Home » Glossary

Glossary

Have a question about some of the terminology used in the roofing industry? See the extensive list below of commonly used roofing terms. Should you have further questions about any of these terms or need assistance, please contact us.

Aggregate

(1) this is crushed stone; crushed slag, or water-worn gravel that may be used for surfacing a built-up roof; (2) any granular mineral material.

Alligatoring

On a built-up roof, the cracking of the surfacing bitumen, producing a pattern of cracks similar to an alligator's hide; these cracks may or may not extend through the surfacing bitumen.

Application Rate

This is the quantity (mass, volume thickness) of material applied per unit area.

Area Divider

This is a raised, double wood member attached to a properly flashed wood base plate that is anchored to the roof deck. It relieves the stresses of thermal expansion and in a roof system where no expansion joints have been provided. (see nrca + construction detail d-1.)

Asbestos

A group of natural, fibrous, impure silicate materials.

Asphalt

A cementitious material that ranges from dark brown to black in which the predominating constituents are bitumens, which occur in nature or are obtained in petroleum processing.

Asphalt, Air Blown

A type of asphalt produced by blowing air through molten asphalt at an elevated temperature to raise its softening paint and modify other properties.

Asphalt Felt

An asphalt-saturated felt or an asphalt-coated felt.

Asphalt Mastic

This is a mixture of asphaltic material and mineral aggregate that can be poured when heated but requires mechanical manipulation to apply when cooled.

Asphalt, Steam Blown

A type of asphalt produced by blowing steam, through molten asphalt to modify its properties, normally used for highway bitumen.

Backnailing

This is the practice of blind nailing (in addition to hot-mopping) all the plies of a substrate to prevent slippage. (see blind nailing).

Base Flashing

see FLASHING

Base Ply

In a roof membrane assembly, the first ply of roofing material.

Base Sheet/Anchor Sheet

This is roofing felt mechanically attached to a nailable deck with approved fasteners to which other roofing membrane is installed in a solid mopping of asphalt.

Battens

Horizontal wood strips installed on sloped roofs in which the primary roof covering is attached.

Bitumen

An amorphous, semi-solid mixture of complex hydrocarbons derived from any organic source. Asphalt and coal tar are the two bitumens used in the roofing industry.

Bituminous

Containing or having been treated with bitumen. Some examples include: bituminous concrete, bituminous felts and fabrics. Bituminous pavement.

Biiminous Emulsion

(1) a suspension of minute globules of bituminous material in water or in an aqueous solution; (2) a suspension of minute globules of water or an aqueous solution in a liquid bituminous material (invert emulsion).

Bituminous Grout

This is a combination of bituminous material and fine sand that will flow into place without mechanical manipulation when heated.

Blind Nailing

The practice of nailing the back portion of a roofing ply.

Blister

This is a spongy raised portion of a roof membrane, which ranges in area from 1 inch in diameter and barely detectable height upwards. Blisters result from the pressure buildup of gases entrapped in the membrane system. These gases most commonly are air and/or water vapor. Blisters usually involve delamination of the underlying membrane plies.

Bond

The adhesive and cohesive forces holding roofing components in intimate contact.

Brooming

This is embedding a ply of roofing material by using a broom to smooth out the ply and ensure contact with the adhesive under the ply.

BTU

(British Thermal Unit) The heat energy required to raise the temperature of 1 pound of water 1 degree fahrenheit.

Built-up Roof Covering

This is two or more layers of felt cemented together and surfaced with a cap sheet, mineral aggregate, smooth coating or similar surfacing material.

Built-up Roof Membrane

A semi-flexible, continuous roof membrane assembly, consisting of plies of saturated felts, coated felts, fabrics or mats between which alternate layers of bitumen are applied, generally surfaced with mineral aggregate, bituminous materials, or a granule surfaced roofing sheet. (abbreviation: bur.)

Cant Strip

This is a beveled shaped strip of wood or wood fiber that fits into the angle formed by the intersection of a horizontal surface and a vertical surface; the 45" slope of the surface of the cant strip provides a gradual angular transition from the horizontal surface to the vertical surface.

Cap Flashing

see FLASHING.

Capillarity

The action by which the surface of a liquid (where it is in contact with a solid) is elevated or depressed, depending upon the relative attraction of the molecules of the liquid for each other and for those of the solid.

