[porsche930dude]

weather or not your floor sags depends how big your floor joists are and how far they span. If its a relatively new house you shouldnt have a problem. Codes are usually way overkill on these types of things. For your subfloor you can most likely get away with 3/8" cement board to save a little weight. Or if your plywood is sold as can be iv torn up slate floors that have been put down directly to the plywood which was extremely well attatched. They sell bonding agent for this type of application. Im on a job right now that we did just that. We tore up the slate tile that was applyed directly to the subfloor. Then the homeowner wanted heated tile floors so we just left all the crap ont he plywood and they ran their heat tape. then we floated the whole thing in with self leveling thin set and bonding agent and went over it with the new tile. It came out great. I guess time will tell if it holds up or not. But thats what was recommended