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I've ripped out the floor of my bathroom down to the joists. The bathroom is 5 ft x 4 ft. Should I use tongue and groove or can I use standard plywood? Does it matter?

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  • Possible duplicate of Is it OK to use 1/4" concrete backer board over 1/2" plywood as a bathroom subfloor?
    – Mazura
    Jul 8, 2016 at 4:02
  • The linked answer is about what backerboard manufacturers suggest to use at minimum. Were you looking for actual IRC code?
    – Mazura
    Jul 8, 2016 at 4:04
  • @Mazura This sounds like his direct question is whether t+g is better than standard plywood. The other thread reads about concrete board. If I missed it let me know
    – Chris
    Jul 8, 2016 at 4:05
  • Backerboard is more important than using T&G or not, IMO. I'm not sure what code says; I just always use 3/4" (whatever) anyway, and not 5/8". - Wait... it's less than the size of a sheet of plywood. It wouldn't matter what type it is, except it's supposed to be exterior grade OSB.
    – Mazura
    Jul 8, 2016 at 4:07
  • Backerboard provides no support, the important layer is the plywood which depends on joist spacing with a minimum of 1/2 required @16 oc w/ l/360
    – Chris
    Jul 8, 2016 at 4:10

2 Answers 2

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Depending on the direction of the joists, it will only take 1 sheet, the T&G will have no value, unless the floor you pulled up was T&G as well, then it will only help on one edge.

If the T&G was cheaper than square edge, then I would use it. I have seen it cheaper in a big box store, although I could not figure out why it was. It was not on sale....

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  • Actually if the joist run in any direction, it will still take one sheet.
    – Jack
    Jul 8, 2016 at 4:35
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    Plus one; it doesn't matter. What does matter is everything above the page break in my answer on the 'dupe', especially: "minimum 5/8" exterior grade"
    – Mazura
    Jul 8, 2016 at 4:38
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There are advantages to using t&g.

In terms of substrate requirements, it doesn't matter. A 5/8th sheet of t&g will support the floor just as well as a 5/8th sheet of standard.

For your considerations, with standard you'll have to space them with a 1/8th gap between sheets for expansion/contraction, this isn't a problem with t&g, they can be tightly fit.

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    4X5 bathroom - 4x8 sheet of plywood - ¿What joints? I hardly expect a pre-exsisting T or G joint right at the wall line where the old floor was ripped out...
    – Ecnerwal
    Jul 8, 2016 at 13:56
  • You said it yourself, it's a single sheet, and as such either a) Laxmidi has a T or G that he can tie in to, or b) he's overcomplicating the process. In either case my answer provides details on either situation.
    – Chris
    Jul 8, 2016 at 20:51
  • Since the subfloor goes down before the walls go up, the odds that a sheet lines up with the room are just about zero.
    – Ecnerwal
    Jul 8, 2016 at 22:22

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