How does roof pitch work, and what does it mean for working on a pitched roof?
Short answer. Roof pitch is the rise of the roof in inches for every 12 inches of horizontal run, written like 6/12. It controls how fast water drains, which materials are allowed, how much roof surface there is, and how safe the roof is to walk, with anything much steeper than about 6/12 calling for fall protection.
Pitch, slope and angle
- Pitch in everyday roofing talk is rise over 12 inches of run, such as 4/12 or 8/12.
- Slope is often used the same way.
- Angle is the same thing in degrees: 4/12 is about 18 degrees, 6/12 about 27, 8/12 about 34, and 12/12 is 45.
The rough categories
- Low slope: under about 3/12 or 4/12. Porches, additions, some ranches. Limits material choices.
- Conventional: about 4/12 to 8/12. Most Georgia homes. Walkable with care in dry weather.
- Steep: above about 8/12. Common on newer two story fronts. Needs harnesses and roof jacks.
What pitch controls
- Materials: asphalt shingles need at least 2/12, with double underlayment from 2/12 to under 4/12. Flatter roofs need membranes or certain metal panels.
- Surface area: a steeper roof covers more area on the same footprint, so it needs more material.
- Drainage and debris: steeper roofs shed water and leaves faster.
- Cost: steep work is slower and needs more safety gear.
Working on a pitched roof
For homeowners, the safest rule is to stay off anything steeper than a gentle walkable slope, and off every roof when it is wet, dewy or covered in pine needles. Professionals use fall protection on steep and high roofs. Inspect from the ground or a ladder at the eave instead.