Before plywood, how were the flat roofs of 19th century houses and tenements
constructed?  Were they planked, and then coated with bituminous?

This has occurred to me while watching 3-Polish-Guys, Inc., apply rolled
roofing to a pair of 1881 tenements out my window.  I realized that they were
just covering up the existing, without removing it - but then I realized I
didn't know what was "existing".

Sign me,  Notice: Cape Does Not Enable Child to Fly