Absorption: A material’s ability to take in gases or liquids and incorporate them within its body.

Accelerated Weathering: When materials in a controlled environment have exposure to heat, light, water, or condensation in an altered state so that their effects get magnified, they tend to weather at a rapid pace. After this accelerating weathering process, the exposed material’s physical properties will be compared to those of the original unexposed material or that which has gone through natural weathering.

Adhere: When two surfaces bond together, it is called adhesion — for example, asphalt layers and cement membranes in BUR roofing.

Aggregate: Materials like stone, crushed stone, rock, water-worn gravel, crushed slag, or marble chips make up the top surface or as ballast in a roofing system.

Aging: Environmental effects on roofing materials that appear with time.

Alligatoring: Bitumen layers on a built-up roofing system produce a series of cracks that resemble an alligator’s hide on the surface or even the inner layers.

Aluminum: Rust-resistant metal used for flashing and in metal roofing systems.

Ambient Temperature: The temperature of the environment or air around an object.

Application Rate: The quantity of material- volume, mass, or thickness- used per unit area.

Apron Flashing: The flashing applied at the joint where the sloped roof connects to a much steeper roof or the vertical wall.

Architectural Shingle: A high-quality dimensional shingle that beautifies the roof appearance.

Asphalt: Sometimes known as bitumen, it is a highly viscous and sticky brown or black material found as a residue after crude oil or petroleum processing.

Asphalt Emulsion: Asphalt cement components are made less viscous in blending machinery, by adding water and emulsifying agents like bentonite clay.

Asphalt Felt: A uniform flexible felt made with asphalt-saturated material.

Asphalt Roof Cement: A solvent-based asphalt or bitumen used to apply on cracks and glue down loose shingles or other fibers to the roof surface.

Attic: Ventilated cavity or open space in the interior of the property, under a steep-sloped roof deck and above the ceiling.


Back-Nailing: A roofing felt is fastened with nails, connecting it to the next sequential ply or roof to secure it properly and protect it from slippage and weather exposure.

Ballast: An anchoring material that provides stability to the roof structure. It could be heavy substances like aggregates or concrete pavers, which keep the roof membranes in place.

Barrel Vault: A tunnel or vault made of a series of circular or rounded architectural elements that form the ceiling of a building.

Base Flashing: Flashing applied at the intersections of roof and wall or roof and vertical junctures to seal the joints and make them waterproof.

Base Ply: The first ply laid on the roof deck, which becomes the base membrane.

Base Sheet: In a multilayer or built-up roofing system, the base sheet is the bottom-most ply or membrane that is a waterproof, saturated, impregnated, or coated felt.

Batten: Battening or roofing lath can be a metal, wood, or plastic cap or closure set that covers the joints between adjacent panels. Usually, this is fixed over the roof deck to attach tiles, shingles, or base flashing in place.

Batten Seam: A traditional roof covering technique where a metal panel profile runs parallel to the roof, formed around a metal batten.

Bitumen: a black colored, highly viscous, and a semi-solid mixture of hydrocarbons obtained in the petroleum distillation process. This compound is found in asphalt, coal tars, pitches, and wood tars.

Blackberry: Typically, a tar boil that appears on the flood coating of the aggregate-surface in a BUR system.

Blind-Nailing: Driving nails into a finished roof at an angle so that they are not exposed to adverse weather conditions.

Blister: Small bubbles in the roofing membrane occurring due to trapped moisture, enclosed air pockets, loose adhesion, or improper installation of the roofing layers.

Blocking: Wood rafters built into the roofing system provide a stop for ceiling insulation. They lie below the flashing and above the roof deck, and act as a support to the curb.

BOMA: Building Owners & Managers Association

Brake: Manual or mechanical handling machinery that presses the metal.

British Thermal Unit (BTU): A traditional unit of thermal energy, equal to around 1055 joules. It is the quantity needed to increase the temperature of one pound of water by one degree Fahrenheit.

Brooming: The process of embedding a roofing ply material into a layer of hot bitumen with the help of a broom or squeegee. This process smoothes out the ply, making it adhere to the bitumen.

Buckle: A visible, elongated and upward lump that forms due to some movement in the roofing assembly or displacement in the roof deck joints or insulation.

Building Code: A set of regulations and ordinances with which a roofing structure must comply. A recognized agency in a designated jurisdiction prescribes the design loads, construction details, quality of materials, and procedures that must be followed for structures in that area.

Built-Up Roof Membrane (BUR): Multiple layers of fabrics, mats, coated, or saturated felts applied between alternating layers of bitumen form a continuous and semi-flexible roof membrane. The top surface of built-up roof membranes consists of bitumen and mineral aggregate or a granule-surfaced cap sheet.

Bundle: Shakes or shingles available in individual packages.

Butt Joint: Separate sections like materials of insulation, when placed adjacent to each other,  without overlapping, create a butt joint.

Button Punch: A button punch indents several thicknesses of metal pieces pressed together to secure them in place and to prevent slippage.

Butyl: An elastomeric polymer or synthetic rubber, a copolymer of isobutylene and isoprene. Used as primary binders, adhesives, and modifiers, it is available in sheet form, or as elastomeric blends.

Butyl Coating: An elastomeric roof restoration solution that prevents rust, seals metal roofs, and acts as a vapor barrier.

