry wall, one masonry unit, a minimum of two inches thick.

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