The mansard style roof is a mark of French design, with its popularization being attributed to French architect Francois Mansart. The roof has two different slopes on all four sides of the house, with the lower slope being quite steep, almost vertical while the upper slope is very low sloped. The upper slope is just steep enough to allow for water runoff, and generally can't be seen from street level. Because of this a mansard roof usually isn't ideal for regions that received heavy snowfall. This style is very similar to a gambrel roof as seen on many barns and can even be easily mistaken. The thing to remember is a gambrel roof has two different slopes on only two sides of the structure.
The design for a mansard roof has several benefits. First it creates much more livable space in the attic, in fact it is popular for the attic space to be turned into living quarters called a garret. Another benefit to a mansard roof is its ability to house dormers, which are window like structures that protrude vertically from the lower, steeper roof line. Dormers are a major part of the perceived beauty of a mansard roof. Apart from the functionality in extra space a Mansard roof creates, it is also simple and practical to build, saving both time and money during construction.
Pros: Creates additional living space in the attic, allows for use of dormers, aesthetic appeal, ease of construction.
Cons: Low pitched roof portion of roof not ideal for areas receiving heavy snowfall.
MANSARD ROOF TYPE ILLUSTRATIONS