Definitions of common roofing terms
Cornice: The overhang of the roof at the eaves line that forms a connection between the roof and the sidewalls.
Deck/sheathing: The flat, substructure surface, usually plywood or oriented strand board (OSB – see definition below), to which roofing materials are applied.
Dormer: A small structure projecting from a sloped roof, usually with a window.
Drip edge: An L-shaped strip (usually metal) installed along roof edges to allow water runoff to drip clear of the deck, eaves, and siding.
Eave: The overhanging lower edge of a roof.
Fascia: A flat board, band or face located at a cornice’s outer edge.
Felt/underlayment: A sheet of asphalt-saturated material (often called tar paper) used as a secondary layer of protection for the roof deck. Its purpose is to waterproof roofs to prevent moisture from reaching past the top of the roof deck.
Fire rating: System for classifying the fire resistance of various materials. Roofing materials are rated Class A, B or C, with Class A materials having the highest resistance to fire originating outside the structure.
Flashing: Pieces of metal used to prevent the seepage of water around any intersection or projection in a roof system, such as joints at vertical walls, chimneys, vent pipes, and valleys.
Louvers (vents): Slatted devices installed in a gable or soffit to allow ventilation in the space below a roof deck and even out air temperature and moisture.
Oriented strand board (OSB or waferboard): Roof deck panels (4 by 8 feet) made of narrow bits of wood, installed lengthwise and crosswise in layers, and held together with resin glue. OSB often is used as a substitute for plywood sheets.
Penetrations: Anything that penetrates a roof deck, such as vents, pipes, stacks, and chimneys.
Rafters: The supporting framing to which a roof deck is attached.
Rake: The inclined edge of a roof over a wall.
Ridge: The top edge of two intersecting sloping roof surfaces.
Sheathing: The boards or sheet materials that are fastened to rafters to cover a house or building.
Slope/Pitch: Measured by rise in inches for each 12 inches of horizontal run: A roof with an 8-12 slope rises 8 inches for every foot of horizontal distance.
Soffit: The underside area of the overhang of the roof.
Square: The common measurement for roof area. One square is 100 square feet (10 by 10 feet).
Truss: Engineered components that supplement rafters in many newer homes and buildings. Trusses are designed for specific applications and cannot be cut or altered.
Valley: The angle formed at the intersection of two sloping roof surfaces.
Vapor Retarder: A material designed to restrict the passage of water vapor through a roof system or wall.
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