Roofing Terms

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 runoff to drip clear off the deck, eaves and siding.

Eave

The horizontal lower edge of a sloped roof.

Fascia

The material covering the rafter tails at the end of the roof.

Felt/Underlayment

A sheet of asphalt-saturated material (often called tarpaper) 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 resin glue. OSB  is often used as a substitute for plywood sheets.

Penetrations

Vents, pipes, stacks, chimneys anything that penetrates a roof deck.

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.