8/12 Roof Pitch
A 8 in 12 roof rises 8″ for every 12″ of horizontal run. Cape Cods, colonials and homes in snowy regions; often gives a usable attic.
Angle
33.69°
- Percent grade
- 66.7%
- Rafter factor
- 1.2019
- Rafter per foot of run
- 14.42″
- Hip/valley per foot
- 18.76″
- Plumb cut
- 33.7°
- Seat cut
- 56.3°
On a speed square, pivot to 8 on the "common" scale for the plumb cut. On a framing square, set 8″ on the tongue and 12″ on the body.
Steep: most roofers set roof jacks or toe boards; many contractors add a steep-roof charge from 7/12.
8/12 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: 14 7/16" of rafter per foot of level overhang.
| Building span | Rafter run | Rise | Rafter length | With 12″ overhang |
|---|---|---|---|---|
| 12 ft | 5′ 11 1/4" | 3′ 11 1/2" | 7′ 1 5/8" | 8′ 4 1/16" |
| 16 ft | 7′ 11 1/4" | 5′ 3 1/2" | 9′ 6 1/2" | 10′ 8 7/8" |
| 20 ft | 9′ 11 1/4" | 6′ 7 1/2" | 11′ 11 5/16" | 13′ 1 3/4" |
| 24 ft | 11′ 11 1/4" | 7′ 11 1/2" | 14′ 4 3/16" | 15′ 6 9/16" |
| 28 ft | 13′ 11 1/4" | 9′ 3 1/2" | 16′ 9" | 17′ 11 7/16" |
| 30 ft | 14′ 11 1/4" | 9′ 11 1/2" | 17′ 11 7/16" | 19′ 1 7/8" |
| 32 ft | 15′ 11 1/4" | 10′ 7 1/2" | 19′ 1 7/8" | 20′ 4 1/4" |
| 36 ft | 17′ 11 1/4" | 11′ 11 1/2" | 21′ 6 11/16" | 22′ 9 1/8" |
| 40 ft | 19′ 11 1/4" | 13′ 3 1/2" | 23′ 11 9/16" | 25′ 1 15/16" |
Different span, ridge or overhang? The rafter calculator works out the birdsmouth, HAP and ridge height for your roof.
Roof area at 8/12
Roofing materials allowed at 8/12
- 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.