2/12 roof pitch in degrees
A 2/12 roof pitch is 9.4623°. That is a 16.67% grade, a slope ratio of 1 : 6, and a rafter factor of 1.013794, and the angle is irrational so it carries the ≈.
Change the pitch
9.4623°≈
Multiply your run by 1.013794 for the rafter length. The cuts and the birdsmouth are in the app.
Rafter length at 2/12, by span
Run is half the span on a symmetrical gable. Length is along the rafter, before any birdsmouth, ridge or tail is taken off.
| Building span | Run | Rafter length | Decimal feet |
|---|---|---|---|
| 20 ft | 10 ft | 10' 1-5/8" | 10.138 ft |
| 24 ft | 12 ft | 12' 2" | 12.166 ft |
| 28 ft | 14 ft | 14' 2-5/16" | 14.193 ft |
| 32 ft | 16 ft | 16' 2-5/8" | 16.221 ft |
| 36 ft | 18 ft | 18' 3" | 18.248 ft |
Every row is the run multiplied by 1.013794, the rafter factor for 2/12. The same figure for every pitch is on the full roof pitch chart.
What 2/12 means on the roof
Two in twelve is the shallowest roof the IRC will allow asphalt shingles on at all, and then only with a doubled underlayment. Below it, shingles are off the table and the roof wants a membrane or standing seam instead.
The working is the arctangent of the rise over the run: atan(2 ÷ 12) = 9.4623°. The rafter factor is the hypotenuse of the same triangle over its base, √(12² + 2²) ÷ 12, which is why multiplying any run by 1.013794 gives the rafter. That figure is the roof pitch multiplier, and it is the same number whatever the size of the roof.
Shingle slope limits quoted here are from the IRC, the United States model code. Your state, province or county may amend them, and several do.