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I am remodeling my kitchen. I removed several layers of flooring.

At the bottom there is some 3/8" ply. On top of that was tar paper and some 5/8" particle board.

I removed everything but the ply at the bottom due to glued flooring and 18000 staples.

To reassemble it I bought more 5/8" osb and 1/4" tile backer.

Questions:

  • Do I need to reapply the layer of tar paper between the two wood layers (or some other material)?

  • Are screws or nails generally recommended for fastening subfloor?

  • Should the subfloor panels have gaps where they meet or be flush?

  • Why did you remove particle board only to reinstall it? (Particle board isn't something that's put in modern homes--it's considered a low-quality product.) – isherwood Apr 14 '17 at 14:49
  • I think he means OSB that is used extensively in new homes. The tar paper acts as a bond break and possibly for moisture. Usually used on the exterior of a house behind brick or siding. Doesn't seem to be a reason to have it under flooring in a kitchen. I would definitely use screws. – ArchonOSX Apr 14 '17 at 14:53
  • In my experience, OSB hasn't been commonly installed over plywood. I'm hoping that James will clarify. – isherwood Apr 14 '17 at 14:57
  • I had to remove the existing particle board because of the previously mentioned gaggle of staples, it also had old flooring glued directly to it. And yes I bought osb – James Apr 14 '17 at 15:39
  • Update your post to indicated OSB. – isherwood Apr 14 '17 at 15:54
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We use to specify building paper between the underlayment and subfloor. About 10-15 years ago we stopped. Now, we worry about moisture (vapor) getting trapped between the underlayment and subfloor.

Nail or screw: Either...the key is to drive 100% of the fasteners flush or slightly recessed. (Be careful the head of the fastener does not "lift" the wood around the head.) Screws hold better (won't back out) but harder to drive flush with top of underlayment. Power-driven nails are fine, but depth will vary due to consistency of compressor. (When the nail-gun is used a lot in a short time, the compressor will be slightly "weaker" and a few nails won't be driven to same depth, until the compressor turns on.) Hand-driven nails are ok, but use ring-shank nails.

Space between sheets of underlayment: Yes, it is recommended....about 1/16" space or less.

Make sure you follow the flooring manufacturer's recommendation when installing your floor covering. Most laminated wood flooring manufacturers recommend a vapor barrier on the underlayment, but read the instructions carefully.

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  • I have decades of building and remodeling experience and have very rarely (if ever) encountered asphalt felt between layers of subfloor. It's probably a regional thing, and may be obsolete as a building technique. I wouldn't reinstall it unless you have some compelling reason to do so. It's smelly and not particularly something I'd want in a living space.

  • Any subfloor should be screwed or glued and nailed using ring shank pneumatic nails. To not do so is asking for squeaks.

  • Really, you should consider using proper tongue-and-groove OSB. It's designed to minimize flex at the spanning joints. Your 3/8" plywood below doesn't adequately do that job, in my opinion. T&G subfloor has a built-in gap, and ends are supposed to also be gapped. I'd follow that practice and gap 1/8".

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