Theoretically, it sounds okay. But I'm not one for reinventing the wheel unless it's gone thru a vigorous R&D process. I'll be honest with you. If I were going to be your installer, I'd pass on it, because I wouldn't feel that I could warranty it.

Just as an engineer / DIY'er who has remodeled his 3 bathrooms. The floor should be well supported - subfloor + 3/4" exterior plywood + preslope.

To me it sounds like a PITA to notch the joists.

And all that work is going to save you, what, a hundred bucks? I probably wouldn't do it.

What about building up the joists on a slope, rather than cutting into them? That might be supportable.

Well, the tray would be $358 minimum. Not a deal-breaker, but still considerable. If it only takes me a couple hours to set up the cuts and do the blocking, it's a pretty good return on investment. The other thing I would gain is i would avoid the 1.5-2" height gain the foam would necessitate. That would mean a significant threshold between the bedroom and bathroom, with about a 1.5" disparity between finished floor heights . If the shower had a curb it wouldn't be an issue, but I want to go curbless. I would add 2x10 blocking on each side of the subfloor seam, so I'm not too worried about rigidity. I don't think a foam board offers any real deflection resistance anyway, and I assume those usually just go atop a single layer of 3/4"? I suppose I could double up on the 3/4" just to be safe, but 3/4" Advantech over 12" OC joists is pretty burly.

As for it being a pain, that doesn't really bother me. I was initially considering doing a fully recessed soaking tub (which would have required _serious_ support work), until I measured under the house and found the drain would have ended up about 4" below the main soil pipe. Shaving down 36" of a few joists seems like a breeze in comparison. I don't know- I'm still thinking about it. I need to get under the house and check all my clearances. It seems we all concur that it could conceivably work on a theoretical level, so I may just offer myself up as a guinea pig and get that R&D process rolling. Either way, I'll let you all know how it goes. The bathroom is a complete train-wreck (1909 Victorian, subdivided and rented for 50 years), so it should make for great forum fodder.

The pre-slope Kerdi foam is junk. I just ripped it out on my last job. It looks like some kind of spray adhesive is used to set a kerdi like material to the foam. When I removed the Kerdi from the Kerdi Line drain it looks like that connection is made with construction adhesive.

You decide: Check out this Kerdi removal video

The original Kerdi Line drain did not use this adhesive for this step. I'm not sure when they made the switch. I always thought that construction adhesive gets brittle in time.

The shower shown above has been a bear of a build with many hurdles. The complete process mapped out here:

Using Hydro Ban Sheet Membrane with a Kerdi Line Drain

It's a lot to read through but if your planning a Kerdi shower this post might save you a hassle or two.

Any good barrier free shower design has a slope outside the shower back to the shower. I like 4"-6" of space.

Tile layout becomes key and adding in a capillary break is a wise idea in my book.

If you can lower your framing by a couple inches you get a few more options. Lower it 3.5" and in most cases the sky is the limit.

In these high risk builds my goto membrane is made by Noble Company. I like a traditional clamping drain and tie the bonded waterproofing to the rise of the drop down and up over the non-wet zone.

Then I set my ACO linear drain and grade with laticrete 3701 at 2" with a 2"x2" galvanized wire mesh.

Bomb proof and fully functional.

Prepping for a new one right now. These pictures taken a couple weeks back. The home gets a 1.5" concrete pour over some heating pipes not yet installed. The drop is 2" as shown so I have 3.5" of real estate to work with.

Maybe these photo's give you some ideas.

This is from below looking up. The plumber has removed some key blocking that I still need to fix but the framer did an OK job with the drop down. I beefed it up some since the work was about 80% OK.

In this photo the subfloor has been clad with WOnderBoard lite as a prep step for the pre-slope. The periscope will grow out from the drain at 2% or 1/4" per foot. The other side of the 2"x4" frame gets 1.5" of concrete some time next week.

Then I'm back to complete the job.

Last year I showcased this shower.

