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I have 2 options for a new floor:

  1. 9mm plywood on joists, with tongue and groove floorboards on top 19mm thick

  2. 28mm tongue and groove floorboards on joists (no plywood subfloor)

Which is the better option?

  • What is the spacing of the floor joists? – Lee Sam Feb 23 '17 at 20:49
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If there is another space below, then you want the subfloor for no other reason that to prevent dust, air, sound and light from leaking between the floors.

  • and the thickness of the suggested plywood will not be an issue? – Marty Wallace Oct 25 '16 at 21:55
  • @MartyWallace yea, that's an issue too. That is thin. Why are you limited to only that thickness of subfloor? Can you go with engineered flooring? That'd let you have a proper subfloor but keep the overall thickness the same. – DA01 Oct 25 '16 at 21:58
  • The finished height of the overall floor must be 28mm - it meets another floor in the house and the top of a staircase – Marty Wallace Oct 25 '16 at 21:59
  • @MartyWallace is a transition strip out of the question? I'd personally rather not under-build a floor just to make it level with another spot. The top of the staircase is a bit of a concern, though. How was the rest of the flooring installed? – DA01 Oct 25 '16 at 22:00
  • The rest of the floor is 28mm boards directly on joists. But to save costs on the new boards it was suggested to put 9mm ply down and thinner boards on top – Marty Wallace Oct 26 '16 at 7:38
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I would want the T&G on the bottom and use the thin stuff as an underlayment. If you put the T&G on top your finished floor will not look as good. I have used T&G plywood with nice results but I normally put a thin underlayment on top and make sure the seams are off set for the best results.

  • The way I read the question is that the T&G floorboards are the finished floor (with some sanding & sealing ofc). – brhans Oct 26 '16 at 11:20
  • yes that is correct - plywood subfloor and T&G finished floor – Marty Wallace Oct 27 '16 at 8:51
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I've been on a lot of decks that are made from 1.25" (31 mm) softwood planks, not grooved, and they aren't bouncy. I suspect that using 28mm T&G boards (stress is spread from one board to the next one) would be sufficient by itself.

The 9 + 19 may work if you glued the finish floor to the subfloor in addition to fastening at the joists.

Is the difference in price between 19 mm and 28mm enough to compensate for the cost of the plywood and the aggravation of putting down another layer?

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