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A mono-pitched roof, often referred to as a pent roof, shed roof, lean-to roof , and/or skillion roof (in Australia and New Zealand), is a single-sloped roof surface, often not attached to another roof surface. This is in contrast to a dual-pitched roof, also known as a gabled roof, which is pitched in two different directions.
A mono-pitched roof can be a smaller addition to an existing roof, where keeping to the same slope (roof pitch) puts the mono-pitched roof lower than the ceiling height of the main structure. In this case, even though the main roof has a flat ceiling, the mono-pitched part has a sloping or raked ceiling line to maximize the ceiling height. The name lean-to roof comes from this form of addition.
Mono-pitched roofs can be used to provide clerestory windows for a hallway or similar room where a row of windows is placed below the edge of the mono-pitched section reaching above the other roof below.