Replies

1. Expert Member
   Antonio Bettencourt | Jul 21, 2026 12:50pm | #1

   T&G will do little to nothing to increase the floor stiffness in that application with solid 2x boards under it. Consider running the plywood sheets lengthwise perpendicular to the 2x boards. If you're gluing the sheets with full glue coverage you are creating a very stiff, 2 inch deep section.
   I really don't see an issue with bounciness, deflection or vibration.

   On a subject I'm less knowledgeable about, I would would be mildly concerned about shrinkage in the recently milled 2x boards. How much cross grain shrinkage can be expected? If the boards are laid tight, how much of a gap might open between them? Is a gap, visible from below as the ceiling, a problem? If not then fine. How about board attachments. Should they be nailed near their centerlines to allow for that shrinkage? Might nailing near the edge cause shrinking boards to split lengthwise?

   How about cupping as the boards shrink? Is some to be expected as the boards dry? How will that be handled?

   These are questions someone really familiar with timber framing should be able to answer. Unfortunately that's not me.

   If I were in this situation I would place the boards so that cupping would be face down. I would give each board 2 nails, about 2" apart near the centerline of the board, at each beam. I would use ring shank nails with a full head to resist pullout. This would restrain cupping, allow for cross grain shrinkage and avoid splitting. I would place the plywood perpendicular to the boards, fully glued, and with nails at a 12" spacing.

   Best of luck on your project. It sounds like it will be beautiful.

2. 
   AdamPNW | Jul 21, 2026 02:45pm | #2

   Thanks! Great tips, I’ll plan to use full glue coverage, sheets perpendicular, full ring shank nails.
   As for the decking, it was milled several years ago and air-dried/stickered since then. Not super dry like kiln-dried, but probably 12% now (I’m in the Pacific Northwest). Plus it will dry a bit more this summer. I’m predicting 1/16” shrinkage, so 1/8” gap if laid tight. We can live with that.
   I’m more concerned with preventing squeaking, so I might nail across the width (but definitely cup down) even though it may result in more cracks. I’m no expert either, so I’ll just shoot for “pretty good”.
   Adam

3. 
   paulmagnuscalabro | Jul 21, 2026 05:06pm | #3

   Gluing seems like a good idea, as mentioned above.

   I wonder if structural screws, something like GRKs, would be better here than ring shank nails? Albeit likely more work.

   Also, might consider painting the bottom side of the plywood black, at least where it'll be above seams in the boards below. That way, if (when) the 2x boards move, you'll just see black rather than seeing plywood from below.

1. 
   AdamPNW | Jul 21, 2026 09:42pm | #5

   I thought about that too, perhaps I can find some black subfloor glue

4. Expert Member
   Akos | Jul 21, 2026 09:15pm | #4

   I would install the decking with a gap. This way when it shrinks a bit, you won't notice. It would also avoid the boards rubbing against each other and squeaking as they deflect which is the bane of T&G decks for me.

   Instead of using the Dug fir as a deck, you could install a regular OSB deck that is span rated over the beams, strap the side of the beams just under the OSB with 2x2 or 2x3s and nail the fir 2x10 to that. This now gives you a cavity to run wiring or plumbing plus lets you install a bit of insulation to give some level of sound isolation.