Okay. First, you want to use cement board behind the Kerdi. Schluter will warranty sheetrock, but personally I don't trust it because of condensation, so to be safe, I'll always use cement board. As for where you want to put the grab bar, just put a piece of 2x10 blocking between the studs behind the cement board wherever the grab bar will bolt up. Make sure you use a good amount of caulking (or Kerdi-fix) in the bolt holes to seal them back up. As for the seat, The top of it should be plywood, and then cement board under the Kerdi. The front of it can just be the cement board.

As for a bolt on seat, you CAN do that, but my own thought is that the less holes you have to make through the membrane, the better chance you have of that steam shower lasting a long time. If you want one of those wood slat seats, maybe think about one that stands alone, that you can take out when not in use.

Can I assume the wood tile would be an unsuitable size for the shower floor?

Yes. If you're going to put a wood slat floor OVER the tile floor, you can use just about anything you like, 6x6 or smaller (so that it conforms to the pitch of the floor to the drain).

Thank you Bill. I can't believe how fast you respond.
Sally

I just happened to be in the neighborhood. :-)

Sally,

Just to agree with Bill. My DH has now done three Kerdi showers in our house and is starting to do them for some clients. He always does cement board behind it. It may be belt and suspenders, but it's good insurance.

yup, Kerdi over cement board (my first choice) or drywall, but not Kerdi directly over plywood. Kerdi is the best for steam showers. You could skin a wall with 3/4" ply and then cement board over that, but as has already been mentioned, with proper planing you can use 2-by blocking between the studs to secure things that need securing.

Bench, I personally prefer a movable wood bench instead of a built-in. If you do a built-in watch where the steam nozzle goes. Normally it'll be under the bench, but just be aware of the leg location versus steam nozzle location during design.

I've also done a slatted teak bench seat (no legs) that was removable, when in the shower it rested on a couple of tiled nubs that stuck out of the opposing walls. Lift off the nubs and set wherever you want when not using it. Against the wall, or outside the shower in a closet.

When traction is desired I've used the ceramic faux-slate tiles like the DAL continental Slate series on several shower floors. Each tile has a bit of cleft, enough for sure-footedness, but not so mush as to hinder floor drainage. 4" squares work well, traction from the tile surface as well as traction from the grout lines.

I'd be wary of the large gloss 6" by 26" wood tiles in a steam shower.

Mongo

Done a bunch of Kerdi showers. At first, I only used Durock. Just the way I learned it. After a couple, I only use it if the client insists. Why? Kerdi is waterproof. NO chance of it penetrating the wall, if properly applied. At the Schluter training class, there is a cardboard box, covered with Kerdi. It's been sitting there for four years...used as a cooler with ice and water for the guest's drinks.

Make no mistake, I like Durock and use it often for a conventional shower. With a Kerdi shower, these are the disadvantages: Heavier...hard to deal with. More expensive than drywall. More difficult to cut and attach. Tends to crumble more around the corners. Does not absorb water out of the morter like Durock does. Need to spray it and keep it damp as you work. Drywall is smoother and easier to "bed" the Kerdi.

In my opinion, it's a "wash." CBU is a bit of "overkill," but if you're OK with the additional hassle...guess it's worth the "Peace of Mind..."

guess it's worth the "Peace of Mind..."

That's exactly what it is. I won't get into this again. :-)