Deck: Roofing materials are applied to the deck, which is usually made from plywood or oriented strand board (OSB). Dormer: Dormers are small structures that project from a sloped roof. They usually have a window. Drip edge: The drip edge is attached to the edge of the roof. It channels water away from siding, eaves or the deck. Eave: The eave is a sloped roof’s horizontal lower edge. Fascia: The fascia is found at the cornice’s outer edge. It can be a flat board, band or face. Felt/underlayment: A secondary layer of protection for the roof deck is called the felt or underlayment. It is a sheet of tar paper, which is an asphalt-soaked paper. Fire rating: Roofing materials are rated according to their fire resistance. The three classes are A, B, and C. Class A is the most fire resistant. Flashing: Flashing is installed around intersections or projections including valleys, chimneys, vent pipes and joints on vertical walls. It prevents water seepage. Louvers: Louvers ventilate the area beneath a roof deck. They’re installed in a soffit or gable. They equalize air temperature and humidity. Penetrations: Anything that penetrates the roof deck, such as chimneys, stacks, pipes and vents. Rafters: The rafters are support framing to which a roof deck is attached. Sheathing: Sheathing is attached to the rafters to cover a building. Soffit: A soffit is the underside of the eaves. Square: One square equals 100 square feet (10 by 10 feet). A roof’s surface area is measured in squares. Valley: The intersection of two sloping roof surfaces. Vapor retarders: Vapor retarders restrict the passage of water vapor through a roof system or wall.