What a 4/12 pitch means
A 4/12 roof rises 4 inches for every 12 inches it runs horizontally, which is an angle of 18.43° from level and a 33.3% slope. It is a conventional roof, walkable without roof jacks.
Roofing for a 4/12 roof
Suits almost every roofing: asphalt shingles, metal, wood shakes, clay or concrete tile.
Rise and rafter length at 4/12
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 | 1' 4" | 4' 2 5/8" |
| 6 ft | 12 ft | 2' | 6' 3 7/8" |
| 8 ft | 16 ft | 2' 8" | 8' 5 3/16" |
| 10 ft | 20 ft | 3' 4" | 10' 6 1/2" |
| 12 ft | 24 ft | 4' | 12' 7 13/16" |
| 14 ft | 28 ft | 4' 8" | 14' 9 1/16" |
| 16 ft | 32 ft | 5' 4" | 16' 10 3/8" |
| 20 ft | 40 ft | 6' 8" | 21' 1" |
Roof area at 4/12
Multiply the building footprint (including the overhangs) by 1.054 to get the roof surface. A 30 × 40 ft footprint has 1265 sq ft of roof at 4/12 — about 40 sheets of 4 × 8 sheathing before waste.