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Old 05-24-2010, 08:54 PM   #1
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replacing bathroom subfloor


I ripped out the rotten subfloor completely. I am gonna tile the floor when complete. What size plywood should I put down before the concrete board? Do I need to put down two layers of plywood or just one and what size

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Old 05-25-2010, 11:04 PM   #2
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replacing bathroom subfloor


Gee Nickel, you didn't supply much info.

What kind of tiles? Regular ceramic, porcelain, natural stone.
How is the framing built? Regular joists? 2x8, 2x10 or other.
How old, 1st floor or second? What part of the world?
What is the unsupported span of the joists?
What is the spacing of the joists?
What species and grade? They should be stamped someplace.

In general 3/4" subfloor grade exposure 1 plywood is enough in most cases, unless you're installing natural stone tiles. There may be a few other exceptions. It's always better to add a second sheet of plywood if you can. Make it underlayment grade, not the cheap sheathing stuff, and gotta be 3/8" or thicker. This is assuming the framing meets certain standards.

Jaz

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Old 05-30-2010, 02:00 AM   #3
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replacing bathroom subfloor


3/4 inch , what joists 2x10 16 inches on center or 2x8 2 feet on center ? If small joists span more than the general rule of thumb . You will have a flexation problem , The general rule is if 2x8 they can span 8 feet , 16 inches on center
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Old 05-30-2010, 01:20 PM   #4
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replacing bathroom subfloor


Deflection movement in floor joists also varies with the species of wood. Span Tables are available to tell you what the span maximums should be for the size of and species of joist being used.
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Old 05-30-2010, 11:04 PM   #5
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replacing bathroom subfloor


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Originally Posted by Bud Cline View Post
Deflection movement in floor joists also varies with the species of wood. Span Tables are available to tell you what the span maximums should be for the size of and species of joist being used.
Correct info , But I have fixed a number of engineered floor joist's , There is a difference in strength between Hem fir .doug fir , And I joists , if it flexes add a beam[if possible] to cut the span , tacomahardwoodfloors.com I know a span we use to build when I framed that called for doug fir 2X12 to span 21 feet 1 foot on center , And it was a shakey floor , I have frame 14 inch I joists on a long span to approved engineer spec and I had to put in extra beams , so yes the Span tables are good but they don't always work , I was just trying to give a general rule of thumb so He could generaly surmise if something was way wrong , I have seen old houses span 12 feet with 2X8 16 on center , the whole floor bowed down ,
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