Roof Pitch (Slope)

Roof pitch determines almost everything about a roofing project — material options, install time, safety requirements, water shedding, even insurance pricing. Knowing how to read pitch quickly is one of the first skills any new estimator develops. The notation: - **Flat (0/12 to 2/12)** — Requires membrane (TPO, EPDM, modified bitumen), not shingles - **Low slope (2/12 to 4/12)** — Asphalt shingles work but need doubled underlayment per code - **Conventional (4/12 to 9/12)** — The shingle sweet spot. 4/12-6/12 covers most US residential - **Steep (9/12 to 12/12)** — Requires roof brackets or scaffold; harder installs, higher cost - **Very steep (over 12/12)** — Specialized crew, fall arrest, often 50%+ higher labor cost Pitch affects: **Material selection.** Below 2/12, asphalt won't shed water — you need a continuous membrane. Above 12/12, tile and slate become harder to anchor. **Walkability.** Up to 6/12 is generally walkable in good shoes. 7/12-9/12 requires roof brackets or harnesses. 10/12+ requires fall arrest systems and slows production by 30-50%. **Material quantity.** Pitch multiplier (the secant of the angle) determines how much sloped area exists relative to footprint. A 12/12 pitch has 41% more surface area than a flat roof on the same building. **Insurance.** Some carriers charge more or refuse coverage for very steep roofs (over 12/12) due to elevated repair costs and worker injury risk. For estimating: pitch is one of the inputs SatelliteQuotes detects automatically from aerial imagery. The multiplier applies to material quantity calculations automatically, but you should also bump your labor multiplier for steep installs — a 10/12 install typically takes 1.5-2× the crew time of a 4/12 install on the same square footage.