Glossary of Roofing Terms
As one of the premier roofing contractors in the Southern California area over the past 35 years, we at Shadowcrest Roofing have learned that a knowledgeable customer is a happy customer. Not only are they more understanding about the difficult aspects of the job, but they can better explain their roofing problem so we can fix that problem more quickly and efficiently. This is why we have a complete roofing glossary for our customer’s convenience.
Adhere: to cause two surfaces to be held together by adhesion, typically with asphalt or roofing cements in built-up roofing and with contact cements in some single-ply membranes.
Adhesion: the state in which two surfaces are held together by interfacial forces which may consist of molecular forces or interlocking action, or both.
Aggregate: rock, stone, crushed stone, crushed slag, water-worn gravel or marble chips used for surfacing and/or ballasting a roof system.
Alligatoring: Shrinkage cracking of the bituminous surface of built up or smooth surface roofing, producing a pattern of deep cracks resembling an alligator hide.
Asbestos: a group of natural, fibrous, impure silicate materials used to reinforce some roofing products which have been outlawed and are the responsibility of the building owner to abate.
Asphalt Roof Cement: a trowelable mixture of solvent-based bitumen, mineral stabilizers, other fibers and/or fillers.
ASTM: American Society for Testing and Materials
Ballast: an anchoring material, such as aggregate, or precast concrete pavers, which employ the force of gravity to hold (or assist in holding) single-ply roof membranes in place.
Base Flashing (membrane base flashing): plies or strips of roof membrane material used to close-off and/or seal a roof at the roof-to-vertical intersections, such as at a roof-to-wall juncture. Membrane base flashing covers the edge of the field membrane. (Also see Flashing.)
Base Ply: the lowermost ply of roofing in a roof membrane or roof system.
Base Sheet: an impregnated, saturated, or coated felt placed as the first ply in some multi-ply built-up and modified bitumen roof membranes.
Batten: (1) cap or cover; (2) in a metal roof: a metal closure set over, or covering the joint between, adjacent metal panels; (3) wood: a strip of wood usually set in or over the structural deck, used to elevate and/or attach a primary roof covering such as tile; (4) in a membrane roof system: a narrow plastic, wood, or metal bar which is used to fasten or hold the roof membrane and/or base flashing in place.
Batten Seam: a metal panel profile attached to and formed around a beveled wood or metal batten.
Bitumen: (1) 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 petroleum asphalts, coal tars and pitches, wood tars and asphalts; (2) a generic term used to denote any material composed principally of bitumen, typically asphalt or coal tar.
Bleeder Strip: see Rake-Starter.
Blind-Nailing: the use of nails that are not exposed to the weather in the finished roofing system.
Blister: an enclosed pocket of air, which may be mixed with water or solvent vapor, trapped between impermeable layers of felt or membrane, or between the membrane and substrate.
Blocking: sections of wood (which may be preservative treated) built into a roof assembly, usually attached above the deck and below the membrane or flashing, used to stiffen the deck around an opening, act as a stop for insulation, support a curb, or to serve as a nailer for attachment of the membrane and/or flashing.
Brake: hand- or power-activated machinery used to form metal.
Brooming: an action carried out to facilitate embedment of a ply of roofing material into hot bitumen by using a broom, squeegee, or special implement to smooth out the ply and ensure contact with the bitumen or adhesive under the ply.
Buckle: an upward, elongated tenting displacement of a roof membrane frequently occurring over insulation or deck joints. A buckle may be an indication of movement within the roof assembly.
Built-Up Roof Membrane (BUR): a continuous, semi-flexible multi-ply roof membrane, consisting of plies or layers of saturated felts, coated felts, fabrics, or mats between which alternate layers of bitumen are applied. Generally, built-up roof membranes are surfaced with mineral aggregate and bitumen, a liquid-applied coating, or a granule-surfaced cap sheet.
Cant Strip: a beveled or triangular-shaped strip of wood, wood fiber, perlite, or other material designed to serve as a gradual transitional plane between the horizontal surface of a roof deck or rigid insulation and a vertical surface.
Cap Sheet: a granule-surface coated sheet used as the top ply of some built-up or modified bitumen roof membranes and/or flashing.
Capillary Action: the action that causes movement of liquids by surface tension when in contact with two adjacent surfaces such as panel side laps.
Caulking: (1) the physical process of sealing a joint or juncture; (2) sealing and making weather-tight the joints, seams, or voids between adjacent units by filling with a sealant.
Cavity Wall: a wall built or arranged to provide an air space within the wall (with or without insulating material), in which the inner and outer materials are tied together by structural framing.
Channel Flashing: (for steep-slope roof construction) a type of flashing used at roof-to-wall junctures and other roof-to-vertical plane intersections where an internal gutter is needed to handle runoff. Commonly used with profile tile.
Cladding: a material used as the exterior wall enclosure of a building.
Cleat: a metal strip, plate or metal angle piece, either continuous or individual (“clip”), used to secure two or more components together.
Clerestory: an upward extension of enclosed space created by carrying a setback vertical, wall (typically glazed) up and through the roof slope. Two intersecting shed roofs on different planes. (See Figure 1.)
Clip: an individual (discrete) cleat. (See Cleat.)
Coping: the covering piece on top of a wall which is exposed to the weather, usually made of metal, masonry, or stone. It is preferably sloped to shed water back onto the roof.
Counterflashing: formed metal sheeting secured on or into a wall, curb, pipe, rooftop unit, or other surface, to cover and protect the upper edge of the membrane base flashing or underlying metal flashing and associated fasteners from exposure to the weather.