Cap Sheet

This is the top layer of roofing felt which is designed to act as a primary water barrier. It may be covered with tiles or left uncovered. See modified bitumen.

Caulking

A composition of vehicle and pigment, used at ambient temperatures for filling joints, that remains plastic for an extended time after application.

Class A Roof Assemblies

Roof assemblies that are effective against severe fire test exposure.

Coal Tar Bitumen

A semi-solid hydrocarbon, dark brown to black in color, that’s formed as a residue from the partial evaporation or distillation of coal tar. It is used as the waterproofing agent in dead-level or low-slope built-up roofs. It differs from coal tar pitch in having a lower front-end volatility. (for specification properties, see astm standard d 450, type ill.)

Coal Tar Felt

See TARRED FELT.

Coal Tar Pitch

A semi-solid hydrocarbon, dark brown to black in color, that’s formed as a residue from the partial evaporation or distillation of coal tar. It is used as the waterroofing agent in dead-level or low-slope built-up roofs. (for specification properties, see astm d 450, types i and 11.)

Coated Base Sheet

A felt that has been impregnated and saturated with asphalt and then coated on both sides with harder, more viscous asphalt to increase its impermeability to moisture; parting agent is incorporated to prevent the material from sticking in the roll.

Cold-Process Roofing

A semi-flexible, continuous roof membrane, which consisting of plies of felts, mats, or fabrics that are laminated on a roof with alternate layers of cold-applied roof cement and surfaced with a cold-applied coating.

Condensation

The conversion of water vapor or other gas to liquid as the temperature drops or the atmospheric pressure rises. (see dew-point.)

Coping

This is the covering piece placed on top of a wall that is exposed to the weather. It is usually sloped to shed water.

Cornice

The overhang of a pitched roof at the eave line, usually consisting of, a facia board, a soffit for a closed cornice, and appropriate moldings.

Counterflashing

Counterflashing is formed metal sheeting secured to walls, curbs, or other surfaces, for use in protecting the top edge of base flashings from exposure to weather. Counterflashing may also refer to a method of counterflashing used over the termination of flashing to maintain a watertight seal.

Stucco Stop Counterflashing

The stucco stop method of counterflashing over the termination of flashing maintains a water tight seal. Stucco stops are used behind a wall or flashing as they have a smooth top horizontal edge so they are less visible and also block any water that penetrated the wall from getting under the flashing. The stucco stop has a flat top section so it can be used under other materials (stucco or modified bitumen).

Caulk Stop Counterflashing

Caulk stops are used on the exterior of a parapet wall and have a bead of caulking applied to the top horizontal edge to form a seal to the wall its attached to.

Course

(1) a term used for each application of material that forms the waterproofing system or the flashing; or, (2) one layer of a series of materials applied to a surface (for instance, a five course wall flashing is composed of three applications of mastic with one ply felt sandwiched between each layer of mastic).

Coverage

The surface area (in square feet) to be continuously coated by a specific roofing material, with allowance made for a specfic lap.

Crack

A separation and/or fracture occuring in a roof membrane or roof deck, generally caused by thermally induced stress or substrate movement.

Creep

A roof system caused by the movement of the roof membrane that results from continuous thermal stress or the permanent deformation of a roofing material.

Cricket

A superimposed construction placed in a roof area to assist drainage. (see nrca construction detail p).

Cutback

A term that refers to any bituminous roofing material that at has been solvent thinned. Cutbacks are used in cold-process roofing adhesives, flashing cements, and roof coatings.

Cutoff

This is a material seal that is designed to prevent lateral water movement into the edge of a roof system where the membrane terminates at the end of a day's work or used to isolate sections of the roof system. Cutoffs are usually removed before the continuation of work.

Dampproofing

Treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.

Dead Level

A descriptive term of an absolutely horizontal roof. Zero slope. (see slope.)

Dead Level Asphalt:

A roofing asphalt that has a softening point of 140°f and that conforms to the requirements of astm standard d 312, type i..

Dead Loads

A term that refers to non-moving rooftop loads, such as mechanical equipment, air conditioning units, and the roof deck itself.

Deck

The structural surface to which the roofing or waterproofing system (including insulation) is applied.

De-Laminatlon

The separation of the plies in a roof membrane system or separation of laminated layers of insulation.

