Commercial Roofing Glossary of Terms


  • Algae – Rooftop fungus that can leave dark stains on roofing.
  • Alligatoring – The cracking of the surfacing bitumen on a bituminous roof or coating on a SPF roof, producing a pattern of cracks similar to an alligator’s hide.
  • Angled fasteners – Roofing nails and staples driven into decks at angles not parallel to the deck.
  • APA – American Plywood Association. Tests and sets standards for all varieties of plywoods used in the U.S.
  • Apron flashing – Metal flashing used at chimney fronts.
  • Architectural Panel – A metal roof panel, typically a double standing seam or batten seam; usually requires solid decking underneath and relies of slope to shed water.
  • ARMA – Asphalt Roofing Manufacturer’s Association. Organization of roofing manufacturers.
  • Asphalt – A bituminous waterproofing agent used in various types of roofing materials.
  • Asphalt concrete primer – Asphalt based primer used to prepare concrete and metal for asphalt sealant.
  • Asphalt Emulsion – A mixture of asphalt particles and emulsifying agent, such as bentonite clay and water.
  • Asphalt plastic cement – Asphalt based sealant material, meeting ASTM D4586 Type I or II. Used to seal and adhere roofing materials. Also called mastic, blackjack, roof tar, bull.
  • ASTM – The American Society for Testing and Materials. Organization that sets standards for a wide variety of materials, including roofing.


  • Back-surfacing – Granular material added to shingle’s back to assist in keeping separate during delivery and storage. Barrel Vault – A building profile featuring a rounded profile to the roof on the short axis, but with no angle change on a cut along the long axis.
  • Barrier Board – Noncombustible board stock material of low thermal conductivity placed between two elements of a roof assembly.
  • Base Flashing – Plies or strips of roof membrane material used to close off and/or seal a roof at the horizontal-to-vertical intersections. Membrane base flashing covers the edge of the field membrane.
  • Base Sheet – An impregnated, saturated, or coated felt placed as the first ply in some low-slope roof systems.
  • Bermuda Seam – A metal panel profile featuring a step-down profile that runs perpendicular to the slope of the roof.
  • Blistering – Bubbles or pimples in roofing materials. Usually moisture related. In shingles blisters are either moisture under the material or moisture trapped inside the material.
  • Blow-offs – When shingles are subjected to high winds, and are forced off a roof deck. Brooming – To improve the embedding of a membrane by using a broom or squeegee to smooth it out and ensure contact with the adhesive under the membrane.
  • Buckling – When a wrinkle or ripple affects shingles or their underlayments.
  • Built-up Roof – A continuous, semi-flexible roof membrane, consisting 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.


  • Cant Strip – a beveled strip used under flashings to modify the angle at the point where the roofing or waterproofing membrane meets any vertical element.
  • Cap flashing – Usually composed of metal, used to cover or shield the upper edges of the membrane base flashing; wall flashing can also be used to cover the top of various building components, such as parapets or columns.
  • Combing Ridge – A topmost row of roofing slates that project above the line of the ridge.
  • Closed-cut valley – A shingle valley installation method where one roof plane’s shingles completely cover the other’s. The top layer is cut to match the valley lines.
  • Cobra® – GAFMC’s respected brand name for ventilation products.
  • Corrosion – When rust, rot or age negatively affect roofing metals.
  • Counter-flashing – The metal or siding material that is installed over roof-top base flashing systems.
  • Course – A row of material that forms the roofing, waterproofing or flashing system.
  • Cover Board – An insulation board used over closed cell plastic insulation (e.g., polyisocyanurate) to prevent blistering when used in conjunction with hot bituminous membranes.
  • Crickets – A peaked water diverter installed behind chimneys and other large roof projections. Effectively diverts water around projections.
  • Cupping – When shingles are improperly installed over an existing roof or are over-exposed, they form a curl or cup.
  • Cutback – Solvent-thinned bitumen used in cold process roofing adhesives, cements and coatings.


