We've recently discovered a slow leak in our bathroom that, over a few years, has rotted out the subflooring underneath. The area is approx. 6ft by 6ft and is primarily in the open area of the bathroom. However, a portion of the rotten subflooring is underneath (or nearly underneath) a whirlpool tub. All of the affected area is covered with ceramic tile. From general contractors, I'm getting estimates of up to $3,000 to rip up the tile, replace the subflooring, and put everything back again. With an "unknown" factor in that they may discover more of a problem. My builder suggests that I simply go under the house and cut out the rotten subflooring and somehow put new subflooring in there. Basically, to replace from underneath instead of top-down (and not have to replace all the tile). My question is...is this a viable solution? Is it possible and acceptible to replace subflooring from underneath a tile floor? Two other notes, there is a concrete layer between the subflooring and tile, and, the joists have not been damaged. Thanks for your help...

:( I have a cocnrete basement floor that is essentially level save for one area near a corner in which there is a slight a gradual rise, maybe a 1/4 inch - 1/2 inch . It could be described a hump I suppose, maybe 2ftX4ft in size. I would like to put a floating floor down but I know this area needs to be fixed first. Question is, can I use self levelling concrete to address this issue, feathering it out around the raised hup to basically make the floor a gradual slope in one direction? Another detail, we had old tile removed and the mastic sealed - is concrete still usable over this subfloor? Thanks.