So, before I get started with this one, I'd like to mention that this will ulitimately be designed by a licensed SE. But, this won't occur for some time and I am interested in learning about what I should expect as it will affect some layout that I'm doing for another project.
I have completed the basic design for reconfiguring about 80% of the second floor in my house. The design will require no exterior mods and only minor structural modification (installation of a short L/B beam for a passageway). In the master bedroom, my wife and I would like to remove the existing flat ceiling and create a vaulted ceiling based on the existing roof framing. In that ceiling, we'll be installing either two or three sky lites.
Our house is 100 yrs. old. It is balloon framed and all lumber is old-growth pine. Now I do know that those joists are integral to the roof structure and to simply remove them would tend to make the roof want to collapse. I would also imagine that as installed now, they serve to keep the walls from kicking out as well.
I'm guessing that prior to their removal, some vertical support would probably be needed beneath the ridge line to transfer load. This is probably not too awful since my existing load bearing walls on 1st and 2nd floor are pretty much running beneath/parallel to the ridge line as it stands today. In addition to this, would some sort of lateral ties need to be made between the top plates of the exterior wall and the new bearing wall? I don't see this as too big of a deal if needed since we were already planning on having a couple of exposed built-up beams running the width of the room to hide some small diameter ducts and electrical.
Any thoughts, ideas, etc., are welcome!
Well, now, there's what's right and what's right and never the twain shall meet.
Your assumptions are pretty much dead-on. Your ceiling joists keep your exterior walls from thrusting outward under the live and dead load from the roof. Proper support of the ridge will do the same thing, and will typically negate the need to tie the walls together at the plateline. Unless you're vaulting the ceiling all the way up, you can still install collar ties from rafter to rafter. Combined with ridge support, it'll be solid.
I imagine your engineer will confirm this, but be sure you follow their instructions to the letter.