4/12 Roof Pitch
A 4 in 12 roof rises 4″ for every 12″ of horizontal run. Ranch houses and garages across the southern and western US; the most common low-pitch shingle roof.
Angle
18.43°
- Percent grade
- 33.3%
- Rafter factor
- 1.0541
- Rafter per foot of run
- 12.65″
- Hip/valley per foot
- 17.44″
- Plumb cut
- 18.4°
- Seat cut
- 71.6°
On a speed square, pivot to 4 on the "common" scale for the plumb cut. On a framing square, set 4″ on the tongue and 12″ on the body.
Low slope: easy to walk on. Roofers price it as standard work.
4/12 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: 12 5/8" of rafter per foot of level overhang.
| Building span | Rafter run | Rise | Rafter length | With 12″ overhang |
|---|---|---|---|---|
| 12 ft | 5′ 11 1/4" | 1′ 11 3/4" | 6′ 3 1/8" | 7′ 3 3/4" |
| 16 ft | 7′ 11 1/4" | 2′ 7 3/4" | 8′ 4 3/8" | 9′ 5 1/16" |
| 20 ft | 9′ 11 1/4" | 3′ 3 3/4" | 10′ 5 11/16" | 11′ 6 3/8" |
| 24 ft | 11′ 11 1/4" | 3′ 11 3/4" | 12′ 7" | 13′ 7 5/8" |
| 28 ft | 13′ 11 1/4" | 4′ 7 3/4" | 14′ 8 5/16" | 15′ 8 15/16" |
| 30 ft | 14′ 11 1/4" | 4′ 11 3/4" | 15′ 8 15/16" | 16′ 9 5/8" |
| 32 ft | 15′ 11 1/4" | 5′ 3 3/4" | 16′ 9 5/8" | 17′ 10 1/4" |
| 36 ft | 17′ 11 1/4" | 5′ 11 3/4" | 18′ 10 7/8" | 19′ 11 9/16" |
| 40 ft | 19′ 11 1/4" | 6′ 7 3/4" | 21′ 3/16" | 22′ 13/16" |
Different span, ridge or overhang? The rafter calculator works out the birdsmouth, HAP and ridge height for your roof.
Roof area at 4/12
Roofing materials allowed at 4/12
- 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.