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Old 09-26-2011, 04:47 PM   #1
mmullen
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Bathroom renovation

I've been browsing these forums for a couple months now but recently registered because some guidance from more experienced tilers would be helpful. I've already gleaned much useful info so kudos to those who so freely share their wealth of knowledge!

The current project is a rectangular bathroom 9 feet deep and 60" wide. The door is on one small end while the short back wall and long right side wall are both on the corner of a concrete perimeter foundation. The floor joists run perpendicular to the long direction of the room and are 1 3/4" x 9" on 16" centers but there are a couple of extra joists near the back wall (8" centers). The joists span 14' and the bathroom is built on the corner of the foundation. The joists have blocking in two places along their 14" span. and are accessible via crawlspace. It is warm and dry down there. The subfloor is a single layer of 5/8 plywood glued and screwed to the joists but it has no gaps between the seams. It feels solid in all areas but I have not performed any deflection measurements. The floor is level.

I'm going crazy trying to decide how to handle the tile floor. It will have electric wire floor heat and I don't mind over-building the sub-floor except that I really want to avoid having a high transition from the hallway to the bathroom. The hallway is vinyl on thin (1/4 or 3/8") particle board on the same plywood sub-floor.

Intuition tells me that I might not need to go overboard to achieve good stability due to the fact that no part of the floor will be further than 60" from the foundation. There will be a Kerdi shower with a mortar base in the back corner (the floor heat will extend into the shower) and a stacking washer/dryer adjacent (this is the area where the extra floor joists are). I would also like to water proof the tile floor in front of the shower and under the laundry and, since the remaining area is so small and the room is gutted I'm thinking it would be a good idea to waterproof the entire area with short extensions up the wall in case of flooding when the home is not occupied. So how much structure do I really need to achieve a lasting install? I am not opposed to the extra labor or cost of beefing it up but I would like to keep the floor as low as possible. I also want to avoid having to support the floor joists underneath with a cross beam due to the fact that this will make access to other areas of the crawlspace more difficult.

My original plan was to lay 1/4" cement fiber board, heating wire in thinset, then Kerdi and tile (until I read that industry titans determined that cement board does not add to the structural integrity). I am aware the cement board is not required with the Kerdi membrane but I still like the idea.

Another thought was to use Ditra which would double as a water barrier (no Kerdi). It looks like I would still need to add 1/2" plywood and this would be getting thicker than I would like with the heating wire and Ditra. One confusing thing is the Ditra Handbook indicates a vapor barrier on crawlspace floors. Wouldn't that create a "moisture sandwich"? Also, due to the geology of the building site, the foundation is well above the water table and the crawlspace is unusually dry at all times.

I imagine no one here will recommend anything less than the manufacturer minimums but why are the minimums set to "one size fits all situations"? Suggestions on solutions that minimize floor height would be welcome.
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Old 09-26-2011, 04:58 PM   #2
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Mike, your joists are fine as long as they are in good condition.

The subfloor is a bit skimpy since it is no longer in pristine condition. I would add a layer of 3/8" plywood, if you can find good quality, non-wavy as a potato chip stuff. Otherwise, use 1/2". I know what you said about floor height, but the idea is to build a tile floor that will last, not an even floor that fails.

Set the heat mat directly on the plywood, using thinset or SLC. If using SLC, follow their directions to the letter.

Use Ditra as your tile underlayment. Kerdi is a waterproofing membrane, not an underlayment for wood floors. Waterproof the floor by covering the Ditra seams with Kerdi-band. Flash the walls with Kerdi-band, too. Keep in mind that this will only direct water out the bathroom door or through any floor penetrations like the toilet.

Your crawlspace vapor barrier would be a plastic sheet over the earthen floor.

One-size-fits-all solutions helps remove confusion and misapplication from the product manufacturer's list of things to worry about.
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Old 09-27-2011, 10:42 AM   #3
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Thanks for the feedback. I think one reason I was being driven crazy is because I have a hang-up with thinset directly on plywood - it just seems wrong even though I understand why it's OK and that the manufacturers endorse it. But if an additional layer of plywood will create a superior installation compared to fiber cement board, I will use plywood.

I understand Kerdi is only a waterproofing membrane but I thought with fiber cement it could be used without much of a height penalty.

Thanks for clearing up my confusion on the crawlspace vapor barrier - I don't think of dirt as a "floor" so I had interpreted "crawlspace floor" to mean the floor above a crawlspace.

Do I need to open up the seams in the tightly butted plywood sub-floor?

