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12-22-2016, 03:00 PM
New User here and love the sage advice on this board.

Currently doing a master bath remodel (late planning, early demo stages) and have been reading about curb height and a few other topics. I get that 2" min. height is code in many areas but it also seems that many folks use 3 2x4's, which is my mind creates a curb about 6" on the outside and 5" on the shower side [assumes using 1 1/8" Kerdi tray, 3/4" granite (or whatever) sill, and 1/2" backer board, plus 4 1/2" of 2x4, all covered by Kerdi].

So my questions are:
Would not 2 2x4's be preferable?

Also, I will not do the tiling (I leave that to the Pros) but is there a minimum height (say on the shower side of the curb) that should be kept so tile is not to narrow a sliver? [Using 2 2x4's I figure this will call for about a 2" wide tile.

Lastly, I have seen mixed opinions on the use of wood (KD vs PT vs Don't Use). FYI, my bath is on 2nd floor and will have Ply subfloor. I happen to have a few solid PVC 2x4's from a previous project and am thinking this is an ideal material to use. Any thoughts?

Thanks to all

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12-22-2016, 03:14 PM
Welcome, Dave. :)

I've separated your post from the other visitor's old thread to prevent confusion on both projects.

You can use whatever size curb suits your fancy, including no curb at all. The only "code" issue that comes into play is the plumbing code that requires that the drain be 2" lower than the top of the curb and even that is negotiable when there is no curb at all.

The use of 3 stacked 2x4s was a common curb framing when building traditional shower receptors that had a pre-slope, liner, and at least 1 1/2" of the top mud bed. If you plan to use one of the pre-fabricated foam shower trays, you may be able to get by with less if you can still remain 2 inches above your drain.

You do not want to use any treated wood anywhere in your assembly to be tiled. Plain kiln dried lumber is fine for your application.

My opinion; worth price charged.

12-22-2016, 06:48 PM

Don't want to hijack the thread, but can you lay Kerdi over the kiln dried 2x4's assuming you're using a modified thinset?

12-22-2016, 06:52 PM
Nope. See the Kerdi website for suitable substrates.

12-23-2016, 10:01 AM
CX, Thanks for the reply. I will basically be using Kerdi materials for the entire project, except for the curb. I will steer clear of PT, which makes sense. Hope to be able to provide updates as we move along.

Thanks again

12-23-2016, 10:36 AM
About to start a complete redo of our Master Bath. I'll be taking down everything down to studs/joists. Currently the floor is tile, with 1/4 ply over 3/4 ply (based on test cut made in floor). Seems when this house was built in 1990, rooms with tile have the 2 ply ply subfloor and carpeted rooms just have 3/4 ply.

Anyway, the question is: If I use Schluter Ditra-Heat (still undecided on whether we will go for radiant heat or not) is the 2nd layer (1/4") of ply needed? The Schluter Ditra installation manual says single layer (joists are 16" OC) but would like real-world opinions. FYI, will be using fairly large porcelain tiles (9" x 18").

My concern: 2 layers of ply + Ditra will cause transition height issues with bedroom and possibly toilet flange (which I am hoping to not touch).


12-23-2016, 10:46 AM
Dave, it'll help if you'll keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered. We can give it a more generic title any time you'd like to suggest one.

The 1/4" plywood has no business in a subfloor for a ceramic tile installation unless it is a specialty type of plywood not normally available from lumber suppliers.

Was your tile installed directly on that second plywood layer?

Lots of folks install tile over single layer plywood subfloors under Ditra and you can certainly do that in your application if you want. Presuming, of course, that your joist structure meets the required L/360 deflection maximum.

My opinion; worth price charged.

12-23-2016, 11:22 AM
Still learning the ropes on this forum but will keep my posts in one related thread from now on.

Yes, the existing tile is set directly on the top plywood layer, which is overlapped on top of the 3/4 ply, attached with about a million 1" sheetrock screws.

Deflection may be a problem (L/306) based on what I know at the present time. I won't know the full story until I pull the floor. On the up side, all current tile is rock solid and has been for 20 years.

12-30-2016, 11:54 AM
So the deflection problem is dealt with. It helps if you use correct lumber dimensions. L=380.

Today's question has to do with built-in niches. I plan on installing one using a pre-fab Kerdi product. The wife wants it on the side wall of the shower, which aesthetically is preferred. The concern I have is, this is an exterior wall. I realize that will be a cold/warm spot (we're in the northeast) as it would lack insulation (I should be able to get a bit of insulation behind the niche as the wall is 2x6 construction). The question is, does anyone think there may be a problem down the road with tile delamination resulting from frequent fluctuations in temperature. I'm not concerned with the niche material (foam with a coefficient of expansion near zero) but I do not know how thinset may react over time.

Thanks & Happy New Year

12-30-2016, 12:19 PM
Dave, you've got an advantage in that you have 2x6 construction. When faced with similar, I've endeavored to (sort of) integrate the niche into the interior envelope and separate it from the exterior.

In your case I'd probably build a five sided box of 2" board foam to surround the backside of niche...kinda isolating that area from remainder of wall. Board foam, XPS and ISO in particular, have much higher R value per inch than fiberglass.

No problem with using common setting materials is such a scenario.

12-30-2016, 02:39 PM
Drywall screws have no place when installing plywood for flooring...ring-shank nails or deck screws. Drywall screws are quite brittle and not actually all that strong.

01-03-2017, 04:00 PM
Thanks for the advice. Pretty much exactly what I was planning to do, in addition to needing to frame out the space between the studs.

Re the Sheetrock Screws, I don't disagree but you would love this house where sheetrock screws where used by the builder for all sub-flooring and even the original kitchen cabinets/bath vanities were hung with them (long since gone). At least they used supplied screws on door hinges.