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Roof shape decides framing cost, wind performance, attic volume and which coverings are even permitted, so it is worth understanding before any other decision. This guide covers ten shapes: the gable, two planes and a ridge, cheapest to frame and easiest to ventilate; the hip, four slopes that brace one another and remove the tall gable wall wind pushes against; the dutch gable, a hip with a small gable at the ridge for light and headroom; the mansard, four sides each with a steep lower and shallow upper slope, which turns the roof into a full extra storey; the gambrel barn profile; the single slope shed or lean-to; the low slope flat roof that only membranes can cover; and the butterfly, saltbox and combination forms. Each entry lists what it is good at and what it costs you. The second half maps twelve roofing materials to their commonly cited lifespans and explains which slopes each one is allowed on, from membrane below 2:12 through to slate on steep decorative roofs.
Roof shape decides more than appearance. It changes the surface area for a given footprint, the waste factor, how the roof behaves in wind and snow, how it can be ventilated, and whether there is usable space underneath.
| Shape | Description | Strengths | Watch for |
|---|---|---|---|
| Gable | Two slopes meeting at a ridge | Cheapest, simplest, easy to vent | Gable-end wall catches wind |
| Hip | Slopes on all four sides | Excellent in wind; no gable wall | Higher waste; short ridge limits venting |
| Gambrel | Two pitches per side | Usable loft space | Break-line flashing; steep lower slope |
| Mansard | Two pitches on all four sides | Maximum usable top floor | Complex; the steep face is nearly a wall |
| Shed / mono-pitch | One plane | Simplest of all; modern look | No ridge, so venting needs edge vents |
| Flat / low-slope | Minimal fall | Usable roof space; simple form | Drainage is everything |
| Cross gable / cross hip | Intersecting sections | Complex, articulated elevations | Valleys — the highest waste and most leak risk |
Ridge length is what limits exhaust. A gable has the longest ridge for its footprint and vents easily. A hip roof has a much shorter ridge and often needs hip vents to make up the exhaust area. A shed roof has no ridge at all and needs an edge or closure vent along the high side. Intake at the soffit is the same requirement for all of them.
The gable — two slopes meeting at a ridge. It is the cheapest to build, the simplest to reroof and the easiest to ventilate because it has the longest ridge for its footprint.
A hip roof. There is no gable-end wall for wind to push against and the shape is more aerodynamic, which is why hip roofs are common in hurricane regions and can attract an insurance discount.
A gable and a hip of the same footprint and pitch have the same surface area, but the hip wastes 15% against the gable's 10% and needs cap on four hips as well as the ridge.
Gambrel and mansard, which use a steep lower slope to create near-vertical walls in the roof space. Both cost more in material and flashing for the same footprint.
Sizing a mansard? The mansard roof calculator gives the area of the lower slopes and the top.
Pricing a Spanish or Mediterranean roof? The clay tile roof cost calculator covers clay, terracotta and concrete tile.
Building a barn-style roof? The gambrel roof calculator gives area, trusses and bundles.