What a 23/12 pitch means
A 23/12 roof rises 23 inches for every 12 inches it runs horizontally, which is an angle of 62.45° from level and a 191.7% slope. It is a steep roof, too steep to walk safely without roof jacks or a harness.
Roofing for a 23/12 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 23/12
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 | 7' 8" | 8' 7 3/4" |
| 6 ft | 12 ft | 11' 6" | 12' 11 5/8" |
| 8 ft | 16 ft | 15' 4" | 17' 3 9/16" |
| 10 ft | 20 ft | 19' 2" | 21' 7 7/16" |
| 12 ft | 24 ft | 23' | 25' 11 5/16" |
| 14 ft | 28 ft | 26' 10" | 30' 3 3/16" |
| 16 ft | 32 ft | 30' 8" | 34' 7 1/16" |
| 20 ft | 40 ft | 38' 4" | 43' 2 7/8" |
Roof area at 23/12
Multiply the building footprint (including the overhangs) by 2.162 to get the roof surface. A 30 × 40 ft footprint has 2594 sq ft of roof at 23/12 — about 82 sheets of 4 × 8 sheathing before waste.