Roof pitch reference
10/12 roof pitch
A 10/12 roof rises 10 inches per 12 inches of run: 39.8°, a 83.3% grade, slope factor 1.3017. Each foot of run is 15.62 inches along the slope.
√(1 + (10 ÷ 12)²) = 1.3017 · between 9/12 (+25%) and 11/12 (+35.7%).
Roof area at 10/12
| Footprint | Roof at 10/12 | Squares |
|---|---|---|
| 1,200 sq ft | 1,562 sq ft | 15.6 |
| 1,600 sq ft | 2,083 sq ft | 20.8 |
| 2,000 sq ft | 2,603 sq ft | 26 |
| 2,600 sq ft | 3,384 sq ft | 33.8 |
Rafter length at 10/12
| Run (half span) | Rafter, no overhang |
|---|---|
| 10 ft | 13 ft 0.25 in (13.02 ft) |
| 12 ft | 15 ft 7.5 in (15.62 ft) |
| 14 ft | 18 ft 2.75 in (18.22 ft) |
| 16 ft | 20 ft 10 in (20.83 ft) |
Ice barrier on a 10/12 roof in Ohio and Michigan
Freeze-thaw winters in both states make eave protection one of the most important details on a 10/12 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 39.8° slope that distance grows by 30.2% when measured up the roof:
| Overhang | Horizontal | Up the 10/12 slope | 36-in courses |
|---|---|---|---|
| 12 in | 36 in | 46.9 in | 2 |
| 18 in | 42 in | 54.7 in | 2 |
| 24 in | 48 in | 62.5 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 10/12
At 10/12 (39.8°, 83.3% grade) asphalt shingles install with standard underlayment under the IRC, plus ice barrier where the local code requires it.
Working on a 10/12 roof
At 39.8°, crews need roof jacks, harnesses or staging, and every square takes longer. Snow tends to slide off a 10/12 roof in sheets, so guards over doors and walkways are worth asking about. OSHA treats anything steeper than 4/12 as a steep roof, so 10/12 falls under steep-roof fall protection rules.
Frequently asked questions
What angle is a 10/12 roof?
A 10/12 roof is about 39.8° from horizontal, a 83.3% grade. Over a 10-foot run it rises 8.33 feet.
How much bigger is a 10/12 roof than the footprint?
The slope factor is 1.3017, so the roof is 30.2% larger than the flat area under it. A 1,600 sq ft footprint has about 2,083 sq ft of roof (20.8 squares).
Can you put asphalt shingles on a 10/12 roof?
At 10/12 (39.8°, 83.3% grade) asphalt shingles install with standard underlayment under the IRC, plus ice barrier where the local code requires it.
How much ice barrier does a 10/12 roof need at the eaves?
With a 12-inch overhang, reaching 24 inches inside the wall takes about 46.9 inches measured up a 10/12 slope, which is 2 courses of 36-inch membrane with a 3-inch lap. Your local code decides whether ice barrier is required.