The following is a dictionary of basic roofing terms from the NRCA Roofing and Waterproofing Manual.
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
R-value: see Thermal resistance.
Racking: a method of asphalt shingle application, also referred to as the straight-up method, whereby shingle courses are applied vertically, up the roof rather than laterally or across and up. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 997
Rafter: one of a series of sloped structural members, that extend from the ridge or hip to the downslope perimeter or eave, designed to support the roof deck and its associated loads.
Raggle: a groove or slot, often cut in a masonry wall or other vertical surface adjoining a roof, for inserting an inset flashing component such as a reglet.
Rake: the sloped edge of a roof at or adjacent to the first or last rafter.
Rake-starter (Bleeder strip): starter-strip used along rake edges in conjunction with asphalt shingle roofing.
Re-cover: the addition of a new roof membrane or steep-slope roof covering over a major portion of an existing roof assembly. This process does not involve removal of the existing roofing.
Reflectivity: see Light reflectance.
Reglet: a sheet metal receiver for the attachment of counterflashing. A reglet may be surface-mounted, inset into a raggle or embedded behind cladding.
Reinforced membrane: a roofing or waterproofing membrane that has been strengthened by the addition or incorporation of one or more reinforcing materials, including woven or nonwoven glass fibers, polyester mats or scrims, nylon, or polyethylene sheeting.
Relative humidity (RH): the ratio of the pressure of water vapor present in a given volume of air to the pressure of fully saturated water vapor at the same temperature, expressed as a percentage.
Release tape (or Strip): a plastic film or paper strip that is applied to the back of self-sealing shingles and other materials. The strip prevents the material from sticking together in the roll or bundle. With asphalt shingles, the strip need not be removed for application of the shingles.
Replacement: the practice of removing an existing roof system down to the roof deck and replacing it with a new roofing system.
Reroofing: the process of re-covering, or tearing-off and replacing an existing roof system.
Resin: component B in SPF. This component contains a catalyst, blowing agent, fire retardants, surfactants and polyol. It is mixed with the A component to form polyurethane.
Ridge: highest point on the roof, represented by a horizontal line where two roof areas intersect, running the length of the area.
Ridge cap: a material or covering applied over the ridge of a roof.
Ridge course: the last or top course of roofing materials, such as tile, roll roofing, shingles, etc., that covers the ridge and overlaps the intersecting field roofing.
Ridge vent: a ventilator located at the ridge that allows the escape of warm and/or moist air from the attic area or rafter cavity.
Ridging: see Buckle.
Roll materials: a general term applied to rolls of roofing felt, ply sheet, etc., which are typically furnished in rolls.
Roll roofing: coated felts, either smooth or mineral-surfaced.
Roof: (1) the cover of a building; (2) to cover with a roof.
Roof area divider: refer to area divider. Roof area expansion Joint: see expansion joint. The NRCA Roofing and Waterproofing Manual—Fifth Edition 998 Glossary
Roof assembly: an assembly of interacting roof components including the roof deck, vapor retarder (if present), insulation and roof covering.
Roof cement: see Asphalt roof cement or Coal tar roof cement.
Roof covering: the exterior roof cover or skin of the roof assembly, consisting of membrane, panels, sheets, shingles, tiles, etc.
Roof curb: raised frame used to mount mechanical units (such as air conditioning or exhaust fans), skylights, etc. on a roof.
Roof jack: a metal or wood bracket used to support toe-boards on steep-slope roofs. (also see Flashing Collar.)
Roof overhang: a roof extension beyond the exterior wall of a building.
Roof seamer: (1) machine that crimps neighboring metal roof panels together; (2) machine that welds laps of membrane sheets together using heat, solvent, or dielectric energy.
Roof slope: the angle a roof surface makes with the horizontal, expressed as a ratio of the units of vertical rise to the units of horizontal length (sometimes referred to as run). For English units of measurement, when dimensions are given in inches, slope may be expressed as a ratio of rise to run, such as 4:12 or as an angle.
Roof system: a system of interacting roof components, generally consisting of a membrane or primary roof covering and roof insulation (not including the roof deck) designed to weatherproof and, sometimes, to improve the
building’s thermal resistance.
Rosin paper (specifically Rosin-sized sheathing paper): a nonasphaltic paper used as a sheathing paper or slip sheet in some roof systems.
Rubber: a material that is capable of recovering from large deformations quickly and forcibly.
Run: horizontal dimension of a slope.
Tab: the exposed portion of strip shingles defined by cutouts.
Tack-free time: in SPF-based roofing, a curing phase of polyurethane foam to when the material is no longer sticky. When the polyurethane foam is tack free, it can be sprayed over with another pass, referred to as a “lift”.
