They don't have to be old, for the entire place to go up, we have see plenty of new 30 units and more, both condo, and town house, go to the ground
The townhouse across the street from mine almost burned to the ground and the townhouses on either side were pretty much unharmed.
The standard here is two layers of 1" drywall in a metal track as the party/common wall, and type X drywall installed under the roof adjacent to the party wall. I've seen it installed about 4 feet from the party wall. This is to prevent fire spread from the adjacent roof.
Guess what..I've seen townhouses built without the type X drywall under the roof. Somehow they passed the building inspection.
Roof replacements are another problem..how many roofing contractors do you suppose are going to re-install the type X drywall, if it was even there to begin with?
Then there's the townhouse I saw with concrete block party wall that had holes in it where someone ran a coaxial cable for a master antenna TV system. It ran from attic to attic through a 1" hole. Doesn't that kind of defeat the fire protection that the party wall provides?
