A flat roof is a roof which is almost level in contrast to the many types of sloped roofs. The slope of a roof is properly known as its pitch and flat roofs have up to approximately 10°. Flat roofs are an ancient form mostly used in arid climates and allow the roof space to be used as a living space or a living roof.

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The most obvious advantage for flat roofs is the cost: the materials are cheaper, as they don't need to have as much “curb appeal”; the labour is cheaper because there is less risk in installing them; and these roofs are easier and quicker to install so there is less labour overall.