What is a walkable roof pitch?
Up to about 6:12 is generally walkable with care. From 7:12 upwards roofers need harnesses and roof jacks, which raises labour costs.
Calculate roof pitch in degrees, ratio, and percentage. Find rafter length and roof area based on rise and run measurements.
Pitch = rise ÷ run (expressed as x-in-12). Angle = arctan(rise ÷ run). Roof area = footprint × pitch multiplier, where multiplier = √(rise² + 12²) ÷ 12.
A 6:12 pitch is 26.57° with a multiplier of 1.118. A 1,500 sq ft footprint therefore has about 1,677 sq ft of roof surface — roughly 17 squares of shingles.
Up to about 6:12 is generally walkable with care. From 7:12 upwards roofers need harnesses and roof jacks, which raises labour costs.
Asphalt shingles need at least 2:12 with a double underlayment, and 4:12 for standard installation. Below 2:12 you need a membrane roof instead.
Steeper roofs have more surface area for the same footprint. A 12:12 pitch adds 41% more area than a flat plan view of the same house.