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Old 02-28-2018, 03:52 PM   #16
ss3964spd
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Durock Shower tray - subfloor cut out for drain assembly

All, for anyone with experience with Durock's foam shower pans, I'm trying to confirm the size of the subfloor cut out for their drain assembly.

I'm about to start the rough-in plumbing and, as usual, joists are near by. Knowing the size of that cut out will tell me how far I need to stay off the joists.

Durock's tech line was not as technical as hoped. The have a CAD file on their site that suggests 6" but I'd love to confirm with someone who knows.

Many thanks,

Dan
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Old 03-08-2018, 07:20 AM   #17
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Help me noodle out this floor build up

Rough in plumbing is nearly finished, the in-floor work passed inspection yesterday, so I'm about ready to close up the floor and need to get my head around the next steps.

I'm doing a curbless shower using the Durock shower system, using one of their custom sized pans. The pan will be 1" thick at it's perimeter. I am also installing a heated floor (probably Ditra Heat), but not running it into the shower. Shower floor tile and main floor tile will be the same thickness.

I have 3/4" T&G ply set between the joists on full length cleats, done to both increase strength for the large format tile and to get the floor both level and flat.

My current thinking is to lay another layer of 3/4" ply over the entire floor, staggering the seams from the first layer, then the pan on top of that. Durock says to set the pan using a 1/4" X 3/8" square or U notch trowel. Then mortar and their membrane on top of the pan using a 3/16" x 3/16" v-notched trowel or 1/8" x 1/8" square or u-notched trowel. The membrane is 1/64" (12 mil). I will probably run the membrane onto the main floor by a couple of inches. to cover the main to shower floor transition.

I don't know what the mortar layers will squish down to. My brain already hurts.

Now onto the main floor. which needs to match the height of the membrane'd shower pan. Can anyone suggest what combination of CBU or ply, mortar, and Ditra heat mat will get me there? I can certainly use thinner ply under the shower pan. I don't have the mortar or Ditra heat thickness spec's.

Any and all feedback is most appreciated!
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Old 03-10-2018, 08:30 AM   #18
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Is it safe to assume.....

.....that mortar applied with, say, a 1/4 X 1/4 square notch trowel will smooch down to 1/8"? And 1/8 X 1/8 will reduce to 1/16? 1/2 X 1/2 down to 1/4?

Am trying to work through the numbers from the post above. I found that Ditra Heat mat is 1/4" thick and they want it installed with a 1/4 X 1/4 square notch trowel (which seems like a lot for a sheet product).
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Old 03-10-2018, 09:35 AM   #19
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No, that would only be true if you held your trowel perpendicular to the substrate. You need to multiple the result by the sine of the angle at which you hold your trowel. For a 45 degree angle, it would a multiplier of 0.707.

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Old 03-10-2018, 10:40 AM   #20
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Thanks for chiming in Wayne. I did think about the application angle after I posted but I wasn't sure if trowels were made to account for the usual 45* angle.

Sounds like I need to subtract about 1/3rd ish.
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Old 03-10-2018, 11:32 AM   #21
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So if you're going to run the USG membrane out on top of the Ditra Heat a few inches, then it seems to me you need to get the top of the Ditra heat flush with the edge of the USG pan. Relative to their substrates, the USG pan will be about 1-1/8" tall (1" pan plus 3/8" notch), while the Ditra Heat will be about 11/32" tall (1/4" plus 1/4" notch).

That makes a 29/32" difference. You could probably use 1/2" plywood under the USG pan and two layers of 3/4" plywood outside of the pan. Or if the cleated plywood between the joists is sufficient support for the USG pan (I don't know), then you could just use two layers of 1/2" plywood outside of the pan. Or perhaps one layer of 7/8" plywood would be close enough, but that's typically a special order item, you may not be able to buy it by the sheet.

Please double check my accounting.

Cheers, Wayne
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Old 03-14-2018, 02:56 PM   #22
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Wayne,

USG is ok with the 3/4" ply but because the top of the joists are slightly below the top of the cleated 3/4" I feel like I want some more ply under it to bridge over the joists tops.

You are correct - as far as I can tell I do want the top edge of the pan, once set in mortar, to be at the same height as the top of the Ditra heat mat.

Let's assume I lay another 3/4" of ply on the entire floor, then set the pan on that, and the pan height comes out at 1 1/8" with mortar under it. I now have to get the top of the Ditra up to 1 1/8". If I now add another layer of 3/4" ply outside of the pan, and then mortar and Ditra, it seems that combination gets me in the ball park, no?

I was having trouble understanding your suggestion of 1/2" of ply under the pan (totaling 1 5/8) and two layers of 3/4" under the Ditra (putting it just over the top of the pan).

Thanks so much for letting me bounce this off of ya.
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Old 03-14-2018, 04:00 PM   #23
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If you have 3/4" plywood on cleats over the whole bathroom floor, wouldn't another layer of 3/4" everywhere be overkill? Unless you want all the build up for some reason, I would think that your second layer could be 1/2" plywood, before considering height matching concerns.

Since you've intentionally set the 3/4" plywood on cleats just above the top of the joists, and since I assume you won't be fastening the second layer of plywood to the joists, I could see using a cementitious patching compound over the joists to fill in between the strips of cleated 3/4" plywood. I suggest getting a second opinion on that idea, though, as I've not seen it discussed here before. Perhaps with the patching compound you'd be happier with the idea of setting the USG foam base directly on your cleated 3/4" plywood.

