3/12 Roof Pitch
A 3/12 roof (also written 3:12 or "3 on 12") rises 3 inches for every 12 inches of horizontal run: 14.04°, a 25.0% slope, and 3.1% more surface than its footprint.
| Measure | 3/12 value |
|---|---|
| Angle | 14.04° |
| Slope percent | 25.0% |
| Rise per foot of run | 3 in |
| Pitch multiplier (area factor) | 1.0308 |
| Hip/valley factor | 1.4361 |
| Common rafter length per foot of run | 12-3/8" |
| Plumb cut / seat cut | 14.0° / 76.0° |
Where you see a 3/12 roof
Typical uses: ranch homes, porches, garages, sheds and pole barns. A 3/12 roof is a classic low-slope pitch for ranch houses and metal buildings. Shingles are allowed with double underlayment, and many exposed-fastener metal panels list 3/12 as their minimum without lap sealant. It is easy to walk and cheap to frame, but it gives little attic room.
Roof area at 3/12
3/12 formulas
Worked examples
3/12 rafter lengths and ridge heights
| Building span | Run | Rafter (no overhang) | Ridge rise |
|---|---|---|---|
| 16 ft | 8 ft | 8' 2-15/16" | 2' 0" |
| 20 ft | 10 ft | 10' 3-11/16" | 2' 6" |
| 24 ft | 12 ft | 12' 4-7/16" | 3' 0" |
| 28 ft | 14 ft | 14' 5-3/16" | 3' 6" |
| 32 ft | 16 ft | 16' 5-15/16" | 4' 0" |
| 36 ft | 18 ft | 18' 6-5/8" | 4' 6" |
Roof area by footprint at 3/12
| Footprint (incl. overhang) | 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 |
Materials and walkability
- Shingles: Yes, but codes require double underlayment (or an approved equivalent) between 2/12 and 4/12.
- Walkable? Generally yes, in dry conditions with proper footwear and fall protection where required.
- OSHA class: Low-slope (OSHA): OSHA treats anything steeper than 4/12 as a steep roof for fall-protection rules.
Roofing materials allowed on a 3/12 roof
| Roof covering | Code minimum | OK at 3/12? |
|---|---|---|
| Standing-seam metal panels | 0.25/12 (IRC R905.10.2) | Yes |
| Built-up, modified bitumen, single-ply membrane (TPO, EPDM, PVC) | 0.25/12 (IRC R905.9, R905.11, R905.12) | Yes, design slope for drainage |
| Lapped metal panels with lap sealant | 0.5/12 (IRC R905.10.2) | Yes |
| Mineral-surfaced roll roofing | 1/12 (IRC R905.5.2) | Yes |
| Asphalt shingles | 2/12 (IRC R905.2.2) | Yes, double underlayment from 2/12 up to 4/12 |
| Clay and concrete tile | 2.5/12 (IRC R905.3.2) | Yes, double underlayment from 2.5/12 up to 4/12 |
| Metal roof shingles | 3/12 (IRC R905.4.2) | Yes |
| Lapped metal panels, no sealant (exposed-fastener) | 3/12 (IRC R905.10.2) | Yes |
| Wood shingles and shakes | 3/12 (IRC R905.7, R905.8) | Yes, shorter exposure below 4/12 |
| Slate | 4/12 (IRC R905.6.2) | No |
Sources
- International Code Council, International Residential Code (2021 and 2024), Section R905 minimum slopes, as summarized in IRC 2024 Chapter 9 (UpCodes) and the MyBuildingPermit residential re-roof checklist. Local amendments and manufacturer instructions can be stricter.
- OSHA, 29 CFR 1926.500(b): a low-slope roof is 4 in 12 or less; a steep roof is greater than 4 in 12. 1926.501(b)(13) requires fall protection for residential construction work 6 ft or more above a lower level.
← 2/12 pitch · 4/12 pitch → · All pitches in degrees
Frequently asked questions
How many degrees is a 3/12 roof pitch?
A 3/12 roof pitch is 14.04 degrees.
What is the multiplier for a 3/12 pitch?
The pitch multiplier for 3/12 is 1.0308. Multiply the footprint area or horizontal run by it to get the sloped area or rafter length.
Can you put shingles on a 3/12 roof?
Yes, but codes require double underlayment (or an approved equivalent) between 2/12 and 4/12.
Is a 3/12 roof walkable?
Generally yes, in dry conditions with proper footwear and fall protection where required.
Last reviewed 2026-10-21. Results are estimates for planning; confirm quantities with your supplier and requirements with your local building code and the manufacturer's instructions.