  • Deck – The substrate over which roofing is applied. Usually plywood, wood boards, or planks.
  • Dormer – A raised roof extending out of a larger roof plane.
  • Double Coverage – Application of asphalt, slate, or wood roofing such that the lapped portion is at least two inches wider than the exposed portion, resulting in two layers of roofing material over the deck.
  • Drip-edge – An installed lip that keeps shingles up off of the deck at edges, and extends shingles out over eaves and gutters, and prevents water from backing up under shingles.
  • Dubl-Coverage® Mineral Guard – Roll roofing material with 19″ selvage edge for double coverage over roof deck.


  • Eaves – The roof edge from the fascia to the structure’s outside wall. In general terms, the first three feet across a roof is termed the eave.
  • Edge Venting – The practice of providing regularly spaced or continuously protected openings along a roof edge or perimeter, used as part of a ventilation system to dissipate heat and moisture vapor.
  • End-laps – When installing rolled products in roofing, the area where a roll ends on a roof, and is overlapped by the next section of rolled material. (underlayments, rolled roofing)
  • Expansion Cleat – A cleat designed to accommodate thermal movement of metal roof panels.
  • Exposure – The area on any roofing material that is left exposed to the elements.


  • Fasteners – Nails or staples used in securing roofing to the deck.
  • Feathering Strip – Tapered wood filler strips placed along the butt ends of old wood shingles to create a relatively smooth surface when reroofing over existing wood shingle roofs.
  • Felt – Organic or paper-based rolled material saturated with asphalt to serve as roofing underlayment.
  • FHA – The Federal Housing Authority. Sets construction standards throughout the U.S.
  • Fiberglass mat – fibers condensed into strong, resilient mats for use in roofing materials.
  • Flange – Metal pan extending up or down a roof slope around flashing pieces. Usually at chimneys and plumbing vents
  • Flashing – Materials used to waterproof a roof around any projections through the roof deck.
  • Flashing cement – Sealant designed for use around flashing areas, typically thicker than plastic cement.
  • Fly-In – method of application for roll materials by which the dry sheet is set into the bitumen or adhesive applied to the roof surface.


  • Gable roof – Traditional roof style; two peaked roof planes meeting at a ridge line of equal size.
  • GAFCant® – GAFMC cant strips for deflecting water away from flashing areas. Typically used on low slope roofs.
  • Glass Felt – Glass fibers bonded into a sheet with resin and suitable for impregnation with asphalt in the manufacture of bituminous waterproofing, roofing membranes and shingles.
  • Glaze Coat – A thin protective coating of bitumen applied to the lower plies or top ply of a roof membrane when application of additional felts or surfacing are delayed.
  • Golden Pledge® – GAFMC’s strongest limited warranty for shingles. America’s strongest steep slope warranty.
  • Grand Sequoia® – GAFMC shingle with wood shake appearance.
  • Grand Slate™ – GAFMC shingle with slate appearance.
  • Granules – Crushed rock that is coated with a ceramic coating and fired, used as top surface on shingles.


  • Hand-sealing – The method to assure sealing of shingles on very steep slopes, in high wind areas, and when installing in cold weather.
  • High nailing – When shingles are nailed or fastened above the manufacturer’s specified nail location.
  • Hip legs – The down-slope ridges on hip roofs.
  • Hip roof – A roof with four roof planes coming together at a peak and four separate hip legs.


  • Ice Dam – When a snow load melts on a roof and re-freezes at the eave areas. Ice dams force water to “back-up” a roof and cause leakage.
  • Interlayment – A felt, metal, or membrane sheet material used between courses of steep-slope roofing to improve the weather and water-shedding characteristics of the primary roof covering during times of wind-driven precipitation.


  • Knee Cap – A metal cover trim that fits over a panel rib after it has been cut and bent.


  • “L” flashing – Continuous metal flashing consisting of several feet of metal. Used at horizontal walls, bent to resemble an “L”.
  • Laminated shingles – Shingles made from two separate pieces that are laminated together. GAFMC Timberline® Series, Country Mansion® and Grand Sequoia® Shingles. Also called dimensional shingles and architectural shingles.
  • Laps – The area where roll roofing or rolled underlayments overlap one another during application (see also side laps and end laps).
  • Live Load – Temporary load that the roof structure must be designed to support, as required by governing building codes. Live loads are generally moving and/or dynamic or environmental, (e.g., people, installation equipment, snow, ice or rain, etc.).
  • Low slopes – Roof pitches less than 4/12 are considered low sloped roofs. Special installation practices must be used on roofs sloped 2/12-4/12.


