Okay-- concerning 2 vs 3 2x4's, I don't really see a problem with it. it'd be a little unorthodox, but you could actually "form" the shower pan with the 2 2x4's, and then bring the mud pan all the way to the top (including cement board on top of the 2x4's). Use a Kerdi drain, and either Kerdi Membrane of Laticrete Hyroban liquid membrane (either way, a surface applied shower pan), and just make an elevated curbless shower base, mounting your glass over the 2x4's. if you want to have some sort of curb, though, I would strongly suggest going up the third 2x4, or you're going to have a very small piece between the top of the curb and the top of the shower floor. You really want to have a little bigger piece-- won't collect "junk" as easily. As for your shower pan question, Below is a link to the step by step construction of a standard shower pan. Additionally, For the standard pan, if the plumber's going to install it, and he balks at the thought of a preslope under the pan membrane, you can show him this: Uniform Plumbing Code related to shower pan construction. "412.8 When the construction of on-site built-up shower receptors is permitted by the Administrative Authority, one of the following means shall be employed: (1) Shower receptors built directly on the ground: Shower receptors built directly on the ground shall be watertight and shall be constructed from approved type dense, non-absorbent and non-corrosive materials. Each such receptor shall be adequately reinforced, shall be provided with an approved flanged floor drain designed to make a watertight joint in the floor, and shall have smooth, impervious, and durable surfaces. (2) Shower receptors built above ground: When shower receptors are built above ground the sub-floor and rough side of walls to a height of not less than three (3) inches (76 mm) above the top of the finished dam or threshold shall be first lined with sheet plastic*, lead* or copper* or shall be lined with other durable and watertight materials. All lining materials shall be pitched one-quarter (1/4) inch per foot (20.9 mm/m) to weep holes in the subdrain of a smooth and solidly formed sub-base. All such lining materials shall extend upward on the rough jambs of the shower opening to a point no less than three (3) inches (76 mm) above the top of the finished dam or threshold and shall extend outward over the top of the rough threshold and be turned over and fastened on the outside face of both the rough threshold and the jambs. Non-metallic shower sub-pans or linings may be built-up on the job site of not less than three (3) layers of standard grade fifteen (15) pound (6.8 kg) asphalt impregnated roofing felt. The bottom layer shall be fitted to the formed sub-base and each succeeding layer thoroughly hot mopped to that below. All corners shall be carefully fitted and shall be made strong and watertight by folding or lapping, and each corner shall be reinforced with suitable webbing hot-mopped in place. All folds, laps, and reinforcing webbing shall extend at least four (4) inches (102 mm) in all directions from the corner and all webbing shall be of approved type and mesh, producing a tensile strength of not less than fifty (50) psi (344.5 kPa) in either direction. Non-metallic shower sub-pans or linings may also consist of multi-layers of other approved equivalent materials suitably reinforced and carefully fitted in place on the job site as elsewhere required in this section. If you want to go with the Kerdi/ Hydroban hybrid, Laticrete WILL warranty it, so long as you follow their spec. Email me, and I';ll send it to you (for some reason, I can't upload it to Photobucket, and therefore can't post it here). Here is a link that might be useful: Harry Dunbar's Showerpan tutorial

If you look to general standards youll get caught up in a long hotly debated topic. The topic is 2" as written in certain code. This means the finished height of the threshold or curb is to be 2" above the showers drain strainer. How people in California have curbless barrier free showers built is another drama altogether. Bypass the interweb and call your local Plumbing inspector for the most direct undebateable answer. A few things to look out for if you get stuck or bamboozled into a hot mop. Most hot moppers skip the REQUIRED preslope and most will mop over a treated stacked 2x4 curb. Both of which can be fatal in short order. I suggest you take your time and source and hire A proven tile professional and try hard to avoid the hot mop..

Position of toilet and door are pretty fixed although we may configure the door to swing out I get that moving a toilet is pretty expensive ... how fixed is "pretty fixed" when it comes to the door? Walking in and seeing the toilet first-thing isn't ideal ... if you could move the door to mid-room, I'd do it. Swing out is no big deal ... I have that now, and I never think about it. A 36" vanity is probably too tight, so looking at something just under that. A 36" vanity is small ... and you don't have other storage in the room. I'd give up a bit of shower width to bump up a bit in the vanity. Also, most ready-made vanities have awfully small drawers ... if at all possible, I'd go custom so you can maximize drawer size. Do I think giving up shower width is good? Of course not, but it's a trade-off between the shower and the sink ... and a 36" shower is better than a less-than-36" vanity. I'm thinking right now of frameless glass for the shower with a door that can swing in and out toward the blank wall side of the room. Does this seem ok or do I need sliders Why not eliminate the glass cleaning chore and bring in some color /softness with a shower curtain? Clearly need lots of planning/engineering together for that to work but does anyone see any immediate red flags that mean I should abandon curbless from the start? I thought you needed 4' of shower width for a curbless shower? With your vanity already unreasonably small, I'd consider giving up the curbless shower ... and instead go with a 2" curb. Look at just how small 2" is. That's all you're required to have ... but most builders put in something much higher. Don't neglect good grab bars too. And seriously considered the pocket door but apparently there are heating ducts in that wall that make it a Big Pain to do :-) Having the door swing out is an easier option (and there is nothing currently obstructing the outswing into the master anyway. No to pocket doors in bathrooms. They're harder to open, and they will fail ... especially in a humid environment. Perhaps worst of all for your specific situation, they require a slightly thicker wall, and you're not in a position to give up even an inch. Please reconsider not having a bench especially if you have "hip" issues. Also, super easy to shave your legs with one. Keep in mind that you don't have to have a built-in bench. You can find waterproof teak benches at Bed, Bath & Beyond. If you ever need a hospital chair, it's easy to move out the bench.

We did have our sunken tub flood. It wasn't from the drain being clogged. The sewer pipe from our house to the main sewer was clogged by tree roots so all drainage from the house stopped. Because our house is elevated a bit from the street level, the clog was around 5 feet lower than the house. Being higher than where the clog was didn't help. The sewer pipe filled. The water didn't come from the shower above the tub. The tub drain was just the lowest drain in the house. So water from anything drain that was used (the clothes washer, dishwasher, sinks, toilets, other showers) came out that drain once the pipe filled. The tub bottom was about 3.5 x 5 feet (the lowest part so not counting the area of the step in the tub. It filled to above the step in the tub so deeper than 6". That means more than 8 cubic feet of water. Now that the lowest drain will be in a shower, a curb wouldn't have contained the water. As myrica4 points out, there are other sources of flooding. The one that happened to us once in a prior house was a toilet tank that cracked. Nothing hit it - just one night it gave way. I got up to use the bathroom (pregnant at the time so not uncommon) and my feet slipped in the water. At least that was clean water, but a pretty unpleasant surprise at 2 AM or whatever. We cleaned it up and no permanent damage. The place where being on a hill helps is if the sewer line clogs below at least your next lowest neighbor. Then the water will come out of their drain and the pipe to your house won't back up. But if it clogs close to your house, the elevation of your house won't make a difference.