The following is a list of commercial roofing terms commonly used in the roofing industry.
Each term is followed by a short description.
Absorption: The process by which a substance or object takes in a liquid, gas, waves, or chemical and makes it a part of itself.
Adhesive: A substance used to adhere materials together.
Aggregate: A surfacing or ballast for a roof system. Aggregate can be rock, stone, crushed stone or slag, water-worn gravel, crushed lava rock or marble chips.
Aging: The effect on materials that are exposed to an environment for an interval of time.
Algae: A rooftop fungus that can both stain and damage your roofing system.
Alligatoring: The cracking of the surfacing bitumen on a built-up roof, producing a pattern of cracks similar to an alligator’s hide; the cracks may or may not extend through the surfacing bitumen.
Aluminum: A non-rusting metal material sometimes used for metal roofing and flashing.
Aluminized Steel: Sheet steel with a thin aluminum coating on the surface to enhance the steel’s ability to withstand weathering.
Application Rate: The rate (measured in mass, volume, or thickness) at which a material is applied per unit area.
Asbestos: A group of natural, fibrous, impure silicate materials.
Air Blown Asphalt: Asphalt produced by blowing air through molten asphalt held at an elevated temperature.
Area Divider: A raised, double wood member attached to a properly flashed wood base plate that is anchored to the roof deck.
Asphalt: A dark brown to black cementitious material in which the predominating constituents are bitumens, which occur in nature or are obtained in petroleum processing.
ASTM: American Society for Testing and Measurement is a not-for-profit organization which provides a forum for producers and consumers to meet on common ground and to write standards for materials, products, systems, and services.
Bond: The adhesive and cohesive forces holding two roofing components in intimate contact.
Back-Nailing: The method of fastening the back or upper side of a ply of roofing felt or other component in a roof system so the fasteners are covered by the ply and not exposed to the elements.
Ballast: Ballast materials (like precast concrete or aggregate) use gravity to hold a single-ply roofing in place.
Base Sheet: A saturated or coated felt placed as the first ply in some multiply built-up roof membranes.
Bitumen: A class of amorphous, black or dark-colored, cementitious substances, either natural or manufactured, composed principally of high-molecular-weight hydrocarbons, soluble in carbon disulfide, and found in asphalts, tars, pitches and asphaltites.
Bituminous Emulsion: Bituminous particles suspended in water or other aqueous solution.
Bitumen-Stop: A continuous seal for preventing bitumen from leaking down into or off a building.
Blind Nailing: The practice of nailing the back portion of a roofing ply in a manner that the fasteners are not exposed to the weather in the finished product.
Breaking Strength: The amount of tension required to cause material or a system to give way or collapse.
Brooming: Embedding a ply of roofing material by using a broom, or other piece of equipment, to smooth out the ply and ensure contact with the adhesive under the ply.
Building Code: The minimum construction requirements established by local or national governing authorities.
Built-Up Roof Membrane: A continuous and semi-flexible roofing membrane that consists of multiple plies of saturated felts, coated felts, fabrics or mats assembled in place with alternate layers of bitumen and surfaced with mineral aggregate, bituminous materials, a liquid-applied coating or a granule-surfaced cap sheet.
Butyl: A hydrocarbon radical. Butyl has a rubber-like consistency, is formed from the copolymerization of isobutylene and isoprene and is used primarily in sealants and adhesives.
Butyl Rubber: A butyl-based, synthetic rubber made by polymerizing isobutylene and isoprene.
Butyl Tape: A sealant tape that’s sometimes used between metal roof panel seams and/or end laps. It’s also used to seal other types of sheet metal joints in various sealant applications.
Cavitation: The vaporization of a liquid under the suction force of a pump which can create voids within the pump supply line.
Cellulose: A complex carbohydrate, (C6H10O5)n, that’s composed of glucose units, forms the main constituent of the cell wall in most plants, and is used to manufacture organic roofing materials.
