My guess would be that the walls were framed with sheathing intact on the floor and lifted into place from the INSIDE. Maybe the windows were placed that way as well.
Gotta love old BG&E. Their union contract doesn't cover tree trimming ("Hey, that's the tree trimmer's job"). Any tree trimmer that touched that would be a fool. Maybe that's why it's the way it is; nobody wants to be responsible for it.
