What a 1/12 pitch means
The roof goes up 1 inch for every 12 inches it runs level. That works out to an angle of 4.76 degrees, a slope of 8.3 percent, and a pitch multiplier of 1.003.
A 1/12 roof is nearly flat. Water drains slowly, so it needs a continuous waterproof surface rather than overlapping pieces. Over the same house, it has 0.3 percent more surface than a flat roof.
Rafter lengths at 1/12
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 | 6' 0 1/4" | 6" | 6 ft |
| 16 ft | 8' 0 5/16" | 8" | 8 ft |
| 20 ft | 10' 0 7/16" | 10" | 10 ft |
| 24 ft | 12' 0 1/2" | 1' 0" | 12 ft |
| 28 ft | 14' 0 9/16" | 1' 2" | 14 ft |
| 32 ft | 16' 0 11/16" | 1' 4" | 16 ft |
| 36 ft | 18' 0 3/4" | 1' 6" | 18 ft |
| 40 ft | 20' 0 13/16" | 1' 8" | 20 ft |
Roof area at 1/12
Multiply the flat area the roof covers, overhangs included, by 1.003. One roofing square is 100 square feet.
| Area covered | Roof area | Squares |
|---|---|---|
| 1,000 sq ft | 1,003 sq ft | 10.0 |
| 1,500 sq ft | 1,505 sq ft | 15.1 |
| 2,000 sq ft | 2,007 sq ft | 20.1 |
| 2,500 sq ft | 2,509 sq ft | 25.1 |
| 3,000 sq ft | 3,010 sq ft | 30.1 |
Roofing that works at 1/12
The International Residential Code sets a lowest pitch for each kind of roofing. Here is how a 1/12 roof compares. Your local code and the maker instructions can be stricter.
| Roofing | Lowest pitch allowed | On a 1/12 roof |
|---|---|---|
| Asphalt shingles | 2 in 12 | No |
| Clay or concrete tile | 2 1/2 in 12 | No |
| Wood shingles or shakes | 3 in 12 | No |
| Metal roof shingles | 3 in 12 | No |
| Slate | 4 in 12 | No |
| 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 | Only with lap sealant |
Working on a 1/12 roof
A 1/12 roof is easy to stand on, but the edge is still a fall hazard. 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 2/12 roof pitch, or see every pitch in the chart on the roof pitch calculator.
Common questions
What is a 1/12 roof pitch in degrees?
A 1/12 pitch is 4.76 degrees. The roof rises 1 inch for every 12 inches of level run, which is a 8.3 percent slope.
What is the pitch multiplier for a 1/12 roof?
It is 1.003. Multiply a level distance by 1.003 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 1/12?
About 12' 0 1/2" from the ridge to the outside of the wall, before any overhang or ridge board deduction. The ridge sits 1' 0" above the top of the wall.
Can you put asphalt shingles on a 1/12 roof?
No. The International Residential Code allows asphalt shingles only on roofs of 2 in 12 or steeper. A 1/12 roof needs a membrane, built-up roofing, roll roofing or standing seam metal.
Is a 1/12 roof walkable?
A 1/12 roof is easy to stand on, but the edge is still a fall hazard. 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.