What a 11/12 pitch means
A 11/12 roof rises 11 inches for every 12 inches it runs horizontally, which is an angle of 42.51° from level and a 91.7% slope. It is a steep roof, too steep to walk safely without roof jacks or a harness.
Roofing for a 11/12 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 11/12
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' 8" | 5' 5 1/8" |
| 6 ft | 12 ft | 5' 6" | 8' 1 11/16" |
| 8 ft | 16 ft | 7' 4" | 10' 10 1/4" |
| 10 ft | 20 ft | 9' 2" | 13' 6 13/16" |
| 12 ft | 24 ft | 11' | 16' 3 3/8" |
| 14 ft | 28 ft | 12' 10" | 18' 11 7/8" |
| 16 ft | 32 ft | 14' 8" | 21' 8 7/16" |
| 20 ft | 40 ft | 18' 4" | 27' 1 9/16" |
Roof area at 11/12
Multiply the building footprint (including the overhangs) by 1.357 to get the roof surface. A 30 × 40 ft footprint has 1628 sq ft of roof at 11/12 — about 51 sheets of 4 × 8 sheathing before waste.