The style became popular in the 1850's in France, and quickly was adopted in England and the United States during the Victorian era. A restored Second Empire Mansard. The roof is the main characteristic of a Mansard.
Mansards have a hip roof with dormer windows.
The roof has two pitches - a flatter pitch on top, and a much steeper pitch on the sides. Many original Mansard roofs are slate, but architectural shingles are also used. The Mansard style became very popular because the roof is very efficient for allowing the top floor to be completely used. The Mansard style was originated during this period, hence the name. And, no, there is no such thing as a First Empire Mansard.