1/12 Roof Pitch
A 1/12 roof (also written 1:12 or "1 on 12") rises 1 inch for every 12 inches of horizontal run: 4.76°, a 8.3% slope, and 0.3% more surface than its footprint.
| Measure | 1/12 value |
|---|---|
| Angle | 4.76° |
| Slope percent | 8.3% |
| Rise per foot of run | 1 in |
| Pitch multiplier (area factor) | 1.0035 |
| Hip/valley factor | 1.4167 |
| Common rafter length per foot of run | 12-1/16" |
| Plumb cut / seat cut | 4.8° / 85.2° |
Where you see a 1/12 roof
Typical uses: carports, patio covers, shed-style additions and commercial-style low-slope roofs. At under 5 degrees, a 1/12 roof looks flat from the street. It still drains, which is the point: a little slope keeps water from ponding. Shingles are not allowed this low, so the usual coverings are single-ply membranes (TPO, EPDM, PVC), modified bitumen, mechanically seamed standing-seam metal, or mineral-surfaced roll roofing, which the IRC allows down to 1/12.
Roof area at 1/12
1/12 formulas
Worked examples
1/12 rafter lengths and ridge heights
| Building span | Run | Rafter (no overhang) | Ridge rise |
|---|---|---|---|
| 16 ft | 8 ft | 8' 5/16" | 0' 8" |
| 20 ft | 10 ft | 10' 7/16" | 0' 10" |
| 24 ft | 12 ft | 12' 1/2" | 1' 0" |
| 28 ft | 14 ft | 14' 9/16" | 1' 2" |
| 32 ft | 16 ft | 16' 11/16" | 1' 4" |
| 36 ft | 18 ft | 18' 3/4" | 1' 6" |
Roof area by footprint at 1/12
| Footprint (incl. overhang) | 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 |
Materials and walkability
- Shingles: No. Below 2/12, use a membrane, roll roofing or low-slope metal.
- 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 1/12 roof
| Roof covering | Code minimum | OK at 1/12? |
|---|---|---|
| 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) | No |
| Clay and concrete tile | 2.5/12 (IRC R905.3.2) | No |
| Metal roof shingles | 3/12 (IRC R905.4.2) | No |
| Lapped metal panels, no sealant (exposed-fastener) | 3/12 (IRC R905.10.2) | No |
| Wood shingles and shakes | 3/12 (IRC R905.7, R905.8) | No |
| 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 → · All pitches in degrees
Frequently asked questions
How many degrees is a 1/12 roof pitch?
A 1/12 roof pitch is 4.76 degrees.
What is the multiplier for a 1/12 pitch?
The pitch multiplier for 1/12 is 1.0035. Multiply the footprint area or horizontal run by it to get the sloped area or rafter length.
Can you put shingles on a 1/12 roof?
No. Below 2/12, use a membrane, roll roofing or low-slope metal.
Is a 1/12 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.