Cricket: an elevated roof substrate or structure, constructed to divert water around a chimney, curb, away from a wall, expansion joint, or other projection/penetration. (See Saddle.)
Cross Ventilation: the effect that is provided when air moves through a roof cavity between the vents.
Curb: (1) a raised member used to support roof penetrations, such as skylights, mechanical equipment, hatches, etc. above the level of the roof surface; (2) a raised roof perimeter relatively low in height.
Dead Loads: permanent non-moving loads that result from the weight of a building’s structural and architectural components, mechanical and electrical equipment, and the roof assembly itself. Essentially the same as “dead weight” or “dead weight loads.”
Deck: a structural component of the roof of a building. The deck must be capable of safely supporting the design dead and live loads, including the weight of the roof systems, and the additional live loads required by the governing building codes. Decks are either non-combustible (e.g., corrugated metal, concrete, or gypsum) or combustible (e.g., wood plank or plywood), and provide the substrate to which the roofing or waterproofing system is applied.
Deflection (Bowing, Sagging): the downward displacement of a structural member or system under load.
Degradation: a deleterious change in the chemical structure, physical properties, or appearance of a material due to natural or artificial exposure (e.g., exposure to radiation, moisture, heat, freezing, wind, ozone, oxygen, etc.).
Delamination: separation of the laminated layers of a component or system.
Design Loads: those loads specified in building codes or standards published by federal, state, county, or city agencies, or in owners’ specifications to be used in the design of a building.
Drain: an outlet or other device used to collect and direct the flow of runoff water from a roof area.
Eave: a projecting edge of a roof that extends beyond the supporting wall.
Edge Stripping: membrane flashing strips cut to specific widths used to seal/flash perimeter edge metal and the roof membrane.
Efflorescence: the formulation of crystalline deposits, generally whitish in color, on the surface of stone, brick, concrete, or other masonry surface when moisture moves through and evaporates on the masonry. May also be caused by free alkalies leached from mortar, grout, or adjacent concrete.
Elasticity: the property of matter by virtue of which it tends to return to its original size and shape after removal of a stress or force which caused a deformation.
Elastomer: natural or synthetic material which, at room temperature, can be stretched under low stress and, upon immediate release of the stress or force, will return quickly to its approximate original dimensions.
Elastomeric: the elastic, rubber-like properties of a material that will stretch when pulled and will return relatively quickly to its original shape when released.
Elastomeric Coating: a coating system which, when fully cured, is capable of being stretched at least twice its original length (100% elongation) and recovering to its original dimensions.
Elongation: the ability of a material (e.g., roofing membrane) to be stretched by the application of a force.
Embedment: (1) the process of installing or pressing-in a reinforcement felt, fabric, mat or panel uniformly into bitumen or adhesive; (2) the process of pressing granules into coating during the manufacture of factory-prepared roofing; (3) the process whereby ply sheet, aggregate, or other roofing components settle into hot- or cold-applied bitumen via the force of gravity.
Emulsion: a dispersion of fine particles or globules in a liquid. (See Asphalt Emulsion and Bitumen Emulsion.)
End Lap: the distance of overlap where one ply, panel, or piece extends beyond the end of the immediately adjacent underlying ply, panel, or piece.
EPDM: Ethylene Propylene Diene Monomer (See also Ethylene Propylene Diene Terpolymer.)
EVT: Equiviscous Temperature
Expansion Cleat: a cleat designed to handle thermal movement of the metal roof panels.
Expansion Joint: a structural separation between two building elements that allows free movement between the elements without damage to the roofing or waterproofing system.
Exposed-Nail Method: a method of asphalt roll roofing application in which all nails are driven into the adhered, overlapping course of roofing. Nails are exposed to the weather.
Exposure: (1) the traverse dimension of a roofing element or component not overlapped by an adjacent element or component in a roof covering.
Eyebrow: a dormer, usually of small size, whose roof line over the upright face is typically an arched curve, turning into a reverse curve to meet the horizontal at either end. Also, a small shed roof projecting from the gable end of the larger, main roof area.
Fabric: a woven cloth or material of organic or inorganic filaments, threads, or yarns used for reinforcement in certain membranes and flashings.
Factory Mutual Research Corporation (FMRC): (commonly referred to as “FM”) a research and testing organization that classifies roofing components and assemblies for their fire, traffic, impact (hail), weathering, and wind-uplift resistance for four major insurance companies in the United States.
Fascia: a vertical or steeply sloped roof or trim located at the perimeter of a building. Typically, it is a border for the low-slope roof system that waterproofs the interior portions of the building.
Fasteners: any of a wide variety of mechanical securement devices and assemblies, including nails, screws, cleats, clips, and bolts, which may be used to secure various components of a roof assembly.
Feathering Strips: tapered wood filler strips placed along the butt ends of old wood shingles to create a relatively smooth surface when reroofing over existing wood shingle roofs. Referred to in some regions of the country as “horse feathers” or leveling strips.
Felt: a flexible sheet manufactured by the interlocking of fibers through a combination of mechanical work, moisture, and heat. Roofing felts may be manufactured principally from wood pulp and vegetable fibers (organic felts), asbestos fibers (asbestos felts), glass fibers (fiberglass felts or ply sheet), or polyester fibers.
Felt Machine (Felt Layer): a mechanical device used for applying bitumen and roofing felt or ply sheet simultaneously.
Ferrule: a small metal sleeve placed inside a gutter at the top. A spike is nailed through the gutter into the fascia board to hold the gutter in place. The ferrule acts as a spacer in the gutter to maintain its original shape.
Field of the Roof: the central or main portion of a roof, excluding the perimeter and flashing.