With some care the polyurethane foam can be walked on soon after it is tack free.
Talc: whitish powder applied at the factory to the surface of some roofing materials (e.g., vulcanized EPDM membranes), used as a release agent to prevent adhesion of the membrane to itself.
Tapered edge strip: a tapered insulation strip used to (1) elevate and slope the roof at the perimeter and at curbs, and (2) provide a gradual transition from one layer of insulation to another.
Taping: (1) the technique of connecting joints between insulation boards or deck panels with tape; (2) the technique of using self-adhering tape-like materials to seam or splice single-ply membranes.
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.
Tar boils: bubbles of moisture vapor encased in a thin film of bitumen, also known as “blackberries.”
Tarred felt: see Coal tar felt.
Tear-off and reroof: the removal of all roof system components down to the structural deck, followed by installation of a completely new roof system.
Tear resistance: the load required to tear a material, when the stress is concentrated on a small area of the material by the introduction of a prescribed flaw or notch. Expressed in psi (pounds force) per inch width or kN/m (kilonewton per meter width).
Tear strength: the maximum force required to tear a specimen.
Tensile strength: the strength of a material under tension as distinct from torsion, compression or shear.
Tension leveling: the process of pulling metal coil stock between two spools under a certain pressure to help reduce side camber and potential oil canning in the coil stock caused by manufacturing and cutting processes.
Termination: the treatment or method of anchoring and/or sealing the free edges of the membrane in a roofing or waterproofing system.
Terne: an alloy of lead and tin, used to coat sheets of carbon steel or stainless steel for use as metal roofing sheet.
Terra cotta: low-fired clay, either glazed or unglazed.
Test cut: a sample of the roof system or assembly which exposes the roof deck and is used to diagnose the condition of the membrane, evaluate the type and number of plies or number of membranes, or rates of application (e.g., the weight of the average interply bitumen moppings).
Thermal block: a compression-resistant insulation block installed between structural steel roof panels and their supporting members to help maintain insulation R-values and reduce condensation.
Thermal bridge: the penetration of a material of high thermal conductivity (e.g., a metal insulation or roof membrane fastener) through a material of low thermal conductivity (e.g., thermal insulation); the result is a lowered thermal resistance for the assembly. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 1005
Thermal cycling: sequence of values caused by a repetitive temperature differential due to changes in radiant energy.
Thermal conductance (C): the time rate of heat flow through a unit area of a body induced by a unit temperature difference between bodies. In English (inch-pound) units of measurement, the number of BTUs that pass through a specified thickness of a one square foot (0.09 m2) sample of material in one hour with a temperature difference between the two surfaces of 1° F. In English (inch-pound) units it is expressed as Btu/h•ft2•F.
Note 1: A thermal conductance (C) value applies to a specific thickness of a specific material. Note 2: It is mathematically incorrect to multiply or divide the thermal conductance (C) value for a specific thickness of a material to determine the thermal conductance value of a different thickness of the same material. Note 3: It is mathematically incorrect to add thermal conductance (C) values to determine overall thermal performance. If it is necessary to determine the overall thermal performance of a construction, it is appropriate to convert the individual thermal conductance (C) values to thermal resistance (R) values (i.e., R= 1/c), and then add the thermal resistance values (i.e., RT=R1, + R2 + …).
Thermal conductivity (k): the time rate of heat flow through a unit area of a homogeneous material in a direction
perpendicular to isothermal planes induced by a unit temperature gradient is called thermal conductivity (k or kvalue). In English (inch-pound) units of measurement, it is the number of BTUs that pass through a 1 inch (25 mm)
thickness of a 1 square foot (0.09 m2) sample of material in one hour with a temperature difference between the two surfaces of 1°F. In English (inch-pound) units it is expressed as Btu•inch/h•ft2•°F. Note 1: A thermal conductivity (k) value applies to 1 inch (25 mm) thickness of a specific material.
Note 2: It is mathematically incorrect to add, multiply, or divide the thermal conductivity (k) value of a material to determine the thermal performance value of a different thickness of the same material. If it is necessary to determine the thermal performance of a specific thickness of a material, it is appropriate to convert the thermal conductivity (k) of the material to a thermal resistance (R) value (i.e., R = 1/k), and then perform the mathematical calculation.
Thermal expansion: the increase in the dimension or volume of a body due to temperature variations.
Thermal insulation: a material applied to reduce the flow of heat.
Thermal movement: changes in dimension of a material as a result of temperature changes.
Thermal resistance (R): under steady conditions, thermal resistance is the mean temperature difference between two defined surfaces of material or construction that induces unit heat flow through a unit area. In English
(inch•pound) units it is expressed as °F•ft2•h/Btu. Note 1: A thermal resistance (R) value applies to a specific thickness of a material or construction. Note 2: The thermal resistance (R) of a material is the reciprocal of the thermal conductance (C) of the same material (i.e., R = 1/C).
