What a 10/12 pitch means
A 10/12 roof rises 10 inches for every 12 inches it runs horizontally, which is an angle of 39.81° from level and a 83.3% slope. It is a steep roof, too steep to walk safely without roof jacks or a harness.
Roofing for a 10/12 roof
Suits shingles, metal, slate and tile. Steep enough that roofers need roof jacks or harnesses, which adds to labour cost.
Rise and rafter length at 10/12
For a gable roof, the run is half the building width. Rafter lengths are before the ridge deduction and overhang.
| Run | Building width | Rise | Rafter length |
|---|---|---|---|
| 4 ft | 8 ft | 3' 4" | 5' 2 1/2" |
| 6 ft | 12 ft | 5' | 7' 9 3/4" |
| 8 ft | 16 ft | 6' 8" | 10' 4 15/16" |
| 10 ft | 20 ft | 8' 4" | 13' 3/16" |
| 12 ft | 24 ft | 10' | 15' 7 7/16" |
| 14 ft | 28 ft | 11' 8" | 18' 2 11/16" |
| 16 ft | 32 ft | 13' 4" | 20' 9 15/16" |
| 20 ft | 40 ft | 16' 8" | 26' 7/16" |
Roof area at 10/12
Multiply the building footprint (including the overhangs) by 1.302 to get the roof surface. A 30 × 40 ft footprint has 1562 sq ft of roof at 10/12 — about 49 sheets of 4 × 8 sheathing before waste.