Dew-Point

Refers to the temperature at which water vapor starts to condense in cooling air at the existing atmospheric pressure and vapor content.

Dormer

This is an opening in a sloping roof, the framing of which projects out to form a vertical wall suitable for windows other openings.

Downspout

A pipe, usually of metal, for carrying rainwater from roof gutters.

Drain

A device that allows for the flow of water from a roof area. (See NRCA Construction Detail W-2.)

Dropback

A term that refers to a reduction in the softening point of bitumen that occurs when bitumen is heated in the absence of air. (see softening point drift.)

Dry in

Process of applying the first layer of felt in a roofing system.

Edge Sheets

Felt strips that are cut to widths narrower than the standard width of the full felt roll. They are used to start the felt-shingling pattern at a roof edge.

Edge Stripping

The application of felt strips cut to narrower widths than the normal width of the full felt roll. They are used to cover joints.

Edge Venting

The practice of providing regularly spaced protected openings along a roof perimeter to relieve moisture vapor pressure.

Elastomer

This is a macromolecular material that returns rapidly to its approximate initial dimensions and shape after substantial deformation by a weak stress and the subsequent release of that stress.

Elastomeric

The term used to describe the elastic, rubber-like properties of a material.

Embedment

(1) the process of pressing a felt, aggregate, fabric, mat, or panel uniformly and completely into hot bitumen or adhesive; or, (2) the process of placing a material into another material so that it becomes an integral part of the whole material.

Emulsion

A term that refers to the intimate dispersion of an organic material and water achieved by using a chemical or clay emulsifying agent.

Envelope

A continuous felt fold formed by wrapping and securing a portion of a base felt back up and over the felt plies above it. Envelopes help prevent the seepage of bitumen.

Expansion Joint

This is a structural separation between two building elements designed to minimize the effect of the stresses and movements of a building's components and to prevent these stresses from splitting or ridging the roof membrane. (see nrca construction detail c-i.)

Exposure

(1) the transverse dimension of a roofing element not overlapped by an adjacent element in any roof system. The exposure of any ply in a membrane may be computed by dividing the felt width minus 2 inches by the number of shingled plies: thus, the exposure of a 36 inch wide felt in a shingled, four-ply membrane should be 8-12 inches; or, (2) the time during which a portion of a roofing element is exposed to the weather.

Fabric

This is a woven cloth of organic or inorganic filaments, threads, or yarns.

Facia

A term used to describe a flat board, band, or face used sometimes by itself but usually in combination with moldings, often located at the outer face of the cornice.

Factory Mutual (FM)

An organization which classifies roof assemblies for their fire characteristics and wind-uplift resistance for insurance companies in the United States.

Factory Square

108 square feet (10 square meters) of roofing material.

Felt

Refers to a fabric manufactured from vegetable fibers (organic felts), asbestos fibers (asbestos felts), or glass fibers (glass fiber felts). The manufacturing process involves mechanically interlocking the fibers of the particular felt material in the presence of moisture and heat.

Fine Mineral Surfacing

An inorganic, water-insoluble material, more than 50% of which passes through the no. 35 sieve, that may be used on the surface of roofing material.

Fishmouth

A half-cylindrical or half conical opening formed by an edge wrinkle.

Flashing

A term used to describe a system used to seal the edges of a membrane at walls, expansion joints, drains, gravel slopes, and other areas where the membrane is interrupted or terminated.

Flat Asphalt

A roofing asphalt that has a softening point of approximately 170°f and that conforms to the requirements of ASTM Standard D 312, Type 11.

Flood Coat

This is the top layer of bitumen into which the aggregate is embedded on an aggregate surfaced built-up roof.

Fluid Applied Elastomer

A term that refers to an elastomeric material, which is fluid at ambient temperature, that dries or cures after application to form a continuous membrane.

Glass Fiber Felt

This is a felt sheet in which glass fibers are bonded into the felt sheet with resin. They are suitable for impregnation and coating. They are used in the manufacture and coating of bituminous waterproofing materials, roof membranes, and shingles.

Glass Fiber Mat

A thin mat composed of glass fibers wlth or without a binder.

Gutter

A shallow channel along the eaves of a house to control the flow of rainwater from the roof.

