Can 3/4' Oak Hardwood floor be put over OSB?

lombardguyJanuary 15, 2006

Hello. I am hoping there will be experts in this forum to help me. It seems like every flooring store I go to I get a different answer... Three stores have said that you cant put it over OSB, two have said there shouldn't be any problem and one said to glue it... All of the stores answer with complete conviction and insist they are correct.

Can anyone here please guide me on this topic. I dont want to end up with loose boards in 5-10 years. I would have this professionally installed and I am sure it would come with some type of installation guarantee but I dont want the aggravation down the road from an improper install.

Your response are appreciated.

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You can install it over OSB. I would suggest using a flooring edger or a large sander to cut the seams of the OSB down flat, and if you live in an area with high moisture content, you may want to seal the OSB with a water retardent. A layer of 4mil plastic followed with 15lb roofing felt will reduce your risk of troubles also.


    Bookmark   January 16, 2006 at 4:46PM
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I have 3/4" hardwood floor that I want to install also. A contractor said DO NOT install hardwood flooring over OSB. Instead he recommended laminate wood floor over OSB. In about 2 or 3 years the hardwood flooring will pull loose. Nails will not hold onto the OSB through the hardwood floor and will come loose in a couple of years causing uneveness, which is a very dangerous situation to try to walk over.
My question is what do I put down instead of OSB so I can install the 3/4" hardwood floor?

    Bookmark   June 4, 2006 at 2:12PM
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OSB can be ok if it has a rating of ps-2-92. Others won't work as when you nail if will shatter the osb and it won't hold tight. This is from the Armstrong or Bruce website. If you don't know I wouldn't try it.

    Bookmark   June 4, 2006 at 4:19PM
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It is GOING to be OK to install over OSB, because OSB is becoming the subfloor of choice for builders. They are, of course, using OSB with the proper rating for use as a subfloor.

What others have said about preparing the surface is good advice.

Don't expect anything more than the standard one year warranty on workmanship from anyone; it's unrealistic to expect a tradesperson to warrant an installation or provide free service on any installed product after that.

All naildown wood flooring will loosen some over time. The worst problems are with floors that are installed over "wet" subfloors. Be absolutely sure that the OSB is dried in enough to proceed with a wood floor installation. The flooring and the subfloor needs to be to within 4% moisture content of each other. The use of a moisture retarder between the OSB and the flooring is also good advice. Be sure the retarder is lapped at least 4".

Of course, floating wood floors avoid many of the potential pitfalls with a real solid hardwood floor...but they are not real solid hardwood floors.

    Bookmark   June 4, 2006 at 6:18PM
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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.

    Bookmark   June 6, 2006 at 9:58AM
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We had major headaches getting wood floors installed upstairs in our house. The subfloor was OSB. The flooring company said the subfloor was fine but after 4 tries they finally screwed down 1/4 inch luan & laid the floor on top of it. Cost a bit more but I wanted to be sure there wouldn't be issues down the road.

    Bookmark   June 7, 2006 at 8:39AM
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We are also planning 3/4" oak hardwood. Can someone please explain what OSB is? Is it a type of subfloor? I have no idea what our subfloor is made of (house is about 35 years old).

    Bookmark   June 8, 2006 at 2:05PM
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Oriented Strand Board.
Am improvement over chip/flake boards, but still not as good at holding nails as plywood (or even better is actual wood).

    Bookmark   June 8, 2006 at 8:35PM
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Thanks! Sounds like plywood/wood is the best subfloor then?

I'm crossing my fingers that's what I have for my 35-year old subfloors.

    Bookmark   June 9, 2006 at 12:34AM
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I'm going to bump this old thread back up.....

Does Advantech subfloor take nails better than OSB? or not?

    Bookmark   April 5, 2007 at 12:24PM
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I don't know about holding nails better, probably does, but is a far superior product than OSB. I have installed many jobs over AdvanTech with nary a problem. I've not had any problems with 3/4 OSB either. Recently I was in 2 houses I installed hardwood over 3/4 OSB about 9 years ago...I was amazed at how good they looked, no squeaks or gapping either. I use staples instead of cleats.

    Bookmark   April 5, 2007 at 5:41PM
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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 !

    Bookmark   April 5, 2007 at 5:56PM
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thanks for the input.

we're building right now and using Advantec with 3/4" red oak nailed over it.

sounds like it is at least equal to plywood as far as holding a wood floor.

thanks again. :)

    Bookmark   April 5, 2007 at 10:08PM
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Cleats don't hold well in either OSB & Advantec

    Bookmark   April 5, 2007 at 10:27PM
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thanks. I'll stress, staples.

