Shed Roof (Skillion, Mono-Pitch, Lean-To)

A shed roof is the simplest pitched roof: a single, flat sloping plane. One wall is taller than the opposite wall and the roof runs between them. It is known by many regional names: skillion roof in Australia and New Zealand; mono-pitch, pent or lean-to roof in the UK and Ireland; and shed roof in North America. A lean-to specifically describes a mono-pitch roof whose high side leans against a taller wall of the main building.

Uses

• Extensions, porches, verandas, carports, garden sheds and outbuildings.
• Contemporary houses, where tilted planes create tall clerestory walls and dramatic interiors.
• Combined in multiple offset planes with clerestory windows between them.
• Solar installations, since a single plane can be oriented toward the sun; in the northern hemisphere a south-facing mono-pitch suits photovoltaic panels.

Pitch

Shed roofs range from very low slopes that require membrane roofing to steep slopes clad in tiles or metal. UK guidance commonly quotes a minimum of around 15° for pitched coverings on pent roofs, though the actual minimum depends on the covering manufacturer's specification. Standing-seam and other metal roofs can be used at lower pitches.

Advantages

• Simple framing, often with rafters or mono-pitch trusses spanning from wall to wall.
• Few joints: no ridge, hips or valleys, reducing leak points.
• Easy drainage to a single gutter along the low eave.

Considerations

• All water drains to one edge, so the gutter and downpipes must be sized for the whole roof area.
• The high wall and the top edge of the roof need careful detailing; where a lean-to meets a main wall, an apron or headwall flashing seals the joint.
• Large rooms under a single slope can have uneven ceiling heights.
• On long spans, a shed roof may need intermediate beams.