As to using different build ups under the USG foam base and under the Ditra Heat, I calculated a height difference to make up of 29/32". A single layer of 3/4" plywood is actually 23/32", so you'd be 3/16" low. That's why I suggested two layers of 1/2" plywood (actual 15/32"), which would be 1/32" high. Or a layer of 7/8" plywood (not sure if actual is 7/8" or 27/32"), which would be 1/16" or 1/32" low. Or if you want plywood under your USG foam base, you could use 1/2" plywood under it and two layers of 3/4" plywood elsewhere; then I think the Ditra Heat would be 1/16" higher than the USG foam base.

Cheers, Wayne
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Old 03-15-2018, 09:15 AM   #24
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Thank you again Wayne.

I actually need the extra build up on the floor outside of the shower. As shown in the photos in my 1st or 2nd post the floor had a massive crown to it where the joists lapped each other above a beam below. While I was able to address it in the bathroom, that same crown carries through the doorway into the bedroom. If I were to lay 3/4" ply over the entire cleated floor I'll still have more than an inch to build up so the finished floor is somewhere close to even with the top of the threshold(the height of which I will be able to adjust to some extent). And since it was neither flat or level, and because I err towards overkill, well, hence the sisters and cleats. It was truly a mess but I'm pleased with the results; the floor is level and flat, length (14') and width (7'), to within 1/16" and very stout.

So that's the background. With now having an idea how much the mortar will collapse given the various notch sizes I'll have to use (thank you so much for that) I should be able to get the Ditra very close to even with the installed pan.
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Old 03-19-2018, 07:21 AM   #25
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Electrical lines in plumbing wall?

Because I can't seem to find the answer......

To satisfy Va code requirements which say I need a dedicated 20A line for GFCI receptacles in the bathroom (house was built in 1980, and one 15A GFCI circuit served the original 3 bathrooms with a single outlet in each) I had to pull a new line from the panel in the basement. I decided to pull two 12/2's, one for the GFCI's, one for the heated floor. There's already one spare 12/2 in the attic I pulled years ago, use that for the lighting.

Pulling them was approximately zero fun. Sparing the details of why, the new lines come up in a stud bay occupied by copper supply lines. The question is - is it code compliant? I spent hours trying to find the answer yesterday to no avail. See attached photo.

Many thanks....
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Old 03-19-2018, 07:25 AM   #26
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No violation that I'm aware of, Dan, but to be safe you should check with your local inspector. He's the one you have to please.
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Old 03-19-2018, 08:20 AM   #27
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If memory serves me right you can run electrical with plumbing so long as you don't attach it to the plumbing. Like zip tying the electrical wire to the water line. Not sure about the code there in your state but here that is the stipulation
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Old 03-19-2018, 08:34 AM   #28
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Thanks Kevin.

The first inspector came out to inspect the "ground" work (drain and supply lines within the floor). Passed it all with nothing more than eyeballs, no checking pitch or anything else. Once the rest of the rough in was finished (in-wall vent connections to existing ABS, and finish plumbing to the electronic shower valve) I called them out for the concealment inspection. This fellow was more through; passed all the plumbing but flagged me on fire stops, some nailing plates, etc. I knew about those issues but thought there were part of the framing inspection - for which I also have a permit pulled.

Different inspectors seem to allow different things. I have a call into them now to see what they say about those electrical lines.

Thanks Shawn. I've been reading the same thing. I'll note the name, date, and time when I talk to them.
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Old 03-19-2018, 09:59 AM   #29
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As Shawn says, if you keep the electrical and plumbing physically independent, there's no problem occupying the same stud bay. I'm personally confident that nothing in the NEC would be an issue, and I'd be very surprised if the plumbing code had anything to say about it.

I take it your circuit for the bathroom GFCIs was #14 copper, rather than #12 copper? I guess the 20 amp requirement wasn't in place in the 1980. You'd need a new circuit for the floor warming anyway, though.

Cheers, Wayne
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Old 03-19-2018, 12:43 PM   #30
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The existing circuit serves 1 outdoor receptacle and 3 bathroom (one is a powder room, and the basement bath got it's own when I finished it years ago)receptacles, all through a 15A GFCI breaker and 14/2 wiring. To code in 1980, but evidently not so much now.

If I'm reading it right, current code wants a dedicated 20A GFCI per bathroom, and current code must be applied if any significant changes are made to the room. In other words, if you're simply doing a remove and replace no need to comply.

I did have the forethought to pull an extra 12/2 into the attic years ago when I was in the process of doing the basement. So my original plan was to use that one for the floor, leave all the bathroom lights on their existing circuit, and use the existing 15A GFCI as it is.

Then I found out about the dedicated 20A GFCI code. So I resolved myself to pulling another 12/2, and decided it is barely more difficult to pull 2 of them at the same time, and only 50.00 ish more. So two 100 ft rolls of 12/2, some careful measuring and routing, a day and a half of work, and wham - plenty of juice.

I did speak with one of the inspectors a bit ago, who confirmed there's no problem with the wiring being in the wall with the plumbing - so long as they are not touching. By the time I snake them into the attic and drop them back down into the necessary stud bays I'll have used almost every foot of that 12/2 pair!

Thanks for everyone's input, much appreciated.
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