11/12 Roof Pitch
A 11 in 12 roof rises 11″ for every 12″ of horizontal run. Very steep decorative gables and dormers.
Angle
42.51°
- Percent grade
- 91.7%
- Rafter factor
- 1.3566
- Rafter per foot of run
- 16.28″
- Hip/valley per foot
- 20.22″
- Plumb cut
- 42.5°
- Seat cut
- 47.5°
On a speed square, pivot to 11 on the "common" scale for the plumb cut. On a framing square, set 11″ on the tongue and 12″ on the body.
Very steep: not walkable without roof jacks, harnesses and anchors; expect steep-slope labor pricing.
11/12 rafter length by building span
Gable roof, 1½″ ridge board, measured along the top edge from the ridge to the outside of the wall. Add the overhang: 16 1/4" of rafter per foot of level overhang.
| Building span | Rafter run | Rise | Rafter length | With 12″ overhang |
|---|---|---|---|---|
| 12 ft | 5′ 11 1/4" | 5′ 5 5/16" | 8′ 5/8" | 9′ 4 15/16" |
| 16 ft | 7′ 11 1/4" | 7′ 3 5/16" | 10′ 9 3/16" | 12′ 1 1/2" |
| 20 ft | 9′ 11 1/4" | 9′ 1 5/16" | 13′ 5 3/4" | 14′ 10 1/16" |
| 24 ft | 11′ 11 1/4" | 10′ 11 5/16" | 16′ 2 5/16" | 17′ 6 5/8" |
| 28 ft | 13′ 11 1/4" | 12′ 9 5/16" | 18′ 10 7/8" | 20′ 3 3/16" |
| 30 ft | 14′ 11 1/4" | 13′ 8 5/16" | 20′ 3 3/16" | 21′ 7 7/16" |
| 32 ft | 15′ 11 1/4" | 14′ 7 5/16" | 21′ 7 7/16" | 22′ 11 3/4" |
| 36 ft | 17′ 11 1/4" | 16′ 5 5/16" | 24′ 4" | 25′ 8 1/4" |
| 40 ft | 19′ 11 1/4" | 18′ 3 5/16" | 27′ 9/16" | 28′ 4 13/16" |
Different span, ridge or overhang? The rafter calculator works out the birdsmouth, HAP and ridge height for your roof.
Roof area at 11/12
Roofing materials allowed at 11/12
- Asphalt shingles
Allowed; single underlayment layer (R905.2.2). - Clay and concrete tile
Allowed (R905.3.2). - Wood shingles
Allowed from 3/12 (R905.7.2). - Wood shakes
Allowed from 3/12 (R905.8.2). - Slate
Allowed from 4/12 (R905.6.2). - Metal panels, lapped without sealant
Allowed from 3/12 (R905.10.2). Standing-seam and sealed-lap panels go lower. - Low-slope membrane (EPDM, TPO, modified bitumen)
Allowed, but usually reserved for slopes under 2/12.
Minimum slopes from the 2021 International Residential Code, Section R905. Manufacturers and local amendments can be stricter.