11/12 roof pitch: 42.51 degrees
A 11/12 roof pitch is 42.5104° to four places. Its multiplier, or rafter factor, is 1.356568, its grade is 91.67% and its slope ratio is 1 : 1.0909.
Change the pitch
42.5104°≈
Multiply your run by 1.356568 for the rafter length. Hips and valleys at this pitch are in the app.
Rafter length at 11/12, 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 | 13' 6-13/16" | 13.566 ft |
| 24 ft | 12 ft | 16' 3-3/8" | 16.279 ft |
| 28 ft | 14 ft | 18' 11-7/8" | 18.992 ft |
| 32 ft | 16 ft | 21' 8-7/16" | 21.705 ft |
| 36 ft | 18 ft | 24' 5" | 24.418 ft |
Every row is the run multiplied by 1.356568, the rafter factor for 11/12. The multiplier for every pitch is on the roof pitch multiplier table.
What 11/12 means on the roof
Eleven in twelve is the last pitch where the run is still longer than the rise. At 12/12 the two are equal, and past that each half of the roof is taller than it is wide. At 42.5104° it is close enough to 45 that a framing square set on 11 and 12 reads square by eye and is not.
The working is the arctangent of the rise over the run: atan(11 ÷ 12) = 42.5104°. The rafter factor is the hypotenuse of the same triangle over its base, √(12² + 11²) ÷ 12, which is why multiplying any run by 1.356568 gives the rafter. That figure is the roof pitch multiplier, and it is the same number whatever the size of the roof.
A hip or valley where both roofs are 11/12 runs at 45° across the plan, so it is longer than the common rafter beside it: 1.6853 ft of hip for every foot of common run, which is 16' 10-1/4" over a 10 ft common run against 13' 6-13/16" for the rafter.
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.
Other pitches: 1/12 · 2/12 · 3/12 · 4/12 · 4.5/12 · 5/12 · 6/12 · 6.5/12 · 7/12 · 8/12 · 9/12 · 10/12 · 12/12. Every pitch from 1/12 to 24/12 is on the roof pitch to degrees chart.
