Roofing Glossary

Refer to our roofing glossary to help you better understand words and phrases you may hear during your roof replacement project.

Understanding Roofing Terminology

When working with your roofing contractor, you may hear them use industry-specific terms related to your roofing project. While you can certainly ask them to clarify anything unfamiliar for you, it can be helpful to have a handy reference guide.

Browse our roofing glossary to familiarize yourself with the meanings of commonly used residential roofing construction terms.

Algae Discoloration: A type of roof discoloration caused by algae. Commonly described incorrectly as fungus growth.

ARMA: The Asphalt Roofing Manufacturers Association, a trade association for North American manufacturers of asphalt roofing.

ASTM International: A voluntary organization concerned with development of consensus standards, testing procedures and specifications.

Asphalt: A bituminous waterproofing material applied to roofing materials during manufacture.

Asphalt Primer: A thin liquid bitumen applied to a surface to improve the adhesion of self-adhering membranes and to absorb dust.

Asphalt Roof Cement: An asphalt-based cement used to bond roofing materials. Also known as flashing cement or mastic; should conform to ASTM D4586 (Asbestos Free).

Architectural Shingles: See Laminated Shingles.

Back Surfacing: Fine mineral matter applied to the back side of shingles to keep them from sticking together.

Base Flashing: That portion of the flashing attached to or resting on the deck to direct the flow of water onto the roof covering.

Base-ply sheet: A product intended to be the base or middle ply in a residential self-adhering roll roofing system.

Base Sheet: A product intended to be used as a base ply in a self-adhering roll roofing system.

Blisters: Bubbles that may appear on the surface of asphalt roofing after installation.

Bridging: A method of reroofing with metric-size shingles.

Built-Up Roof: A flat or low-sloped roof consisting of multiple layers of ply sheets embedded in hot asphalt.

Bundle: A package of shingles. There are typically 3, 4 or 5 bundles per square.

Butt edge: The lower edge of the shingle tabs. (See Figure A.)

Cap Sheet: A mineral surfaced material that is used by itself or as the top layer of multi-layer rolled roof covering system.

Caulk: To fill a joint with mastic or asphalt cement to prevent leaks.

Cement: See Asphalt Roof Cement.

Chalk Line: A line made on the roof by snapping a taut string or cord dusted with chalk. Used for alignment purposes.

Class “A” Fire Resistance: The highest fire test classification for roofing as per ASTM E108 or UL790. Indicates roofing is able to withstand severe exposure to fire originating from sources outside the building.

Class “B” Fire Resistance: Fire test classification that indicates roofing material is able to withstand moderate exposure to fire originating from sources outside the building.

Class “C” Fire Resistance: Fire test classification that indicates roofing material is able to withstand light exposure to fire originating from sources outside the building.

Class 4 Impact Resistance: The highest impact resistance classification as per the UL 2218 Impact test indicating that shingles are more resistant to impacts resulting from hail storms.

Closed Cut Valley: A method of valley treatment in which shingles from one side of the valley extend across the valley while shingles from the other side are trimmed 2” from the valley centerline. The valley flashing is not exposed.

Collar: Pre-formed flange placed over a vent pipe to seal the roof around the vent pipe opening. Also called a vent sleeve.

Concealed Nail Method: Application of roll roofing in which all nails are driven into the underlying course of roofing and covered by a cemented, overlapping course. Nails are not exposed to the weather.

Condensation: The change of water from vapor to liquid when warm, moisture-laden air comes in contact with a cold surface.

Counter Flashing: That portion of the flashing attached to a vertical surface to prevent water from migrating behind the base flashing.

Course: A row of shingles or roll roofing running the length of the roof.

Coverage: The number of layers of material between the exposed surface of the roofing and the deck; i.e., single coverage, double coverage, etc.

Cricket: A peaked saddle construction at the back of a chimney to prevent accumulation of snow and ice and to deflect water around the chimney.

Cutout: The open portions of a strip shingle between the tabs. (See Figure A.)

Deck: The surface, installed over the supporting framing members, to which the roofing is applied. The minimum thickness of a wood deck is a 15/32” exterior grade plywood or 7/16” exterior grade OSB or as required by local building codes.

Dormer: A framed window unit projecting through the sloping plane of a roof.

Double Coverage: Application of asphalt roofing such that the lapped portion is at least 2” wider than the exposed portion, resulting in two layers of roofing material over the deck.

Downspout: A pipe for draining water from roof gutters. Also called a leader.

Drip Edge: A corrosion-resistant, non-staining material used along the eaves and rakes to allow water run-off to drip clear of underlying construction.

Eave: The horizontal, lower edge of a sloped roof. (See Figure B.)

Eave Flashing: Additional layer of roofing material applied at the eaves to help prevent damage from water back-up.