Field Seam: a splice or seam made in the field (not factory) where overlapping sheets are joined together using an adhesive, splicing tape, or heat- or solvent-welding.
Filler: a relatively inert ingredient added to modify physical characteristics.
Fine Mineral-Surfacing: water-insoluble, inorganic material, more than 50 percent of which passes through a No. 35 sieve. Used on the surface of various roofing materials and membranes to prevent sticking.
Fire Resistance: the ability of a building component to act as a barrier to the spread of fire and confine it to the area of origin.
Fishmouth: (also referred to as an Edge Wrinkle) (1) a half-cylindrical or half-conical shaped opening or void in a lapped edge or seam, usually caused by wrinkling or shifting of ply sheets during installation; (2) in shingles, a half-conical opening formed at a cut edge.
Flaking: detachment of a uniform layer of a coating or surface material, usually related to internal movement, lack of adhesion, or passage of moisture.
Flame Retardant: a substance which is added to a polymer formulation to reduce or retard its tendency to burn. Flammability: the characteristics of a material to burn or support combustion.
Flange: the projecting edge of a rigid or semi-rigid component, such as a metal edge flashing flange, skylight flange, flashing boot, structural member, etc.
Flash Point: the lowest temperature of a liquid at which it gives off vapors sufficient to form an ignitable mixture with air near its surface.
Flashing: components used to weatherproof or seal the roof system edges at perimeters, penetrations, walls, expansion joints, valley, drains, and other places where the roof covering is interrupted or terminated. For example, membrane base flashing covers the edge of the field membrane, and cap flashings or counterflashings shield the upper edges of the base flashing.
Flashing Cement: as used by the roofing industry, an ASTM D 2822 Type II roof cement that is a trowelable mixture of solvent-based bitumen and mineral stabilizers that may include asbestos or other inorganic or organic fibers. Generally, flashing cement is characterized as vertical-grade, which indicates it is intended for use on vertical surfaces. (See Asphalt Roof Cement and Plastic Cement.)
Flashing Collar: (sometimes referred to as a Roof Jack or Flashing Boot) an accessory flashing used to cover and/or seal soil pipe vents and other penetrations through the roof.
Fleece: mats or felts composed of fibers (usually non-woven polyester fibers), often used as a membrane backer.
Flood (Pour) Coat: the surfacing layer of bitumen into which surfacing aggregate is embedded on an aggregate-surfaced built-up roof. A flood coat is generally thicker and heavier than a glaze coat, and is applied at approximately 45-60 pounds per square (2-3 kilograms per meter).
Flood Test: the procedure where a controlled amount of water is temporarily retained over a horizontal surface to determine the effectiveness of the waterproofing.
Fluid-Applied Elastomer: a liquid elastomeric material that cures after application to form a continuous waterproofing membrane.
FM: see Factory Mutual Research Corporation.
Gable: a triangular portion of the endwall of a building directly under the sloping roof and above the eave line.
Gable-Shaped Roof: a single-ridge roof that terminates at gable end(s).
Galvalume®: trade name for a coating, used over metal, that is composed of aluminum zinc for corrosion protection.
Galvanic Action: an electroylic reaction between dissimilar metals in the presence of an electrolyte.
Galvanize: to coat with zinc.
Galvanized Steel: steel coated with zinc for corrosion resistance.
Gambrel: a roof that has two pitches on each side.
Gauge: a measurement of rating metal thickness.
Glass Felt: a sheet composed of bonded glass fibers, suitable for impregnation and coating in the manufacture of bituminous roofing and waterproofing materials, and shingles.
Glaze Coat: (1) the top layer of asphalt on a smooth-surfaced built-up roof membrane; (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. (Also see Flood Coat.)
Granule: (also referred to as Mineral or Ceramic Granule) opaque, natural, or synthetically colored aggregate commonly used to surface cap sheets, shingles, and other granule-surfaced roof coverings.
Gravel: aggregate resulting from the natural erosion of rock.
Gravel Stop: a low profile upward-projecting metal edge flashing with a flange along the roof side, usually formed from sheet or extruded metal. Installed along the perimeter of a roof to provide a continuous finished edge for roofing material. Acts as a bitumen-stop during mop application of hot bitumen along a perimeter edge.
Gutter: a channeled component installed along the downslope perimeter of a roof to convey runoff water from the roof to the drain leaders or downspouts.
Headlap: the distance of overlap measured from the uppermost ply or course to the point that it laps over the undermost ply or course.
Heat Welding: method of melting and fusing together the overlapping edges of separate sheets or sections of polymer modified bitumen, thermoplastics or some uncured thermoset roofing membranes by the application of heat (in the form of hot air or open flame) and pressure. (See Heat Seaming.)
Hem: the edge created by folding metal back on itself.
Hip: the inclined external angle formed by the intersection of two sloping roof planes.
Hip Roof: a roof that rises by inclined planes to form one or more hips.
Hoist: a mechanical lifting device.
Holiday: an area where a liquid-applied material is missing or absent.
“Hot” or “Hot Stuff”: the roofer’s term for hot bitumen.
Humidity: the amount of moisture contained in the atmosphere. Generally expressed as percent relative humidity (the ratio of the amount of moisture [water vapor] actually present in the air, compared to the maximum amount that the air could contain at the same temperature.)
HVAC: heating, ventilating, and air conditioning equipment.
Hydration: the chemical reaction by which a substance (such as Portland cement) combines with water, giving off heat to form a crystalline structure in its setting and hardening.
Hypalon™: a registered trademark of E.I. duPont de Nemours, Inc., for “chlorosulfonated polyethylene” (CSPE). (See Chlorosulfonated Polyethylene.)
