Shed Roof 3/12 Pitch on a 10 by 12 Foot Building
A small shed roof. The full 10 ft width is the run, not half of it.
Formula SSC-2026.1
3.00 / 12 · 14.04°
Pitch angle
14.04°
Multiplier 1.0308
Common rafter
11 ft 4 1/16 in
Tail 0 ft 6 3/16 in
Cuts
14.04° plumb
75.96° seat
Roof area
147 ft²
1.47 squares
Shingle bundles
5
3 bundles per square + 10% waste
Sheathing / felt
6 sheets
1 underlayment rolls
Delivery weight
654 lb
297 kg · 70 lb bundles, 46 lb sheets, 28 lb rolls
Rise and run are scaled from the span, overhang, and pitch. The small triangle is the pitch ratio.
| Item | Net | Waste | Order | Unit price | Line total |
|---|---|---|---|---|---|
| Architectural shingle bundles | 1.47 squares | 10% | 5 bundles | USD | $210.00 |
| 4x8 CDX sheathing | 4.6 sheets | 10% | 6 sheets | USD | $168.00 |
| Underlayment rolls | 147 ft² | overlap allowance | 1 rolls | USD | $55.00 |
| Ridge cap bundles | 0.0 ft ridge | — | 0 bundles | 25 ft per bundle | — |
| Pitch | Degrees | Multiplier | Rafter | Squares | Bundles | Sheets |
|---|---|---|---|---|---|---|
| 2.0/12 | 9.46° | 1.014 | 11 ft 1 13/16 in | 1.45 | 5 | 5 |
| 3.0/12 | 14.04° | 1.031 | 11 ft 4 1/16 in | 1.47 | 5 | 6 |
| 4.0/12 | 18.43° | 1.054 | 11 ft 7 1/8 in | 1.51 | 5 | 6 |
| 6.0/12 | 26.57° | 1.118 | 12 ft 3 9/16 in | 1.60 | 6 | 6 |
Show the deterministic formula
Angle = arctan(rise ÷ 12). Multiplier = √(1 + (rise ÷ 12)²). Gable run = span ÷ 2 − ridge thickness ÷ 2. Rafter length = (run + horizontal overhang) × multiplier.
Plumb cut = pitch angle. Seat cut = 90° − pitch angle. Area uses both slopes on a gable and one slope on a shed, and it includes a rake overhang equal to the eave overhang.
Bundles = ceiling of squares × 3 × 1.10. Sheets = ceiling of area × 1.10 ÷ 32. Rolls use 360 ft² effective coverage. Delivery weight plans 70 lb per bundle, 46 lb per sheet, and 28 lb per roll, then the header converts that pound total at 1 lb = 0.45359237 kg.
Contractor sign-off
Project: Shed Roof 3/12 Pitch on a 10 by 12 Foot Building
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This sheet is an estimate for ordering and layout discussion. It is not a sealed design. Confirm the quantities with a licensed local professional and the authority having jurisdiction before you buy or build.
Engineering notes
On a shed roof the span is the whole run. A 3/12 pitch on 10 ft of run is a low slope. The rafter adds overhang at the low eave and at the high side. There is no ridge board, so the ridge thickness is ignored. Shingle counts still use 3 bundles per square plus 10 percent, but many shingle warranties want a steeper slope. Check the bundle wrapper before you order a 3/12 roof.
Code reference
IRC R905 slope limits for asphalt shingles are product-specific. A 3/12 roof may need a different underlayment. This quantity is not that product approval.
Field questions
- Why is the shed run the full width?
- A shed has one slope from the high wall to the low wall. A gable splits the span at the ridge.
- Is 3/12 steep enough for shingles?
- Some asphalt shingles allow 2/12 or 3/12 only with a special underlayment. Read the bundle. The bundle math here does not check that warranty.
- How many slopes are in the area?
- One. The area is the sloped rafter length times the building length plus the rake overhangs.