Roof pitch reference
2/12 roof pitch
A 2/12 roof rises 2 inches per 12 inches of run: 9.5°, a 16.7% grade, slope factor 1.0138. Each foot of run is 12.17 inches along the slope.
√(1 + (2 ÷ 12)²) = 1.0138 · between 1/12 (+0.3%) and 3/12 (+3.1%).
Roof area at 2/12
| Footprint | Roof at 2/12 | Squares |
|---|---|---|
| 1,200 sq ft | 1,217 sq ft | 12.2 |
| 1,600 sq ft | 1,622 sq ft | 16.2 |
| 2,000 sq ft | 2,028 sq ft | 20.3 |
| 2,600 sq ft | 2,636 sq ft | 26.4 |
Rafter length at 2/12
| Run (half span) | Rafter, no overhang |
|---|---|
| 10 ft | 10 ft 1.75 in (10.14 ft) |
| 12 ft | 12 ft 2 in (12.17 ft) |
| 14 ft | 14 ft 2.25 in (14.19 ft) |
| 16 ft | 16 ft 2.75 in (16.22 ft) |
Ice barrier on a 2/12 roof in Ohio and Michigan
Freeze-thaw winters in both states make eave protection one of the most important details on a 2/12 roof. Where the locally adopted code requires it, the model IRC (R905.1.2) extends ice barrier from the eave to at least 24 inches inside the exterior wall. On a 9.5° slope that distance grows by 1.4% when measured up the roof:
| Overhang | Horizontal | Up the 2/12 slope | 36-in courses |
|---|---|---|---|
| 12 in | 36 in | 36.5 in | 2 |
| 18 in | 42 in | 42.6 in | 2 |
| 24 in | 48 in | 48.7 in | 2 |
Courses assume a 3-inch lap (33 inches of coverage per 36-inch roll). Wall thickness adds a few inches. Check the product and your building department.
Shingles at 2/12
At 2/12 (9.5°) asphalt shingles are allowed, but the IRC calls for double underlayment between 2/12 and 4/12 because water moves slowly on a 16.7% slope.
Working on a 2/12 roof
Water on a 16.7% grade drains slowly, and snow on a 9.5° roof in an Ohio or Michigan winter tends to sit rather than slide. Flashing and underlayment details carry more of the load at 2/12. OSHA classifies roofs at 4/12 or less as low-slope, so 2/12 falls under the low-slope rules.
Frequently asked questions
What angle is a 2/12 roof?
A 2/12 roof is about 9.5° from horizontal, a 16.7% grade. Over a 10-foot run it rises 1.67 feet.
How much bigger is a 2/12 roof than the footprint?
The slope factor is 1.0138, so the roof is 1.4% larger than the flat area under it. A 1,600 sq ft footprint has about 1,622 sq ft of roof (16.2 squares).
Can you put asphalt shingles on a 2/12 roof?
At 2/12 (9.5°) asphalt shingles are allowed, but the IRC calls for double underlayment between 2/12 and 4/12 because water moves slowly on a 16.7% slope.
How much ice barrier does a 2/12 roof need at the eaves?
With a 12-inch overhang, reaching 24 inches inside the wall takes about 36.5 inches measured up a 2/12 slope, which is 2 courses of 36-inch membrane with a 3-inch lap. Your local code decides whether ice barrier is required.