ICBO: International Conference of Building Officials. Author of The Uniform Building Code.
Impact Resistance: the ability of a roofing material to resist damage (e.g., puncturing) from falling objects, application equipment, foot traffic, etc. The impact resistance of the roofing assembly is a function of all of its components, not just the membrane itself.
Incline: the slope of a roof expressed either in percent or in the number of vertical units of rise per horizontal units of run. (See Slope.)
Inorganic: any chemical or compound that is derived from minerals, does not contain carbon, and is not classified as organic; being or composed of materials other than hydrocarbons and their derivatives; not of plant or animal origin.
Insect Screen: wire mesh used to prevent insects from entering the building through ventilators, louvers, or other openings.
Insulation: any of a variety of materials designed to reduce the flow of heat, either from or into a building.
Intake Ventilation: the fresh air that is drawn into a passive ventilation system through vents typically installed in the soffit or eave of a roof.
Interlayment: a felt, metal, or membrane sheet material used between courses of steep-slope roofing to improve the weather- and water-shedding characteristics of the primary roof covering during times of winddriven rain and snow. Typically used with wood shakes.
Interlocking Shingles: individual shingles that mechanically attach to each other to provide wind resistance.
Internal Pressure: pressure inside a building that is a function of ventilating equipment, wind velocity, and the number andlocation of openings and air leaks.
Joist: any of the small timbers, metal or wood beams arranged parallel from wall to wall to support a floor, ceiling, or roof of a building.
Laminate: to bond two or more layers of a material together to make a finished product.
Laminated Shingles: see Dimensional Shingles or Architectural Shingles.
Lap: that part of a roofing, waterproofing, or flashing component that overlaps or covers any portion of the same or another type of adjacent component.
Lap Cement: an asphalt-based roof cement formulated to adhere overlapping plies or asphalt roll roofing.
Lap Seam: occurs where overlapping materials are seamed, sealed, or otherwise bonded.
Latex: a colloidal dispersion of a polymer or elastomer in water which coagulates into a film upon evaporation of the water.
Lead: a soft workable metal used for miscellaneous flashings.
Leader Head: see Conductor Head.
Life Cycling Costing: a method of economic analysis that takes into account expected costs over the useful life of an asset.
Lift: the sprayed polyurethane foam that results from a pass. It usually is associated with a certain pass thickness and has a bottom layer, center mass, and top skin in its makeup.
Light Reflectance: the percentage of light that is not absorbed by the surface of a material.
Live Loads: temporary loads that the roof structure must be designed to support, as required by governing building codes. Live loads are generally moving and/or dynamic or environmental, (e.g., people, installation equipment, wind, snow, ice or rain, etc.).
Load Deflection: see Deflection.
Loose-laid Membranes: membranes that are not attached to the substrate except at the perimeter of the roof and at penetrations. Typically, loose-laid membranes are held in place with ballast, such as water-worn stone, gravel, pavers, etc.
Low Temperature Flexibility: the ability of a membrane or other material to remain flexible (resist cracking when flexed), after it has been cooled to a low temperature.
Mansard: a decorative steep-sloped roof on the perimeter of a building.
Mansard Roof: a steeper roof that terminates into a flat roof at its high point. (See Figure 18.)
Masonry: anything constructed of such materials as bricks, stone, concrete blocks, ceramic blocks, or concrete.
Mastic: see Asphalt Roof Cement.
Mat: a thin layer of woven, non-woven, or knitted fiber that serves as reinforcement to the material or membrane.
Material Safety Data Sheets (MSDS): a written description of the chemicals in a product, and pertinent other data including such things as safe handling and emergency procedures. In accordance with OSHA regulations, it is the manufacturer’s responsibility to produce an MSDS and the employer’s responsibility to communicate its contents to employees.
Mechanically-Fastened Membranes: generally used to describe membranes that have been attached at defined intervals to the substrate. Mechanical fastening may be performed with various fasteners and/or other mechanical devices, such as plates or battens.
Membrane: a flexible or semi-flexible material, which functions as the waterproofing component in a roofing or waterproofing assembly, and whose primary function is the exclusion of water.
Metal Flashing: accessory components fabricated from sheet metal and used to weatherproof terminating roof covering edges. Frequently used as through-wall flashing, cap flashing (coping), counterflashing, stepflashing, etc. (See Flashing)
Migration: the absorption of oil or vehicle from a compound into an adjacent porous surface.
Mil: a unit of measure, one mil is equal to 0.001 inches or 25.400 microns, often used to indicate the thickness of a roofing membrane.
Mildew: a superficial coating or discoloring of an organic material due to fungal growth, especially under damp conditions.
Millimeter: a unit of measure equal to one thousandth (0.001) of a meter, or 0.03937 inches.
Mineral-Surfaced Roofing: roofing materials whose surface or top layer consists of mineral granules.
Mineral-Surfaced Sheet: a roofing sheet that is coated on one or both sides with asphalt and surfaced with mineral granules.
Miter: the joint produced by joining two diagonally cut pieces.
Moisture Scan: the use of a mechanical device (capitance, infrared, or nuclear) to detect the presence of moisture within a roof assembly. (See Non-Destructive Testing.)
Mole Run: a meandering buckle or ridging in a roof membrane not associated with insulation or deck joints.
Monolithic: formed from or composed of a single material; seamless.
Monomer: a simple molecule that is capable of combining with a number of like or unlike molecules to form a polymer.
Mopping: the application of hot bitumen, with a roofer’s hand mop or mechanical applicator, to the substrate or to the felts of a bituminous membrane.
Solid Mopping: a continuous mopping of a surface.