Chemical Resistance: The ability of a material to withstand contact with specified chemicals without adverse effect.
Coal Tar Felt: A type of roofing membrane saturated with refined coal tar.
Coal Tar Roof Cement: A mixture of processed coal tar base, solvents, mineral fillers and/or fibers.
Color Stability: A property of a material to retain its original color after environmental exposure.
Compressive Strength: A property of a material to resist deformation caused by compression
Condensation: As it relates to water, the conversion of water vapor to a liquid as the temperature drops.
Coping: The covering on top of a wall that is exposed to weather and other elements.
Counterflashing: Formed metal or elastomeric sheeting secured on or into a wall, curb, pipe, rooftop unit or another surface, to cover and protect the upper edge of a base flashing and its associated fasteners.
Coverage: The surface area continuously covered by a specific quantity of a particular roofing material.
Crack: A separation or fracture occurring in a roof membrane or roof deck, generally caused by thermal induced stress or substrate movement.
Creep: The permanent deformation of a roofing material or roof system caused by the movement of the roof membrane that happens because of continuous thermal stress or loading.
Curb: A raised member used to support roof penetrations.
Cure: A process where the material forms a permanent molecular bond after being exposed to a chemicals, heat, or pressure.
Damp-proofing: The treatment of a surface or structure so it’s resistant to the passage of water in the absence of hydrostatic pressure.
Dead Level: Also referred to a zero slope. A horizontal or flat, as in a roof deck or rooftop with no intentional slope to the roof drains.
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.
Deck: The structural component of the roof to which the waterproofing system is applied.
Determinations: "Core" the roof to determine existing roof assembly as well as the state of the current insulation's “R-Value.”
Dimensional Stability: The change in a material that results from exposure to elevated temperature.
Double Graveling: The process of applying two layers or flood coats of bitumen and aggregate to a built-up roof.
Downspout: A vertical pipe for draining water from roof gutters.
Drain: A device on the roof used to collect and direct the flow of water away from the roofing area.
Drip Edge: A metal flashing or other overhanding component intended to control the direction of dripping water.
Edge Details: Rigid edge terminations that help make perimeters on the roof watertight.
Edge Stripping: The roofing material that’s used to seal perimeter edge metal and the roof itself.
Edge Venting: Practice of providing regularly spaced or protected openings along the edge or perimeter of the roof. This is used as part of the roof’s ventilation system.
Elastomeric: A rubber-like synthetic polymer that will stretch when pulled and will return quickly to its original shape when released.
Elongation: The ability of a roofing material to be stretch by the application of force.
Embedment: The process of pressing a felt, aggregate, fabric, mat, or panel uniformly and completely into hot bitumen or adhesive coating.
Emissivity: A measure of the efficiency in which a surface can release thermal energy.
Envelope: A continuous membrane edge seal formed at the perimeter and at penetrations by folding the base sheet or ply over the plies above and securing it to the top of the membrane. The envelope prevents bitumen seepage from the edge of the membrane.
EPDM: An extremely durable synthetic rubber roofing membrane (ethylene propylene diene terpolymer) widely used in low-slope buildings worldwide. Its two primary ingredients, ethylene, and propylene are derived from oil and natural gas.
Exhaust Ventilation: Air that is vented from the roof cavity.
Expansion Joint: A structural separation between two building elements that allows for expansion and contraction without damage to the roofing materials or waterproofing system.
Exposure: The area(s) on a roofing system that’s exposed to the elements after installation.
Fabric: A woven cloth composed of organic or inorganic filaments, threads or yarns that are used to reinforce certain membranes.
Fasteners: A wide array of mechanical fastening devices including clips, screws, or bolts that are used to secure roofing materials to the deck.
Felt: A flexible roofing sheet made of interwoven fibers through a combination of mechanical work, moisture and heat. The fibers can be manufactured from vegetable, asbestos, or glass fibers.
