What a 17/12 pitch means
A 17/12 roof rises 17 inches for every 12 inches it runs horizontally, which is an angle of 54.78° from level and a 141.7% slope. It is a steep roof, too steep to walk safely without roof jacks or a harness.
Roofing for a 17/12 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 17/12
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 | 5' 8" | 6' 11 1/4" |
| 6 ft | 12 ft | 8' 6" | 10' 4 7/8" |
| 8 ft | 16 ft | 11' 4" | 13' 10 1/2" |
| 10 ft | 20 ft | 14' 2" | 17' 4 1/16" |
| 12 ft | 24 ft | 17' | 20' 9 11/16" |
| 14 ft | 28 ft | 19' 10" | 24' 3 5/16" |
| 16 ft | 32 ft | 22' 8" | 27' 8 15/16" |
| 20 ft | 40 ft | 28' 4" | 34' 8 3/16" |
Roof area at 17/12
Multiply the building footprint (including the overhangs) by 1.734 to get the roof surface. A 30 × 40 ft footprint has 2081 sq ft of roof at 17/12 — about 66 sheets of 4 × 8 sheathing before waste.