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

Your "better bet" is to have the shower floor slope away from the entry and to have the linear drain on the back wall of the shower. That will allow you to minimize floor slope to get the required 2" drop if you are required to have a code-compliant shower. There are no out-of-the-ordinary issues with linear drains stopping up or clogging. An occasional problem with them is having the drain at the shower entry. Sudsing action from soap/shampoo can sometimes cause suds and water to sheet right over the drain's grate and puddle out on the bathroom floor. There are some locales that prohibit trench drains at the entry to the shower. The idea of dropping the floor framing in the shower is an excellent idea. If you do go with the drain at the shower entry, use a membrane to waterproof your bathroom floor out a few feet away from the shower entry. With a linear drain you'll be using a topical membrane throughout the shower floor. That can usually be carried out onto the bathroom floor. And one clarification regarding your post: "The contractor says he will lower the floor (via the floor joists) to be about 3in lower than the bathroom floor then build the shower floor up with mud?. He says the initial entry to the shower will be flat and then slope downward to a central drain in the floor. Then: "The linear drain would be placed under the shower door where the entry to the shower begins. " Is that a description of two different showers? The first being with a central drain, the second with a linear drain? The thing is, if you're going with a linear drain at the shower entry then you really don't need to drop the framing in the shower at all. You can pretty much build the "upslope" right on top of the shower subfloor that is the same elevation as the bathroom's subfloor.

It took me years of study online to get my bathroom as functional as it is. Part of that is due to the newness of trench drains when I started reading. The hours and hours I put in reading this forum allowed me to judge which pros had an attitude and knowledge base that I respected and could trust. Then I read everything they wrote! Same with ADA design, read and think and decide for yourself what your needs are and are going to be in the future. No ADA design guideline is going to give you the bathroom you need for your particular issues, because they were written to make a bathroom that is accessible to their "defined handicapped person" who may not have the same needs as you. My best example of this is the 5 foot radius around a toilet that is part of the ADA guidelines. Well, if you have arthritis in both knees and cannot rise without a good strong handrail or counter on each side to push off of, then that 5 foot radius around the toilet is going to have you stranded with no way to get up. The "trombone" style bars that hinge up out of the way are absolutely necessary on either side of an ADA 5 ft radius toilet, but the place that you place them on the wall will differ for a "normal" sized person and the 300# - 800# person with the disorder I have. So you have to have a designer who understands your medical problems almost better than you do to plan well. THAT is why I did it all myself. Another issue I encountered were ADA vanities. They almost all hang on the wall (and cost thousands of dollars) to allow a wheelchair with leg rests to have access. Well, I am currently walking, and my knees will collapse without warning and I grab the nearest damned thing I can get to keep from falling. I am going to take a toll on that wall-hung vanity I spend a small fortune on! My 330# weight, pressing down through my arms until I can flex my knee to get it back into joint is going to eventually break that vanity, if I don't pull it off the wall the first time. I had to design my own vanity with legs that rest on the floor and bracing to the back wall to work for my needs. Wall-hung toilets are another favorite of an ADA bathroom. Nice and easy to clean under. You can find them that "hold" 300-600 lbs, but you have to understand a bit of physics to understand why this is inadequate. They are saying the toilet can hold that much weight when it is sitting still on the toilet. Lets say that you find that you have to shift your weight while sitting, or that your knees tend to collapse just before you get to the sitting position. We are now talking about kinetic weight, which triples the amount of weight the toilet actually "feels." Now, that toilet that holds 600 lbs is only good for up to a 200 lb person. This is not explained anywhere. I knew about this issue because I once majored in physics in college. It took hours of internet searching for me to find something that addressed kinetic weight in relation to these toilets and confirm my suspicion. Their weight rating is for static weight only. This shows how individual an ADA bathroom can be. Your designer had better understand the issues of a lot of disorders in order to design one that suits your needs. THAT is why I did mine myself.

Rai- Yes, it's a Luxe drain. I have a different one in another bathroom, too (one that has a stainless steel drain cover rather than the tile insert style). I'm happy with both. I like Luxe because the build quality is high, they have a pretty wide variety of sizes and styles, and the prices are much more reasonable than some other name brands. If you are interested in this brand, check out the prices on build.com for starters.