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.
Nailer: (commonly referred to as Blocking) a piece or pieces of dimensional lumber and/or plywood secured to the structural deck or walls, which provide a receiving medium for the fasteners used to attach membrane or flashing. Generally, it is recommended that nailers be the same thickness as the adjacent insulation, and may be treated with a non-oil-borne preservative, and be of sufficient width to fully support the horizontal flashing flange of a metal flashing (where used).
Nailing: the application of nails. May be: (1) exposed nailing of roofing wherein nail heads are exposed to the weather; (2) concealed nailing of roofing wherein nail heads are concealed from the weather by an overlapping material.
Neoprene: a synthetic rubber (polychloroprene) used in liquid-applied and sheet-applied elastomeric roof membranes or flashings.
Net Free Vent Area: the area, measured in square inches, open to unrestricted air flow and commonly used as a yardstick to measure relative vent performance.
Non-Destructive Testing (NDT): a method to evaluate the disposition, strength, or composition of materials without damaging the object under test. Typically used to evaluate moisture content in roofing assemblies, the three common test methods are electrical capacitance, infrared thermography, and nuclear back-scatter.
Non-Flammable: liquid having no measurable flash point.
Non-Friable: a material that, when dry, cannot be crumbled, pulverized or reduced to powder by hand pressure.
Non-Traffic Bearing: for waterproofing purposes, a membrane system requiring some form of protection barrier and wearing surface.
Open Valley: a method of valley construction in which the steep-slope roofing on both sides are trimmed along each side of the valley, exposing the valley flashing.
Organic: being or composed of hydrocarbons or their derivatives originating from plant or animal matter.
Organic Felt: an asphalt roofing base material manufactured from cellulose fibers.
Organic Shingle: an asphalt shingle reinforced with material manufactured from cellulose fibers.
Ozone Resistance: the ability of a material to resist the deteriorating effects of ozone exposure.
Pallet: a platform (typically wooden) used for storing and shipping materials.
Pan: the bottom flat part of a roofing panel which is between the ribs of the panel.
Parapet Wall: that part of a perimeter wall immediately adjacent to the roof which extends above the roof.
Penetration: (1) any object passing through the roof; (2) the consistency (hardness) of a bituminous material expressed as the distance, in tenths of a millimeter (0.1 mm), that a standard needle penetrates vertically into a sample of material under specified conditions of loading, time, and temperature.
Percent Elongation: in tensile testing, the increase in the gauge length of a specimen measured at or after fracture of the specimen within the gauge length. Usually expressed as a percentage of the original gauge length.
Perlite: an aggregate used in lightweight insulating concrete and in preformed perlitic insulation boards, formed by heating and expanding siliceous volcanic glass.
Permeability: (1) the capacity of a porous material to conduct or transmit fluids; (2) the amount of a fluid moving through a barrier in a unit time, unit area, and unit pressure gradient not normalized for, but directly related to, thickness.
Phased Application: the installation of separate roof system or waterproofing system component(s) during two or more separate time intervals. Application of surfacings at different time intervals are typically not considered phased application. (See Surfacing.)
Picture Framing: a square or rectangular pattern of buckles or ridges in a roof covering generally coinciding with insulation or deck joints; generally, a function of movement of the substrate.
Pigment: fine solid particles, which are insoluble in the vehicle, used to impart color in a coating.
Pinhole: a tiny hole in a coating, film, foil, membrane, or laminate.
Pipe Boot: prefabricated flashing piece used to flash around circular pipe penetrations.
Pitch-Pocket (Pitch-Pan): a flanged, open bottomed enclosure made of sheet metal or other material, placed around a penetration through the roof, filled with grout and bituminous or polymeric sealants to seal the area around the penetration.
Plastic Cement: a roofing industry generic term used to describe Type I asphalt roof cement that is a trowelable mixture of solvent-based bitumen, mineral stabilizers, other fibers and/or fillers. Generally, intended for use on relatively low slopes — not vertical surfaces. (Also see Asphalt Roof Cement and Flashing Cement.)
Plastic Film: a flexible sheet made by the extrusion of thermoplastic resins.
Plasticizer: a material, frequently solvent-like, incorporated in a plastic or a rubber to increase its ease of workability, flexibility, or extensibility.
Pliability: the material property of being flexible or moldable.
Ply: a layer of felt, ply sheet, or reinforcement in a roof membrane or roof system.
Polyester Fiber: a synthetic fiber usually formed by extrusion. Scrims made of polyester fiber are used for fabric reinforcement.
Polymer: a natural or synthetic chemical compound of high molecular weight, or a mixture of such compounds, formed when monomers (small individual molecules) are combined to form large long-chain molecules.
Polymerization: the process whereby monomers are combined to form large, chainlike molecules.
Polypropylene: a tough, lightweight plastic made by the polymerization of high-purity propylene gas.
Ponding: the excessive accumulation of water at low-lying areas on a roof.
Pop Rivet: a relatively small headed pin with an expandable head for joining relatively light gauge metal.
Positive Drainage: the drainage condition in which consideration has been made during design 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, during ambient drying conditions.
Pourable Sealer: a type of sealant often supplied in two parts, and used at difficult-to-flash penetrations, typically in conjunction with pitch-pockets to form a seal.
Pre-Tinning: coating a metal with solder or tin alloy, prior to soldering or brazing it.
Press Brake: a machine used in cold-forming sheet metal or strips of metal into desired profiles.
Primer: (1) a thin, liquid-applied solvent-based bitumen that may be applied to a surface to improve the adhesion of subsequent applications of bitumen; (2) a material which is sometimes used in the process of seaming single-ply membranes to prepare the surfaces and increase the strength (in shear and peel) of the field splice.