Butyl Rubber: An elastomer rubber based on isobutylene-isoprene copolymer. This high-performance product is impermeable to gases and moisture.

Butyl Tape: A high-performance butyl rubber compound used as an adhesive for metal roof panel seams, end laps and to seal other sheet metal joints.


Camber: A slight convexity or curve of the roof deck surface, arch, or truss.

Canopy: An overhead roof, usually unsupported at the end, that is a projecting structure which protects the entrances or doors from sun, rain, hail, or snow.

Cant: Foam, wood, or other material in a beveling angle placed perpendicularly for joint strength and water runoff.

Cant Strip: A beveled and triangular-shaped material placed at the joining between a roof or an insulating and waterproof material and a vertical wall, so that the roof does not bend sharply and to facilitate the flow of water.

Cap Flashing: Flashing made of metal, which covers or shields the exposed and upturned edges of various building components like the base flashing and prevents water intrusion.

Cap Sheet: A multilayer sheet made of asphalt, tar, or fiberglass, used to create a water-tight surface. Also known as reinforced bitumen membranes, these are gravel coated surfaces and are used as the top plies.

Capillary Action: The movement of water or liquids between adjacent surfaces in contact, like panel side laps, due to surface tension.

Caulking: sealing a joint, seam, void, or juncture between two adjacent units using a sealant, and making it weather-tight.

Cavity Wall: A double wall with two vertical layers built with the purpose to create an air space within the structural framing. It has a lower heat-flow rate and allows moisture to drain.

CCF: 100 cubic feet.

Chalk: A powdery residue used to mark lines on the roof material.

Chalk Line: A line marked on the roof by snapping a taut string dusted with colored chalk; done for alignment purposes – for laying of shingles, etc.

Chalking: Residue that forms over time, on a roofing material – the degradation of paints, or coatings on a metal surface.

Chimney: A pipe projecting through the roof, made of stone, prefabricated metal, or wood, which allows for smoke and combustion gases from the interior to escape into the air.

Cladding: Roof cladding is a material that becomes the exterior layer of a building; it provides weather resistance and thermal insulation.

Cleat: A metal strip made of continuous or individual clips or plates, angled and used to secure roofing components together.

Closed-Cut Valley: A method of application of shingles where you extend them across the valley. The shingles on the other side of the valley get trimmed by about 2 inches from the centerline.

Closure Strip: Sections made of metal or any flexible material like neoprene foam seal the raised openings formed between metal sheets, panels, and flashings.

Coal Tar: A thick, black or brown colored, high-viscous hydrocarbon liquid formed as a by-product of the distillation of coal to make coke and coal gas. Refined coal tar pitch is an ingredient of built-up roof membranes.

Coal Tar Bitumen: For low-slope BURs or dead-level built-up roof membranes, Type III coal tar that conforms to ASTM D 450 is used for waterproofing and dampproofing. Coal Tar Bitumen is its proprietary trade name.

Coal Tar Pitch: Type I or Type III coal tar that conforms to ASTM D 450 used as the waterproofing agent for dead-level or low-slope BURs.

Coal Tar Waterproofing Pitch: Type II coal tar pitch that conforms to ASTM D 450, used in below-grade structures for waterproofing.

Coated Base Sheet: Asphalt impregnated or filled felt, which is later coated with more viscous and harder asphalt to make it more impermeable to moisture.

Closed-Cut Valley: A method of application of shingles where you extend them across the valley. The shingles on the other side of the valley get trimmed by about 2 inches from the centerline.

Closure Strip: Sections made of metal or any flexible material like neoprene foam seal the raised openings formed between metal sheets, panels, and flashings.

Coal Tar: A thick, black or brown colored, high-viscous hydrocarbon liquid formed as a by-product of the distillation of coal to make coke and coal gas. Refined coal tar pitch is an ingredient of built-up roof membranes.

Coal Tar Bitumen: For low-slope BURs or dead-level built-up roof membranes, Type III coal tar that conforms to ASTM D 450 is used for waterproofing and dampproofing. Coal Tar Bitumen is its proprietary trade name.

Coal Tar Pitch: Type I or Type III coal tar that conforms to ASTM D 450 used as the waterproofing agent for dead-level or low-slope BURs.

Coal Tar Waterproofing Pitch: Type II coal tar pitch that conforms to ASTM D 450, used in below-grade structures for waterproofing.

Coated Base Sheet: Asphalt impregnated or filled felt, which is later coated with more viscous and harder asphalt to make it more impermeable to moisture.

Coated Fabric: Fabrics coated and/or impregnated with a solution, powder, or molten, of protective acrylic, plastic, or similar material. The calendering process also results in coated fabrics, which have a top coat of a preformed film.

Coated Felt (Sheet): (1) an asphalt-impregnated felt coated with a more viscous and harder “coating” asphalt on both sides; (2) a glass fiber sheet simultaneously coated and saturated on both sides with asphalt.

Coating: Top layer that covers a surface to increase protection or for decoration, and then cured until it achieves an elastomeric consistency. Materials used for SPF can be liquids, semi-liquids, or roof mastics generally applied using a roller or brush or sprayed onto the surface.

Cohesion: The ability of the molecules of a substance to bond with other molecules of the same.

