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A shed roof is one sloping plane, which makes it the simplest roof to build and the easiest to get wrong on paper. This calculator takes the width and depth of the structure plus your chosen pitch and returns the rafter length including the overhang tail, the total rise across the span, the rafter count at your spacing, the roof surface area in square feet and roofing squares, the number of four by eight sheathing sheets, and the covering quantity for asphalt shingles, metal panels or rolled roofing. Switch to the gable option and it splits the depth into two runs and doubles the sloped surface. Because the whole rise happens across the depth on a lean-to, the high wall grows quickly as the pitch increases, and the tool shows that rise in inches so you can frame the tall side correctly. It also flags when your chosen pitch falls below the practical range for shingles. Works equally for carports, patio covers, garage lean-tos and small workshop roofs.
A shed roof, sometimes called a mono-pitch or skillion, is a single plane sloping one way. It is the simplest roof there is to calculate: one rectangle, one pitch, one multiplier.
| Building size | Roof area | Squares | Bundles at 10% waste | Sheets of 4x8 |
|---|---|---|---|---|
| 8 x 10 ft | 84 sq ft | 0.8 | 3 | 3 |
| 10 x 12 ft | 126 sq ft | 1.3 | 5 | 5 |
| 12 x 16 ft | 202 sq ft | 2 | 7 | 7 |
| 16 x 20 ft | 337 sq ft | 3.4 | 12 | 12 |
| 20 x 24 ft | 506 sq ft | 5.1 | 17 | 18 |
The run on a shed roof is the full width of the building, not half of it as on a gable. That is why a shed roof gains height quickly and why steep pitches over a wide span get tall fast.
At least 2/12 for asphalt shingles and 3/12 for exposed-fastener metal. Most sheds and outbuildings sit between 2/12 and 4/12, which drains well without making the high wall excessive.
Usually. One plane, no ridge, no valleys, no hips and the simplest possible framing. The trade is the height difference between the two walls, which grows with the span.
Intake low and exhaust high — a vented soffit at the eave and a vented closure or edge vent along the top edge. There is no ridge, so a ridge vent is not an option.
Yes: the eave, both rakes, and the high edge. The high edge also needs a flashing detail if it abuts a wall.
Putting metal on it? The purlin spacing calculator spaces the purlins for a single slope.
Adding headroom to an attic? The shed dormer calculator finds the dormer pitch from your wall height and tie-in.
Too flat for shingles? The rolled roofing calculator counts rolls for single or double coverage down to 1/12.
Ridge off-centre? The saltbox roof calculator works each slope separately and gives the back wall drop.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.