We are going to be tiling our second-story kitchen in our 1920's home. The joists are 2x10's, 16" o.c., with a span of 14 feet. These barely meet the deflection requirements for porcelain tile, and certainly fail for natural stone. We're still considering travertine, and even if we don't go that route, it seems clear that reinforcing the joists is a good idea.
Since the joisting system is completely exposed from below, I'd like to sister 2x10s to the originals, as well as add some blocking. None of the joists appear to be sagging so at this point I don't think I need any jacking and so far this still seems like a DIY job. I spoke to a framing professional about it, and it didn't seem like it was worth his time, so as long as it doesn't require some major jacking, I'd like to tackle it myself.
What I'm unsure about (don't have any framing experience) is the best way to attach the lumber. Reading online, I've seen everything from construction adhesive plus nails to decking screws to bolts/washers, etc. Could anyone be so kind as to spell out your preferred way to do this? Thanks in advance!