How thick are most residential subfloors?

The previous owner of my ranch house added a large room on the back that serves as a dining/family room. The dining room floor is level with the rest of the house, but the family room steps down. I'm going to raise the family room to match the rest of the house because I'm putting an 8' pass thru from the kitchen to the family room that will have a countertop and bar stools. The addition is on a concrete slab. To raise the dining room floor, the previous owner laid down pressure treated lumber (on the short side) and put regular 2x6's that had been cut for height on top of that. Do I need pressure treated wood if it comes into contact with the concrete when its inside the house? I had originally intended to just lay down mil plastic and use untreated 2x8's and 3/4" plywood to match the floor level.

I am adding a new tub that will weigh over 1,200 lb when full. I have 2X10 Floor joints supporting the floor and I have been told that this is not strong enought to support the weight of the tub. I want to add 2X10 across the floor joints and then brace them using 4X4 poles that will be run to the basement floor and then just build a walk in closet around them. I can find anybody to answer if that will work for adding support to my floor joints to make them handle the weight. thanks.