Protected Membrane Roof (PMR): an insulated and ballasted roofing assembly, in which the insulation and ballast are applied on top of the membrane (sometimes referred to as an “inverted roof assembly”).
Puncture Resistance: extent to which a material is able to withstand the action of a sharp object without perforation.
Purlin: horizontal secondary structural member that transfers loads from the primary structural framing.
PVC: Polyvinyl Chloride.
R-Value: the resistance to heat transfer of a material. Insulators have relatively high R values. Units are °F•Ft2•Hr/Btu.
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.
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 inset into a raggle, embedded behind cladding, or be surface mounted.)
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: 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 the same temperature, the relative humidity (RH) is 50 percent.
Replacement: the practice of removing an existing roof system down to the roof deck and replacing it with a new roofing 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.
Resistance, Thermal: the average temperature difference between two defined surfaces of a particular body or assembly when unit thermal transmission in unit time through unit area is established between the surfaces.
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. Most ridge vents are either premanufactured metal or flexible, shingle-over type.
Roll Goods: a general term applied to rolls of roofing felt, ply sheet, etc., which are typically furnished in rolls.
Roll Roofing: smooth-surfaced or mineral-surfaced, coated, prepared felts.
Roof Assembly: an assembly of interacting roof components (includes the roof deck, vapor retarder [if present], insulation, and roof covering).
Roof or Roofer’s 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.
Roof Jack: a metal 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 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 a percent.
Roof System: a system of interacting roof components, generally consisting of membrane or primary roof covering and insulation (not including the roof deck) designed to weatherproof and, sometimes, to improve the building’s thermal resistance.
Roofer: craftsman who applies roofing materials.
Rosin Paper (specifically Rosin-Sized Sheathing Paper): a non-asphaltic paper used as a sheathing paper or slip sheet in some roof systems.
Saddle: a relatively small raised substrate or structure constructed to channel or direct surface water to drains or off the roof. A saddle may be located between drains or in a valley, and is often constructed like a small hip roof or like a pyramid with a diamond-shaped base. (See Cricket.)
Sag: undesirable excessive flow in material after application to a surface.
Saturated Felt: a felt that has been partially saturated with low softening point bitumen.
Scrim: a woven, nonwoven, or knitted fabric, composed of continuous strands of material used for reinforcing or strengthening membranes. Scrim may be incorporated into a membrane by the laminating or coating process.
Sealant: a single- or multi-component polymeric or bituminous-based material used to weatherproof many types of construction joints where moderate movement is expected. The material comes in various grades: pourable, self-leveling, non-sag, gun grade, and cured or uncured tapes.
Sealer: a coating designed to prevent absorption of finish coats into porous surfaces; a coating designed to prevent bleeding.
Seam: a joint formed by mating two separate sections of material. Seams may be made or sealed in a variety of ways, including adhesive bonding, hot-air welding, solvent welding, using adhesive tape, sealant, etc.
Seam Strength: the force or stress required to separate or rupture a seam in the membrane material.
Self-Adhering Membrane: a membrane that can adhere to a substrate and to itself at overlaps without the use of an additional adhesive. The undersurface of a self-adhering membrane is protected by a release paper or film, which prevents the membrane from bonding to itself during shipping and handling.
Self-Drilling Screw: a fastener that drills and taps its own hole during application.
Self-Sealing Shingle: an asphalt shingle containing factory-applied strip or spots of heat sensitive adhesive intended to adhere the overlying shingle once installed on the roof and warmed by the sun.
Self-Tapping Screw: a fastener that forms receiving threads when turned into a previously drilled hole.
Selvage: (1) an edge or edging that differs from the main part of a fabric, granule-surfaced roll roofing or cap sheet, or other material; (2) a specially defined edge of the material (lined for demarcation), which is designed for some special purpose, such as overlapping or seaming.
Selvage Edge: an edge designed for certain sheet good materials, e.g., mineral-surfaced sheets. With mineral surfaced sheets, the surfacing is omitted over a portion of the longitudinal edge of the sheet (e.g., mineral surface cap sheet) in order to obtain better adhesion of the overlapping sheet.
Shear Strength: (in roofing) the stress required to disrupt a seam or bonded joint or attachment by forcing the substrate material to slide out from the overlying material or vice versa.
Shed Roof: a roof containing only one sloping plane. Has no hips, ridges, or valleys.
Sheet Metal Flashing: see Metal Flashing.
Shingle: (1) individual unit of prepared roofing material designed for installation with similar units in overlapping rows or courses on inclines normally exceeding 3:12 slope (25%); (2) to cover with shingles; (3) to apply any roofing material in succeeding overlapping rows or courses similar to shingles.
Shingling: (1) the application of shingles; (2) the procedure of applying shingles or laying parallel felts so that one longitudinal edge of each felt overlaps and the other longitudinal edge of the adjacent shingle or felts underlaps. Felts are normally shingled from a downslope portion of the roof to the upslope portion of the roof area so that runoff water flows over rather than against each felt lap. Felts are also applied in shingle fashion on relatively low slopes.
Shrinkage Crack: in waterproofing, a separation in a material, like a concrete substrate, caused by the inability of the material to resist a reduction in size which occurs during its hardening process, curing process, or both.
Siding: the exterior wall finish material applied to a light frame wood structure.
Silicone-based Water Repellants: any of the organopolysiloxanes (silicone derivative) applied to masonry materials for dampproofing or repelling water.
Sill: the bottom horizontal framing member of an opening, such as below a window or door.
Sill Flashing: a flashing of the bottom horizontal framing member of an opening, such as below a window or door.
