Roof pitch reference
17/12 roof pitch
A 17/12 roof rises 17 inches per 12 inches of run: 54.8°, a 141.7% grade, slope factor 1.7341. Each foot of run is 20.81 inches along the slope.
√(1 + (17 ÷ 12)²) = 1.7341 · between 16/12 (+66.7%) and 18/12 (+80.3%).
Roof area at 17/12
| Footprint | Roof at 17/12 | Squares |
|---|---|---|
| 1,200 sq ft | 2,081 sq ft | 20.8 |
| 1,600 sq ft | 2,774 sq ft | 27.7 |
| 2,000 sq ft | 3,468 sq ft | 34.7 |
| 2,600 sq ft | 4,509 sq ft | 45.1 |
Rafter length at 17/12
| Run (half span) | Rafter, no overhang |
|---|---|
| 10 ft | 17 ft 4 in (17.34 ft) |
| 12 ft | 20 ft 9.75 in (20.81 ft) |
| 14 ft | 24 ft 3.25 in (24.28 ft) |
| 16 ft | 27 ft 9 in (27.74 ft) |
Ice barrier on a 17/12 roof in Ohio and Michigan
Freeze-thaw winters in both states make eave protection one of the most important details on a 17/12 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 54.8° slope that distance grows by 73.4% when measured up the roof:
| Overhang | Horizontal | Up the 17/12 slope | 36-in courses |
|---|---|---|---|
| 12 in | 36 in | 62.4 in | 2 |
| 18 in | 42 in | 72.8 in | 3 |
| 24 in | 48 in | 83.2 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 17/12
At 17/12 (54.8°, 141.7% grade) asphalt shingles install with standard underlayment under the IRC, plus ice barrier where the local code requires it.
Working on a 17/12 roof
A 54.8° slope behaves almost like a wall. A 17/12 roof needs full staging and fall protection, and shingle makers publish separate steep-slope application steps, such as extra nails and hand-sealing, for pitches like 17/12. OSHA treats anything steeper than 4/12 as a steep roof, so 17/12 falls under steep-roof fall protection rules.
Frequently asked questions
What angle is a 17/12 roof?
A 17/12 roof is about 54.8° from horizontal, a 141.7% grade. Over a 10-foot run it rises 14.17 feet.
How much bigger is a 17/12 roof than the footprint?
The slope factor is 1.7341, so the roof is 73.4% larger than the flat area under it. A 1,600 sq ft footprint has about 2,774 sq ft of roof (27.7 squares).
Can you put asphalt shingles on a 17/12 roof?
At 17/12 (54.8°, 141.7% 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 17/12 roof need at the eaves?
With a 12-inch overhang, reaching 24 inches inside the wall takes about 62.4 inches measured up a 17/12 slope, which is 2 courses of 36-inch membrane with a 3-inch lap. Your local code decides whether ice barrier is required.