A glossary of commercial roofing terminology.

Aggregate – Stone, slag, crushed lava rock, marble chips or river rock used as ballast and/or UV protection for certain roof systems, such as BUR, EPDM, etc.

Alligatoring – A characteristic of asphalt that occurs during aging. Over time, exposed asphalt loses volatile oils and together with oxidation through UV exposure, creates a pattern of cracks that resemble alligator hide.

Apron Flashing – Flashing located at the top of a sloped roof and a vertical wall, chimney or steeper sloped roof.

ARMA – An acronym for Asphalt Roofing Manufacturers Association.

Architectural Shingle – A laminated, asphalt shingle with a dimensional appearance.

Asphalt – Composed mainly of hydrocarbons, asphalt is a dark bituminous substance found in natural beds as well as a residue in petroleum refining.

Asphalt Shingle – A type of shingle made by coating a reinforcing material (felt or fibrous glass mat) with asphalt. Mineral granules are applied to the weather-exposed side.

ASTM – An acronym for American Society for Testing and Materials.


Ballast – Various materials installed over the top of a roof membrane to help hold it in place and protect from UV rays.

Back Nailing – Nails installed in roof felts attaching it to the deck under overlaps in conjunction with hot mopping to prevent slippage during the installation process.

Base Sheet – An asphalt-saturated or coated felt installed as the first layer with 4” laps in some built-up roof (BUR) and modified bitumen roof systems.

Base Flashing – That portion of flashing that is attached to the deck and used to direct water flow onto the roof covering.

Bitumen – Various mixtures of hydrocarbons, occurring naturally or through the distillation of coal or petroleum, and forms a component of asphalt and tar used in waterproofing. Applicable to both asphalt and coal tar pitch.

Blistering – Formed when a pocket of air is trapped between layers of felt or membrane.

Blocking – Pieces of wood used in a roof assembly to stiffen the deck around an opening or for use as a nailer in the attachment of flashing or membranes.

Built-Up Roof (BUR) – Plies of roofing felt, bonded with hot bitumen, usually finished with a flood coat of hot bitumen and a coating of aggregate, asphalt, emulsion or granule-surfaced cap sheet.

Bundle – A single package of shakes or shingles.


Canopy – An overhang typically over driveways or entrances.

Cant Strip – A triangular-shaped piece of wood, wood fiber, perlite or other material used to ease the transition from a horizontal to a vertical plane.

Cap Sheet – A granulated surface bitumen membrane often used as the top ply of a built-up roof system (BUR). If a cap sheet is installed, use of aggregate is not necessary.

Calender – The machine used to apply coating with a specific thickness and/or surface characteristic and also used to laminate sheeting.

Calendering – A process used in the manufacturing of membranes, such as PVC.

Caulk – A material with no elastomeric properties used for sealing joints.

CCF – Represents 100 cubic feet.

Channel Flashing – Used where roof planes intersect other vertical planes, channel flashing has a built-in channel for runoff.

Cladding – Material used to cover the exterior wall of a building.

Class “A” – The highest of fire-resistant ratings relative to roofing materials per ASTM E-108. Class “A” materials will not support a flame on its own and is able to withstand severe exposure to fire from outside the building in which the material was installed.

Closed Cut Valley – A technique of valley application in which shingles from one side extend across the valley, while shingles from the other side are installed over the top of those and then trimmed back from the valley centerline.

Coal Tar – A semi-solid hydrocarbon produced by the distillation of coal. It is futher refined to conform to specific roofing grade specifications.

Coal Tar Bitumen – A propriety name for Type III coal tar used as waterproofing or damp-proofing in dead-level or low-slope built-up roofs. Conforms to ASTM D 450 Type III and not for use in roofs with a slope greater than 2% (1/4” in 12”).

Coal Tar Pitch – A form of coal tar used as the waterproofing agent in dead-level or low-slope built-up roof membranes and membrane waterproofing systems. Not for use in roofs with a slope greater than 2%.

Coal Tar Felt – A roofing membrane saturated with refined coal tar.

Coal Tar Roof Cement – A mixture of processed coal tar base, solvents, mineral filler and/or fibers.

Cold Roof Assembly – A roof assembly in which the insulation is located below the deck. The insulation is not typically in contact with the deck, allowing for ventilation space.

