Roofing Term Glossary

Deck/Sheathing: The surface, usually plywood or oriented strand board (OSB), 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 run off to drip clear of the deck, eaves and siding.

Eave: The horizontal lower edge of a sloped 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.

Fire Rating: System for classifying the fire resistances 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 vent pipes, chimneys, valleys and joints at vertical walls.

Louvers: Slatted devices installed in a gable or soffit (the underside of eaves) to ventilate the space below a roof deck and equalize air temperature and moisture.

Oriented Strand Board (OSB): Roof deck panels (4 by 8 feet) made of narrow bits of wood, installed lengthwise and crosswise in layers, and held together with a resin glue. OSB often is used as a substitute for plywood sheets.

Penetrations: Vents, pipes, stacks, chimneys-anything that penetrates a roofdeck.

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: Measured by rise in inches for each 12 inches of horizontal run: A roof with a 4-in-12 slope rises 4 inches for every foot of horizontal distance.

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.