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Roofing Dictionary

The following is a dictionary of basic roofing terms and phrases.  I don't know why we put this in?  Never-the-less here it is...

-A-

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

Alligatoring: The cracking of the surfacing bitumen on a built-up roof, producing a pattern of cracks similar to an alligator's hide; the cracks may or may not extend through the surfacing bitumen.

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 Detail D-1).

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.

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 grade 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, normally used for highway bitumen.
-B-

Backnailing: The practice of blind nailing (in addition to hot-mopping) all the plies of a substrate to prevent slippage. (See BLIND NAILING.)

Base Flashing: See FLASHING.

Base Ply: The base ply is the first ply when it is a separate ply and not part of a shingled system.

Base Sheet: A saturated or coated felt placed as the first ply in some multi-ply, built-up roof membranes.

Bitumen: The generic term for an amorphous, semi-solid mixture of complex hydrocarbons derived from any organic source. Asphalt and coal tar are the two bitumens used in the roofing industry.

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

Bituminous Emulsion: (1) A suspension of minute globules of bituminous material in water or in an aqueous solution; (2) 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.

Blind Nailing: The practice of nailing the back portion of a roofing ply.

Blister: A spongy raised portion of a roof membrane, ranging in area from 1 inch in diameter and of barely detectable height upwards. Blisters result from the pressure buildup of gases entrapped in the membrane system. These gases most commonly are air and/or water vapor. Blisters usually involve delamination of the underlying membrane plies.

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

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

BTU: (British Thermal Unit) - The heat energy required to raise the temperature of 1 pound of water 1 degree Fahrenheit.

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.)
-C-

Cant Strip: A bevelled shaped strip of wood or wood fiber that fits into the angle formed by the intersection of a horizontal surface and a vertical surface. The 45 degree slope of the exposed surface of the cant strip provides a gradual angular transition from the horizontal surface to the vertical surface.

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 of 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 Bitumen: A dark brown to black, semi-solid hydrocarbon formed as a residue from the partial evaporation of distillation of coal tar. It is used as the waterproofing agent in dead-level or low-slope built-up roofs. It differs from COAL TAR PITCH in having a lower front-end volatility. (For specification properties, see ASTM Standard D 450, Type III.)

Coal Tar Felt: See TARRED FELT.

Coal Tar Pitch: A dark brown to black, semi-solid hydrocarbon formed as a residue from the partial evaporation or distillation of coal tar. It is used as the waterproofing agent in dead-level or low-slope built-up roofs. (For specification properties, see ASTM Standard D 450, Types I and II.)

Coated Base Sheet (or Felt): A felt that has been impregnated and saturated with asphalt and then coated on both sides with harder, more viscous asphalt to increase its impermeability to moisture; a parting agent is incorporated to prevent the material from sticking in the roll.

Cold-Process Roofing: A continuous, semi-flexible roof membrane, consisting of plies of felts, mats, or fabrics that are laminated on a roof with alternate layers of cold-applied roof cement and surfaced with a cold-applied coating.

Condensation: The conversion of water vapor or other gas to liquid as the temperature drops or the atmospheric pressure rises. (See DEW-POINT.)

Coping: The covering piece placed on top of a wall that is exposed to the weather. It is 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 area (in square feet) to be continuously coated by a specific roofing material, with allowance made for a specific lap.

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

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

Cricket: A superimposed construction placed in a roof area to assist drainage. (See NRCA Construction Detail P.)

Cutback: Any bituminous roofing material that has been solvent thinned. Cutbacks are used in cold-process roofing adhesives, flashing cements, and roof coatings.

Cutoff: A material seal that is designed to prevent lateral water movement into the edge of a roof system where the membrane terminates at the end of a day's work or used to isolate sections of the roof system. Cutoffs are usually removed before the continuation of work.
-D-

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

Dead Level: The term used to describe an absolutely horizontal roof. Zero slope. (See SLOPE.)

Dead Level Asphalt: A roofing asphalt that has a softening point of 140 degrees F. (60 degrees C.) and that conforms to the requirements of ASTM Standard D 312, Type I.

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.

Drain: A device that allows for the flow of water from a roof area. (See NRCA Construction Detail W-2.)

Dropback: A reduction in the softening point of bitumen that occurs when bitumen is heated in the absence of air. (See SOFTENING POINT DRIFT.)
-E-

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

Edge Stripping: Application of felt strips cut to narrower widths than the normal width of the full felt roll. They are used to cover joints.

Edge Venting: The practice of providing regularly spaced protected openings 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: The term used to describe the elastic, rubber-like properties of a material.

Embedment: (1)The process of pressing a felt, aggregate, fabric, mat or panel uniformly and completely into hot bitumen or adhesive; (2) The process of placing a material into another material so that it becomes an integral part of the whole material.