Thanks,
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Old 09-27-2011, 01:34 PM   #4
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If you used a backerboard on the floor, you could use Kerdi. I wasn't sure if you weren't mixing the products. However, you can get a stiffer floor that meets all requirements if you used more plywood and a Ditra/Kerdi-band. Tiles want a stiffer floor more than they want waterproofing. As far as thinset on plywood, just be sure to use a modified thinset. Modified thinset is designed to stick to plywood.

If these plywood panels are original, and the joints are tight without any puckering or swelling, you don't need to open them. They've done all the growing they want by now. Do gap the new ones, though.
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Old 09-27-2011, 04:09 PM   #5
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OK, and not to belabor the point, but is using backerboard and Kerdi still a viable option in this situation? If it is, it seems like 1/2" fiber cement board could offer benefits in contact with the heating wires due to it's higher thermal conductivity which would minimize temperature gradients in the tile/grout layer as well as in the subfloor. The reason this is of even a concern is the bathroom is in a ski cabin which is mostly unheated when it is not occupied and will be cranked up upon arrival. Also, the heating is by loose wire and I want to use a fairly dense pattern as I have removed the electric baseboard.

And I realize this will not be ultimately as stiff as two layers of plywood but, given the narrowness of the room and it's location on the foundation I'm not sure this is an issue.

As a side note, the tile installer I met said he had always put the heating wire set in thinset on top of Ditra and was surprised when I mentioned the Ditra Booklet calls for the wire to go underneath. Anyone have the pros/cons of the two methods?
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Old 09-27-2011, 05:09 PM   #6
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Welcome, Mike.

The addition of a CBU over your less than absolute minimum subflooring will do nothing quantifiable to improve your between-joist deflection nor your thermal striping concerns with a radiant wire system above the CBU.
Quote:
Originally Posted by Mike
...why are the minimums set to "one size fits all situations
They're not. They're minimums. That means they represent the very lowest possible acceptable category. They're usually established by actual testing and if they can be made to pass one time at that particular level, that establishes the bottom. Lotta folks like a little more structure than that for their relatively expensive tile installations.

Consider also that those minimums are established using new material, in perfect condition, near perfectly installed over joists with zero deflection. You'll have none of those conditions.

I'd strongly recommend you follow Injineer Bob's suggestion of another layer of plywood.

Quote:
Originally Posted by Mike
As a side note, the tile installer I met said he had always put the heating wire set in thinset on top of Ditra and was surprised when I mentioned the Ditra Booklet calls for the wire to go underneath. Anyone have the pros/cons of the two methods?
Pro would be that one method would be in compliance with manufacturer's recommendations.

Con would be that one method would not be in compliance with manufacturer's recommendations.

Pretty simple, that.
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Old 09-19-2012, 01:34 PM   #7
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Quick update

Bob and CX, thanks for the valuable feedback. I did decide to go with 1/2" ply and it looks great. Yes, it's a year later so this may be the slowest bathroom renovation ever!

But life is funny that way.

More later.
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Old 11-14-2012, 03:04 PM   #8
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Installing tempered glass in tile shower wall

I'm preparing to frame a shower that will be Kerdi/tile. The shower space is rather narrow (about 27" x 36" inside dimensions) so I would like to gain some width by using a short 2"x4" knee wall (24" tall) with a tempered/frosted glass pane installed as near to the outside edge of this knee wall as practical. The glass will extend upward to above head height to within 12" of the ceiling where it will abut the upper counterpart to the lower knee wall. The tempered glass will be about 31" wide x 60" tall.

I would like to support the tempered glass without using a metal frame. I am open to using metal clips but would prefer the glass to appear to be embedded in the tile and sealed with caulk. Since the point of the glass pane is to increase the width of the shower, a solution that allows the pane to be mounted approximately flush with the outside of the 2x4 framing would be preferable.

What are my options?
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Old 11-14-2012, 04:18 PM   #9
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Use 100% clear silicone caulk as this piece was installed
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Old 11-14-2012, 04:22 PM   #10
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Your 27" shower dimension is too small according to modern building codes.

2006 International Residential Code - Section R307.1, Figure 307:
Shows a drawing indicating a minimum width of 30" AND a minimum depth of 30", with a minimum of 24" of clear space in front of the shower door.

2006 International Plumbing Code - Section 417.4:
"All shower compartments shall have a minimum of 900 square inches of interior cross-sectional area. Shower compartments shall not be less than 30 inches in minimum dimension measured from the finished interior dimension of the compartment, exclusive of fixture valves, showerheads, soap dishes, and saftey grab bars or rails. ... the minimum required area and dimension shall be measured from the finished interior dimension at a height equal to the top of the threshold ... up to a height not less than 70 inches above the shower drain outlet."

