If I were lucky enough to have the bathroom ceiling fall between two trusses (meaning, the trusses are spaced more than 5' apart, and fall outside the walls of the bathroom), would I still have to be concerned with removing the ceiling joists? I do not believe that the trusses are spaced very close. There are 'roof rafters' every 16" or 24" (don't remember), but I believe that the truss framing is only present every 'few' 'roof rafters'.
With trusses, are the ceiling joists still acting as collar-ties?
I like the idea of creating a passage up to the roof for the skylight - a lot less work! In that case, I would only be removing 1 or 2 joists for just the length of the skylight, and framing new 'walls' to the roof. It would also eliminate the need to create a new ceiling.
I understand that I may still require some additional support framing, and will talk with an engineer.