  • Mansard – A roof design with a nearly vertical roof plane that ties into a roof plane of less slope at its peak.
  • Mats – The general term for the base material of shingles and certain rolled products.
  • Modified bitumen – Rolled roofing membrane with polymer modified asphalt and either polyester or fiberglass reinforcement. Mole Run – A meandering ridge in a roof membrane not associated with insulation or deck joints.
  • Mop-and-flop – an application procedure in which roofing elements (insulation boards, felt plies, cap sheets, etc.) are initially placed upside down adjacent to their ultimate location; coated with adhesive or bitumen; and turned over and adhered to the substrate.
  • Mortar – Mixture of sand, mortar, limestone and water used in bonding a chimney’s bricks together.


  • Nail-guide-line – Painted line on laminated shingles, to aid in the proper placement of fasteners.
  • Nail-pop – When a nail is not fully driven, it sits up off the roof deck.
  • Nesting – Installing a second layer of shingles aligning courses with the original roof to avoid shingle cupping.
  • NRCA – The National Roofing Contractors Association. Respected national organization of roofing contractors.


  • Open valley – Valley installation using metal down the valley center.
  • Organic mat – Material made from recycled wood pulp and paper.
  • Organic Shingles – Shingles made from organic (paper) mats.
  • OSB – Oriented Strand Board. A decking made from wood chips and lamination glues.
  • Over-driven – The term used for fasteners driven through roofing material with too much force, breaking the material.
  • Over-exposed – Installing shingle courses higher than their intended exposure.
  • Overspray Surface Texture – In SPF roofing, a condition of the foam in which the surface shows a linear course textured pattern and/or a pebbled surface. This surface is generally downwind of the sprayed polyurethane path and, if severe, unacceptable for proper coating and protection.


  • Pan – The bottom flat part of a roofing panel that is between the ribs of the panel.
  • Pitch – ratio of the rise of the roof to the span of the roof.
  • Power vents – Electrically powered fans used to move air from attics and structures.
  • Plastic cement – Asphalt based sealant. Also called bull, mastic, tar, asphalt cement.
  • Plumbing vents – Term used to describe plumbing pipes that project through a roof plane. Also called vent stacks.
  • Prevailing wind – The most common direction of wind for a particular region.
  • Protected Membrane Roof – an insulated and ballasted roofing assembly in which the insulation and ballast are applied on top of the membrane (sometimes referred to as an “inverted roof assembly”).


  • Quarter sized – Term for the size of hand sealant dabs, size of a U.S. 25c piece.


  • Racking – Method of installing shingles in a straight up the roof manner.
  • Rake edge – The vertical edge of gable style roof planes.
  • Release film – The plastic sheet installed on the back of Weather Watch(R) and StormGuard(R) underlayments. Used for packaging and handling. Remove before installation.
  • Rigid vent – Hard plastic ridge vent material.
  • Recover – To add a new roof membrane over an existing one.
  • Roof Assembly – An assembly of interacting roof components including the roof deck, vapor retarder (if needed), insulation and roof covering.
  • Roof Curb – Raised frame used to mount mechanical units (such as air conditioning or exhaust fans), skylights, etc. on a roof.
  • Roof louvers – Rooftop rectangular shaped roof vents. Also called box vents, mushroom vents, airhawks, soldier vents.
  • Roof plane – A roofing area defined by having four separate edges. One side of a gable, hip or mansard roof.