Single Coverage: roofing material that provides one layer over the substrate to which it is applied.
Single-Ply Membranes: roofing membranes that are field applied using just one layer of membrane material (either homogeneous or composite) rather than multiple layers.
Single-Ply Roofing: a roofing system in which the principal roof covering is a single layer flexible membrane, often of thermoset, thermoplastic, or polymer modified bituminous compounds.
Single-Ply System: generally, there are six types of single-ply roofing systems: 1) Fully-adhered 2) Loose-laid 3) Mechanically-fastened 4) Partially-adhered 5) Protected membrane roof 6) Self-adhering
Slag: a hard, air-cooled aggregate that is left as a residue from blast furnaces, which may be used as a surfacing material on certain (typically bituminous) roof membrane systems.
Slate: a hard, brittle metamorphic rock consisting mainly of clay minerals, used extensively as dimensional stone for steep roofing, and in granular form as surfacing on some other roofing materials.
Slating Hook: a steep-slope roofing attachment device, shaped like a hook, that can be used for fastening roofing slate.
Slip Sheet: sheet material, such as reinforced kraft paper, rosin-sized paper, polyester scrim, or polyethylene sheeting, placed between two components of a roof assembly (such as between membrane and insulation or deck) to ensure that no adhesion occurs between them, and to prevent possible damage from chemical incompatibility, wearing, or abrasion of the membrane.
Smooth Surfaced Roof: a roof membrane without mineral granule or aggregate surfacing.
Snap-On Cap: a separate cap that snaps on over the vertical legs of some single standing or batten seam metal roof systems.
Soffit: the enclosed underside of any exterior overhanging section of a roof eave.
Soffit Vent: a premanufactured or custom built air inlet source located at the downslope eave or in the soffit of a roof assembly.
Softening Point: the temperature at which bitumen becomes soft enough to flow, as determined by a closely defined method (ASTM Standard test method D 36 or D 3461).
Solder: a lead/tin mixture that is melted and used to bond two pieces of some metals together.
Solvent: liquid used to dissolve or disperse film-forming constituents, and which evaporates during drying and does not become a part of the dried film.
Specification: a statement of requirements for a given job or project. Usually describes products, materials,and processes to be used. A specification may also contain terms of the contract.
Splash Block: a small masonry or polymeric block laid on the ground or lower roof below the opening of a downspout used to help prevent soil erosion and aggregate scour in front of the downspout.
Splice: bonding or joining of overlapping materials. (See Seam.)
Splice Plate: a metal plate placed underneath the joint between two pieces of metal.
Splice-Tape: cured or uncured synthetic rubber tape used for splicing membrane materials.
Split: a rupture (generally linear) or tear in a material or membrane resulting from tensile forces.
Split Sheet: see Nineteen-Inch Selvage.
Split Slab: a term used to describe two separate concrete slabs. The first is placed as a slab-on-grade or suspended slab, and covered with waterproofing and a drainage system. The second slab, also referred to as a topping slab, is then placed over the underlying slab and waterproofing.
Sprayed Polyurethane Foam (SPF): a foamed plastic material, formed by spraying two components, PMDI ([A] component) and a resin ([B] component) to form a rigid, fully adhered, water-resistant, and insulating membrane.
Sprinkle Mopping: see Mopping.
Spunbond: a type of nonwoven fabric formed from continuous fiber filaments that are laid down and bonded continuously, without an intermediate step.
Square: 100 square feet (9.29 m2) of roof area.
Square-Tab Shingles: shingles with tabs that are all the same size and exposure.
Standing Seam: a metal roof system that consists of an overlapping or interlocking seam that occurs at an upturned rib. The standing seam may be made by turning up the edges of two adjacent metal panels and overlapping them, then folding or interlocking them in a variety of ways.
Starter Course: the first layer of roofing, applied along a line adjacent to the downslope perimeter of the roof area. With steep-slope watershedding roof coverings, the starter course is covered by the first course.
Starter Sheets: (1) felt, ply sheet, or membrane strips that are made or cut to widths narrower than the standard width of the roll, used to start the shingling pattern at an edge of the roof; (2) particular width sheets designed for perimeters in some mechanically attached and fully adhered single-ply systems.
Starter Strip: roll roofing or shingle strips applied along the downslope eave line, before application of the first course of roofing, intended to fill spaces between cutouts and joints of the first course.
Static Load: any load, as on a structure, that does not change in magnitude or position with time.
Steel Joist (open web steel joist): normally used as a horizontal supporting member between beams or other structural members, suitable for the support of some roof decks.
Steep Asphalt: Type III Asphalt. (See Asphalt.)
Steep-Slope Roof: a roof of suitable slope to accept the application of water shedding roofing materials.
Steep-Slope Roofing: a category of roofing that includes water shedding types of roof coverings installed on slopes exceeding 3:12 or 25%.
Steeple: a tower or spire, usually located on a church.
Step Flashing: individual pieces of material used to flash walls, around chimneys, dormers, and such projections along the slope of a roof. Individual pieces are overlapped and stepped up the vertical surface.
Strain: the dimensionless expression for the elongation of a material under stress. Strain is expressed as the ratio of elongation per unit length.
Strapping (felts): a method of installing roofing rolls or sheet good materials parallel with the slope of the roof.
Straw Nail: a long-shanked nail. Sometimes used for fastening over tile at hips and ridges.
Stress: the internal resistance of a material to a force, measured as a force per unit area.
Stress-Crack: external or internal cracks within a material caused by long-term stress. Environmental factors, such as contact with corrosive material, usually accelerate stress-cracking.