Film: A membrane or sheeting material with a nominal thickness no greater than 10 mils (0.010 inches).
Film Thickness: The thickness of a membrane or coating usually expressed in mils (thousandths of an inch).
Flashing: The Weatherproofing components used to seal membrane edges at walls, expansion joints, drains, gravel stops, and other places where the membrane is interrupted or terminated.
Flood Coat: The top layer of bitumen into which the aggregate is embedded on an aggregate-surfaced built-up roof.
Galvalume: The trademarked name for a metal alloy coating that is composed of 55% aluminum, 43.4% zinc and 1.6% silicon.
Galvanized Steel: Steel that is coated with zinc to aid in corrosion resistance.
Gauge: A metal thickness measurement.
Gravel: Coarse, granular aggregate, with pieces larger than sand grains, used in a bitumen aggregate on built-up roofs.
Gravel Stop: A device, frequently metallic, designed to provide a continuous finished edge for roofing material and to prevent loose aggregate from washing off the roof.
Gutter: A channeled metal trough-like element installed along the downslope perimeter of a roof to direct runoff water away from the roof and building structure.
Heat Welding: Method of melting or fusing together sheets of thermoplastic and polymer modified bitumen
Hem: The edge created by folding metal back on itself.
HVAC: Heating, ventilating, and air conditioning equipment.
Ice Dam: A mass of ice formed at the transition from a warm to a cold roof surface, frequently formed by refreezing meltwater at the overhang of a steep roof, causing ice and water to back up under roofing materials.
Infrared Thermography: Roof analysis technique used to measure the temperature gradient of a roof surface to locate areas of moisture.
Insulation: Materials used to reduce the flow of heat.
Intake Ventilation: A ventilation system that allows for the flow of fresh air into the building.
Interlayment: A material usually installed between adjacent rows of wood shakes to help with the roof’s waterproofing characteristics.
Impregnate: To surround roofing fibers in a felt or mat with bitumen with the spaces between the fibers partially or completely filled without a continuous coating of bitumen on the surface.
Job-Average Basis: A technique for determining the average dimensions or quantities of material, by analysis of roof test cuts.
Joist: Timber, metal or wooden beams arranged parallel to each other to support a floor or ceiling of a building.
Laitance: An accumulation of fine, powdery aggregate particles on fresh cement caused by the upward movement of water; indicates that too much water was used in the mix resulting in poor surface adhesion for a waterproofing layer.
Laminate: To join layers of material together via heat and/or pressure.
Lap: The part of a roofing membrane that covers any portion of another section of membrane and is then sealed to form a watertight connect.
LEED Certification: Leadership in Energy and Environmental Design is a rating system developed by the United States Green Building Council to evaluate the environmental performance of a building.
Live Loads: Moving roof installation equipment, wind, snow, ice or rain.
Loose-Laid Roof Membranes: Roofing material attached only at the perimeter and at penetrations and held in place by ballast, pavers, or other materials.
Membrane: A flexible or semi-flexible material whose primary function is to prevent water penetration.
Metal Retrofit: A metal retrofit roofing system is a prefabricated, single-ply membrane that protects your commercial roof from ice buildups, leaks, rust, and more.
Mildew: A superficial coating or discoloration of organic materials caused by fungi, especially under damp conditions.
Mineral Stabilizer: A fine, water-insoluble inorganic material, used in a mixture with solid or semi-solid bituminous materials.
Modified Bitumen: Composite sheets consisting of a copolymer modified bitumen often reinforced and sometimes surfaced with various types of films, foils, and mats.
Moisture Relief Vent: A vent installed through the roofing membrane to relieve moisture vapor pressure that has been trapped within the roofing system.
Mopping: The application of hot bitumen (asphalt or tar coating) with a mop to the substrate of a bituminous membrane.
Nailer: A piece of dimensional lumber or plywood which serves as a receiving medium for the fasteners.
Nailing Pattern: Specific method or pattern at which nails are applied.