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

Envelope: A continuous felt fold formed by wrapping and securing a portion of a base felt back up and over the felt plies above it. Envelopes help prevent the seepage of bitumen.

EPDM: Ethylen Propylene Diene Monomer, the technical name for rubber roofing material similar to inner-tube rubber.

Equilibrium Moisture Content: (1) The 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.

Equiviscous Temperature (EVT) Range: The optimum application temperature of asphalt. It is the temperature range at which a viscosity of 125 centistokes is attained, plus or minus 25 degrees F.

Expansion Joint: A structural separation between two building elements designed to minimize the effect of the stresses and movements of a building's components and to prevent these stresses from splitting or ridging the roof membrane. (See NRCA Construction Detail C-1.)

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

-F-

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

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

Factory Square: 108 square feet (10 square meters) of roofing material.

Felt: A fabric manufactured from vegetable fibers (organic felts), asbestos fibers (asbestos felts), or glass fibers (glass fiber felts). The manufacturing process involves mechanically interlocking the fibers of the particular felt material in the presence of moisture and heat.

Felt Mill Ream: The mass in pounds of 480 square feet of dry, unsaturated felt; also termed "point weight."

Fine Mineral Surfacing: A water-insoluble, inorganic material, more than 50% of which passes through the No. 35 sieve, that may be used on the surface of roofing material.

Fishmouth: (1) A half-cylindrical or half-conical opening formed by an edge wrinkle; (2) in shingles, a half-conical opening formed at a cut edge.

Flashing: The system used to seal the edges of a membrane at walls, expansion joints, drains, gravel stops and other areas where the membrane is interrupted or terminated. BASE FLASHING covers the edges 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: A roofing asphalt that has a softening point of approximately 170 degrees F. (77 degrees C.) and that conforms to the requirements of ASTM Standard D 312, Type II.

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

Fluid Applied Elastomer: An elastomeric material, which is fluid at ambient temperature, that dries or cures after application to form a continuous membrane.
-G-

Glass Fiber Felt: A felt sheet in which glass fibers are bonded into the felt sheet with resin. They are suitable for impregnation and coating. They are used in the manufacture and coating of bituminous waterproofing materials, roof membranes, and shingles.

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

Glaze Coat: (1) The top layer of asphalt in a smooth-surface 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.

Grain: The weight unit equal to 1/7000 lb.; used in measuring atmospheric moisture content.

Gravel: Coarse, granular aggregate, containing pieces approximately 5/8 inch to 1/2 inch in size and suitable for use in aggregate surfacing on built-up roofs.

Gravel Stop: A flanged device, frequently metallic, designed to provide a continuous finished edge for roofing
-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 roofer's term for hot bitumen.

Hygroscopic: The term used to describe a material which attracts, absorbs and retains atmospheric moisture.materials and to prevent loose aggregate surfacing on built-up roofs.
-I-

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: A material applied to reduce the flow of heat.
-K-

Knot: An imperfection or nonhomogeneity in materials used in fabric construction, the presence of which causes surface irregularities.

-L-

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

Manufacturer's Bond: A security company's guarantee that it will stand behind a manufacturer's liability to finance membrane repairs occasioned by ordinary wear within a period generally limited to 5, 10, 15 or 20 years.

Mastic: See FLASHING 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 or circular 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 wool as its principal component.

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

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

Mopping: An application of hot bitumen applied to the substrate or to the felt of a built-up roof membrane with a mop or mechanical applicator. (SEE SOLID MOPPING, SPOT MOPING, SPRINKLE MOPPING, AND STRIP MOPPING)
-N-

Nailing: (1) In the EXPOSED NAIL METHOD, nail heads are exposed to the weather; (2) in the CONCEALED NAIL METHOD, nail heads are concealed from the weather. (See also BLIND NAILING.)

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

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

-O-

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

-P-

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 = 0.491 psi). The formula for perm is:

P= GRAINS OF WATER VAPOR/SQUAREFOOTHOURINCH MERCURY

Permeance: An index of a material's resistance to water vapor transmission. (See Perm.)

Phased Application: The installation of a roof system or waterproofing 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 Pocket: A flanged, open-bottomed, metal container placed around columns or other roof penetrations that is filled with hot bitumen and/or flashing cement to seal the joint. The use of pitch pockets is not recommended by NRCA.

Plastic Cement: See FLASHING CEMENT.

Ply: A layer of felt in a built-up roof membrane system. A four-ply membrane system has four plies of felt. The dimension of the exposed surface (the "exposure") of any ply may be computed by dividing the felt width (minus 2 inches) by the number of plies; thus, the exposed surface of a 36 inch wide felt in a four-ply membrane should be 8-1/2 inches. (See exposure.)

