Roof pitch reference
8/12 roof pitch
An 8/12 roof rises 8 inches per 12 inches of run: 33.7°, a 66.7% grade, slope factor 1.2019. Each foot of run is 14.42 inches along the slope.
√(1 + (8 ÷ 12)²) = 1.2019 · between 7/12 (+15.8%) and 9/12 (+25%).
Roof area at 8/12
| Footprint | Roof at 8/12 | Squares |
|---|---|---|
| 1,200 sq ft | 1,442 sq ft | 14.4 |
| 1,600 sq ft | 1,923 sq ft | 19.2 |
| 2,000 sq ft | 2,404 sq ft | 24 |
| 2,600 sq ft | 3,125 sq ft | 31.2 |
Rafter length at 8/12
| Run (half span) | Rafter, no overhang |
|---|---|
| 10 ft | 12 ft 0.25 in (12.02 ft) |
| 12 ft | 14 ft 5 in (14.42 ft) |
| 14 ft | 16 ft 10 in (16.83 ft) |
| 16 ft | 19 ft 2.75 in (19.23 ft) |
Ice barrier on an 8/12 roof in Ohio and Michigan
Freeze-thaw winters in both states make eave protection one of the most important details on an 8/12 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 33.7° slope that distance grows by 20.2% when measured up the roof:
| Overhang | Horizontal | Up the 8/12 slope | 36-in courses |
|---|---|---|---|
| 12 in | 36 in | 43.3 in | 2 |
| 18 in | 42 in | 50.5 in | 2 |
| 24 in | 48 in | 57.7 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 8/12
At 8/12 (33.7°, 66.7% grade) asphalt shingles install with standard underlayment under the IRC, plus ice barrier where the local code requires it.
Working on an 8/12 roof
Most crews can work a 33.7° roof with standard setups. At 8/12, snow usually sheds after a few sunny days, but eaves over unheated overhangs still ice up in freeze-thaw weather. OSHA treats anything steeper than 4/12 as a steep roof, so 8/12 falls under steep-roof fall protection rules.
Frequently asked questions
What angle is an 8/12 roof?
An 8/12 roof is about 33.7° from horizontal, a 66.7% grade. Over a 10-foot run it rises 6.67 feet.
How much bigger is an 8/12 roof than the footprint?
The slope factor is 1.2019, so the roof is 20.2% larger than the flat area under it. A 1,600 sq ft footprint has about 1,923 sq ft of roof (19.2 squares).
Can you put asphalt shingles on an 8/12 roof?
At 8/12 (33.7°, 66.7% grade) asphalt shingles install with standard underlayment under the IRC, plus ice barrier where the local code requires it.
How much ice barrier does an 8/12 roof need at the eaves?
With a 12-inch overhang, reaching 24 inches inside the wall takes about 43.3 inches measured up a 8/12 slope, which is 2 courses of 36-inch membrane with a 3-inch lap. Your local code decides whether ice barrier is required.