What a 12/12 pitch means
The roof goes up 12 inches for every 12 inches it runs level. That works out to an angle of 45.00 degrees, a slope of 100.0 percent, and a pitch multiplier of 1.414. It is 2.5 degrees steeper than an 11/12 roof.
A 12/12 roof is steep. It sheds water and snow fast and leaves more room in the attic, but it takes more material and more safety gear to build. Over the same house, it has 41.4 percent more surface than a flat roof.
Rafter lengths at 12/12
These are measured from the ridge to the outside of the wall on a simple gable roof, before any overhang or ridge board is taken into account. For an exact length, use the rafter length calculator.
| Building width | Rafter length | Rise at ridge | Run |
|---|---|---|---|
| 12 ft | 8' 5 13/16" | 6' 0" | 6 ft |
| 16 ft | 11' 3 3/4" | 8' 0" | 8 ft |
| 20 ft | 14' 1 11/16" | 10' 0" | 10 ft |
| 24 ft | 16' 11 5/8" | 12' 0" | 12 ft |
| 28 ft | 19' 9 9/16" | 14' 0" | 14 ft |
| 32 ft | 22' 7 1/2" | 16' 0" | 16 ft |
| 36 ft | 25' 5 1/2" | 18' 0" | 18 ft |
| 40 ft | 28' 3 7/16" | 20' 0" | 20 ft |
Roof area at 12/12
Multiply the flat area the roof covers, overhangs included, by 1.414. One roofing square is 100 square feet.
| Area covered | Roof area | Squares |
|---|---|---|
| 1,000 sq ft | 1,414 sq ft | 14.1 |
| 1,500 sq ft | 2,121 sq ft | 21.2 |
| 2,000 sq ft | 2,828 sq ft | 28.3 |
| 2,500 sq ft | 3,536 sq ft | 35.4 |
| 3,000 sq ft | 4,243 sq ft | 42.4 |
Roofing that works at 12/12
The International Residential Code sets a lowest pitch for each kind of roofing. Here is how a 12/12 roof compares. Your local code and the maker instructions can be stricter.
| Roofing | Lowest pitch allowed | On a 12/12 roof |
|---|---|---|
| Asphalt shingles | 2 in 12 | Yes |
| Clay or concrete tile | 2 1/2 in 12 | Yes |
| Wood shingles or shakes | 3 in 12 | Yes |
| Metal roof shingles | 3 in 12 | Yes |
| Slate | 4 in 12 | Yes |
| Roll roofing, mineral surfaced | 1 in 12 | Yes |
| Standing seam metal | 1/4 in 12 | Yes |
| Membrane or built-up roofing | 1/4 in 12 | Yes |
| Metal panels with lapped seams | 3 in 12 | Yes |
Working on a 12/12 roof
A 12/12 roof is too steep to walk on. Work at this pitch calls for roof jacks, staging and a harness. Any roof is dangerous when wet or frosty. In the US, OSHA requires fall protection for workers doing residential construction 6 feet or more above a lower level.
Nearby pitches
Compare with the 11/12 roof pitch, or see every pitch in the chart on the roof pitch calculator.
Common questions
What is a 12/12 roof pitch in degrees?
A 12/12 pitch is 45.00 degrees. The roof rises 12 inches for every 12 inches of level run, which is a 100.0 percent slope.
What is the pitch multiplier for a 12/12 roof?
It is 1.414. Multiply a level distance by 1.414 to get the distance along the roof, or multiply the area a roof covers by it to get the roof area.
How long is a rafter on a 24 foot wide building at 12/12?
About 16' 11 5/8" from the ridge to the outside of the wall, before any overhang or ridge board deduction. The ridge sits 12' 0" above the top of the wall.
Can you put asphalt shingles on a 12/12 roof?
Yes. A 12/12 roof is above the 4 in 12 mark, so asphalt shingles go on with standard single underlayment.
Is a 12/12 roof walkable?
A 12/12 roof is too steep to walk on. Work at this pitch calls for roof jacks, staging and a harness. Any roof is dangerous when wet.
Sources
- International Residential Code 2021, Chapter 9: roof coverings (R905)
- OSHA 29 CFR 1926.501: fall protection in construction
Facts on this page were last checked against these sources in October 2026.