We're gutting our 1940 bathroom and in the process we'll be completely ripping out the floor, which is dropped 2 by 8 joists with a cracked mudbed. We'll most likely be installing some type of marble tile and I've been playing around with deflection calculations to make sure we won't have any problems. The joists have an 8' unsupported span and we will be replacing with new 2 by 8s. The neighboring hall floor has a depth of about 1.5" (3/4" subfloor with 3/4" hardwood over). We will also be installing SunTouch radiant heat. What would be the best design for the floor in this situation? The joists in the rest of the house are 16" OC, but I guess we could install them 12" OC to meet stone deflection requirements? What about the subfloor? How thick should it be? And how much height will the radiant heat add? And just to add in another variable, I really want the new tub to be cast iron, but that will also add substantial load to the floor. Are floors typically beefed up in some way to support cast iron tubs? Help! My head hurts just from thinking about all the potential ways this could go wrong.