My son just purchased his first house, a real project house. Built in 1950, the original single story structure was modified in the 70's to add a second floor. Covering a total span of approximately 15 ft on the second floor is a bath (about 10 ft) and part of a bedroom (5 ft). Each end of this total span is on top of a first floor load bearing wall which is in turn above a concrete block basement wall. The floor joists are dimensional 2 x 8s, 16" O.C. and appear to be fir. My son and I were gutting the bathroom for a remodel when we made this discovery. I'm pretty positive the 15' total span is beyond the maximum span for 2 x 8s. The existing ceiling height is already constrained so we really don't want to put in wider joists. My preferred option would be to sister another 2 x 8 to each joist or perhaps put in 2 x 8s in between the the existing ones, making them 8" O.C. The span calculators and tables I've looked at don't address either of these options. Any advice will be much appreciated. TIA.