Every once in a while, someone asks, "Why is the sky blue?" While not really a roofing question, we like to be helpful and enjoy passing on little bits of knowledge.....

Deck/sheathing
The flat, substructure 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 of the deck, eaves and siding.
Eave
The horizontal under 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 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 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.
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.