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Old 09-26-2011, 03:47 PM   #1
mmullen
Registered User
 
Join Date: Sep 2011
Location: Anacortes, Washington
Posts: 138
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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