Hot Mopping

Refers to the application of hot asphalt used to secure multiple layers of roofing felt.

Hip

A term that describes the external angle formed from intersecting planes from all four sides of a roof.

Hip roof

A roof that rises by inclined planes from all four sides of a building.

Insulation

A substance that aids in the prevention in the passage of water and air.

Lightweight Concrete

A term used to describe concrete with a lower density, providing a more lightweight product.

Lintel

A horizontal structural material that supports load over an opening such as a door or window.

Mansard

A steep-sloped decorative roof.

Masonry

A term used to describe stone, brick, concrete, concrete-blocks.

Modified Bitumen

One or more layers of polymer-modified asphalt sheets that is fully adhered or mechanically attached to the substrate.

Ply

Layer of reinforcement

Pitch Pan

This is a container situated around rooftop machinery and filled with pitch or another substance to seal water out.

Ponding Water

Water that collects at low points in a roof.

Ridge Vent

A ventilator located near the ridge that allows warm air or moisture to escape from the attic area.

Sheathing

The flat surface between rafters and roofing materials. Also referred to as decking.

Shingle

The term shingle refers to a single piece of prepared roofing material, either asphalt or wood, for use in steep slope roof systems; or, (2) to install a wood or asphalt shingle roof system.

Asphalt Shingle - Two types of asphalt shingles are used: organic and fiberglass or glass fiber. Organic shingles are generally paper (felt) saturated with asphalt to make it waterproof, then a top coating of adhesive asphalt is applied and ceramic granules are then embedded. In the case of algae-resistant shingles, a portion of the granules contain leachable copper or tin designed to inhibit moss growth and discoloration from algae on the roof.

Shingles are judged by weight per square. Organic shingles contain around 40% more asphalt per square (100 sq ft.) Than fiberglass shingles which makes them weigh more and gives them excellent durability and blow-off resistance. Shingle durability is ranked by warranteed life, ranging from 20 years to 50 years; in some cases lifetime warranties are available.

Fiberglass Shingle - Fiberglass shingles consist of a base layer of glass fiber reinforcing mat. The glass fiber mat is not waterproof by itself. Fiberglass mat is made from wet, random-laid fiberglass bonded with urea-formaldehyde resin. The mat is then coated with asphalt which contains mineral fillers and makes the fiberglass shingle waterproof. Fiberglass reinforcement was devised as the replacement for asbestos paper reinforcement of roofing shingles and typically ranges from 1.8 to 2.3 pounds/square foot.

Scupper

An opening in a parapet wall that allows water to drain.

Tiles, roof

An all-encompassing term, roof tiles are thin slabs designed mainly to keep out rain, and are traditionally made from locally available materials such as clay or slate. Modern materials such as concrete and plastic are also used and some clay tiles have a waterproof glaze. A large number of shapes (or "profiles") of roof tiles have evolved. These include:

Flat – the simplest type, these tiles are laid in regular overlapping rows, and suitable for stone and wooden tiles, and most recently, solar cells.

Roll – an ancient roman pattern of curved and flat tiles that make rain channels on a roof.

Spanish S – these tiles feature an s-shaped profile, allowing adjacent tiles to interlock. These result in a ridged pattern resembling a ploughed field.

Barrel – these semi-cylindrical tiles are made by forming clay around a curved surface, often a log or one's thigh, and laid in alternating columns of convex and concave tiles.

Roof tiles are 'hung' from the framework of a roof by fixing them with nails. The tiles are usually hung in parallel rows, with each row overlapping the row below it to exclude rainwater and to cover the nails that hold the row below.

Other roof tiles include ridge, hip and valley tiles, which are roof tiles for special positions, particularly where the planes of the several pitches meet.

Tin Caps

A term that refers to a corrosion resistant device for use as a part of the securing process of roofing felt (tar paper, roll roofing, etc.). Essentially acting as a large washer.

Tapered Insulation

A product used in transitions between substrate levels to create a slope.

Underlayment

A term that refers to one or more water shedding layers applied to a sloped roof designed to function with a prepared roof covering.

Valley Metal

This is a metal that’s usually galvanized, stainless, or copper used to reinforce to opposing slopes of a roof where positive drainage is to be accomplished.

Waterproofing

A term that refers to the treatment of a surface or structure in order to prevent the passage of water under hydrostatic pressure.