Cold Process Built-Up Roof: Alternating layers of roof cement applied with asphalt-solvent liquid and plies of felts, other reinforced sheets, or fabrics, laminated together with adhesives installed at slightly elevated temperature form a semi-flexible and continuous roof membrane.

Combustible: The ability of a substance to catch burn.

Compatible Materials: Two materials are compatible with each other when they have the ability to blend or attach without causing adverse reactions to the materials.

Composition Shingle: A unit of shingle roofing with an asphalt composition on the outer layer and on the underside, it has a fiberglass reinforcing mat that makes it waterproof.

Concealed-Nail Method: A method of application of asphalt roll roofing material where the nails are fastened to the underlying roofing and concealed by a cemented, overlapping course.

Condensation: The process where water vapor or any other gaseous substance converts into its liquid state with a drop in temperature drops or a rise in atmospheric pressure. (Also see Dew Point.)

Conductor Head: A custom fabricated part of the roof plumbing that is installed to the gutter system, lying between the downspout and a through-wall scupper. It acts as a catch basin for the run-off water downspout.

Contact Cements: Bonding material used to adhere to various roofing components. Contact cements or adhesives effectively create a permanent bond between the components immediately.

Contamination: Making surfaces or materials unclean or impure by adding undesirable foreign substances and rendering them unsuitable for its intended purpose.

Coping: A specially designed piece, typically made of masonry, stone, or metal, which covers the top of a wall that is exposed to the elements and protects the walls and flashing from moisture intrusion.

Copper: A malleable, ductile, and natural weathering metal, an important component used in metal roofing; usually of 16 or 20 ounces per sq.ft thickness.

Cornice: An ornamental horizontal molding located just below the roof, a projected roof overhang.

Counterflashing: Metal sheeting or barrier installed at the intersection of the roof and vertical walls, chimneys, or any vertical surface, to protect the flashing and associated fasteners from weather exposure and water infiltration.

Course: (1) A row of shingles installed on the roofing material; (2) number of layers of materials applied onto a roof surface (e.g., a five-course wall flashing consists of three layers of roof cement, each sandwiched by a layer of felt or fabric).

Coverage: The surface area where a particular roofing material is applied.

Cricket: A ridge structure in the roof or an elevated substrate constructed behind a chimney or a vertical wall to divert water away and prevent roof leaks. (See Saddle.)

Cross Ventilation: A natural cooling effect obtained when warm interior air escapes through a roof cavity and allows cool exterior air in through the vents.

Cupola: A dome-like structure crowning the ridge of the roof to increase ventilation.

Curb: (1) A roof member on an elevated level than the roof surface, which supports skylights, hatches, mechanical equipment, and more; (2) can also be a prefabricated raised roof perimeter that is relatively low in height.

Cure: A process in which a material is made to form permanent molecular bonds by exposing it to heat, pressure, chemicals, and/or weathering.

Cure Time: The time required for the curing process in which a material reaches its desirable physical characteristics, which it retains for a long while.

Cutoff: A permanent seal designed to isolate roofing sections and prevent lateral water movement in the insulation system. (Note: Not to be confused with a tie-off, which is either temporary or permanent.) (See Tie-Off.)

Cutout: The open gaps between the tabs of a strip shingle.


Dead Level: Also referred to as a zero-slope roof, the dead level is essentially a horizontal or flat roof deck that has no slope or slanting.

Dead Loads: Permanent non-moving loads on a roof resulting from the combined weights of structural and architectural components of a building. Mechanical and electrical equipment installed on the roof assembly is also “dead weights” or “deadweight loads.”

Deck: Roof deck of a building is the structural component that safely supports the design loads – both live and dead – including the roof systems and any additional live load requirements found in the building codes. The deck may be either non-combustible (e.g., concrete, gypsum, or corrugated metal) or combustible (e.g., wood or plywood.) It provides the substrate for waterproofing layers and the insulation system to be applied.

Deflection (Bowing, Sagging): Excessive load on the roof causes a downward displacement in its structure.

Delamination: A tear-off caused by trapped moisture between the laminated layers of a roof system.

Design Loads: The building has to be designed as per design loads – the specifications recommended by the federal, state, county, or city agencies.

Dew Point Temperature: The specific temperature where water vapor condenses and turns into liquid. At this point, the air has a relative humidity of 100% and condensation forms.

Dome: A curved roof of a hemispherical shape, oval, or other circular variations.

Dormer: A vertical framed projection constructed through and beyond the sloping roof.

Double Graveling: In tar-and-gravel roof systems or BURs, two layers of bitumen and gravel is applied. After the first coating is applied, loose aggregate will be swept away from the surface before the application of the second layer of bitumen and aggregate. This process ensures that approximately 50% of the applied second aggregate layer adheres to the bitumen flood coat permanently unless physically removed.

Double Lock Standing Seam: A standing seam between two panels that features an overlapping interlock, creating a double fold. (See Standing Seam.)

Downspout: A vertical pipe or other conduit attached to the side of the building that carries runoff water from a scupper, gutter, or conductor head to the ground, a lower level in the roof, or stormwater runoff system.

Drain: A device that collects the runoff water from the downspout and directs it away from the building.

Drip Edge: A metal sheet or other component overhanging the edge of the roof. It has an outward projecting metal flange which controls the flow of dripping water away from the underlying building components and protects them. A drip edge prevents capillary action by breaking the contact between wall components and the roof perimeter.

