Roofing Glossary
Common roofing terms and definitions. Click any linked calculator to put these concepts into practice.
Square (Roofing)
A unit of measurement equal to 100 square feet of roof area. Roofing materials, labor, and costs are commonly priced per square.
Pitch
The slope or steepness of a roof expressed as a ratio of vertical rise to 12 inches of horizontal run. A 6/12 pitch rises 6 inches for every 12 inches of horizontal distance.
Soffit
The underside of the roof overhang. Soffits often contain vents that provide intake air for attic ventilation. They protect rafters from weather exposure.
Fascia
The vertical board that runs along the edge of the roof, mounted to the ends of the rafters. Gutters are typically attached to the fascia board.
Flashing
Thin metal pieces installed at joints, valleys, and penetrations to prevent water intrusion. Common materials include aluminum, copper, and galvanized steel.
Drip Edge
An L-shaped metal strip installed along roof edges to direct water away from the fascia and into gutters. Required by most building codes.
Ridge
The horizontal line at the top of the roof where two sloping sides meet. Ridge vents installed along this line provide exhaust ventilation for the attic.
Valley
The internal angle formed where two roof slopes meet. Valleys channel large volumes of water and require special waterproofing with ice shield or metal flashing.
Eave
The lower edge of the roof that overhangs the exterior wall. Eaves protect walls from rain and are where gutters are installed and ice dams commonly form.
Rake
The sloped edge of a gable roof that runs from the eave to the ridge. Rake edges need trim and drip edge to protect against wind-driven rain.
NFA (Net Free Area)
The unobstructed area of a vent through which air can freely pass, measured in square inches. NFA is always less than the vent's physical dimensions due to screens and louvers.
Underlayment
A water-resistant barrier installed on the roof deck beneath shingles or other roofing material. Types include asphalt-saturated felt (tar paper) and synthetic materials.
Sheathing (Roof Deck)
The structural boards or plywood panels nailed to the rafters, forming the base surface for roofing materials. Common materials are OSB and plywood, typically 7/16" or 1/2" thick.
Ice Dam
A ridge of ice that forms at the eave and prevents melting snow from draining. Ice dams can cause water backup under shingles. Prevention includes proper insulation, ventilation, and ice shield.
Dormer
A windowed structure that projects vertically from a sloped roof, adding usable space and light. Dormers create additional valleys and require careful flashing.
Rafter
A sloped structural member that extends from the ridge to the wall plate, supporting the roof deck and roofing materials. Common sizes are 2Ã6, 2Ã8, and 2Ã10.
Birdsmouth Cut
A notch cut into a rafter where it meets the wall plate, consisting of a horizontal seat cut and a vertical plumb cut. The seat cut should not exceed one-third of the rafter depth.
Starter Strip
The first row of roofing material installed at the eave, designed to seal under the tabs of the first course of shingles and prevent wind uplift and water intrusion.
Ridge Cap
Specially shaped shingles or metal pieces installed over the ridge to seal the joint where two roof planes meet. Ridge cap shingles are cut from full shingles or purchased as pre-formed pieces.
Standing Seam
A type of metal roofing panel with raised interlocking seams that connect panels together. Standing seam roofs use concealed fasteners, making them more weather-resistant than exposed-fastener panels.
Pitch Multiplier
A factor used to convert flat (plan-view) roof area to actual sloped area. Calculated as â(1 + (rise/12)²). A 6/12 pitch has a multiplier of 1.118, meaning the actual roof area is 11.8% larger than the footprint.
EPDM
Ethylene Propylene Diene Monomer â a synthetic rubber membrane used for flat and low-slope roofs. EPDM is durable, UV-resistant, and commonly available in 45-mil and 60-mil thicknesses.
TPO
Thermoplastic Polyolefin â a single-ply roofing membrane for flat and low-slope roofs. TPO is heat-welded at seams, reflects UV light, and is one of the fastest-growing commercial roofing materials.