Roof 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 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.