Bathroom floors are often neglected and passed over during remodeling considerations.  Even a small, insignificant  bathroom can be revitalized with a ceramic or laminate wood floor uplift. There are considerations, depending on the age of the home, having to do with the composition of the existing floor or sub-floor.  If in the case of an older home, there is a couple of inches of cement with the old, one by one inch ceramic tiles embedded, one might be compelled to hammer out the whole thing and rebuild with two layers of three quarter inch plywood and a layer of half inch Durock before installing a finish flooring. 

      Nevertheless, laminate floors can float on an existing or older flooring, unless there is mold, moisture damage or an extremely uneven surface.  If the existing sub-floor is not cement, It may be necessary to remove a rotten layer and install a luan backer board before applying the finish floor.  I replaced a 60 inch cast-iron tub with a Schluter preformed styrofoam shower pan and in the process, found that under the 12X12 ceramic tiles was an original layer of 1X1's and over two inches of cement.  The customer wanted to keep the floor, so I ended up with a depression where the tub had been.  With two layers of 3/4" plywood on the sub-floor, the bottom of the new shower pan (floor) ended up being even with the original floor and the curb overlapped the space between the pan and the cement floor. 

      Included here is a photo of the cement floor with original 1x1 ceramic and a newer layer of 12X12 tiles, attached with construction glue.