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Unread 12-06-2005, 09:31 PM   #1
Hickory
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Kerdi drain near edge of shower and Noble ProSlope vs. Kerdi Tray vs. mud

John Bridge commented, in the "Shared Shower, between two bathrooms" thread: "Without seeing it, I'm going to give you a thumbs down on your idea. Kerdi drains won't work near the edge of a shower. They need to be more toward the center because of the way they are made (fixed pitch all the way around)."

That caught my attention. I am replacing a tub, whose drain is near one edge, with a shower. Although I have access to the floor, and am putting in new drain pipe, my plumber tells me that I should keep the drain near the edge so that he won't have to install an additional vent. I am trying to figure out whether to go to the extra plumbing/venting expense so that the drain can be centered, so I would like to understand John's remark more completely.

I am guessing that the reason for centering the Kerdi drain is that it has a fixed pitch all around --> the floor at the far end would wind up intersecting the wall tiles much higher than the wall close to the drain. True or False?

Are there other reasons for centering Kerdi drain?

How close to the edge of the shower wall can you put the Kerdi drain?

Unrelated question: I am tending toward the mud floor, but what do you tihnk of the Noble ProSlope vs. the Kerdi shower tray?

Thanks!!

-- Hick
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Unread 12-06-2005, 09:46 PM   #2
jadnashua
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You need a slope of 1/4" per foot, so if the drain is on one end, if you want the floor to be the same height all around, it will be very steep on the short end. ALternatively, you could have each wall at a different elevation, but then that looks funky not counting the really hard transitions at the corners. The normal compromise on a rectangle (vs a square) is to have the shorter side a little steeper than the longer side and have the outside edge even all the way around.
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Unread 12-06-2005, 10:25 PM   #3
cx
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What Jim said.

The Kerdi drain is a really big thing on top. Don't recall just how big and it's too cold to go to the shop and measure, but it's like a foot across. On a standard tub rough-in, you'll be real close to the wall and you'll have trouble gettin' the Kerdi attached to the drain and up a slope.

I'm confused about your plumber's comments, too. If the current tub drain is vented in the adjacent wall, there's no reason not to move it a couple feet to the center of the old tub footprint. You got any pichers of the situation? We like pichers.

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Unread 12-07-2005, 01:47 AM   #4
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First -- I really appreciate your generous and incredibly well-informed help. Here (I hope) are some pictures. First time for that so I'm sorry if they don't work out.

There is a joist running lengthwise, almost dead center in the shower. The drain goes off to the upper left. The vertical orange line is the limit of how far to the right I can put the drain without adding a vent. (CX, the vent is is the sewer stack itself.)

My goal is to see how far "south" -- how close to the joist -- I can place the Kerdi drain. I think I could put the narrowest part of the Kerdi right against the joist. (Underlayment plus mortar bed gives at least 2", and I could always increase the plywood underlayment's depth.)

If I could put the narrowest, lowest part of the Kerdi drain right next to the joist, that would put the center of the Kerdi drain 1 3/8" away from the joist, or 14 5/8" from the nearest shower wall, and the top flange about 9" away.

If I added a vent, I could put the drain dead center, lengthwise, in the shower. But no matter what I do, I can't move the joist. So... can I use the Kerdi drain? And if not, any recommendations as to what I can put in there?
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Unread 12-07-2005, 01:48 AM   #5
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one more picture that shows where I think the Kerdi could go -- bird's eye view.
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Unread 12-07-2005, 11:17 AM   #6
geniescience
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Hick,
I'm the guy with the big long thread you quoted at the beginning. My idea was at that time to make a channel drain, but I didn't have the terminology at that time. See the third illustration below.

The Kerdi drain is about 12" wide all around. If you place it real close to a wall, AND if you keep a continuous 'plane' in your shower floor, then you have the problem of the floor being highly sloped near the wall. See the first and second illustrations below. A plane can be sloped and curved, and vary along the way.

You can get around the steep slope, if you build a discontinuity into your shower floor, but so far no-one has ever recommended that here. On another thread in the Pro forum, I said that it's the word used to describe it that scares people away from ever having a ledge in their shower floor, and I did mean it. The word is 'gang'. ("A gang ___"). Elsewhere in the world I don't think it would be a problem to build something custom to accommodate this situation. I mean it. Even if you call it a channel drain or a long drain.

Another way to get around the steep slope is to plan NOT to have a level top all around, and that is best illustrated in the second drawing below. Then, water will touch your wall at one end before it even gets half way over to the other end. No big deal, in my opinion. Also, the way your space is configured, it seems that no-one will ever see closely the fact that your wall tiles go down different lengths before reaching the floor.

Perhaps David Taylor of Tile-Experts can get you something custom with Kerdi and a Troba-like system; he has told me that Schluter is still looking at how to deal with this in a truly foolproof and modular system. Hope I'm not giving away any trade secrets here; he didn't say it was.
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Unread 12-07-2005, 01:28 PM   #7
cx
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That drain location would be technically workable, Hick.

Still don't know why he won't move your drain to the center in the direction parallel to the joists, though. What code is he citing for that restriction?

My opinion; worth price charged.
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Unread 12-07-2005, 01:34 PM   #8
Hickory
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Thanks David. I appreciate seeing the drawings, but I don't understand the third possibility. I tend to think that #1 would work. The fact that Schl├╝ter sells a 32x60 shower pan gives me hope that the 9" from drain lip to wall isn't really a problem. After all, putting the Kerdi in the middle of a 32" width gives a smidge over 10" from lip to wall.

What do you think about the possibility of jamming the Kerdi drain up against the joist?

Again, I'd appreciate advice before I commit to Kerdi.

Thanks!

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Unread 12-07-2005, 03:42 PM   #9
geniescience
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It seems workable to me

Hick

What you drew in Post #5 seems to work OK by me. If no-one contradicts me, that may or may not be sufficient confirmation for you. Call David Taylor or send a private message to a chosen expert and have him/her come here and comment.

My third illustration may not be relevant to you. It was to show the idea of a single flat slope going down to a drain channel, which is what I tried to explain in my very first post ('Shared Shower...') that you quoted. If I drew the same 'plane' from a top view, you would see arrows showing a slope, all parallel. The sloped plane is 100% flat (but not level) with a slope going to a side wall not and NOT split into four quarters like the Schluter Kerdi system or any other highly engineered or well-designed system -- they all have four flat quarter panels. The drain channel then would then need its own slope in its bottom, going toward the drain. This takes a bit more height overall since the 'X' and 'Y' directions have been separated and each distance needs its own slope.
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