Cpartist, where were you in 2012 and 2015? :) If the question was asked implying that people who weren't here in 2012 or 2015 might be interested in the info, I hear you, IF the person pulling the thread up had asked a question or was looking for new info. But that's not what happened. A brand new member chimed in. It's their only comment on this site and it was a comment trying to show how knowledgeable they are. However to answer your comment. I was here in 2015. :) And I've been a member since 2010.

We are in the process of interviewing several potential contractors. After these screening interviews, we will ask for bids from the 2 or 3 contractors who are most knowledgeable and compatible with us and our project. We know what we want for most parts of this bathroom, but we are still trying to understand the best way to design an accessible shower. We want to add it now as we rework our main floor so that we can eventually "age in place". The four contractors we have spoken to so far have looked at the joists, sub-floor and open access from below; and all confirm that we can readily recess the floor under the shower. They differ, however, in how they would handle the shower pan and drain for this curbless accessible shower. A couple of them have suggested the Wedi system with a linear drain. Another talked about the Schluter system, and a fourth contractor said his tile man only does a traditional mud base with a central drain. They all said that floor in the main part of the bathroom could be level and the sloping would all occur within the 4' x 4' shower (1/4" per foot). Most would put waterproofing under the whole floor, but one typically extends the waterproofing just a foot or two beyond the shower entrance. Are there reasons to go with the traditional mud base vs the Wedi (or other foam type backer)?

You've apparently thought this out, and you seem to know shower requirements. But just to clarify let me drone on a bit so I know we're on the same page so to speak: There are a few rules for shower construction, you're apparently aware of them but I'll repost for the heck of it: 1) When the shower is complete and with the drain plugged, the shower needs to be able to hold a 2" depth of water over the drain before water flows out of the shower. 2) The waterproof membrane in the shower must be pitched to the drain. 3) The shower floor should be pitched to the drain a minimum of 1/4" per foot and a maximum of 1/2" per foot. "Regardless of whether I use a preformed pan or build a mud bed, doesn't the fact that the entire pan will be lowered 2" below floor grade remove the need to slope the shower 1/2" per foot?" You want a "curbless shower", which means a non-vertical transition at the shower threshold. Meaning at the shower entry there is simply an "angled" transition from the flat bathroom floor to the sloped shower floor. With a 36" by 48" shower with a center drain, the drain will be 18" and 24" from the walls of the shower. To lose 2" of vertical over that short of a distance, you'd have to pitch the floor steeper than the 1/2" per foot maximum pitch allowed by code. That is for a shower with a sloped floor transition at the shower entry, what we refer to as "curbless". If you are willing to have a vertical drop at the shower entry, then you could use a premade pan like the laticrete pan. In general, the pans use a 1/4" per foot slope. The pans will also have a thickness of material at the drain. I don't have a schematic that shows the cross-section thickness of the hydroban pan, so I'll use the equivalent measurements from a Kerdi Tray for illustrative purposes only: Let's say you're going to use the hydroban pan, 36" by 48". The pan will have a thickness at the drain, let's say 1" thick. The longest dimension from the drain to the pan perimeter is 24"; half of the 48" dimension. The minimum shower slope is 1/4" pitch per foot, so the vertical drop over those 24" will be 1/2". Your pan will be 1-1/2" thick at the perimeter, the pan will have a vertical drop from the edge of the pan to the drain of 1/2", and at the drain the pan will be 1" thick. Getting back to the required 2" depth of water requirement: The pan only has a drop of 1/2". For code purposes, you need 2". So the edge of your pan will have to be 1-1/2" below the height of your bathroom subfloor. With the pan having a total thickness of 1-1/2", you'd need to cut down the joists in your shower enough so the top surface of the subfloor within the shower is 3" below the top surface of the subfloor in the bathroom. With the pan installed this way, you'll have a flat bathroom subfloor, then a 1-1/2" vertical drop down into the shower before you hit the edge of the pan, then the pan will slope another 1/2" to the drain. There's your 2" requirement. Made up of 1-1/2" of vertical drop at the shower entry, and 1/2" of pitch across the pan. So while there may be no traditional curb that you have to step up and over to get into the shower, there is a small step down. So by definition it's not what we call "curbless". I hope that makes sense. "With a 36" x 48" shower, I don't see there being the option of keeping a linear drain 48" from shower opening. [Drain placed on the back wall, is the 48" length, putting the drain less than 36" from the opening.] " With no drawing showing your door location, we're simply looking at this from different perspectives. You know your overall design. I don't. The description I wrote would require the entry to be on a 36" dimension of the shower and the linear drain to be 48" from the entry, on the other 36" wall. That 48" run will allow you to pitch the floor 1/2" per foot over a 4' distance for a total of a 2" vertical drop. That's simply one description of how you could get a true curbless shower (with a simple sloped floor transition) using the dimensions you gave. I hope all that helps, at least a little! lol

Make sure you and your contractor understand the difference between a roll-in shower and a transfer shower. Transfer shower means the user has enough upper body strength or ability to stand long enough to move from a wheelchair to a bench. A roll-in shower means there must be enough space to roll in with a wheelchair. My BIL is a paraplegic who must always be in a wheelchair, and we frequently have problems with hotels not understanding what he needs. He used to transfer and use a bench in the shower, but as he ages and his shoulders take more of a beating, he does not want to transfer to take a shower. He is afraid of slipping or losing strength at the wrong time, and then ending up on the shower floor. He brings a separate shower chair with him (actually one of his old chairs with most of the accessory pieces stripped off), transfers to that chair to roll into the shower, and then goes back to his regular wheelchair later on. Kerdi and other manufacturers recommend that if you use a curbless or zero entry shower design, you should plan for the entire bathroom area around it as a wet room. That is relatively easy to do when you prep the floor for tile, since they just use waterproof membrane and sealed seams under the tile. Its not a lot different than the decoupling membrane they use for a standard tile installation. Bruce