9/12 pitch at a glance
| Angle | 36.87° |
|---|---|
| Slope | 75.0% (9 in of rise per foot of run) |
| Pitch multiplier | 1.2500 |
| Hip and valley factor | 1.6008 per foot of common run |
| Type | Conventional |
A 9/12 roof gives a steep roof with a usable attic, common on Cape Cod and Tudor style houses. Its surface is 25.0% larger than the flat area it covers, so a 2,000 sq ft footprint needs about 2,500 sq ft of roofing.
Rafter length and ridge height by building width
On a simple gable at 9/12, a 24 ft wide building needs a 15 ft 0 in rafter measured from the outside of the wall to the center of the ridge, and a 32 ft wide one needs 20 ft 0 in. For 9/12, 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 | 7 ft 6 in | 12 ft 6 in |
| 24 ft | 12 ft | 9 ft 0 in | 15 ft 0 in |
| 28 ft | 14 ft | 10 ft 6 in | 17 ft 6 in |
| 32 ft | 16 ft | 12 ft 0 in | 20 ft 0 in |
| 36 ft | 18 ft | 13 ft 6 in | 22 ft 6 in |
Roof area, squares and shingle bundles
At 9/12 the multiplier is 1.250, so every 1,000 sq ft of footprint becomes 1,250 sq ft of roof. The order column for 9/12 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 | 1,500 sq ft | 15.0 | 16.5 | 50 |
| 1,600 sq ft | 2,000 sq ft | 20.0 | 22.0 | 66 |
| 2,000 sq ft | 2,500 sq ft | 25.0 | 27.5 | 83 |
| 2,400 sq ft | 3,000 sq ft | 30.0 | 33.0 | 100 |
What roofing can go on a 9/12 roof?
Allowed: Asphalt shingles; Clay and concrete tile; Metal shingles; Wood shingles; Slate.
At 9/12, 5 of the 5 roofing types in the code table are allowed outright. At 9/12 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 9/12 roof?
At 9/12: This roof is too steep to walk safely. Work is done from roof jacks, staging or a lift with fall protection, and roofing labor is priced higher because every bundle has to be handled on the slope.
How to check that your roof is 9/12
Level a board against a rafter in the attic, mark 12 inches along it and measure straight down: 9 inches means 9/12. A phone level that reads 36.9 degrees says the same thing, and the roof pitch calculator converts either reading.
A worked example: a 28 by 40 ft house at 9/12
Half the width is 14 ft, so the ridge sits 10 ft 6 in above the top plate and each rafter is 17 ft 6 in long before overhang. The roof surface is 28 × 40 × 1.250 = 1,400 sq ft, which is 14.0 squares. On a 40 ft long 9/12 roof, rafters at 24 inches on center come to 21 per side.
Cutting rafters at 9/12
Each foot of horizontal run adds 15.00 inches of rafter length. On a speed square, put the pivot on the board edge and swing it until the 9 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 36.9 degrees off square, and the horizontal seat cut is 53.1 degrees off square.
Attic headroom at 9/12
At least 5 ft of headroom for 14.7 ft of the 28 ft width, measured from the top plate. A usable attic room needs more than that at 9/12, because the floor joists and ceiling take up some of the height.
9/12 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 |
|---|---|---|---|---|
| 7/12 | 30.3° | 1.158 | 2,315 sq ft | -185 sq ft |
| 8/12 | 33.7° | 1.202 | 2,404 sq ft | -96 sq ft |
| 9/12 | 36.9° | 1.250 | 2,500 sq ft | this pitch |
| 10/12 | 39.8° | 1.302 | 2,603 sq ft | +103 sq ft |
| 11/12 | 42.5° | 1.357 | 2,713 sq ft | +213 sq ft |
Other pitches: 8/12 pitch and 10/12 pitch, or the full roof pitch chart.
Frequently asked questions
What angle is a 9/12 roof pitch?
36.87 degrees. The slope is 75.0%.
What is the multiplier for a 9/12 pitch?
1.2500. Multiply the flat footprint by 1.250 to get the roof surface area.
Can you put shingles on a 9/12 roof?
Asphalt shingles can go on a 9/12 roof under the International Residential Code.
Is a 9/12 roof walkable?
This roof is too steep to walk safely.
Sources
- Cornell LII: 29 CFR 1926.500, definitions of low-slope and steep roofs
- LSU AgCenter: Code-Compliant Roofing Installations (PDF)