Dynamic Load: A non-static load that is changing its position, size, or direction, e.g., wind load.


Eave: Edge of a roof that overhangs the wall and projects beyond the side of the building.

Efflorescence: White-colored crystalline deposits left behind on the surface of stone, concrete, brick, or other surfaces when water evaporates from the masonry and salt remains. Adjacent concrete, grout, or mortar may also release free alkalies to form efflorescence.

Elastomeric Coating: A high build coating system that can be applied to the interior and exterior walls and helps protect masonry surfaces. When fully cured, the elastomeric coating has the capability of 100% elongation and can recover to its original dimensions.

EPDM: Ethylene Propylene Diene Monomer (See also Ethylene Propylene Diene Terpolymer.)

Expansion Joint: A structural assembly designed to facilitate the free movement between two building elements and withstand heat-induced expansion and reduction without causing any damage to the roof or waterproofing system.

Exposed-Nail Method: A method of application of asphalt roll roofing where the nails are visible and exposed to the weather. Nails are fastened to the cemented overlapping course.

Exposure: (1) The part of the roofing component that is open to weather and not overlapped by another component of the roofing system. For example, to compute the exposure of a ply in a shingled, four-ply BUR membrane, divide the felt width 36 inch (914mm) by the number of shingled plies to get the individual felt width and remove 2 inches (51mm) to get the exposure of wide felt, which is approximately 8 1/2 inches (216mm); (2) The unconcealed portion of the sidewall that is not overlapped by the upslope side of the roof, which is 5 inches (127mm) for a standard-size, 3-tab shingle roof.

Extrusion: A manufacturing process where batched and formulated molten material is forced through an orifice known as “die.” The finished product varies in shape and size, depending on the shape and dimensions of this die. Extrusion is used to manufacture a few types of single-ply roofing membranes.

Eyebrow: A small-sized dormer, whose roofline that projects beyond the upright face is in an arched shape and turns into a reverse curve before it meets the horizontal on both ends. Also, a shed roof projecting from the main roof area at the gable end.


Fabric: Reinforcement material used in certain membranes and flashings; a cloth or other material woven with organic or inorganic threads, yarns, or filaments.

Factory Seam: Manufacturer seam/splice is a large sheet made in a process that involves assembling various sections of materials.

Fading: Initial color of a substance wears off with time.

Fascia: A horizontal band that runs beneath the roof exterior, at the ends of the rafters. It disguises attic ventilation, prevents intrusion from birds, or pests, and keeps the interior of the building dry and comfortable.

Fasteners: Nails, screws, bolts, clips, and many other mechanical devices which are used to secure a variety of roofing assembly components.

Felt: Roofing felts are company manufactured flexible sheets made from interlocking various kinds of fibers. A combination of heat, moisture, and mechanical methods are used to make glass, organic, asbestos, or polyester felts from fiberglass, wood pulp, vegetable, asbestos, or polyester fibers.

Ferrule: A part of spike and ferrule gutter hanger combination. Ferrule is a metal sleeve fit inside a gutter when it is fastened to the fascia with spikes. It retains the shape of the gutter and keeps it from getting battered.

Fiberglass Insulation: A rigid board or blanket insulation made by binding faced or unfaced glass fibers together for wall or attic roof insulation. The rigid board traps cold air and heat from being transferred to and from the home exteriors.

Field of the Roof: The main roof area, excluding the flashing and perimeter.

Fishmouth: (Also known as Edge Wrinkle) (1) Distortions caused due to the aging of the roof shingles or wrinkling of ply sheets, which lead to half-cylindrical or half-conical shaped voids or gaps in the seams; (2) Upward curling of shingles occurring over a butt-joint or at a cut edge; sign of asphalt shingle roof wear.

Flaking: Delamination of the uniform coating layer or any roof surface material as a result of internal movement, aging, lack of adhesion, or moisture intrusion.

Flame Retardant: A fire-resistant substance added to a polymer formulation so that fire cannot penetrate the roof or reduce its tendency to burn.

Flange: The projecting rim or collar of a rigid or semi-rigid roof component, e.g., metal edge flashing flange, flashing boot, skylight flange, or structural member.

Flash Point: The lowest temperature at which the vapor of a volatile material or liquid starts combusting in the presence of an ignition source.

Flashing: A thin, water-impervious material used to seal off the ends of roof covering at the walls, perimeters, field membranes, expansion joints, drains, and other places. For instance, cap flashings help weatherproof the upper edges of the base flashing.

Flashing Cement: The roofing industry terms the ASTM D 2822 Type II roof cement typically characterized as vertical-grade flashing cement – intended for vertical surfaces. This trowelable mixture comprises mineral stabilizers and solvent-based bitumen and includes inorganic or organic fibers.

Flashing Collar: (also known as a Flashing Boot or Roof Jack) A flashing component used to cover soil pipe vents and/or seal other types of roof penetrations.

Flat Lock: An interlocking method for metal panels where a panel edge folds back over itself, while the other panel folds under, and then these two panels get hooked together.

Flood Coat: (Also, Pour Coat) A flood coat is a bitumen surfacing layer of a BUR roofing system, into which the surfacing aggregate gets embedded. Compared to a glaze coat, this is generally thicker and heavier, with an application rate of about 45-60 pounds per square.

