What a 2/12 pitch means
A 2/12 roof rises 2 inches for every 12 inches it runs horizontally, which is an angle of 9.46° from level and a 16.7% slope. It is a low slope roof, walkable without roof jacks.
Roofing for a 2/12 roof
Asphalt shingles are allowed from 2/12 with double underlayment (IRC R905.2.2); standing-seam metal also works. Clay and concrete tile need 4/12 or more with standard underlayment.
Rise and rafter length at 2/12
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" | 4' 11/16" |
| 6 ft | 12 ft | 1' | 6' 1" |
| 8 ft | 16 ft | 1' 4" | 8' 1 5/16" |
| 10 ft | 20 ft | 1' 8" | 10' 1 5/8" |
| 12 ft | 24 ft | 2' | 12' 2" |
| 14 ft | 28 ft | 2' 4" | 14' 2 5/16" |
| 16 ft | 32 ft | 2' 8" | 16' 2 5/8" |
| 20 ft | 40 ft | 3' 4" | 20' 3 5/16" |
Roof area at 2/12
Multiply the building footprint (including the overhangs) by 1.014 to get the roof surface. A 30 × 40 ft footprint has 1217 sq ft of roof at 2/12 — about 39 sheets of 4 × 8 sheathing before waste.