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Unread 03-30-2022, 05:26 PM   #1
vinmassaro
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Schluter curbless shower with recessed floor, how to make up height

Hello, I'm renovating my master bath and have a question when using the Schluter KST965/1525S shower tray that is 1-1/8" in thickness for a curbless shower installation.

I've got an existing 3/4" plywood subfloor and will recess the floor for the foam tray per the Schluter manual by adding blocking and 2x4s inside the joists so that I can install plywood on top, so it is flush with the top of the joists. I will be using DITRA-HEAT membrane for the entire bathroom floor, including the shower area.

When recessing the shower area that still leaves me with 3/8" to make up outside the shower area for a flush transition to the bathroom floor. What is the expected way to make up this height? I see Schluter also has thinner trays but they are only square and not the rectangular shape I will be building the shower. I mocked up what the shower will look like in the image below. Thank you.

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Unread 03-30-2022, 06:24 PM   #2
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Is there a reason you can't drop the shower area 3/8" more?

If you can't, the only thing I can think of would be to add 3/8" plywood to the rest of the bathroom.
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Unread 03-30-2022, 06:30 PM   #3
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Welcome, Vincent.

Couple questions:

You have evaluated your joist structure to determine that the floor qualifies for a ceramic tile installation?

What is the joist spacing?

You are using tiles 2"x2" or larger in all areas to qualify for use over the DitraHeat?

Will there be a door on the shower or will it be doorless as well as curbless?

If you need to raise the bathroom floor 3/8ths" of an inch, you could use nominal 3/8ths" exterior glue plywood and get pretty close. Presuming, of course, that you can find such material that's sufficiently flat and are able to install it flat on your existing floor. You might even find that nominal half-inch plywood would work a little better. You'll need to deal with the transition to whatever floor is outside the room, of course.

Kevin's fast, non?

My opinion; worth price charged.
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Unread 03-31-2022, 06:15 PM   #4
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I've used the deflection calc and plan to use 12x24 ceramic tile:

Quote:
For joists that are SYP or Douglas Fir, in good condition, 9 inches tall, 1.5 inches wide, 12 inches on center, and 10 feet long between supports, the deflection calculated is 0.112 inches.

This translates to a deflection of L / 1073.

Since the maximum deflection for tile is L / 360, and for natural stone is L / 720, your floor is rated for Ceramic tile or Natural stone, Congratulations!
I'm not sure what the joist length is because I can only see what is cut away right now. The joists run parallel to the shower pan. I plan to use a fixed piece of glass that is set inside Schluter Deco-SG profiles in the floor and wall, so it should look close to my picture above. It sounds like it may be easier to just trim the top of the joists by even just 1/4". What's the easiest way to trim them down?
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Unread 03-31-2022, 10:04 PM   #5
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If the builders gave you that joist structure, they really did you a favor.

If there any walls or beams underneath those joists, that'll indicate the unsupported span.

But to answer your question, you can mark it and use a reciprocating saw or a rotary saw. If you cut it a little short or it's jagged, don't worry, because you can sister the joist with a 2x4, some construction adhesive, and some screws.

But be sure if your deflection rating before cutting your joists.
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Unread 04-01-2022, 09:31 PM   #6
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Below is a photo of this area removed. Looks like my joist length is 16 or 17ft which puts me off a little bit on the calculation for ceramic tile. The house was built in 1958, so did the builders do me a favor? Seems like if the joists ran perpendicular, I'd be in better shape?

This bathroom had a curbed walk in shower and jetted tub with surround walls covered in tile, and thick 12x12 ceramic tile on the floor. It was redone sometime in the early to mid 2000s and was in good shape so I'm skeptical that new tile will be a problem. Thoughts?


I'm considering now just going over the existing subfloor with 3/8" ply since it may be easier than trimming these down. Thanks!

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Unread 04-02-2022, 07:20 AM   #7
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Looks like those waste lines are pretty close to the joist tops, Vincent. What's the measurement from the top of the holes to the top of the joist?