  • Sawteeth – The exposed section of double thickness on Timberline(R) Series shingles. Shaped to imitate wood shake look on the roof.
  • Screen Wall – A nonstructural wall erected around units or curbs on a roof. Typically the framing consists of girts with a wood or metal covering attached to the frame.
  • Self-sealant – Sealant installed on shingles. After installation, heat and sun will activate sealant to seal the shingles to each other.
  • Selvage – The non exposed area on rolled roofing. Area without granules. Designed for nail placement and sealant.
  • Shark Fin – An upward curled felt side lap or end lap.
  • Shed roof – Roof design of a single roof plane. Area does not tie into any other roofs.
  • Shingle-Mate® – GAFMC’s shingle underlayment. Breather type with fiberglass backing to reduce wrinkles and buckles.
  • Side-laps – The area on rolled material where one roll overlaps the rolled material beneath it. Also called selvage edge on rolled roofing.
  • Side-walls – Where a vertical roof plane meets a vertical wall. The sides of dormers etc.
  • Single-ply Membrane – Roofing membranes that are field applied using just one layer of membrane material (either homogeneous or composite) rather than multiple layers.
  • Single-ply Roof – A roof system in which the principal roof covering is a single layer of flexible membrane often thermoset or thermoplastic.
  • Slip Sheet – Sheet material, such as reinforced kraft paper, rosin-sized paper, polyester scrim or polyethylene sheeting, placed between two components of a roof assembly to ensure that no adhesion occurs between them and to prevent possible damage from chemical incompatibility, wearing or abrasion of the membrane.
  • Snow Load – The live load due to the weight of snow on a roof; included in the design calculations.
  • Soffit ventilation – Intake ventilation installed under the eaves, or at the roof edge.
  • Smart Choice® Limited Warranty – GAFMC’s standard shingle limited warranty.
  • Smart Choice® System Plus Limited Warranty – GAFMC’s next grade of enhanced warranty. Extended coverage for owners.
  • Spud – To remove the roofing aggregate and most of the bituminous top coating by scraping and chipping.
  • Square – 100 square feet.
  • Square Tab Shingle – Shingle with tabs that are all the same size and exposure.
  • Standing Seam – A type of seam between adjacent sheets of metal roofing material made by turning up the edges of two adjacent panels and then folding or interlocking them in a variety of ways.
  • Starter strip – The first course of roofing installed. Usually trimmed from main roof material.
  • Steep slope roofing – Generally all slopes higher than 4/12 are considered steep slopes.
  • Step-flashing – Metal flashing pieces installed at side-walls and chimneys for weather-proofing.
  • StormGuard® – GAFMC waterproof underlayment. Film surfaced rolled underlayment, 1.5 squares coverage per roll.
  • Striation – a parallel series of small grooves, channels, or impressions typically within a metal roof panel used to help reduce the potential for oil-canning.


  • Tab – The bottom portion of traditional shingle separated by the shingle cut-outs.
  • Tear-off – Removal of existing roofing materials down to the roof deck.
  • Telegraphing – When shingles reflect the uneven surface beneath them. Shingles installed over buckled shingles may show some buckles.
  • Timberline® Series – GAFMC’s trademark name for laminated wood shake style shingles.
  • TIMBERTEX® – GAFMC enhanced Hip and Ridge Shingles.
  • Transitions – When a roof plane ties into another roof plane that has a different pitch or slope.


  • Under-driven – Term used to describe a fastener not fully driven flush to the shingles surface.
  • Underlayments – Asphalt based rolled materials designed to be installed under main roofing material, to serve as added protection.


  • Valleys – Area where two adjoining sloped roof planes intersect on a roof creating a “V” shaped depression.
  • Vapor – Term used to describe moisture laden air.
  • Ventilation – The term used in roofing for the passage of air from an enclosed space.


  • Warm wall – The finished wall inside of a structure, used in roofing to determine how to install waterproof underlayments at eaves.
  • Warranty – The written promise to the owner of roofing materials for material related problems.
  • Waterproof underlayments – Modified bitumen based roofing underlayments. Designed to seal to wood decks and waterproof critical leak areas.
  • Weather Stopper® Integrated Roofing System™ – GAFMC’s complete roofing system and components.
  • Weather Watch® – GAFMC’s granule surfaced waterproof underlayment.
  • Woven Valleys – The method of installing valleys by laying one shingle over the other up the valley center.