You can plumb the pool & spa to have either separate systems or a shared system. Mine shares the heater and filter but uses a separate pump for the jets. While the spa heats up, I cannot filter the pool but it takes less than an hour to heat up the spa and we usually don't use the spa for very long periods of time. The jets are independent so I can run those any time and it isn't necessary to have a separate filter for that. I have seen completely separate systems where the spa has it's own heater, filter and pumps. It really comes down to cost and what you want to do with it. A shared system is less expensive but you cannot filter the pool while heating/filtering the spa. Most of the time it is not necessary to do both at the same time but if you have the money, why not. A small filter doesn't cost too much but you may want to share the heater and chlorinator (e.g. swg).

If you want to see my slab mess you can look at my demolition diary (scroll down from there). I'm in SoCal, with slab, but I have to admit I don't even know what "post-tension" is. There's some fill in the front of the house, but I don't think this was a concern in the kitchen. Regarding the floor after the trenching, there's goop my artisan tile setter used, called anti-fracture membrane. It takes a couple of days to put down, but not a month of curing. It's supposed to keep the tile from breaking if the new concrete expands and shifts at a different rate than the old. When you're considering the sink relocation, remember the plumbing vent and fall of the drain line, as well as running the water. It's important to be able to drain into your existing line (since you don't want to dig up the whole house), and vent somewhere feasible. For mine, before we even started demolition, the master plumber traced where the vents were, and sent the camera robot into the drains to see where they were, at what depth, and at what rate of fall. I was very lucky that they could tie into what was there without much trouble. It's much better to do it this way than just start digging and take your chances. The dust CAN be controlled. Just act a little hysterical around the GC. :-) Mine brought in the thin plastic sheeting from Home Depot, and put it over everything. Well, his helper did. :) It also drapes the open wall between the dining room and living room, and covers the kitchen door. There isn't an outside lock, so one of the guys comes in, opens the kitchen slider, comes back and tapes the kitchen door, then goes around. Too much dust escaped when they removed the dining room door, however, even though there were drapes between DR and LR. A solid barrier is...solid, and it took them awhile to get the shrouding just right. If you have an open plan, several separate layers become crucial. But it can be done. Although dust is inevitable, I've had remarkably little to deal with, and since I have respiratory issues I was expecting the worst.

It will take 5 minutes to measure the space out and draw a diagram. That will tell you if you have a 60" circle possible. It's not likely without annexing more space. But it's also likely not as necessary as a walk in shower would be to aging in place. That needs at least a 48x48 space, or 48x60 if you truly do want wheelchair accessibility. You should worry more about a cane and walker than a wheelchair though. The more difficult issue is bathing, and it rears it's head before using a walker will.

We are moving forward and will do the work ourselves if it comes to that. At this point the final configuration will be determined by the drains and vents required for a free standing tub, toilet and sink. As shown in the initial post, the existing constraints include log walls which cannot have any plumbing, a single internal wall which holds the vent stack that continues through the roof, maintaining entry and exit points for existing 3 inch line. I also plan to use the internal wall for the tub filler. All other plumbing will be in the existing crawl space which will require putting p traps for both the tub and the sink below the sub-floor (I know not allowed). The previous pedestal sink had the p trap below the sub-floor and we never had any problems. The entire crawl space is accessible and provide plenty of space for proper slope. The biggest challenge is venting each fixture. I really wanted to flip flop the vanity with the toilet but thought it would be really difficult to vent the toilet in that location. The design tool I am using wants to run horizontal vents to the stack. I'm sure this is not optimal. Also the tool refuses to run a vent to the sink. Our kitchen sink has an Air Admittance Valve which works well so I guess we could do the same but would prefer vent to the stack if possible. Any recommendations would be appreciated. Sorry if I don't have the all the proper terms down, hopefully the drawings make it understandable.