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Build & Remodel

OSB bathroom


we had water damage to our bathroom floors and hired a carpenter to tear them up and replace the subfloor over a crawl space.  He put down 2 layers of 3/4" OSB.  When the plumber came, he said the carpenter should have used plywood.  The tub is already installed, so I'm hoping we don't need to tear this up.  We were going to put down concrete backer board under tile.  I'm concerned about water damage, as I have 2 kids.  Any suggestions on water proofing?  I heard that something called ditra is a good choice.

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Posted 2012-09-30T05:51:14+0000  by tabbylaurie tabbylaurie



3/4" OSB plywood it is an approved subfloor underlayment. Actually if you take a look at it you will see an APA stamp on it indicating that is acceptable to be used as a primary subfloor.


This said, your carpenter did not put something down that is not code or that will structurally compromise the integrity of the floor. You’re safe to put down backer board and tiles over it. Deflection should be minimal with double ¾ “sheets.


Water resistance…


CDX plywood does have better resistance to moisture and water penetration than OSB. No way around it.

Ditra is truly a great product. When properly installed it will waterproof the floors to certain extend and it will isolate the tile from any deflection (movement) within subfloor. This translates to solid and lasting installation.

I cannot advise you on how to proceed, the only comment that I can make is that OSB is an approved subfloor that meets minimum building codes.


I would be more adamant on the floor joists. Joist below the tub should be properly sized based on span and loading.


Hope this helps,





Posted 2012-10-01T16:58:25+0000  by George_HD_CHI

Nothing wrong with using OSB. That is the most economical. I like to use a fairly new product called dry-ply as it resists potential moisture from leaks. A bit pricey but nice. The ideal thing is to not have leaks and to address any moisture issues immediately. Regular plywood would be second best product.

Posted 2012-10-07T18:29:24+0000  by Niwroc
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