Exposed Nail Method: Application of roll roofing in which all nails are driven into the cemented, overlapping course of roofing. Nails are exposed to the weather.

Exposure: That portion of the roofing exposed to the weather after installation. (See Figure A.)

Felt: Fibrous material saturated with asphalt and used as an underlayment or sheathing paper.

Fiberglass Mat: The core material in an asphalt roofing shingle manufactured from glass fibers.

Flashing: Pieces of metal used to prevent seepage of water into a building around any intersection or projection in a roof such as vent pipes, chimneys, adjoining walls, dormers and valleys. Galvanized metal flashing should be minimum 26-gauge.

Flashing cement: See Asphalt Roof Cement.

Gable: The upper triangular portion of a sidewall that comes to a point at the ridge of a double sloping roof. (See Figure B.)

Gable Roof: A simple two-sided roof above a gable.

Gambrel Roof: A type of roof containing two sloping planes of different pitch on each side of the ridge. The lower plane has a steeper slope than the upper. Contains a gable at each end.

Granules: Typically ceramic-coated colored crushed rock that is applied to the exposed surface of asphalt roofing products.

Gutter: The trough that channels water from the eaves to the downspouts.

Head Lap: Shortest distance from the butt edge of an overlapping shingle to the upper edge of a shingle in the second course below. The triple coverage portion of the top lap of strip shingles. (See Figure A.)

Hexagonal Shingles: Shingles that have the appearance of a hexagon after installation.

Hip: The inclined external angle formed by the intersection of two sloping roof planes. Runs from the ridge to the eaves. (See Figure B.)

Hip Roof: A type of roof containing sloping planes on each of four sides. Contains no gables.

Hip Shingles: Shingles used to cover the inclined external angle formed by the intersection of two sloping roof planes.

Ice Dam: Condition formed at the lower roof edge by the thawing and re-freezing of melted snow on the overhang. Can force ponded water up and under shingles, causing leaks.

Ice Dam Protection: One or more courses of self-adhering underlayment installed at the eaves of a building to prevent damage from water back-up due to an ice dam. Also known as “Eave Flashing”.

Impact Resistant Shingles: Shingles that are designed to be more resistant to impacts resulting from hail storms. Impact resistant shingles are typically tested and classified in accordance with UL 2218, and may be classified as Class 1 through Class 4, with Class 4 indicating the highest impact resistance classification.

Interlocking Shingles: Individual shingles that mechanically fasten to each other to provide wind resistance.

Laminated Shingles: Shingles containing more than one layer to create extra thickness. Also called three-dimensional shingles or architectural shingles.

Lap: To cover the surface of one shingle or roll with another.

Lap Cement: An asphalt-based cement (conforming to ASTM D3019) used to adhere overlapping plies of roll roofing.

Low Slope Application: Method of installing asphalt shingles and underlayment on roof slopes ranging from 2” to less than 4” per foot.

Mansard Roof: A type of roof containing two sloping planes of different pitch on each of four sides. The lower plane has a much steeper pitch than the upper, often approaching vertical. (See Figure B.)

Mastic: See Asphalt Roof Cement.

Mid-ply Sheet: See Base-ply sheet.

Mineral Stabilizers: Finely ground limestone, slate, trap rock or other inert materials added to asphalt in shingles for durability and increased resistance to fire and weathering.

Mineral-Surfaced Roofing: Asphalt shingles and roll roofing that are covered with granules.

Nesting: A method of reroofing with new asphalt shingles over old shingles in which the top edge of the new shingle is butted against the bottom edge of the existing shingle tab.

No-Cutout Shingles: Shingles consisting of a single, solid tab with no cutouts.

Non-Veneer Panel: Any wood-based panel that does not contain a laminated veneer and carries an APA span rating, such as wafer board or oriented strand board.

Open Valley: Method of valley construction in which shingles on both sides of the valley are trimmed along a chalk line snapped on each side of the valley. Shingles do not extend across the valley. Valley flashing is exposed.

Organic Felt: An asphalt roofing base material manufactured from cellulose fibers.

Overhang: That portion of the roof structure that extends beyond the exterior walls of a building.

Pallets: Wooden platforms used for storing and shipping bundles of shingles.

Ply: A layer of roofing (i.e., one-ply, two-ply).

Ponding: The accumulation of water after rainfall at low-lying areas on a roof that remains wet when other parts of the roof have dried.

Primer: An asphalt-based primer used to prepare surfaces for bonding with self-adhering asphalt sheets.

Racking: Roofing application method in which shingle courses are applied vertically up the roof.

Rafter: The supporting framing member immediately beneath the deck, sloping from the ridge to the wall plate.

Rake: The inclined edge of a sloped roof over a wall. (See Figure B.)

