We have a 1/2 bath in our basement that my wife and I want to expand to accommodate a new 2 person tub. We have the space in our utility room to move the wall back but my question is with regard to framing for this new tub. Will we need the tub before we rough in the frame? Does the tub have to sit on a sub-floor if raised? I'll have to raise it up high enough in order for it to drain properly. This will save me the agony of jack-hammering the concrete floor. Any suggestions would be helpful.