We’re refinishing an attc of a home built in 1915. It has a front gabled roof, that is constructed of 2X6’s (real 2X6’s, not 2X5.5’s), and planked sheathing underneath a slate roof. It currently has 1X6 collar ties on every roof rafter, which are about 20" apart.
The idea is to put in new collar ties that would double as ceiling joists (there will also be knee walls at 5’ high per code). My question is, how high can the new collar ties be? The current collar ties around about 7 feet off the floor. I would think by using a stronger material, we could move the collar ties up a little bit and still maintain structural integrity. But, how high? Can we go up to 9 feet? Only 8.5 feet? How do we figure out what’s possible?