8/12 pitch at a glance
| Angle | 33.69° |
|---|---|
| Slope | 66.7% (8 in of rise per foot of run) |
| Pitch multiplier | 1.2019 |
| Hip and valley factor | 1.5635 per foot of common run |
| Type | Conventional |
A 8/12 roof gives a steep traditional roof, seen on colonial and Cape Cod style houses. Its surface is 20.2% larger than the flat area it covers, so a 2,000 sq ft footprint needs about 2,404 sq ft of roofing.
Rafter length and ridge height by building width
On a simple gable at 8/12, a 24 ft wide building needs a 14 ft 5 1/8 in rafter measured from the outside of the wall to the center of the ridge, and a 32 ft wide one needs 19 ft 2 3/4 in. For 8/12, add your overhang and take off half the ridge board when you cut. Other spans are in the rafter length calculator.
| Building width | Run | Ridge rise | Rafter length |
|---|---|---|---|
| 20 ft | 10 ft | 6 ft 8 in | 12 ft 0 1/4 in |
| 24 ft | 12 ft | 8 ft 0 in | 14 ft 5 1/8 in |
| 28 ft | 14 ft | 9 ft 4 in | 16 ft 9 7/8 in |
| 32 ft | 16 ft | 10 ft 8 in | 19 ft 2 3/4 in |
| 36 ft | 18 ft | 12 ft 0 in | 21 ft 7 5/8 in |
Roof area, squares and shingle bundles
At 8/12 the multiplier is 1.202, so every 1,000 sq ft of footprint becomes 1,202 sq ft of roof. The order column for 8/12 adds 10% for waste and counts 3 bundles per square; include the eaves in your footprint or let the roofing squares calculator do it.
| Footprint | Roof area | Squares | Squares + 10% | Bundles |
|---|---|---|---|---|
| 1,200 sq ft | 1,442 sq ft | 14.4 | 15.9 | 48 |
| 1,600 sq ft | 1,923 sq ft | 19.2 | 21.2 | 64 |
| 2,000 sq ft | 2,404 sq ft | 24.0 | 26.4 | 80 |
| 2,400 sq ft | 2,884 sq ft | 28.8 | 31.7 | 96 |
What roofing can go on a 8/12 roof?
Allowed: Asphalt shingles; Clay and concrete tile; Metal shingles; Wood shingles; Slate.
At 8/12, 5 of the 5 roofing types in the code table are allowed outright. At 8/12 they follow the minimum slopes in the International Residential Code; local code and the maker's installation instructions can be stricter.
Can you walk on a 8/12 roof?
At 8/12: This is a steep roof under OSHA's definition, and most people find it hard to stand on. Roofers usually set roof jacks and planks or work tied off, and many charge a steep-slope rate from about 7/12 or 8/12.
How to check that your roof is 8/12
Level a board against a rafter in the attic, mark 12 inches along it and measure straight down: 8 inches means 8/12. A phone level that reads 33.7 degrees says the same thing, and the roof pitch calculator converts either reading.
A worked example: a 28 by 40 ft house at 8/12
Half the width is 14 ft, so the ridge sits 9 ft 4 in above the top plate and each rafter is 16 ft 9 7/8 in long before overhang. The roof surface is 28 × 40 × 1.202 = 1,346 sq ft, which is 13.5 squares. On a 40 ft long 8/12 roof, rafters at 24 inches on center come to 21 per side.
Cutting rafters at 8/12
Each foot of horizontal run adds 14.42 inches of rafter length. On a speed square, put the pivot on the board edge and swing it until the 8 mark on the common scale lines up with the same edge; the pivot edge now scribes the plumb cut. On a miter saw, the plumb cut is set 33.7 degrees off square, and the horizontal seat cut is 56.3 degrees off square.
Attic headroom at 8/12
At least 5 ft of headroom for 13.0 ft of the 28 ft width, measured from the top plate. A usable attic room needs more than that at 8/12, because the floor joists and ceiling take up some of the height.
8/12 compared with the pitches next to it
The table uses the same 2,000 sq ft footprint for every row, so the last column shows the extra roofing a steeper pitch costs you.
| Pitch | Angle | Multiplier | Roof area | Difference |
|---|---|---|---|---|
| 6/12 | 26.6° | 1.118 | 2,236 sq ft | -168 sq ft |
| 7/12 | 30.3° | 1.158 | 2,315 sq ft | -88 sq ft |
| 8/12 | 33.7° | 1.202 | 2,404 sq ft | this pitch |
| 9/12 | 36.9° | 1.250 | 2,500 sq ft | +96 sq ft |
| 10/12 | 39.8° | 1.302 | 2,603 sq ft | +200 sq ft |
Other pitches: 7/12 pitch and 9/12 pitch, or the full roof pitch chart.
Frequently asked questions
What angle is a 8/12 roof pitch?
33.69 degrees. The slope is 66.7%.
What is the multiplier for a 8/12 pitch?
1.2019. Multiply the flat footprint by 1.202 to get the roof surface area.
Can you put shingles on a 8/12 roof?
Asphalt shingles can go on a 8/12 roof under the International Residential Code.
Is a 8/12 roof walkable?
This is a steep roof under OSHA's definition, and most people find it hard to stand on.
Sources
- Cornell LII: 29 CFR 1926.500, definitions of low-slope and steep roofs
- LSU AgCenter: Code-Compliant Roofing Installations (PDF)