Roof pitch reference
12/12 roof pitch
A 12/12 roof rises 12 inches per 12 inches of run: 45°, a 100% grade, slope factor 1.4142. Each foot of run is 16.97 inches along the slope.
√(1 + (12 ÷ 12)²) = 1.4142 · between 11/12 (+35.7%) and 13/12 (+47.4%).
Roof area at 12/12
| Footprint | Roof at 12/12 | Squares |
|---|---|---|
| 1,200 sq ft | 1,697 sq ft | 17 |
| 1,600 sq ft | 2,263 sq ft | 22.6 |
| 2,000 sq ft | 2,828 sq ft | 28.3 |
| 2,600 sq ft | 3,677 sq ft | 36.8 |
Rafter length at 12/12
| Run (half span) | Rafter, no overhang |
|---|---|
| 10 ft | 14 ft 1.75 in (14.14 ft) |
| 12 ft | 16 ft 11.75 in (16.97 ft) |
| 14 ft | 19 ft 9.5 in (19.8 ft) |
| 16 ft | 22 ft 7.5 in (22.63 ft) |
Ice barrier on a 12/12 roof in Ohio and Michigan
Freeze-thaw winters in both states make eave protection one of the most important details on a 12/12 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 45° slope that distance grows by 41.4% when measured up the roof:
| Overhang | Horizontal | Up the 12/12 slope | 36-in courses |
|---|---|---|---|
| 12 in | 36 in | 50.9 in | 2 |
| 18 in | 42 in | 59.4 in | 2 |
| 24 in | 48 in | 67.9 in | 3 |
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 12/12
At 12/12 (45°, 100% grade) asphalt shingles install with standard underlayment under the IRC, plus ice barrier where the local code requires it.
Working on a 12/12 roof
At 45°, crews need roof jacks, harnesses or staging, and every square takes longer. Snow tends to slide off a 12/12 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 12/12 falls under steep-roof fall protection rules.
Frequently asked questions
What angle is a 12/12 roof?
A 12/12 roof is about 45° from horizontal, a 100% grade. Over a 10-foot run it rises 10 feet.
How much bigger is a 12/12 roof than the footprint?
The slope factor is 1.4142, so the roof is 41.4% larger than the flat area under it. A 1,600 sq ft footprint has about 2,263 sq ft of roof (22.6 squares).
Can you put asphalt shingles on a 12/12 roof?
At 12/12 (45°, 100% 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 12/12 roof need at the eaves?
With a 12-inch overhang, reaching 24 inches inside the wall takes about 50.9 inches measured up a 12/12 slope, which is 2 courses of 36-inch membrane with a 3-inch lap. Your local code decides whether ice barrier is required.