Flood Test: A test procedure to determine the waterproofing levels of a horizontal roof surface. This method requires temporary retention of water in a controlled amount.


Gable: The top portion of the end wall that is above the eave line and under the sloping roof slope forms a triangular-shaped gable.

Gable-Shaped Roof: Also called a pitched roof, it is a single-ridge roof consisting of two roof sections sloping in the opposite directions and meeting at the gable ends.

Galvalume ®: A proprietary steel coating for corrosion protection; it is composed of aluminum, silicon, and zinc.

Galvanic Action: When two electrochemically dissimilar metals come in contact with each other in the presence of an electrolyte, bimetallic corrosion occurs, and ions move from one metal to the other.

Galvanize: The process of coating a metal with a layer of zinc.

Galvanized Steel: Steel is coated with a protective layer of zinc to make it corrosion resistant.

Gambrel: A two-sided, pitched symmetrical roof with two slopes on each side. The upper slope has a shallow angle, while the lower slope is much steeper.

Granule: (also known as Ceramic or Mineral Granule) Colored, opaque surfacing aggregates, either natural or synthetic substances, used for shingles, cap sheets, and other granulated roofing systems.

Gravel: Small stone aggregates or particles obtained from rock as a result of natural erosion.

Gravel Stop: An upward-projecting sheet or extruded metal edge flashing attached to the roof side with a flange. It provides a continuous finished roof edge, stops gravel and bitumen from falling over the perimeter edge, and prevents water penetration.

Gutter: A water collection channel installed below and along the perimeter of a roof to divert rainwater and runoff water to the drain pipes or downspouts.


Heat Welding: Also known as butt-welding or heat fusion, it is a process of heat application via open flame or hot air. Separate sections of thermoplastic, thermoset, or polymer-modified bitumen roofing membranes are melted and fused to form a highly durable roofing membrane.

Hem: The roof edge created when the metal folds back on itself.

Hip: The external angle of inclination between two adjacent sloping roof sections.

Hip Roof: A roof that has no vertical ends, and has inclined slopes that form a hip structure.

Hoist: a mechanical lifting device.

Hot or Hot Stuff: Hot bitumen, commonly referred by roofers.

Humidity: Moisture levels in the atmosphere. Percent relative humidity denotes the ratio of water vapor contained in the air when compared to the maximum amount that can be contained in the air at a given temperature.

HVAC: Common term for heating, ventilating, and air conditioning systems.


Ice Dam: Ice build-up formed on the eaves of the roof, which prevents the snow from melting and getting drained. It is a result of the refreezing of meltwater that overhangs a steep roof and causes water intrusion under roofing materials.

Ignition Temperature: When a combustible solid, liquid, or gas is heated, the lowest temperature at which it starts to burn and continues to do so, irrespective of the presence of an ignition source.

Impact Resistance: The impact resistance of roofing material is its ability to resist damage when it is dropped, or other objects fall on it. For a roofing assembly, impact resistance is the collective ability of the entire components to absorb energy without breaking.

Impregnate: Saturating or coating the fibers of a base roof felt or a reinforcing fabric with asphalt or other enveloping liquid materials to achieve higher durability or waterproofing.

Infrared Thermography: A popular method of roof system analysis that makes use of an infrared camera to detect moist insulation or leaks, by measuring the temperature differential of the roof surface.

Inorganic: Any chemical compound that does not contain a carbon atom bonded to hydrogen. Most salts that are composed of or derived from materials, most single elements, and all metals are inorganic; also, the substances that are not of animal or plant origin.

Interlocking Shingles: Individual shingles that feature interlocking mechanisms, to provide wind uplift resistance, and longer life.

Inverted Roof Membrane Assembly (IRMA TM): A patented, proprietary “Protected Membrane Roof Assembly” owned by the Dow Chemical Company, along with Styrofoam ® Brand Insulation. Styrofoam ® and ballast are laid over the roof membrane, in an extended version of the conventional roof membrane assembly. This is done to withstand extensive roof traffic, extreme weather conditions, or site-specific hazards.


Joist: Parallel horizontal beams, either wood or metal, or any small timber running between opposite walls; load bearing planks that provide support to both the ceiling and the floor above.


Lap: The portion of any roofing component, waterproofing, or flashing material that overlaps with the adjacent part of the same or different kind.

Lap Cement: An asphalt-based adhesive roof cement that is used to overlap plies or roll roofing materials.

Lap Seam: Lap seam forms when the overlapping materials are bonded, seamed, or sealed.

Latex: A film formed by colloidal dispersion polymerization in an aqueous medium, following the evaporation of water.

Lead: A soft, highly dense, and malleable metal with a low melting point; it forms complex shapes and used as a flashing material.

Live Loads: Temporary load attachments applied to the roofing structure over its lifetime. A roof has to be designed to support live loads mentioned by governing building codes. These loads can be dynamic (e.g., people, installation equipment) or environmental (e.g., wind, snow, rain).

Loose-laid Membranes: Roofing membranes or layers that are fastened to the substrate only at the penetrations through the roof and the edges. Ballast loose-laid membranes are attached with gravel, water-worn stone, pavers, etc.


Mansard: A decorative symmetrical steep-sloped roof on the edge of a building.