    Bookmark   April 6, 2007 at 1:44PM
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Appreciate reading the comments on this thread. We're looking at putting down 3/4" hardwood soon; area will include familyroom/livingroom/kitchen. A couple of questions come to mind & wonder if someone here might give me an idea of best practices.

If the OSB is removed, I'm reading that something should be installed in its place? I assume just laying the hardwood over the sheeting isn't advised, but what is the reason for this add'l layer?

Also wondering how best to remove the OSB where is runs up to kitchen cabinet w/ toe-kicks? At the walls, we'll probably find the OSB butts up to the wall. But I would assume the original builder put down the OSB & installed the kitchen cabinets over the top. How does one get a nice clean cut line in the toe-kick areas and even up against the cabinet units?

Altho' hubby & I have done some home improvements, flooring has not been one of them. Fortunately for us, hubby's boss was a very good contractor in his former life and he's willing to give us some assistance if we need it.

I appreciate your comments & thank you.

    Bookmark   April 6, 2007 at 3:10PM
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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.

    Bookmark   April 6, 2007 at 5:50PM
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Thanks Jerry....When we take up the carpet, if it is OSB, will we see it stamped on the boards? Otherwise, how do I know if it's PB or OSB?

    Bookmark   April 6, 2007 at 6:19PM
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OSB is big flakes and strands, of wood going all different directions.

Particle board, looks like saw dust glued together, thus particle in the name.

    Bookmark   April 6, 2007 at 7:00PM
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It looks like we have OSB; it's definitely made up of larger flakes/strands. I'm still wondering it removing the OSB & replacing it w/ the hardwood only is going to give us future problems. The nice thing is that removing the OSB & replacing it w/ the 3/4" means the doors will all still open/close w/o any adjustment. If we add another layer (meaning sheeting, OSB, & hardwood), will the build-up be high enough to require other adjustment such as modifying thresholds into other living spaces, doors, etc.

As you may see from my questions, it's a new experience for me and my hope is that we won't encounter too many surprises from failure to ask beforehand.

Thanks again.

    Bookmark   April 7, 2007 at 11:28AM
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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?

    Bookmark   April 7, 2007 at 4:23PM
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Thank you Jerry_T for responding. I'll check that out & get back to the board asap. Hope you'll be reading over the next day or so.

    Bookmark   April 7, 2007 at 5:05PM
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I'll be around but please keep in mind that there are several top notch installers who contribute here regularly and may not see your questions. You could start a new thread if you like.

Have a great Easter!

    Bookmark   April 8, 2007 at 4:46AM
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Jerry_T: We finally started on our flooring. Took up the carpet & pad and found it wasn't OSB but rather pressboard underneath. Below that is plywood sheeting running across the joists.

We plan to pull the PB and replace with plywood (3/8" enough in your opinion running opposite the main sheeting??) before putting down the moisture barrier and the hardwood. Think we'll be much happier in the long run. A little more work, but this is a lifetime house for us (living on the family farm) and it will be worth it, I'm sure. I so appreciate people like you willing to share your opinions/experiences. Reinventing the wheel isn't something most of us wish to do. Thanks again.

    Bookmark   April 8, 2007 at 7:57PM
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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.

    Bookmark   April 9, 2007 at 4:29AM
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Still need to know which direction you intend to run the hardwood flooring, that fact too needs to be known as far as the underlayment thickness goes.

    Bookmark   April 9, 2007 at 4:36AM
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jerry_t:I appreciate you're still hanging in here w/ my questions.

I believe we have 3/4" plywood underlayment running across the joist; nothing T&G here. We think we'd like the hardwood flooring to run across the joists. Our family & living rooms have a small area where they almost overlap and if the flooring runs across the joists, as you enter these rooms from the outside, the long hardwood seams will run left to right rather than straight ahead of you. Thought that might be more appealing visually. Also means that an approx one foot width of flooring will run thru the familyroom into the living room & down a short hall. That length is about 35' in length. If we chose to run the flooring with the joists, the longest run of flooring might be about 20'. I'm not sure that this really matters, but if it does, then perhaps other thoughts on the direction might change our minds.

Thanks again & I appreciate knowing it's 'sheathing' rather than 'sheeting'. I'm learning. :-)

    Bookmark   April 9, 2007 at 10:45PM
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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.

    Bookmark   April 10, 2007 at 4:00AM
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Thanks jerry_t - this has been a great learning opportunity for me. Think that w/ your help, we're on the right track. I've found these forums to be most helpful over the years & people like yourself help make that so. Thanks again...

    Bookmark   April 10, 2007 at 9:31PM
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