What is the flooring material in the other rooms? If you are going from carpet to tile, you could transition your height under the carpet. If it is hardwood you can make a transition strip. Of course the best way has been mentioned before, remove the underlayment if possiable. If you are building off the subfloor, tile and durock= 1", tile and hardie backer= 3/4" Carpet=1/2" Hardwood=3/4" You are only talking 1/2"max. Another way would be to use durock in the field and hardie backer at the transitions and taper the tile in the doorways?