Nesting: The installation of a new metal roof deck directly on top of an existing metal roof deck.
Night Seal: A temporary seal used during construction to protect the roofing assembly/system from water penetration.
Non-Vulcanized Material: A material that retains its thermoplastic properties throughout the duration of its service life.
Overflow Drainage: Component of a roof drainage system that protects the roof against damage if the primary drainage system is blocked.
Overdriven: An improperly driven screw or fastener that can lead to premature roof leaks.
Overhang: The portion of the roof structure that extends beyond the exterior walls of a building.
Ozone Resistance: A property of a material to resist the effects of ozone exposure.
Parapet Wall: That part of any wall entirely above the roof.
Penetration: Any element (i.e. HVAC, vent stack, skylight) that passes through the roof.
Phased Application: The installation of a roof system or waterproofing system during two or more separate time intervals.
Plenum: A space or enclosure in which air or other gas is at a pressure greater than that of the outside atmosphere.
Ply: A layer of felt, ply sheet or reinforcement in a roof membrane or system.
Positive Drainage: Drainage condition in which all considerations during the design process have been provided to ensure drainage of the roof within 48 hours of a rainfall.
Polyvinyl Chloride (PVC): One kind of single ply roofing, ideal for chemical and grease resistance-based establishments, which means it consists of one layer manufactured in a factory. The membrane is made of thick, flexible UV-resistant thermoplastic material; it may also contain polyester or fiberglass, resins, pigments, plasticizers, and other chemicals.
Ponding: An excess amount of water that hasn’t drained from a roofing system.
Pourable Sealer: A two-part sealer used to form a water-tight barrier around penetrations difficult to flash.
Primer: A thin, liquid substance intended to prepare the roof surface for accepting a coating or improving the overall adhesion of the coating to the substrate.
Purlin: Horizontal lengths of material, wood or metal, that are affixed to the roof and to which the finished roofing material is attached to.
R-Value: The measure of a material’s resistance to heat flow. The higher a material’s R-value is, the more it insulates.
Re-covering/Re-roofing: The process of covering an existing roof system with a new roof system.
Reinforced Membrane: A roofing membrane that has been strengthened by the addition or incorporation of one or more reinforcing materials. (i.e. felts, mats, fabrics, fibers, etc.)
Replacement: The practice of removing an existing roof system and replacing it with a new roofing system.
Resin: The “B” component in SPF that is mixed with the “A” component in order to form polyurethane.
Roof Covering: The exterior of the roof assembly that consists of membrane, panels, sheets, shingles, tiles, etc.
Roof Curb: A raised frame used to mount mechanical units on the roof.
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. It may be expressed as a ratio of rise to run.
Rubber: A material, at room temperatures, capable of recovering substantially in shape and size from large deformations
Saturated Felt: A felt that has been immersed in hot bitumen.
Scaling: Measure roof and its layout to provide a comprehensive and thorough roof plan.
Scupper: A roof drain mounted at the intersection of a roof deck and parapet or building wall.
Scuttle: A hatch that provides access to the roof from the interior of the building.
Sealant: A mixture of polymers, fillers, and pigments used to fill and seal joints where moderate movement is expected. It cures to a resilient solid.
Self-Adhering Membrane: A membrane that adheres to the substrate and overlaps without the use of additional adhesive.
Seam: A joint formed by joining two separate sections of roofing material.
Single-Ply Membranes: Roof membranes that are applied using just one layer of membrane material.
Slag: A hard, air-cooled aggregate that is left as a residue from blast furnaces, used as a surfacing aggregate.
Slope: The angle of incline of a roof expressed as a percent or as a ratio of rise to run.
Snow Load: The live load due to the weight of the snow on a roof that’s included in design calculations.
Solid Mopping: To continuously apply hot asphalt or coal tar leaving no areas uncovered.
Solvent: Any liquid used to dissolve another material.
Split: A membrane tear resulting from substrate or membrane stress.
