Roof pitch reference
9/12 roof pitch
A 9/12 roof rises 9 inches per 12 inches of run: 36.9°, a 75% grade, slope factor 1.2500. Each foot of run is 15 inches along the slope.
√(1 + (9 ÷ 12)²) = 1.2500 · between 8/12 (+20.2%) and 10/12 (+30.2%).
Roof area at 9/12
| Footprint | Roof at 9/12 | Squares |
|---|---|---|
| 1,200 sq ft | 1,500 sq ft | 15 |
| 1,600 sq ft | 2,000 sq ft | 20 |
| 2,000 sq ft | 2,500 sq ft | 25 |
| 2,600 sq ft | 3,250 sq ft | 32.5 |
Rafter length at 9/12
| Run (half span) | Rafter, no overhang |
|---|---|
| 10 ft | 12 ft 6 in (12.5 ft) |
| 12 ft | 15 ft 0 in (15 ft) |
| 14 ft | 17 ft 6 in (17.5 ft) |
| 16 ft | 20 ft 0 in (20 ft) |
Ice barrier on a 9/12 roof in Ohio and Michigan
Freeze-thaw winters in both states make eave protection one of the most important details on a 9/12 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 36.9° slope that distance grows by 25% when measured up the roof:
| Overhang | Horizontal | Up the 9/12 slope | 36-in courses |
|---|---|---|---|
| 12 in | 36 in | 45 in | 2 |
| 18 in | 42 in | 52.5 in | 2 |
| 24 in | 48 in | 60 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 9/12
At 9/12 (36.9°, 75% grade) asphalt shingles install with standard underlayment under the IRC, plus ice barrier where the local code requires it.
Working on a 9/12 roof
At 36.9°, crews need roof jacks, harnesses or staging, and every square takes longer. Snow tends to slide off a 9/12 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 9/12 falls under steep-roof fall protection rules.
Frequently asked questions
What angle is a 9/12 roof?
A 9/12 roof is about 36.9° from horizontal, a 75% grade. Over a 10-foot run it rises 7.5 feet.
How much bigger is a 9/12 roof than the footprint?
The slope factor is 1.2500, so the roof is 25% larger than the flat area under it. A 1,600 sq ft footprint has about 2,000 sq ft of roof (20 squares).
Can you put asphalt shingles on a 9/12 roof?
At 9/12 (36.9°, 75% 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 9/12 roof need at the eaves?
With a 12-inch overhang, reaching 24 inches inside the wall takes about 45 inches measured up a 9/12 slope, which is 2 courses of 36-inch membrane with a 3-inch lap. Your local code decides whether ice barrier is required.