Mansard Roof: A four-sided steeper roof with two slopes on each side, with dormer windows, terminating into a flat roof at the highest point.

Mechanically-Fastened Membranes: Roof membranes attached to the substrate using mechanical fasteners. Layers are fastened at defined intervals using plates, battens, or other mechanical devices.

Membrane: A thin protective material, either flexible or semi-flexible, which is added to the roofing assemblies for waterproofing.

Metal Flashing: Fabricated sheet metal components used as roof accessories to weatherproof perimeter roof coverings. Frequently used for chimneys, skylights, ridges, vents, and more, as cap flashing, through-wall flashing, step flashing, and others.

Meter: Standard measurement unit of length in the metric system; equal to 100 centimeters or 39.37 inches.

Mil: A unit of measurement, equal to one-thousandth of an inch or 25.400 microns, indicates the thickness of roofing membranes.

Mildew: A superficial fungal growth appearing on the roof or walls due to damp conditions. A discolored coating of organic material.

Millimeter: A Metric unit of measurement, equal to 0.03937 inches or one-thousandth of a meter.

Mineral-Surfaced Roofing: Asphalt roll roofing materials whose top layers are covered with mineral granules.

Mineral-Surfaced Sheet: A roofing sheet coated with asphalt on one or both sides and layered with mineral granules.

Miter: Two diagonally cut pieces, either on the main surface (at 45 degrees) or the side (any angle – beveling), are joined together with a miter joint.

Modified Bitumen: (1) An asphalt product modified through the addition of one or more polymers, such as atactic polypropylene; (2) composite polymer-modified bitumen sheets reinforced with fiberglass mats, felt, or polyester, and/or surfaced with mineral granules.

Mopping: The process of arranging hot bitumen onto a bituminous membrane felts or the roof substrate using a mechanical applicator or a roofer’s hand mop.

Solid Mopping: A continuous mopping process of the roof surface.

Spot Mopping: Mopping hot bitumen in roughly circular spots on the roof, leaving behind perpendicular bands that are not mopped.

Sprinkle Mopping: A pattern of randomly scattering heated bitumen beads onto the substrate and mopping with a mop or broom.

Strip Mopping: A mopping process where hot bitumen is strewn into the substrate in parallel strips.


Nailer (Blocking): Pieces of plywood attached to the structural deck, which act as a receiving medium for the mechanical fasteners for securing the membrane or flashing. It is advisable that the nailers undergo a non-oil-borne preservative treatment, have the same thickness as the adjacent insulation, and have sufficient width to support the entire horizontal flashing flange is used.

Nailing: The process of applying nails. (1) exposed nailing: roof nail heads are open to the weather; (2) concealed nailing: roof nail heads are hidden from the weather with overlapping material.

Neoprene: A flexible synthetic rubber (a result of polymerization of chloroprene) with excellent chemical stability. It is generally used in sheet-applied and liquid-applied elastomeric roof membranes or flashings.

Net Free Vent Area: The minimum area of unrestricted airflow a ventilated space should have. It is measured in square inches and used to determine the relative vent performance.

Night Seal (or Night Tie-Off): A method of temporarily sealing a roof membrane edge during installation, as a way to protect the roofing assembly from water penetration. When roofing construction resumes, the seal is removed.

Nineteen-Inch Selvage (Double-Coverage or Split-Sheet): A prepared roofing sheet that has a 17 inch (430mm) granulated surface area exposed to weather and a non-granule surfaced selvage edge of 19 inches (485mm); also known as double-coverage and SIS. According to Standard Specification for Asphalt Roll Roofing (Organic Felt) Surfaced with Mineral Granules, ASTM Standard D 371-89, it is referred to as Wide Selvage.

Ninety-Pound: A prepared organic roll roofing felt with a granule surfacing, whose mass is approximately 4400 g/m 2 or 90 pounds per 100 square feet.

NRCA: National Roofing Contractors Association.


Open Valley: A valley system of construction, where a metal flashing will be fitted at the joint, and the installed shingles do not run over the valley flashing, but keep it exposed.

Organic: Substances comprising hydrocarbon molecules, or compounds derived from plant or animal matter.

Organic Felt: Base material or underlayment manufactured from organic and superior-grade saturated asphalt.

Organic Shingle: Organic felt roofing shingles made with recycled materials and reinforced with cellulose fiber derivatives or embedded with ceramic granules.


Pallet: Wooden or other material box or crate used to ship or store stuff.

Pan: The bottom flat side or the concave surface of the roof panel that lies between the ribs or touches the roof substrate.

Parapet Wall: Extension of the perimeter wall of the roof that acts as a barrier to the roof edge or balcony.

Penetration: (1) the process of passing an object through the roof; (2) the consistency or hardness of bitumen in constructing a curb or flashing, measured in the distance of vertical penetration of a standard needle under specified loading, time, and temperature conditions.

Perlite: Aggregate used in lightweight concrete roof deck insulation. It undergoes heat and siliceous volcanic glass expansion treatment to achieve better fire imperviousness.

Pitch-Pocket (Pitch-Pan): A flanged, open-bottomed metal flashing that encloses roof penetrations of irregular shapes. It is typically filled with a pourable bituminous or polymeric sealer and grout to avoid leaks and moisture entry.

Pittsburgh Lock Seam: Seam that interlocks separate pieces of metal at the roof slope.

