attic vs dropped ceiling

attic

noun
  • The space, often unfinished and with sloped walls, directly below the roof in the uppermost part of a house or other building, generally used for storage or habitation. 

  • A person's head or brain. 

dropped ceiling

noun
  • A secondary ceiling, suspended from above, used to conceal wiring, plumbing and ducts 

How often have the words attic and dropped ceiling occurred in a corpus of books? (source: Google Ngram Viewer )