(adj) (of a roof) having two slopes on all sides with the lower slope steeper than the upper, Example:the story formed by a mansard roof is usually called the garret
The Collaborative International Dictionary of English (GCIDE) v.0.53 Collaborative International Dictionary (GCIDE)
[ So called from its inventor, François Mansard, or Mansart, a distinguished French architect, who died in 1666. ] (Arch.) A hipped curb roof; that is, a roof having on all sides two slopes, the lower one being steeper than the upper one. [ 1913 Webster ]