Gable, hip and shed roofs look very different, yet over the same building at the same pitch they have the same surface area. The differences that matter for an estimate are elsewhere: in the lengths of ridge, hips and edges, in how high the roof rises and in how much cutting the shape forces.
The three shapes
- Gable. Two rectangular slopes meet at a ridge that runs the length of the building. The triangular walls at each end are the gables; the sloped roof edges above them are the rakes.
- Hip. Four slopes, one rising from each wall. The two long slopes are trapezoids and the two end slopes are triangles. They meet at a shorter ridge and at four hips running down to the corners. There are no gable walls and no rakes; every edge is a level eave.
- Shed. A single slope from a high wall to a low wall. No ridge, no hips.
Why the area is the same
Tilting a flat surface to a given pitch stretches it by the same multiplier whichever way it faces. A hip roof at 6:12 is made of four pieces that each sit at 6:12; a gable roof is two pieces at 6:12; a shed roof is one. Each piece covers part of the footprint, together they cover all of it once, and every part is stretched by √(1 + (6 ÷ 12)²). So the total is footprint times multiplier in all three cases.
This only holds when every face has the same pitch. A hip roof whose end slopes are steeper than its side slopes has to be calculated face by face.
| Shape | Surface area | Ridge | Hips | Roof edge | Rise above the walls |
|---|---|---|---|---|---|
| Gable | 1,502.6 sq ft | 42.0 ft | none | 155.6 ft | 7.5 ft |
| Hip | 1,502.6 sq ft | 10.0 ft | 96.0 ft | 148.0 ft | 7.5 ft |
| Shed | 1,502.6 sq ft | none | none | 155.6 ft | 15.0 ft |
What changes with the shape
Ridge and hip length
The gable roof has a 42.0 ft ridge and nothing else to cap. The hip roof’s ridge is only 10.0 ft, the difference between the roof’s length and width, but it adds four hips with a combined length of 96.0 ft. Its cap length is 106.0 ft against 42.0 ft, 2.5 times as much. The shed roof needs no caps; its top edge is finished with flashing or trim against the high wall or fascia.
A hip runs diagonally across the plan and climbs at the same time, so it is longer than it looks from the ground. Each hip here covers 16.0 ft in both plan directions and rises 8.0 ft, which makes it 24.00 ft long.
Roof edge
Drip edge and starter follow the roof edge. A hip roof’s edge is simply the perimeter of the footprint, 148.0 ft. Gable and shed roofs have sloped rakes, which are longer than their level run by the pitch multiplier, so their edge comes to 155.6 ft.
Height
A shed roof rises over the whole building width, so at the same pitch its high side stands 15.0 ft above the low wall, twice the 7.5 ft of the gable ridge. That affects wall framing and siding on the high side, not the roofing quantity.
Cutting and waste
Area being equal, a hip roof still uses more shingles in practice, because every course is cut at an angle where it meets a hip. The waste factor guide covers how to allow for that.
Materials for the three shapes
| Shape | Shingle bundles | Underlayment rolls | Cap bundles | Drip edge pieces |
|---|---|---|---|---|
| Gable | 50 | 5 | 2 | 18 |
| Hip | 50 | 5 | 5 | 17 |
| Shed | 50 | 5 | 0 | 18 |
Special cases
- Square hip roof (pyramid). When length equals width the ridge shrinks to a point. Over a 30 × 30 ft building the calculator gives a ridge of 0.0 ft and 96.0 ft of hips.
- Gable roof with a different pitch on each side. Enter it as two shed sections, each with its own width and pitch, and add the ridge length to the cap quantity by hand, because a shed section has no ridge.
- Hip and valley roofs. An L- or T-shaped house with hips is several hip and gable pieces joined at valleys. Enter non-overlapping rectangles for the area, and measure valley lengths separately; the calculators do not deduct shared edges or add valleys.
- Gambrel and mansard roofs. Each slope has its own pitch. Treat every pitch as its own section with the horizontal width that slope covers.
Which shape to pick in the calculator
Choose the shape of each section as it is built. The area will not change when you switch between them, which is a useful check that you entered the footprint correctly. The ridge, hip and edge lengths will, and those feed the cap and drip-edge counts in the materials calculator. For a quick area figure alone, the roof area calculator with any shape gives the same answer.