How thick should my backerboard be for a bathroom floor?

I'm tiling my bathroom floor, which is currently linoleum over plywood (not particleboard). I have a bunch of 1/2" Wonderboard, but estimating how high the tiles will end up, adjacent to the carpeted floor of the hallway, I think the tiles will be much higher than the carpet. Would I be OK using 1/4" backerboard? I'll use thinset to attach the backerboard to the plywood, and will be using 1" hex tiles. Any thoughts? Adam
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Dear Sir,
What you haven't told us is the thickness of your plywood, joist spans, etc to ensure that even 1/2" would be sufficient. That said, there is nothing wrong with using 1/4" on floors. You also have very small tiles which will help prevent tile cracking.
Hope this helps, William

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Well, the plywood appears to be 1/2". I haven't pulled up the linoleum yet, so I can't see the joist spans. Can you tell me what considerations would force me to choose 1/2" backerboard? Thanks!
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Greetings,
1/2" backerboard is normally used on walls. Your subfloor may not be thick enough.
" a.. Use minimum 5/8" exterior grade plywood or 23/32" exterior grade OSB, complying with Local Building Codes and ANSI A108.11, over joists. Joists' spacing not to exceed a maximum of 16" on center.
a.. Deflection must not exceed L/360 of the span, including live and dead design loads.*
a.. Do not use glue between grooves of tongue-and-groove subfloor to allow for expansion and contraction of subfloor. "
Please read the following http://www.jameshardie.com/backerboard/homeowner/hardibacker_installation.php http://www.thetiledoctor.com/installations/floors.cfm
Hope this helps, William

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I had just eyeballed the plywood, and now I have measured it to 5/8". There is also a tongue-in-groove under the plywood, I believe. So it sounds like 1/4" HardiBacker will be OK, rather than my 1/2" Wonderboard, assuming all the other specs meet standards once I pull up the linoleum.
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