Point Weight: See FELT MILL REAM.

Pond: A roof surface which is incompletely drained.

Positive Damage: 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 complete drainage of the roof area within 24 hours of rainfall precipitation.

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

-R-


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

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 1 pound and if the air could hold 2 pounds of water vapor at a given temperature, the relative humidity (RH) is 50%.

Reroofing: The practice of applying new roofing materials over existing roofing materials.

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

Roll Roofing: The term applied to smooth-surface or mineral-surfaced coated felts.

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

Roofer: The trade name for the workman who applies roofing materials.

Roof System: A system of interacting roof components (NOT including the roof deck) designed to weatherproof and, normally, to insulate a building's top surface.

-S-


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

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

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 which 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 to be installed with similar units in overlapping rows on inclines normally exceeding 25%; (2) to cover with shingles; (3) to apply any sheet material in overlapping rows like shingles.

Shingling: (1) The procedure of laying parallel felts so that one longitudinal edge of each felt OVERLAPS and the other longitudinal edge UNDERLAPs, an adjacent felt. (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. It is used as a surfacing aggregate and should be surface dry and free of sand, clay or other foreign substances at the time of application.

Slippage: The relative lateral movement of adjacent components of a built-up roof membrane. It occurs mainly in roof membranes on a slope, sometimes exposing the lower plies to the weather.

Slope: The tangent of the angle between the roof surface and the horizontal. It is measured in inches per foot. The Asphalt Roofing Manufacturers Association (ARMA) ranks slope as follows:

Level Slope: Up to 1/2 inch per foot
Low Slope: 1/2 inch per foot to 1-1/2 inches per foot
Steep Slope: Over 1-1/2 inches per foot

Smooth-Surface 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. The softening point of asphalt is measured by the "ring-and-ball" test (ASTM Standard D 2398). The softening point of coal tar pitch is measured by the "cube-in-water" test (ASTM Standard D 61).

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

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

Special Steep Asphalt: A roofing asphalt that has a softening point of approximately 220 degrees F. (104 degrees C.) and that conforms to the requirements of ASTM Standard D 312, Type IV.

Split: A separation in roofing material resulting from movement of the substrate. (See CRACK.)

Split Sheet: See NINETEEN-INCH SELVAGE.
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 wherein heated bitumen bands are strewn onto the substrate with a brush or mop.

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 any pressure exerted by moisture vapor between the roof membrane and the vapor retarder or deck.

Steep Asphalt: A roofing asphalt that has a softening point of approximately 190 degrees F. (88 degrees C.) and that conforms to the requirements of ASTM Standard D 312, Type III.

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

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

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 and hot-applied or cold-applied bitumen; (2) the technique of taping joints between insulation boards on deck panels.

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

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

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

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: A felt that has been saturated with refined coal tar.

Test Cut: A sample of the roof membrane, usually 4" x 36" or 12" x 12" in size, that is cut from a roof membrane to:
1.) Determine the weight of the average interply bitumen poundages. 2.) Diagnose the condition of the existing membrane (e.g., to detect leaks or blisters).

NRCA recommends that the test cut procedure NOT be used as a means of determining the quality of a roof system.

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. The formula for thermal conductance is:

C =k/ thickness in inches

Thermal Conductivity (k): The heat energy that will be transmitted by conduction through one square foot of one inch thick homogeneous material in one hour when there is a difference of 1 degree Fahrenheit perpendicularly across the two surfaces of the material. The formula for thermal conductivity is:

k = BTU/SQUARE FOOT/INCH/HOUR/DEGREE FAHRENHEIT

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

Thermal Resistance (R): An index of a material's resistance to heat flow; it is the reciprocal of thermal conductivity (k) or thermal conductance (C). The formula for thermal resistance is:

R = 1 or R = 1 or R = thickness in inches
C k k

Thermal Shock: The stress-producing phenomenon resulting from sudden temperature changes in a roof membrane. (For example, when 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 any water entering the top of the wall to the exterior.

TPO: Thermoplastic olefin is a lightweight plastic membrane that is heat weld-able.
-U-

Underwriters Laboratories (UL): An organization which classifies roof assemblies for their fire characteristics and wind-uplift resistance for insurance companies in the United States.
-V-

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

Vapor-Pressure Gradient: A graph, analogous to a temperature gradient, indicating the changes in water vapor pressure at various cross-sectional planes through a roof or wall system.

Vapor Retarder: A material designed to restrict the passage of water vapor through a wall or roof. In the roofing industry, a vapor retarder should have a perm rating of 0.5 or less.

Vent: An opening designed to convey water vapor or other gas from inside a building or a building component to the atmosphere, thereby relieving vapor pressure.

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

Water Cutoff: See CUTOFFS.

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

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