I'm going to install a new bathtub in the same spot where the old bathtub was - only this bathtub holds twice as much water and two people (if desired.) I can't find anything that gives the span/weight capacity of lumber (16" o.c.) I think there are 2x6s for floor joists - spanning 8 feet. I don't know how badly they're notched, either. (won't know until I pull up the floor.) Do I need to go to 2x8, or can I get by sistering the 2x6s? Anyone know where to find a table giving the span/load capacities?