Note 3: Thermal resistance (R) values can be added, subtracted, multiplied, and divided by mathematically appropriate methods.
Thermal shock: the stress-producing phenomenon resulting from sudden temperature changes in a roof membrane when, for example, a cold rain shower follows brilliant sunshine.
Thermal stress: stress introduced by uniform or non-uniform temperature change in a structure or material that is contained against expansion or contraction. The NRCA Roofing and Waterproofing Manual—Fifth Edition
Thermal transmittance (U or U-factor): thermal transmittance (U or U-factor) is the time rate of heat flow per unit area under steady conditions from the fluid (e.g., air) on the warm side of a barrier to the fluid (e.g., air) on the cold side, per unit temperature difference between the fluids. In English (inch•pound) units expressed as Btu/h•ft2•°F.
Note 1: A thermal transmittance (U) value applies to the overall thermal performance of a system (e.g., roof assembly).
Note 2: Thermal transmittance (U) is sometimes called the overall coefficient of heat transfer.
Note 3: Thermal transmittance (U) is reciprocal of the overall thermal resistance (RT) of a system (i.e., U = 1/RT).
Thermography, Infrared: see Infrared thermography.
Thermoplastic: a material that softens when heated and hardens when cooled. This process can be repeated provided that the material is not heated above the point at which decomposition occurs.
Thermoplastic olefin membrane (TPO): a blend of polypropylene and ethylene-propylene polymers. Colorant, flame retardants, UV absorbers, and other proprietary substances which may be blended with the TPO to achieve the desired physical properties. The membrane may or may not be reinforced.
Thermoset: a class of polymers that, when cured using heat, chemical, or other means, changes into a substantially infusible and insoluble material.
Thinner: (1) a volatile liquid added to an adhesive or coating material to modify the consistency or other properties; (2) a liquid used to clean equipment or other surfaces.
Thixotropic: the property of a material that enables it to stiffen in a relatively short time on standing, but upon agitation or manipulation to change to a very soft consistency or to a fluid of high viscosity, the process being completely reversible.
Through-wall flashing: a water-resistant membrane or material assembly extending totally through a wall and its cavities, positioned to direct water within the wall to the exterior, usually through weep holes.
Tie-in: in roofing and waterproofing, the transitional seal used to terminate a roofing or waterproofing application at
the top or bottom of flashings or by forming a watertight seal with the substrate, membrane, or adjacent roofing or waterproofing system.
T-joint: the condition created by the overlapping intersection of three or four sheets in the membrane.
Toggle bolt: a bolt having a nut with pivoted, flanged wings that close against a spring when it is pushed through a hole, and open after emerging from the hole; used to fasten objects to a hollow wall or to a wall which is accessible only from one side.
Tongue and groove planks: one of the oldest types of dimensional structural wood used as roof decking. The sides are cut with convex and concave grooves so adjacent planks may join in alignment with each other to form a uniform roof deck.
Torch-applied: method used in the installation of polymer modified bitumen membranes characterized by using open flame propane torch equipment.
TPO: thermoplastic olefin.
Traffic bearing: in waterproofing, a membrane formulated to withstand a predetermined amount of pedestrian or vehicular traffic with separate protection and a wear course.
Transverse seam: the joint between the top of one metal roof panel and the bottom of the next panel, which runs perpendicular to the roof slope.
Treebark surface texture: in SPF roofing, the surface condition of the foam which shows a coarse texture where valleys form sharp angles. This surface is unacceptable for proper coating and protection.
The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 1007
Tuckpointing: the process of removing deteriorated mortar from an existing masonry joint and troweling new mortar or other filler into the joint.
U-Value: see Thermal transmittance.
UBC: Uniform Building Code.
UL: Underwriters Laboratories, Inc.
UL label: an identification label or seal affixed to a roofing product or package with the authorization of Underwriters Laboratories, Inc. The presence of the label indicates that the product has met certain performance criteria.
Ultraviolet (UV): invisible light radiation, adjacent to the violet end of the visible spectrum, with wavelengths from about 200 to 400 nm (nanometres).
Underlayment: an asphalt-saturated felt or other sheet material (may be self-adhering) installed between the roof deck and roof covering, usually used in a steep-slope roof construction. Underlayment is primarily used to separate the roof covering from the roof deck, shed water and provide secondary weather protection for the roof area of the building.
Underwriters Laboratories, Inc. (UL): an organization that tests, rates and classifies roof assemblies for their resistance to fire, impact, leakage, corrosion of metal components and wind uplift.
