Background info: I'm laying ceramic tile in my bathroom (12"x12" tile). There's already an inch of sub floor (with vinyl in there now, which is solid and not pulling up at all) and I'm adding 1/4" backer board before laying the tile. The bathroom is long and narrow - about 3' x 12', and the joists (2x10's) run length-wise down the room. They're 16" OC. Two joists can be completely seen down the length of the room, while the third can be seen in front of the toilet and vanity, but is covered by a wall for the linen closet. I have full access to them from the unfinished basement below. See the attached image for the layout. The problem: The middle joist is between a 1/4" and 3/8" higher than the other two (which appear level with each other from the basement). So while level going length wise, it humps pretty bad in the middle of the room. That obviously won't fly for the tile. Solutions? Since I can't uncover the joists on each side of the high one (because of the linen closet), I can't remove the sub flooring, shave the joist, and replace it easily. So, the two options I thought of, either of which may work or they both might be complete crap: Remove something like 4" of floor on each side of the middle joist, shave it down, and replace the flooring. Since I won't be able to sit the new sub floor on the adjoining joists, I could place 2x10's perpendicular between the middle truss and each side truss for the flooring to sit on. I have to think placing them every 16" going the length of the bathroom would suffice? Use one of those oscillating tools (like this) to just trim the 1/4" I need from the joist in the basement. Would this even be possible to do while leaving the floor in place? There can't be much if any weight on that joist other than the flooring? This idea seems a bit crazier, but it'd be easier (I think). I hope that's enough info. Would either of these ideas work? Any other suggestion? I'd rather do this right - however that may be - rather than using a hack. That auto-leveling liquid stuff that a friend suggested seems cheap, plus it'd raise the toilet, which would mean either extenders or raising the flange. Thanks for the help guys!