Subfloor Considerations

Antwort auf: I have 15/32" PS2 OSB sheathing and I recently added 3/4" thick solid hardwood and so far, after 6 months, I have had no problem. I am a structural engineer and I made sure that the floor framing "I" joist where I added the hardwood was designed very stiff....therefore I did not hesitate to place the hardwood parallel to the joist. I think if your floor is not stiff & flat, that could be the #1 reason that nails could pull out. I also read somewhere in this blog that says cleats are no good. My opinion tend to differ because the cleats are installed along the tongue of the hardwood and driven at an angle. When you drive the cleats at an angle into the OSB, there is a vertical component of bearing of the cleats that is preventing the nails from lifting up. When you nail down the hardwood vertically, as you would a brad nailer, you are relying totally on friction. From a structural standpoint, bearing is always better than friction

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Antwort auf: In regards to using OSB, I have the following comment: I am a structural engineer in California, and I have specified OSB as a subfloor, roof sheathing & shear wall sheathing for hundreds of homes. As far as an underlayment for hardwood floors, there appears to be two issues. 1) is the floor structurally sound for hardwood, and 2) whether attaching the hardwood directly to OSB will result in nail slippage many years down the road. I have comments on both issues. As far as the floor being structurally sound, I have seen a few posts on this issue & I am not one to automatically say that hardwood should be placed perpendicular to the floor joists... But it would definitely be stronger and may help in easily repairing the hardwood attachment if the nails should slip many years down the road. I myself have placed the hardwood parallel to the floor joist because my subfloor is very stiff. To get a stiff floor, this is my recommendations: joist spacing should not exceed 16"o.c.; floor joist span should be designed conservatively (building code minimum is not conservative), and floor sheathing should be 3/4" nominal and placed with the face grain (long dimension) perpendicular to the joist & staggered. In regards to item 2: some national floor associations have said direct OSB attachment is acceptable as long as sheathing is PS2 standard & 23/32" minimum. That is all we can go by. As I mentioned above, let's say the nails do slip after many years... If your hardwood is perpendicular to the joist, couldn't you just screw it down to the joist below as a repair? That is one benefit I can see with placing the hardwood perpendicular to the joist or adding blocking between the joist. In regards to nail slip, I posted a blog regarding using the hardwood nailers that drive the cleats at an angle in the tongue of the hardwood edge. The cleats are locked in place inside the T & G connection. How is this going to lift up? Also when you drive the nail at an angle, there is a vertical bearing component of the nail that is preventing the nails from lifting. This is versus using a brad nailer that goes vertical. The vertical nail would rely totally on friction between the OSB & nail and I can see this possibly slipping down the road.

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Antwort auf: "Its common knowledge in the pro wood floor industry that OSB is not rated for wood installs and is a cut corner that will bite you in time." Thats not true....NWFA does allow for woodfloors to be installed over OSB. "The National Wood Flooring Association and the National Oak Flooring Manufacturers’ Association have issued official policies on the use of hardwood flooring over OSB. Both associations recognize 23⁄32” or thicker OSB panels certified to U.S. D.O.C. Voluntary Product Standard PS2 as an acceptable underlay for nail-down wood strip flooring under prescribed conditions"

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Antwort auf: If you must go over OSB, use divergent staples, not nails and not cleats. Make sure the length, does not break through the OSB, or you will lose holding power and a squeak may be heard, as the fastener slides up and down in the OSB.

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Antwort auf: Thats Ok, I only pointed out "sheathing" because it is important for people to know the difference between a sheathing grade plywood and an underlayment grade. Sheathing grades only come in a square edge (no t&G) but underlayment grades can come both ways, thats where it all gets confusing again. Foe example , your subfloor is 3/4" thick, that is OK for installing hardwood. It is made of plywood, that's also good. But, there is no t&G, that is bad and you can be fairly certain that it is a sheathing grade, which means it is not intended to have a finished floor applied directly on top. Sheathing grades have voids (hollow spots) all within the inner plies. Not good for holding thousands of flooring cleats/staples. I suggest adding a "minimum" layer of 3/8" BC underlayment grade (no voids) plywood there after you remove the particle board. That gives you something for the fasteners to hold to and also will take care of the problem of having no T&G which results in sagging between joists. If your subfloor turns out to be a 1/2 or 5/8 thick instead of 3/4", then I would go with a 1/2" BC underlayment.

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Antwort auf: It's good to ask... so I suggest you verify a few things. Do you know for certain that you have a double layered substrate? If you do have two layers you need to determine what the bottom layer (subfloor) is and the thickness of it. If you only have a single layer and the OSB is 3/4" thick and T&G, that is acceptable to leave in place if its in good shape. Better give us your floor joist on-center measurements too while you are at it. last question... will you be installing the wood perpendicular or parallel to the floor joist?

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Antwort auf: It sounds like that may be particle board underlayment instead of OSB. Typically underneath the PB will be a 1/2" CDX plywood subfloor and you will need to go back and add a plywood underlayment over it, 1/2" minimum, but I usually use a 5/8 BC grade square edge plywood for that. A Crain Toekick saw is used to cut within a 1/4" underneath cabinet toe kicks.

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Antwort auf: it all depends on the grade and quality of Oriented Strand Boars (OSB) panels ! There is some OSB (Advantec for example), which is actually a better product than plywood. The right product for the right application. Boxers is completely correct. Check the grade !

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Antwort auf: I WOULD NOT install hardwood directly over OSB. Main concern is nails/staples coming loose from the OSB over time. OSB is fine as a subfloor structurally, but IMO, it won't hold a nail or staple as well as spruce plywood. Especially if you are using a stapler to install the wood. I would overlay your OSB sub with 3/8" spruce plywood and screw it down. First, I would ensure the OSB is securely fastened down by screwing it into the joists with screws and then overlaying the spruce (make sure to tile the 4x8's) and fasten again with screws. You'll have a nice, even and clean surface to install onto, well worth the effort, IMO.

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Antwort auf: You are correct in removing the Particle board. I still don't know what the subfloor is but typically a 1/2" CDX "square edge" plywood "sheathing" grade plywood is used there. Sheathing grades have voids in the inner plies and no T&G joinery. I like to use 5/8" BC (underlayment) grade square edge plywood or at the very minimum a 1/2" BC. The 3/8" will work but going thicker is much better here because nothing is T&G. Run the new the plywood underlayment crossing the joist, which usually means in the same direction as the subfloor. Keep all the sheets offset and staggered so no joints line up with the subfloor underneath and maintain a 1/8" gap alway around each sheet.

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