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Currently my main level subfloor is joist, 1/2" plywood, then 3/4" partical board. I am in the process of replacing the partical board with 3/4" with Oriented Strand Board Tongue and Groove.

After ripping up the partical board - Should I glue & screw the OSB board down? Or just screw with red rosin paper in between?

Note: when the subfloor is complete I'll be laying builders felt paper down prior to installing 3/4" solid oak hardwood.

  • Others may not agree, but I would not hesitate to set the oak floor directly on the 1/2" plywood. If the subfloor was a little thicker, like 5/8" would have been better. Use the proper paper, not rosin paper, it holds water not block it. There is a tar paper out there that is thinner than 15 lb felt, it may be 5 lb or perhaps 10 lb felt. All the floor installers I seen use it. FWIW, the 1/2" plywood used years ago is a much better quality than todays plywood. – Jack Jun 16 '15 at 16:16
  • I plan to use tar paper in between the hardwood and OSB. Are you also saying 5 lb tar paper in between the plywood and OSB? – Kris Krause Jun 16 '15 at 17:18
  • Actually, 5lb paper over the 1/2" subfloor before the 3/4" oak goes down. – Jack Jun 16 '15 at 19:47
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If you truly want to add another layer of subfloor to the existing layer, you will only need to add another layer of 3/8" plywood, or OSB, (I am not a big fan of OSB) glued and screwed. THEN add the 5 lb. flooring paper, and your oak flooring. Otherwise I would go directly over the existing 1/2" subfloor with the flooring paper and oak floor. I suggest the lightweight tarpaper because it reduces moisture from rising into the floor from below, as in a crawl space. Red rosin paper, which I have used also for under wood floors but will no longer, holds moisture. It has been used under many floors over the years, I have demo'ed many floors that had it in place.

My reason for the littlest possible rise in the floor is it affects stairs, which become a safety issue, doors need to be cut, and other things that need to be cut or adjusted from the additional height all the layers produce.

  • Thanks Jack. Replacing 3/4" partical with 3/4" OSB should tie out in height. – Kris Krause Jun 17 '15 at 9:27
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    Then you will still be adding another 3/4" in oak floor? If you do still go over the existing with the 3/4" OSB, I would not glue it, only screws. Later work to do would be made difficult – Jack Jun 17 '15 at 16:15

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