Plastic Cement: Type I asphalt cement used on non-vertical or low-slope roof surfaces. It is a trowel-able mixture of mineral stabilizers, solvent-based bitumen, and fibers or fillers.

Pliability: Ability of the roof shingles to be flexible or moldable to weather changes.

Ply: Roof felt, ply membrane, or a layer of other reinforcement material.

PMR: Protected Membrane Roof.

Polyvinyl Chloride (PVC): A thermoplastic polymer obtained from vinyl chloride through synthetic means. By using plasticizers, stabilizers, and other modifiers, it can be made flexible (sheeting and roof membrane) or rigid (pipes).

Ponding: Excessive water accumulation of at low-lying roof areas.

Pop Rivet: A relatively small metal pin with an expandable head; used to join light gauge metal by inserting through aligned holes.

Positive Drainage: The drainage condition or all loading roof deck deflections, considered and adhered to during design to drain all the precipitation water within 48 hours, under ambient drying conditions.

Primer: In the seaming process of the roof membranes, solvent-based liquid bitumen is applied to the surface to increase its bitumen adhesion ability. It is used to prepare the surface prior to adding subsequent single-ply membranes for increased strength.

Puncture Resistance: The extent to which a material can resist being punctured by a sharp object.

Purlin: A horizontally-positioned secondary structural member to which loads are transferred from the primary structural members.


Rafter: A sloped roofing structure that runs from the roof ridge or hip to the wall perimeter or eave and supports the roof deck, roof coverings, and associated loads.

Raggle: A groove or slot cut into a vertical surface, such as a masonry wall, chimney, or others, to insert an inset flashing element like counter flashing or reglet.

Rake: The sloped exterior trim of the roof running adjacent to one end rafter and perpendicular to the ridge and eaves.

Rake-Starter (Bleeder Strip): A starter strip of asphalt-based shingle installed to waterproof rake edges during re-roofing.

Reglet: A surface-mounted or cladding-embedded sheet metal receiver to which counter flashings are attached.

Reinforced Membrane: A roofing membrane strengthened for increased waterproofing ability by incorporating reinforcing materials like polyester mats, glass fibers, nylon sheeting, or other materials.

Ridge: The peak of the roof where two sloped, opposing roof planes intersect, running a horizontal line along the entire length of the roof.

Ridge Cap: Material applied to cover the roof ridge or hip.

Ridge Course: The final roofing course that covers the ridge, using materials like tile, shingles, roll roofing, etc.

Ridge Vent: An exhaust ventilator installed near the roof ridge that provides attic or rafter cavity ventilation. It is either a pre-manufactured metal device or a flexible shingle-over vent, used along with a soffit vent in a 1:1 ratio.

Roll Roofing: Easy-to-install roof roll; smooth-surface coated with minerals or prepared felts.

Roof Assembly: Roofing components all put together: roof deck, insulation, waterproofing, vapor retarder, and roof covering.

Roof Jack: A metal bracket fastened to a steep-slope roof to support toe boards.

Roof Slope: The steepness of a roof plane expressed as a ratio of rise to run; the angle of inclination between the roof makes and a horizontal surface. It is the ratio of vertical rise measurement to unit horizontal length (all in inches) of the roof surface.

Run: Horizontal length of the roof slope.


Saddle: A small raised pyramid-shaped substrate or structure amid sump drains, constructed to direct surface water away from the roof.

Sag: Undesirable drooping or excessive flow of base flashings as a result of the improper application to a surface.

Saturated Felt: A felt that had been saturated (partially) with bitumen.

Seam Strength: Maximum strength that a seam of membrane material can withstand before rupturing, measured in shear or peel modes, reported as a percent of the sheeting strength or in absolute units.

Self-Adhering Membrane: A membrane that can stick to a substrate it overlaps, without using additional adhesive material. A release paper or film protects the bottom surface of this self-adhering membrane and prevents it from bonding to itself.

Self-Drilling Screw: A screw that has a drill-bit type of a tip and drills its own hole, used as a fastener to attach panels to purlins and girts.

Self-Sealing Shingle: An asphalt shingle with factory-applied adhesive strips that sticks to the overlying roof shingles when warmed by the sun; helps against wind uplift.

Self-Tapping Screw: A fastener that makes receiving threads when screwed into a pre-drilled hole.

Selvage: (1) an edge different from the main fabric, granule-surface of a roll roofing or cap sheet, or any other material; (2) a clearly defined edge of a material or fabric (lined for demarcation), designed for a particular purpose like overlapping or seaming.

Selvage Edge: A portion of the granule or mineral-surfaced membrane designed specially to achieve better adhesion to be overlapped by the subsequent sheets.

Shading: Slight discoloration on the surface like shingle granules, due to manufacturing operations.

Shed Roof (Half Gable): A roof consisting of one sloping plane without ridges, hips, or valleys.

Shingle: A roofing material unit designed to be installed in overlapping rows exceeding a slope of 25%.

Shingling: The procedure of installing shingles or laying parallel felts on the roof, starting at a downslope to upslope portion, to facilitate the flow of runoff water over the shingles or felt laps. The two longitudinal edges of each felt or shingle overlap and underlap with the adjacent felts or shingles on either side.

Side Lap: The longitudinal overlap of adjacent felts or shingles.

