A gambrel roof is a two-sided roof with two slopes on each side, where the pitch (slope) of the upper roof plane is shallow and that of the lower section is steep. The two roof planes intersect along the ‘curb’.
The gambrel roof is similar to a mansard roof, the difference being that the gambrel only has sloping roof planes on two opposing faces, whereas a mansard has sloping roof planes on all four sides. To confuse matters, both gambrel and mansard roofs are called mansards in some of the European countries (e.g. UK and the Netherlands). So, in those countries a mansard roof is a variant of both a gable roof and a hip roof.
But in the US ‘gambrel’ refers to a variant of the gable roof (two sloping sides with curb) and ‘mansard’ only refers to a variant of hip roof (four sloping sides with curb).
Another subtle difference is that a gambrel roof generally overhangs the building’s facades, whereas a mansard roof does not.
A gambrel roof has the advantage of providing more headroom in the attic than a regular gable roof does. For a gable-roofed attic to achieve the same interior volume, it would need a far higher roof ridge.
Synonyms gambrel roof
Once again, depending on the country or region, you’ll hear many different names for the gambrel roof, including curb roof, curb gable roof, curb gable roof, kerb roof, kirb roof, Dutch gambrel, Dutch colonial gambrel, Dutch roof, French roof.