Roof Pitch
roofing
The slope of a roof expressed as inches of vertical rise per 12 inches of horizontal run — a 6/12 roof rises 6 inches every foot.
Pitch determines three separate things: how much roof surface exists above a given footprint, which coverings are permitted, and whether the roof can be walked. Below 2/12 shingles are not an acceptable covering under IRC R905.2.2 and the roof needs a membrane system; between 2/12 and 4/12 a doubled underlayment is required. Roofs up to about 7/12 are generally walkable, 8/12 to 9/12 need roof jacks or a harness, and steeper than that requires staging. Labour rates rise sharply at the point a roof stops being walkable, which is why pitch affects cost twice over.
Formula
Pitch factor = √(1 + (rise ÷ 12)²) · Angle = arctan(rise ÷ run)
Example
A 6/12 pitch is 26.57° and has a pitch factor of 1.118, meaning the roof surface is 11.8% larger than the footprint beneath it.
Common mistake
Confusing pitch with the angle in degrees. A 12/12 roof is 45°, not 12° — and a "45-degree roof" quoted by a supplier means something entirely different from a 45/12 pitch, which does not exist.
Use the Roof Pitch Calculator
Convert between roof pitch, angle in degrees, and slope percentage — and get the pitch factor that turns a building footprint into true sloped roof area.
Open Roof Pitch Calculator →Related Terms
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