Sprinkle Mopping: The act of scattering hot bitumen over a surface.
Step Flashing: Individual pieces of sheet-metal material used to flash walls, around chimneys, dormers and such projections along the slope of a roof.
Strapping: Installing roofing felts so they run parallel with the slope of the roof.
Strip Flashing: Membrane flashing strips used for sealing or flashing metal flashing flanges into the roof membrane.
Square: The term used to describe 100 square feet of roof area.
Substrate: The surface in which the roof is installed upon.
Sump: A deliberate depression around roof drains and scuppers to help promote roof drainage.
Surfacing: The top layer of a roof covering.
Tapered Edge Strip: A tapered insulation strip used to elevate the roof at the perimeter and at curbs that extend through a roof and provide a gradual transition from one layer of insulation to another.
Tear Resistance: The load required to tear a material when the stress is concentrated on a small area of the specimen by the introduction of a prescribed flaw.
Termination: A method of anchoring the free edges of the roofing membrane to the roofing system.
Test Cut: A sample of the roof, which may contain all components or just the membrane, used to diagnose the condition of the existing membrane, evaluate the type and number of plies or number of membranes, or rates of application.
Thermal Insulation: A material applied to reduce the flow of heat.
Thermal Resistance: An index of a material’s resistance to heat flow.
Thermal Shock: The damage to a roof resulting from expansion and contraction which are the result of sudden extreme temperature changes.
Thermal Stress: Stress created by any change in temperature to a material. These stresses can lead to fracture or deformation depending on the other variables of heating.
Thermoplastic: A material that softens when heated and hardens when cooled.
Thermoplastic Polyolefin (TPO): A single-ply reflective roofing membrane (thermoplastic polyolefin) made from polypropylene and ethylene-propylene rubber polymerized together. It is typically installed in a fully adhered or mechanically attached system, allowing the white membrane to remain exposed throughout the life of the roof.
Thermoset: A plastic that is irreversibly cured from a soft solid or viscous liquid prepolymer or resin.
Tuck Pointing: To remove old mortar from between masonry blocks and replace it with new mortar.
Ultraviolent: A form of radiation that is potentially damaging to certain chemical compounds in the roofing membrane.
Underlayment: A sheet-like material that is used to separate the roof deck and the roof system.
U-Value: The overall heat transfer of an assembly measured in BTUs per square foot, per degrees Fahrenheit difference in temperature per hour.
Underlayment: A material installed over the roof deck prior to the application of the primary roof covering.
Valley: The intersection of two sloping roof planes that runs from the eaves to the ridge. This intersection collects the most water run-off.
Vapor Migration: The movement of water vapor from a high vapor pressure region to a lower vapor pressure region.
Vapor Retarder: A material that’s designed and installed to restrict the passage of water vapor through a roofing system.
Vent: An opening designed to allow air, gas, or liquid to pass out of or into a confined space.
Viscosity: The property of a fluid that resists the force tending to cause the fluid to flow.
Viscous: Having or characterized by a high resistance to flow.
Vulcanize: To improve the strength, greater elasticity, durability, etc. of rubber, for example, by combining with sulfur or other additives in the presence of heat and pressure.
Warranty: A written guarantee issued to the purchaser of a roof from the manufacturer, promising to repair or replace it if necessary within a specified time.
Water Absorption: The quantity of water absorbed by a material during a specific period.
Waterproof: A type of material resistant to moisture permeation.
Waterproofing: Treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.
Weep Holes: Small holes, in walls or the foundation, designed to drain moisture that has gathered inside a building component.
Weld: The joining of metal together by heating the surfaces to the point of melting.
Wind Load: The force on a structure arising from the impact of wind on it.
Wind Uplift: The force in pounds per square foot that occurs when the pressure below a roof is greater than that above it.
Wire Tie: A system for attaching heavy roofing materials such as slate or tile by using wire fasteners in addition to or in place of nails.