Assuming your joists are nominal 2X10's (1.5X9.25 actual), and do actually have a free span of 16 or so feet and are spaced at 12",our Deflecto indicates they are just barely under L360. If they are 16' and spaced at 16" they are significantly under L360.
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Unread 04-02-2022, 09:11 AM   #8
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Yes, the hole for the waste line is about 3/4" to the top which is why I was thinking I would just raise up the bathroom floor with 3/8" ply. I will cut that line back right before the tee an add a coupling to redo things. That waste line on the left side going to the tee was for the jetted tub, and I'll need to move the shower drain for the Kerdi tray forward. I could use a hole saw to cut a plug for the hole on the left side once that drain line is removed.

Under the bathroom is a finished lower level and it looks like the span is closer to 17ft. Attached is a photo from a few years back when everything was torn out during my renovation. I put a red dot approximately where that shower drain is that you see in the previous photo.

The joists look to be exactly 9in, not 9.25, and at 17ft makes the deflection L / 283. What are my options here to reinforce things for ceramic tile? Can I sister 2x8s to the three joists? The house was built in 1958 and likely had a poured cement floor with tile originally. The previous owners renovated this bathroom, but the other two I renovated were done with a cement floor.

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Unread 04-02-2022, 09:39 AM   #9
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It's certainly up to you what you're willing to tile over, Vincent, but with the joists you have and the unsupported span you have, you may have met building code when constructed, but only if your joists are of a good grade and species.

But even then, given the unacceptable boring we see in the photos, which do not meet code, I think it's likely that you no longer meet code or the requirements of the ceramic tile industry (same in this case), especially given the increased dead load you'll be adding.

The unacceptable boring is at least less damaging being at the top of the joist, rather than the bottom, but the requirement is still a minimum of two inches from the edge of the member.

I'm guessing, given that you say that space below is now finished living space, you no longer have the option of a mid-span support under your joists?

My opinion; worth price charged.
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Unread 04-02-2022, 09:52 AM   #10
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@CX: agreed, I thought the same thing when I cut back the subfloor and saw the location of the plumbing hole. I don't know who renovated this bathroom prior but there was other very hacky work done.

The lower level is a finished living space now, so you are correct that adding some kind of support there is not possible and a post or column would be right in the middle of the living space.

Do I have any options to reinforce things as they are?
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Unread 04-02-2022, 03:05 PM   #11
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I'd look at cutting back the plumbing, remove the blocking, and sister the full height of the joists, maybe even both sides.

Then replace the plumbing properly. There's a notch and boring guide right here in this site, thanks to CX.
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Unread 04-02-2022, 03:42 PM   #12
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I'd think sistering is likely to be a seriously unwanted option with the room below already finished, Kevin.

I would think a support beam would be the more viable option, but not my house, eh? Could eliminate a post in the center of the living space, which Vincent seems to think is also an unwanted option. Dunno why. Nice post in the middle of the area could easily be decorated to suit Mrs. Vincent and be a nice feature, non?
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Unread 04-02-2022, 05:14 PM   #13
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Would removing the subfloor and sistering each joist on both sides (just the length exposed in the bath) help at all? A post or beam is out of the question. Appreciate the idea but it would start World War III.
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Unread 04-02-2022, 06:58 PM   #14
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No, Vincent, for sistering to be effective in reducing deflection, you must sister at least the center two thirds of the unsupported length.

My opinion; worth price charged.
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Unread 04-03-2022, 09:22 AM   #15
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Ok, understood. I appreciate all the information provided.

Is there anything else I can do from above to stiffen things as much as possible? Add blocking or bracing between joists, replace existing 3/4 OSB subfloor with 1-1/8" ply (since I need to build up 3/8")?

For that incorrectly bored hole, is there any recommended repair other than something like this? https://joistrepair.com/collections/...roducts/2810hr

The tile I am looking at is a porcelain 12x24 that is 9mm thick. My understanding is it's harder than ceramic but I'm not sure if it makes a difference in this case.
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