Strike-Through: a term used in the manufacture of fabric-reinforced polymeric sheeting to indicate that two layers of polymer have made bonding contact through the scrim or reinforcement.
Strip Mopping: see Mopping.
Strip Shingles: asphalt shingles that are manufactured in strips, approximately three times as long as they are wide.
Structural Panel: a panel designed to be applied over open framing in which a structural deck is not required.
Styrene Butadiene Rubber: high molecular weight polymers having rubber-like properties, formed by the random copolymerization of styrene and butadiene monomers.
Styrene Butadiene Styrene Copolymer (SBS): high molecular weight polymers that have both thermoset and thermoplastic properties, formed by the block copolymerization of styrene and butadiene monomers. These polymers are used as the modifying compound in SBS polymer modified asphalt roofing membranes to impart rubber-like qualities to the asphalt.
Substrate: the surface upon which the roofing or waterproofing membrane is applied (e.g., in roofing, the structural deck or insulation).
Sump: an intentional depression around a roof drain or scupper that serves to promote drainage.
Surface Erosion: the wearing away of a surface due to abrasion, dissolution, or weathering.
Surfacing: the top layer or layers of a roof covering, specified or designed to protect the underlying roofing from direct exposure to the weather.
Synthetic Rubber: any of several elastic substances resembling natural rubber, prepared by the polymerization of butadiene, isoprene, and other unsaturated hydrocarbons. Synthetic rubber is widely used in the fabrication of single-ply roofing membranes.
Tab: the exposed portion of strip shingles defined by cutouts. (See Figure 25.)
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.
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.”
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 maximum force (longitudinal pulling stress) a material can bear without tearing or breaking apart.
Termination: the treatment or method of anchoring and/or sealing the free edges of the membrane in a roofing or waterproofing system.
Terra Cotta: low-fired clay, either glazed or unglazed.
Thatch Roof: the covering of a roof usually made of straw, reed, or natural foliage (palms) bound together to shed water.
Thermal Barrier: a material applied over polyurethane foam designed to slow the temperature rise of the foam during a fire and delay its involvement in the fire. Thermal barriers for use with SPF must have a time rating of not less than 15 minutes.
Thermal Insulation: a material applied to reduce the flow of heat.
Thermal Shock: the stress-producing phenomenon resulting from sudden temperature changes in a roof membrane when, for example, a cold rain shower follows brilliant hot sunshine, which may result in sudden cooling or rapid contraction of the membrane.
Thermal Stress: stress introduced by uniform or non-uniform temperature change in a structure or material that is contained against expansion or contraction.
Thinner: a liquid used to reduce the viscosity of coatings or mastic. Thinners evaporate during the curing process. Thinners may be used as solvents for clean-up of equipment.
Through-Wall Flashing: a water-resistant material, which may be metal or membrane, extending through a wall and its cavities, positioned to direct water entering the top of the wall or cavity to the exterior, usually through weep holes.
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.
TPO: Thermoplastic Olefin.
Traffic Bearing: in waterproofing, a membrane formulated to withstand a predetermined amount of pedestrian or vehicular use with separate protection and a wear course.
Ultraviolet (UV): (1) situated beyond the visible spectrum, just beyond the violet end, having wavelengths shorter than wavelengths of visible light and longer than those of X-rays; (2) relating to, producing, or employing ultraviolet radiation.
Underlayment: an asphalt-saturated felt or other sheet material (may be self-adhering) installed between the roof deck and the roof system, usually used in a steep-slope roof construction. Underlayment is primarily used to separate the roof covering from the roof deck, to shed water, and to 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.
Valley: the internal angle formed by the intersection of two sloping roof planes.
Vapor Retarder: material installed to impede or restrict the passage of water vapor through a roof assembly.
Vent: an opening designed to convey air, heat, water vapor or other gas from inside a building or a building component to the atmosphere.
Ventilation Short Circuit: (as it relates to a passive ventilation system where the system is designed for air flow between intake and exhaust vents) a ventilation short circuit occurs when air is introduced into the ventilation system from an area higher than the intake vent thereby minimizing or defeating the effectiveness of the intake vent. One example can be a gable vent in a soffit-to-ridge ventilation system. Air intake from the gable vent can short circuit the stack-effect draw of air through the soffit vents, and interrupt the thorough venting of the roof cavity.
Ventilator: an accessory that is designed to allow for the passage of air.
Void: an open space or break in consistency.
Vulcanization: any of various processes by which natural or synthetic rubber or other polymeric materials may be cured or otherwise treated (i.e., exposed to chemicals, heat, or pressure) to render them non-thermoplastic, and which improve their elastic and physical properties.
Water Absorption: the amount of water absorbed by a material after immersion for a prescribed period of time. May be expressed as a percentage of the original weight of the material.
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.
Wear Course: the top layer of surfacing that carries pedestrian or vehicular traffic. Sometimes referred to as wearing surface.
Weather Infiltration: the negative condition where rain or snow penetrate the roof. The condition is typically wind-driven.
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.
Wicking: the process of moisture movement by capillary action, as contrasted to movement of water vapor.
Wind Load: force exerted by the wind on a structure or part of a structure.
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. This force is then transmitted to the roof surface. Uplift may also occur because of the introduction of air pressure underneath the membrane and roof edges, where it can cause the membrane to balloon and pull away from the deck.
Wire Tie System: a scheme of attachment for steep-slope roofing units (e.g., tile, slate, and stone) utilizing fasteners (nails and/or screws) in conjunction with wire to make up a concealed fastening system.
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.
Zinc: a metal that has application considerations including high expansion-contraction rates and low-temperature Restrictions.