garret vs mansard roof

garret

noun
  • An attic or semi-finished room just beneath the roof of a house. 

mansard roof

noun
  • A roof having two slopes on each side, the lower one having a steeper pitch than the upper; this increases the volume of the enclosed space. 

  • A steeper roof that terminates into a flat roof at its high point. 

How often have the words garret and mansard roof occurred in a corpus of books? (source: Google Ngram Viewer )