Random-Tab Shingles: Shingles on which tabs vary in size and exposure.

Recovering: The process of adding an additional layer of roofing over an existing layer. A maximum of two layers of any roofing type are permitted on a roof at any time.

Release Tape: A plastic strip that is applied to the back of self-sealing shingles. This strip prevents the shingles from sticking together in the bundles and need not be removed for application.

Reroofing: The process of removing existing roof coverings and replacing with a new roofing system.

Ridge: The uppermost, horizontal external angle formed by the intersection of two sloping roof planes. (See Figure B.)

Ridge Shingles: Shingles used to cover the horizontal external angle formed by the intersection of two sloping roof planes.

Rise: The vertical distance from the eaves line to the ridge.

Roll Roofing: Asphalt roofing products manufactured in roll form.

Roofing Tape: An asphalt-saturated tape used with asphalt cements for flashing and patching asphalt roofing.

Run: The horizontal distance from the eaves to a point directly under the ridge. One half the span.

Saturated Felt: An asphalt-impregnated felt used as an underlayment between the deck and the roofing material.

SBS: Styrene-Butadiene-Styrene, which is a synthetic polymer that is mixed with asphalt in some products to increase the flexibility and other attributes of the products.

Self-Adhering Shingle Underlayment: A self-adhering waterproofing underlayment designed to protect against water infiltration due to ice dams or wind driven rain. The code prescribed requirement for this category of products is that they meet ASTM D1970 and bear a label of that designation.

Self-Sealing Shingles: Shingles containing factory-applied strips or spots of self-sealing adhesive.

Self-Sealing Strip or Spot: Factory-applied adhesive that bonds shingle courses together when exposed to the heat of the sun after application.

Selvage: That portion of roll roofing overlapped by the succeeding course to obtain single or double coverage at the lap.

Shading: Slight differences in shingle color that may occur as a result of normal manufacturing operations.

Sheathing: See Deck.

Shed Roof: A roof containing only one sloping plane. Has no hips, ridges, valleys or gables.

Single Coverage: Asphalt roofing that provides one layer of roofing material over the deck.

Slope: The degree of roof incline expressed as the ratio of the rise, in inches, to the run, in inches. For example, roof slope of 4/12 has a 4 inch rise every 12 inches.

Smooth-Surfaced Roofing: Roll roofing that is covered with ground talc or mica instead of granules (coated).

Soffit: The finished underside of the eaves.

Soil Stack: A vent pipe that penetrates the roof.

Span: The horizontal distance from eave to eave.

Square: A unit of roof measure covering 100 square feet.

Square-Tab Shingles: Shingles on which tabs are all the same size and exposure.

Standard Slope Application: Method of installing asphalt shingles on roof slopes 4” to 21” per foot.

Starter Strip: Asphalt roofing applied at the eave that provides protection by an additional layer of material under the cutouts and joints of the first course of shingles.

Steep Slope Application: Method of installing asphalt shingles on roof slopes greater than 21” per foot.

Step Flashing: Base flashing application method used where a vertical surface meets a sloping roof plane.

Strip Shingles: Asphalt shingles made from a single layer that are approximately three times as long as they are wide.

Synthetic Underlayment: An underlayment product that is typically manufactured using polypropylene and is used as an alternative to felt underlayment.

Tab: The exposed portion of strip shingles defined by cutouts. (See Figure A.)

Talc: See Back Surfacing.

Tear Off: To remove an existing roofing system down to the structural deck.

Telegraphing: A shingle distortion that may arise when a new roof is applied over an uneven surface.

Three-Dimensional Shingles: See Laminated Shingles.

Top Lap: That portion of the roofing covered by the succeeding course after installation. (See Figure A.)

UL: Underwriters Laboratories, LLC

UL Label: Label displayed on packaging to indicate the level of fire and/or wind resistance of asphalt roofing.

Underlayment: Asphalt saturated felt or specially engineered synthetic material used beneath roofing to provide additional protection for the deck.

Valley: The internal angle formed by the intersection of two sloping roof planes. (See Figure B.)

Vapor Retarder: Any material used to prevent the passage of water vapor.

Vent: Any outlet for air that protrudes through the roof deck such as a pipe or stack. Any device installed on the roof, gable or soffit for the purpose of ventilating the underside of the roof deck.

Vent Sleeve: See Collar.

Woven Valley: Method of valley construction in which shingles from both sides of the valley extend across the valley and are woven together by overlapping alternate courses as they are applied. The valley flashing is not exposed.

Familiarizing yourself with this list of roofing terms may help you communicate a little better with your roofing contractor.

If you’re looking for a qualified roofing contractor to assist you with your roofing replacement project, browse the network of independent roofing contractors in the Owens Corning Contractor Network to find one in your area.