Tile underlayment- new construction

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Old 05-19-17, 06:21 AM
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Tile underlayment- new construction

New construction, 11-7/8" I-Joists 16" O.C. 3/4" T&G OSB Subfloor Kitchen floor spans 14' between floor joist supports.

I want to prep for general tile, probably ceramic due to budget. 12 x 12 tiles, or 8 x 16 if I get fancy.

Is 1/2" Concrete Board sufficient on top of my 3/4" subfloor? Should I have even more wood before concrete backer board?
 
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Old 05-19-17, 08:04 AM
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Backer board is not structural, the plywood is. FWIW, 1/4" backer board is fine for a floor. Hang tight for one of the pros to assess your structure and subflooring.
 
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Old 05-19-17, 03:51 PM
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Are your joists on 16" oc or 19.2? Curious. 1/4" won't give enough added support. I would opt for 1/2" if you plan on the large format tile.
 
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Old 05-19-17, 05:37 PM
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Hi Nicholas,

When installed according to the manufacturer's specs I-joists meet min. requirements for ceramic/porcelain tiles. You can contact them to make sure your system is stiffer than L360 deflection. Normally I-joists come in at L-480, which is very decent.

3/4" OSB properly installed meets specs for ceramic tiles. More ply is always a good thing if you can do it. 1/2" CBU will do you no additional good, go with 1/4" or a membrane such as Ditra if you want to step up in quality.

Jaz
 
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Old 05-19-17, 05:42 PM
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I-joists 16" OC should be fine. I would use 1/4" backer set in a mud bed. To be sure, you can add 1/2" plywood to beef up the subfloor. I usually shoot for 1 1/4" thickness to make sure there is no deflection between the joist that could give your tile a stress test. If thickness is an issue, you can go with a product like ditra that has a lower profile and is rated for your 3/4" subfloor and eliminate the cement backer board all together.
 
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Old 05-19-17, 05:43 PM
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Jaz and I posted at the same time, with similar direction. Great minds think alike!
 
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Old 05-20-17, 03:55 AM
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And my response was relative to "plywood" overlay, not the size of the underlayment. 1/4" CBU is best for floors, but I was referring to beefing up the subflooring. Sorry for the confusion and not reading the posts correctly.
 
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Old 05-24-17, 12:36 PM
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Replying late here. They are 16" OC not 19.2".

The 3/4" T&G OSB SturdiFloor subfloor seems very beefy. I would add 1/2" Ply if it is necessary, but if the OSB alone is considered sturdy enough, I would just add 1/4" Concrete board. Would 1/4" Ply + 1/4" Concrete Backer be better than no plywood at all, or is 1/4" not enough to even matter? I ask because 1/4" is cheaper than 1/2" and if 1/2" is not needed, I don't want the extra expense.
 
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Old 05-24-17, 12:46 PM
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1/4" plywood is too flimsy and should not be part of your structure at all.
 
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