Sill: The horizontal framing member at the bottom of an opening like a window or door.

Sill Flashing: Flashing used to waterproof the sill or the bottom framing member of an opening.

Skylight: A transparent, raised framed roof accessory installed over a curbed opening to admit light.

Slab-On-Grade: A piece of concrete placed horizontally above a prepared earth substrate.

Slate: A fine-grained, brittle metamorphic rock used as dimensional stone in steep slope roofing or for surfacing applications.

Slope: The angle of inclination of a roof; see Roof Slope.

Snow Guard: Devices attached in a pattern on the roof to retain snow in place, and thereby, prevent sudden snow or ice slides.

Snow Load: Load (live or environmental) exerted on building structures, caused by snowfall on the roof; a primary structural consideration while designing roofs in areas prone to heavy snow.

Soffit: The enclosed and unexposed underside of the overhanging exterior roof section.

Soffit Vent: A pre-manufactured or custom-built air intake vent located in the soffit, designed to ventilate the attic space.

Soil Stack: A sanitation pipe penetrating a roof, designed for ventilation of building’s plumbing fixtures.

Spalling: Chipping or flaking of layers of concrete or masonry.

Splash Block: A fabricated metal, polymeric, or masonry block placed on the ground level, below the opening of a leader pipe or downspout, installed to prevent soil erosion.

Square: 100 square feet or 10 square meters of roof area.

Stainless Steel: An alloy of steel with a high presence of chromium, copper, or nickel, offering a high corrosion resistance.

Standing Seam: A type of metal roofing system with overlapping or interlocking longitudinal seams achieved by upturning the adjacent metal panels to prevent moisture intrusion.

Starter Course: The primary roofing course or layer installed along a line parallel to the roof downslope perimeter edge. It covers the first course in steep-slope roofs with water-shedding coverings.

Starter Sheets: (1) Membrane strips, sheets, or plies cut to a width inversely proportional to the number of plies to be installed, usually narrower than the standard roll width. Eg. For a three-ply BUR, the first starter ply width will be one-third of the roll width. (2) Specific widths designed for fully adhered single-ply or mechanically attached roof systems.

Starter Strip: Strips of shingles or roll roofing material applied along the eave line before applying the first shingle course, used to fill in the spaces created by cutouts and joints.

Static Load: Fixed or permanent, unchanging loads on a roof structure, like HVAC units.

Step Flashing: Flashing used to seal around roof projections such as chimneys, dormers, walls, curbs, etc. Individual pieces are installed by overlapping with the vertical surface.

Substrate: The surface onto which a waterproofing membrane or the roof is installed.

Sump: An intentional depression around a scupper roof drain or scupper, designed to promote roof drainage.


Tab: The exposed portion of asphalt strip shingles outlined by cutouts.

Test Cut: A roof sample containing only the membrane or all components used to diagnose the overall membrane condition evaluate how many plies to be applied, or the average weight of the inter-ply bitumen moppings.

Thermal Shock: The phenomenon where extreme stress is produced in a roof membrane due to rapid expansion and contraction, as a result of sudden temperature changes, such as a cold shower suddenly followed by hot sunshine.

Tie-Off: A watertight transitional seal used to temporarily or permanently terminate waterproofing or adjacent roof membranes at flashings or substrates.

Toggle Bolt: A threaded bolt that has an expanding clip at one end, which can be flattened and fit into a previously drilled hole. The toggle end springs outward and secures the bolt from the blind side when tightened.

Tongue and Groove Planks: One of the oldest roof decking types with dimensional structural wood that has a convex “tongue” and concave “groove” to secure and align adjacent planks in a uniform roof deck.


Ultraviolet (UV): Luminous energy of sunlight, with longer wavelengths compared to X-rays, situated in a position outside of the visible spectrum. UV radiation can expedite the deterioration of roofing materials, which can be avoided by applying protective coatings.

Underlayment: A self-adhering material like asphalt-saturated felt installed over the roof deck before the primary roof covering is applied. In steep-slope roofs, the primary purpose of underlayment is to provide water and weather protection.


Valley: The internal angle of intersection between two sloping roof planes running from the eaves to the ridge.

Vapor Retarder: A material used to impede or restrict water vapor from escaping through a roof assembly.

Vent: An opening or device specifically designed to permit air, heat, or water vapor to escape an enclosed structure and into the atmosphere.

Ventilation Short Circuit: Disruption of airflow between the intake-exhaust vents (e.g., soffit vents and ridge vents) that causes a decrease in the effectiveness of a passive ventilation system. For instance, in a soffit-to-ridge vent system, gable vent air intake can short circuit the soffit vent stack-effect air draw, disrupting the roof cavity ventilation.

Ventilator: An accessory or device designed to circulate fresh air and passage of stale air.


Weep Holes: Small holes whose primary purpose is to drain water accumulated inside a building component like a brick wall or skylight frame.

Wicking: Process of conveying moisture or liquid by capillary action, as opposed to the movement of vapor.

Wind Uplift: The deflection of wind at the roof peaks or edges causes a pressure drop in the air immediately above the surface and transmits this force to the roof surface. Wind uplift can also result from air pressure created under the roof edge or membrane, causing it to balloon or pull away.

Woven Valley: A valley construction method where roof shingles from both sides are woven into overlapping alternate courses.