Uplift: see Wind uplift.
Valley: the internal angle formed by the intersection of two sloping roof planes.
Vapor migration: the movement 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 of a solid or liquid when in equilibrium with the liquid or solid.
Vapor retarder: a layer(s) of material or a laminate used to appreciably reduce the flow of water vapor into a roof assembly.
Veneer: (1) a single wythe of masonry for facing purposes that may not be structurally connected; (2) any of the thin layers of wood glued together to form plywood.
Vent: an opening designed to convey air, heat, water vapor or gas from inside a building or a building component to the atmosphere.
Ventilator: an accessory that is designed to allow for the passage of air.
Verge of popcorn texture: in SPF roofing, the verge of popcorn surface texture is the roughest texture suitable for receiving the protective coating on a sprayed polyurethane foam roof. The surface shows a texture where nodules are larger than valleys, with the valleys relatively cured. This surface is acceptable for receiving a protective coating only because of the relatively cured valleys. However, the surface is considered undesirable because of the additional amount of coating material required to protect the surface properly.
Vermiculite: an aggregate used in lightweight insulating concrete, formed by heating and expanding of a micaceous material.
Viscosity: the resistance of a material to flow under stress. For bitumen, measured in centipoise. (see Viscous.)
Viscous: resistant to flow under stress.
Void: an open space or break in consistency.
Volatile: a relative term expressing the tendency to form vapor.
The NRCA Roofing and Waterproofing Manual—Fifth Edition 1008 Glossary
Volatile organic compounds (VOC): means any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participate in atmospheric
Vulcanization: an irreversible process during which a rubber compound, through a change in its chemical structure (for example, 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.
Warm roof assembly: a roof assembly configured with each component placed immediately on top of the preceding component; each component is in contact with the adjacent component. No space is provided for ventilation of the roof assembly. Also known as a “compact” roof assembly.
Wash coat: a primer, typically provided on the back side of painted metal products to help protect the underlying metal from wear and corrosion.
Water cure: a method of curing a material, such as concrete, by applying a fine mist of water over the surface to control the rate of moisture evaporation from the material.
Water cutoff: see Cutoff.
Water-shedding: the ability of individual, overlapping components to resist the passage of water without hydrostatic pressure.
Water stop: a diaphragm used across a joint as a sealant, usually to prevent the passage of water.
Water table: the level within the ground, below which the soil is saturated with water.
Water vapor transmission: a measure of the rate of transmission of water vapor through a material under controlled laboratory conditions of temperature and humidity. Customary units are grains/h•ft2.
Waterproof: the quality of a membrane, membrane material, or other component to prevent water entry.
Waterproofing: treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.
Wear course: the top layer of surfacing that carries pedestrian or vehicular traffic. Sometimes referred to as wearing surface.
Wearing surface: see Wear course.
Weatherproof: the ability of a membrane or roof covering to prevent the passage of water with a limited amount of hydrostatic pressure.
Weep holes: small openings whose purpose is to permit drainage of water that accumulates inside a building component (e.g., a brick wall, skylight frame, etc.).
Weld: to join pieces of metal together by heat fusion.
Wet: a condition where free water is present in a substance.
Wet bulb temperature: the temperature of air as registered by a thermometer whose bulb is covered by a water wetted wick.
Wet film thickness: the thickness, expressed in mils, of a coating or mastic as applied but not cured. For comparison, see Dry film thickness.
Wicking: the process of moisture movement by capillary action.
Wind clip: a steep-slope roofing attachment device that fits over the butt end of tile, slate and stone to help secure individual roofing units from wind uplift.
Wind load: force exerted by the wind on a structure or part of a structure.
The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 1009
Wind uplift: the force caused by the deflection of wind at roof edges, roof peaks or obstructions, causing a drop in air pressure immediately above the roof surface.
Wire tie system: a system of attachment for steep-slope roofing units (e.g., tile, slate and stone) using fasteners (nails and/or screws) in conjunction with wire to provide a concealed fastening system.
Work slab: see Mud slab.
Woven valley: a method of valley construction in which shingles or roofing from both sides of the valley extend across the valley and are woven together by overlapping alternate courses as they are applied.
Wythe: a masonry wall, one masonry unit, a minimum of two inches thick.
Yield: in SPF-based roofing, the volume of foam per unit weight, normally expressed as board feet per pound or
board feet per 1000 pounds.
Z section: a member formed in the shape of a “Z” from coiled steel stock.
Zinc: a hard bluish white metal, brittle at normal temperatures, very malleable and ductile when heated; not subject to corrosion; used for galvanizing sheet steel and iron, in various metal alloys, and as an oxide for white paint pigment.