What a 8/12 pitch means
A 8/12 roof rises 8 inches for every 12 inches it runs horizontally, which is an angle of 33.69° from level and a 66.7% slope. It is a conventional roof, walkable with care.
Roofing for a 8/12 roof
Suits almost every roofing: asphalt shingles, metal, wood shakes, clay or concrete tile.
Rise and rafter length at 8/12
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 | 2' 8" | 4' 9 11/16" |
| 6 ft | 12 ft | 4' | 7' 2 9/16" |
| 8 ft | 16 ft | 5' 4" | 9' 7 3/8" |
| 10 ft | 20 ft | 6' 8" | 12' 1/4" |
| 12 ft | 24 ft | 8' | 14' 5 1/16" |
| 14 ft | 28 ft | 9' 4" | 16' 9 15/16" |
| 16 ft | 32 ft | 10' 8" | 19' 2 3/4" |
| 20 ft | 40 ft | 13' 4" | 24' 7/16" |
Roof area at 8/12
Multiply the building footprint (including the overhangs) by 1.202 to get the roof surface. A 30 × 40 ft footprint has 1442 sq ft of roof at 8/12 — about 46 sheets of 4 × 8 sheathing before waste.