hammer beam vs ridgepole

hammer beam

noun
  • A member of a kind of roof truss (a hammer-beam truss), so framed as not to have a tiebeam at the top of the wall. Each principal has two hammer beams, which occupy the situation, and to some extent serve the purpose, of a tiebeam. 

ridgepole

noun
  • A beam along the ridge of a roof to which the rafters are attached. 

  • A horizontal pole that supports the roof of a ridge tent 

How often have the words hammer beam and ridgepole occurred in a corpus of books? (source: Google Ngram Viewer )