Of course ever jurisdiction is free to set its own build codes, so you would need to check with the local building authority having jurisdiction over the place where you live to determine what build codes are applicable to you.
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Old 11-14-2012, 04:33 PM   #11
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Welcome back, Mike.

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.

What Joseph said.

While your shower footprint meets the code requirement of 900 square inches, you may be required to to fit a 30-inch hoop inside the shower. I'd sure recommend you check with your code compliance people before you make any commitments to your design.

As for mounting your glass in the tile, I've done it a good number of times. Set the glass on appropriate "bumpers," tile to within an eighth of an inch, and caulk it in.

Here's an after photo of one done that way.

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My opinion; worth price charged.
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Old 11-14-2012, 04:51 PM   #12
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Old 11-15-2012, 03:07 AM   #13
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Ah, yes, codes. Interesting that the International Plumbing Code has an exception to the 30" minimum inside shower dimension:

"Exception: Shower compartments having not less than 25 inches (635 mm) in minimum dimension measured from the finished interior dimension of the compartment, provided that the shower compartment has a minimum of 1,300 square inches (.838 m2) of cross-sectional area."

So the standard minimum is 30" x 30". And, under the exception, a shower can be only 25" wide if it is 52" deep. But, if the shower measures out a fraction of an inch less than 30", it must be 29.9" x 43" (to meet the 1300 sq. inch rule). It would be better if code requirements didn't jump 13" larger because there was a fraction of an inch too little to meet the 30" width rule.

Interestingly, my primary residence has a very nice mud/tile shower built in 1957 as specified by the original architect. It is a thing of beauty and is in perfect original condition. The colors and tiles still look good today. The largest dimensions are only 27" x 37" and it has a 19" wide glass door at an angle such that the total area is only 885 square inches. Although I am a big guy (6'-04" and 220 lbs) I actually find this shower preferable to the much larger shower upstairs. It has enough room to do all necessary bathing functions without touching the tiled walls (including bending to wash feet and reaching around to scrub back). And it has been in faithful service for over 50 years. Plus, I prefer the way it warms up and becomes steamy quickly rather than having cold drafts. So, I wonder who the code people are trying to protect by requiring a shower 47% larger than this very functional classic.

In any case, I am comfortable with the size of the shower from a usability issue and the code is a non-issue here. But I appreciate that you flagged the international standards (which are typically there for good reasons).

This discussion has made me aware that I don't even need a shower with three walls, it could be constructed in the corner of the room with one glass door and one glass wall (on top of a curb). In which case it would easily meet the 30" international standard (not that I am concerned with meeting code but maybe I would like a 31" x 36" shower). There will be a stacking W/D on the other side of the glass pane so I'll have to think about the aesthetic implications of such a change before I commit one way or the other.

Either way I will be setting the tempered glass on a stub wall or a curb so I appreciate the photos and advice. But in Paul's photos it looks like the glass is on top of the tile work and in CX's photo, although it's difficult to tell, it does look like the glass might be supported by the substrate with the tile edges abutting the glass (as described)? If so, I assume I would wrap the Kerdi 1/4" up the tempered glass pane (before tiling and calking with silicone) as John Bridge recommends to do with aluminum or vinyl framed windows (in his Kerdi shower e-book)? And should the pane "bumpers" rest on the wood framing? I know the pane will be heavy so sheetrock support seems out of the question. But I was planning on using some type of 1/2" cement board anyway. Recommendations?

Also, are there any recommendations on how close I can safely set the pane to the edge of the curb or stub wall?

Sorry for so many questions but I am new to most of this.
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Old 11-15-2012, 05:52 AM   #14
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In both cases (glass on top of tile or glass inset between the tiles), the waterproofing is continuous under the glass. Drywall can support compressive loads pretty well if it is well supported. Even a heavy panel of glass won't exceed the compressive load rating of drywall, since the load is spread over a wide area. However, if you still feel the need, you can wrap the curb with backerboard, then apply Kerdi for waterproofing.

I think you can set the glass as close to the edge as you want. Your fastening method will dictate how close you'll want to set it, though. Also, you will need to consider how and what the tile will be setting on. You do not want the glass rest on the edge of the vertical tiles on the face of the curb.
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Old 11-15-2012, 10:25 AM   #15
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What Bob said. In CX's photo the glass is sitting upon thin bumpers (thinner than those depicted by Paul, but similar), which are sitting upon a properly sloped Kerdi membrane. And they are captured within a caulked slot in the tile surface.

For a three sided installation you'll wanna measure very, very carefully for your glass.
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