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I'm working on a remodel of a room that spans two different areas of a house.

Each area has joists 16" OC but where they come together there is a "short" bay; one where it is not a full 16" between joists:

16" 16" 16" 16" 16" 9" 16" 16" 16" 16" 16"

The short bay (9") basically in the center of the room.

Should stay with full sheets and have to install blocking for one-half of the project (which will be a pain since the bays are full of mechanicals and lighting for the floor below) or should I shorten one of the sheets to maintain the OC spacing for each side?

If I shorten the sheet, do I recreate the T&G on the cut edge for that joist or is there another method I should be using?

Note that the finished surface will be tiles on top of Ditra Heat.

  • I'm confused. If you shorten a sheet, how does that affect the t&g sides? (Yes, you simply shorten each sheet that spans the narrow bay.) – isherwood Oct 2 '17 at 16:38
  • @isherwood - but if the OP has sheets which are T&G on all 4 sides (2 T's and 2 G's) and he shortens the sheet, then he'll be missing either a T or a G on that side. – brhans Oct 2 '17 at 17:14
  • I've never seen such a thing. Is it common outside the U.S.? – isherwood Oct 2 '17 at 17:19
  • It's only T&G on two sides, but I am kinda stuck laying the sheets so that the T&G sides are parallel to the joists. It is a rectangular room that is less than 8' wide so there are no joints other than the T&G. – user3802319 Oct 2 '17 at 18:27
  • Plywood is typically laid with the length perpendicular to the joists. If the room is narrower than 8', then joist spacing will be of no concern at all. – Jack Oct 3 '17 at 2:33
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A sketch would help us better answer your question, but per manufacturer installation instructions T&G subflooring should be installed so that the T&G are perpendicular to the joists.

The tongue and groove support systems are not meant to support weight between joists for more than 24", and by the sound of it you are hoping to have a T&G joint that is the whole length of your room. Do not do this!

You should never have two panels butt together between two joists where the joints run parallel to the joists. Those panels should both be cut so that they each lie on half of the joist. So you get 1.5" of the first panel on the joist and 1.5" of the second panel on the same joist.

Simply put, cut your subfloor panels so they both rest on the odd spaced joist. If your measurements above are accurate, you have about a 12'x <8' room. You will need two pieces of 8'x4' subfloor to complete the job.

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