[log in to unmask] writes:

<< In most cases, if a "typical" flat roof on 19th century townhouses exists,
it
 appears (at least in my experience) to have been the following:

 1.  Joists running front to back, usually bearing on a beam somewhere about
 mid-span with the beam running from side to side.
 2.  Wood plank decking approximately 1" thick and of various widths ranging
 from 6" to 10".
 3.  A flat-seamed metal roof was then installed directly on the planking.  I
 have never seen any type of paper as a first layer, but doesn't mean of
 course that it wasn't done.  >>

Mark Clark:  Thank you for your intelligent and discerning post. (Ralph,
yours was nice, too, but later).  I have some more questions:
A) So, given the technology of the 19th C, was that a "good" roof (or good
enough)?
B) What are people putting on new "townhome" roofs these days, or
super-restored urban rowhouses?  I see rolled roofing everywhere - is it
inferior to metal? (Oh damn, I paid the expensive roofer that works with John
Anderson a lot of $$ for rolled roofing on my wife's Vineyard house!!) Does
anyone use metal anymore on flat roofs?
C) And, when the 19th century roof began to fail (c. 1930) , what should the
owner have done instead of covering it with roofing tar?  A complete ground
up rebuild?
D) Who/what invented rolled bituminous roofing?

Sign me,  Shakes