Capillary Breaks for Barrier Free Shower Designs · More Info

It was designed and built the same way.

In this photo the shower is under food test. Flood tests should be for a three day time period. Maybe 48 hours. 24 if your rushed but ideally a three day session.

Learn more about marking flood tests and the shower build above at this link.

In answer to the original question I prefer a flat recess in lu of a sloped one. It is easier to grade with mud than wood in my opinion.

Fair enough- I appreciate the responses. I like the fully recessed framing, and may just pursue that. Sloping the subfloor was going to be a way to circumvent doing a full mud slope, but I know that'll always be the preferred method for the pros. I did a full mud/kerdi-drain shower upstairs that has 5 years on it, so I know I can make it work. However, I've been poking around and like the Laticrete/Noble membranes. John, is there a reason you don't use the Noble linear drain systems? Also, i should mention that this will be curbless, but not barrier-less: I intend to do either half fixed glass, or full sliding doors. One more question:

I'd still like to do heat in the entire 6x10 space, shower included. I like the simplicity and low profile of the Ditra-Heat system, but I'm sure most pros would still prefer a one piece folded corner membrane for the pan (or a roll-on), which sounds better to me anyway. In this case, is it preferential to do heat under or over the membrane? Could I just do Ditra over the whole thing?

I do recommend the Noble Drain on occasion to my clients. I have a current client in the US now doing a slope subfloor and Noble FreeStyle Drain.

Here is a drawing I worked on two months back

What I have learned over the years is that the ease of cleaning these drains is key. The linear drains from many company's have raised grates. This leaves the thin-set and grout open to every shower. This gets nasty in time.

Drains from Laticrete, Noble, Proline and Schluter are all much like this. On my current steamer I had a Kerdi Line drain to deal with. So I tweaked it some and framed it. This will improve the maintenance of the shower drain I think and make the Kerdi Line drain more like a ACO Plain Edge.

I do not think water is migrating to the drains like we are led to believe. I have been design my showers with improved weep hole and weep channel technology.

Lots of theory - not a lot of showers to study. So far my initial builds with my new design are showing great success and looking pretty.

Ditra Heat. Wow - I can not go there. I think you will see this product off the shelves in less than five years. You will never see it in any of my builds. When you study the cross section it contradicts everything we where pitched about Ditra. That with the restrictions in the wire choice and thin sets and you have really dog of a sku in my mind.

I would not use it.

When you plan your wet zone plan on slope outside thew shower back the the shower 4"-6". Plan a capillary break if you think my style (adopted from the Aussies) is worth it. Plan on 1 1/4" of grade change to the top of the drain grate. Skip the tile insert grate for added safety and skip the hair strainer at the same time.

I have helped a lot of people plan these showers. Most of the key planning is in the tile layout and material selection. This past year I have recommend mostly ACO drains but have on certain jobs recommended Schluter, Noble and Quick Drain USA. It depends what the hurdles are.

It is this reason why the first five years I was diligent about working with and understanding all the drains and their limitations. No one online to my knolwledge has installed anywhere close to the number of drains I have. Lots of men have opinions. But I always wonder where they take their data from. Me - I have learned the hard way. In the field. Building these showers.

it does not take much research on the subject to see most men talking about have maybe installed one or two. And then they are the expert.

When heating a shower floor we always add the waterproofing over the heating. Not under it. Ditra would not be wise choice. To get the best heat transfer you need to do a little creative planing and design the shower like a divot method. This gets tricky and to do this I would be recommending a NobleFlexFlashing and standard drain. Then you could do something like this job. The picture below shows a heated shower floor. The tile edging is Pro-Parts by Butech.

I call this a Kwaywk Style shower Drain. Rod Kwawk is one of the Countries top installers and I was inspired to do this build after following his work for many years. In order to achieve the grading with a regular point drain and large format tile I used a medium bed thinnest from Ardex. X32.

The drain is by california faucets and comes with a powder coated cast iron rough in.

Sexy.

Good Luck.