What a 3/12 pitch means
The roof goes up 3 inches for every 12 inches it runs level. That works out to an angle of 14.04 degrees, a slope of 25.0 percent, and a pitch multiplier of 1.031. It is 4.6 degrees steeper than a 2/12 roof.
A 3/12 roof is a low slope roof. It sheds water more slowly than a typical house roof, so the building code asks for extra protection under shingles. Over the same house, it has 3.1 percent more surface than a flat roof.
Rafter lengths at 3/12
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' 2 3/16" | 1' 6" | 6 ft |
| 16 ft | 8' 2 15/16" | 2' 0" | 8 ft |
| 20 ft | 10' 3 11/16" | 2' 6" | 10 ft |
| 24 ft | 12' 4 7/16" | 3' 0" | 12 ft |
| 28 ft | 14' 5 3/16" | 3' 6" | 14 ft |
| 32 ft | 16' 5 15/16" | 4' 0" | 16 ft |
| 36 ft | 18' 6 5/8" | 4' 6" | 18 ft |
| 40 ft | 20' 7 3/8" | 5' 0" | 20 ft |
Roof area at 3/12
Multiply the flat area the roof covers, overhangs included, by 1.031. One roofing square is 100 square feet.
| Area covered | Roof area | Squares |
|---|---|---|
| 1,000 sq ft | 1,031 sq ft | 10.3 |
| 1,500 sq ft | 1,546 sq ft | 15.5 |
| 2,000 sq ft | 2,062 sq ft | 20.6 |
| 2,500 sq ft | 2,577 sq ft | 25.8 |
| 3,000 sq ft | 3,092 sq ft | 30.9 |
Roofing that works at 3/12
The International Residential Code sets a lowest pitch for each kind of roofing. Here is how a 3/12 roof compares. Your local code and the maker instructions can be stricter.
| Roofing | Lowest pitch allowed | On a 3/12 roof |
|---|---|---|
| Asphalt shingles | 2 in 12 | Yes, with double underlayment |
| Clay or concrete tile | 2 1/2 in 12 | Yes, with double underlayment |
| Wood shingles or shakes | 3 in 12 | Yes |
| Metal roof shingles | 3 in 12 | Yes |
| 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 | Yes |
Working on a 3/12 roof
A 3/12 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 and 4/12 roof pitch, or see every pitch in the chart on the roof pitch calculator.
Common questions
What is a 3/12 roof pitch in degrees?
A 3/12 pitch is 14.04 degrees. The roof rises 3 inches for every 12 inches of level run, which is a 25.0 percent slope.
What is the pitch multiplier for a 3/12 roof?
It is 1.031. Multiply a level distance by 1.031 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 3/12?
About 12' 4 7/16" from the ridge to the outside of the wall, before any overhang or ridge board deduction. The ridge sits 3' 0" above the top of the wall.
Can you put asphalt shingles on a 3/12 roof?
Yes, but the International Residential Code requires a double layer of underlayment on roofs from 2 in 12 up to 4 in 12. Check the shingle maker instructions as well.
Is a 3/12 roof walkable?
A 3/12 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.