What a 24/12 pitch means
A 24/12 roof rises 24 inches for every 12 inches it runs horizontally, which is an angle of 63.43° from level and a 200% slope. It is a steep roof, too steep to walk safely without roof jacks or a harness.
Roofing for a 24/12 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 24/12
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 | 8' | 8' 11 5/16" |
| 6 ft | 12 ft | 12' | 13' 5" |
| 8 ft | 16 ft | 16' | 17' 10 11/16" |
| 10 ft | 20 ft | 20' | 22' 4 5/16" |
| 12 ft | 24 ft | 24' | 26' 10" |
| 14 ft | 28 ft | 28' | 31' 3 11/16" |
| 16 ft | 32 ft | 32' | 35' 9 5/16" |
| 20 ft | 40 ft | 40' | 44' 8 11/16" |
Roof area at 24/12
Multiply the building footprint (including the overhangs) by 2.236 to get the roof surface. A 30 × 40 ft footprint has 2683 sq ft of roof at 24/12 — about 84 sheets of 4 × 8 sheathing before waste.