Cold Process Built-Up Roof – A process composed of multiple plies of roof felts, laminated together with adhesives that come straight from a can or barrel and require no heating.

Composition Shingle – A type of shingle that is composed of weathering-grade asphalt, a fiberglass reinforcing mat, an adhesive strip and topped with mineral granules.

Composite Board Roof Insulation – A form of rigid board insulation composed of perlite or wood fiberboard that is factory bonded to polystyrene or polyisocyanurate.

Condensation – The conversion of water vapor or other gas to liquid phase.

Coping – A protective piece of material (metal, masonry or stone) on top of a wall exposed to weather.

Counterflashing – Formed metal or elastomeric sheeting secured to curbs, walls, pipes, rooftop units or other surfaces to protect the upper edge of base flashing and its fasteners from weather exposure.

Course – Each row of roofing material forming the roofing/flashing system. Can also refer to one of multiple layers of materials applied to a surface.

CPA – An acronym for Copolymer Alloy.

Creep – Movement of the roof membrane causing deformation of the roof system.

Cricket – A roof component that diverts water away from a horizontal intersection of the roof with a chimney, curb, wall or other roof projection.

Cross Ventilation – Air moving through a roof cavity between vents.

Curb – Any raised member used to support roof-penetrating fixtures like skylights, HVAC units, hatches, exhaust fans, etc. above the roof surface. Can also refer to a low raised roof perimeter.

Cure – A process through which a material forms a permanent molecular linkage by exposure to chemicals, heat, pressure or weathering.


Dead Level – Absolutely no slope.

Deck – The structural component of the roof that provides support for the weight of the roof system as well as other live loads like snow, according to the prevailing building codes. The deck also serves as the substrate to which the roofing or waterproofing system is applied.

Degradation – A negative change in the appearance, chemical structure or physical properties of a material from natural or artificial causes.

Delamination – The separation of laminated layers.

Dimensional Shingle – A shingle that is textured or laminated to produce a three-dimensional effect. Also known as Architectural Shingle.

Dormer – A framed projection from a sloping roof, usually housing a window or ventilation fixture.

Downspout – A vertical pipe used to direct runoff water from a gutter of a building to a lower-level roof or to the ground or storm drain.

Drip Edge – Metal flashing used along the outer perimeter of steep-sloped buildings in order to direct runoff water away from the building and protect underlying building components, such as fascia.

Dry Rot – The rotting of wood caused by certain fungi that can spread to any wood touching the affected area.

Dynamic Load – Any moving load on a roof (people, equipment). Wind can also be considered a dynamic load.


Eave – The lower edge of a sloped roof extending past the wall.

Eave Vent – The protected openings along the roof perimeter used as the intake of a ventilation system to dissipate heat and moisture.

Elastomeric – The properties of a material that allow it to return to its original form or state after being deformed (stretched, pulled, compressed, etc.).

Elastomeric Coating – A coating that can be stretched to twice its dimensions and then return to its original dimensions with the release of pressure.

Elongation – The ability of a material to be stretched beyond it original state.

Embedment – To uniformly press one material into another.

Emulsion – A mixture of bitumen and water. Typically stabilized by an emulsifying agent with uniform dispersion of the bitumen and water globules.

End Lap – The distance of the overlap of one component of material extending beyond the end of the immediately adjacent underlying material.

EPDM – An acronym for Ethylene Propylene Diene Monomer. Usually black in color, a material used for low slope roof installations.

Epoxy – A class of synthetic, thermosetting resins that produce tough, hard, chemical-resistant coatings and adhesives.

Ethylene Interpolymers (EIP) – Thermoplastic compounds generally based on PVC polymers from which single-ply roofing membranes can be formulated.

Exhaust Ventilation – Exhaust vents are used to vent air from the roof cavity or attic space, usually on or near the ridge of a sloped roof.

Expansion Cleat – Thermal movement of the metal roof panels is handled with a specially-designed cleat.

Expansion Joint – A built-in separation that allows free movement between two building elements without damage to the roofing system.

Eyebrow – A dormer with an arched roof line resembling the curve of an eyebrow.

Exposed-nail Method – Roll roofing installation technique where all nails and fasteners are visible.

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