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3/4" hardwoods on a 5/8" OSB subfloor

wildcard585's picture

Any thoughts on whether it's truly ok to install nail down 3/4" hardwoods on a 5/8" T&G OSB subfloor.  The house is a new construction and the subfloor is in great condition.  No sags.  No creaks and the joints are sanded smooth.  I'm hoping not to have to add additional plywood as this will increase floor height but if installing it in it's current form will cause a headache down the road, I'd be willing to.  I asked my builder and for hardwoods installed by his company, it's routinely done without any additional underlayment (ie right on the subfloor w/rosin paper in between).  Any thoughts?


hardwood over OSB (post #194836, reply #1 of 17)

we had nothing but trouble with OSB floors. God forbid if you spill something. The product swells like crazy and certainly will loosen your hardwood. To renail would be a real pain.

I would go with 5/8 T&G ply over it. At least you have a solid base to nail into. 5/8 OSB is a poor nailing base to begin with.

hardwood over osb (post #194836, reply #2 of 17)

Hi Semar,


Thanks for the advice.  I don't mind putting down additional plywood but there are a few problems:

1)The fireplace surround is a slab of granite and with an additional 5/8" ply, the floor will be higher than the granite surround.  I'd like to avoid using a transition strip if possible...

2)(the main problem) the dishwasher is already installed and while I can run hardwoods underneath, I don't think I can run 5/8" ply with 3/4" hardwoods on top under the first 2 legs to make a clean look.  Plus since the kitchen has already been installed etc, I can't uninstall it.  How do you get around this issue while making it a clean looking installation?


How do you get around this issue (post #194836, reply #3 of 17)

Several yrs ago the hardwood associations pretty much didn't approve of install over/into OSB.  However, times change and you find the practice to be pretty much commonplace.

If in fact you wanted to cut out the osb up to where it makes sense and ease to do (to joists close to the wall and not beyond, up to the kitchen cabs, etc)  you'd need to block beneath all those joints in transition you are making (cross blocking etc). 

That's going to be a lot of extra work.  Will you get squeeks?  maybe, even with ply.  Underlaying with felt paper, screwing subfloor to all joists and blocking, should help.

I've had decent luck with staples to osb, but I don't own a cleat nailer.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


Keep in mind that there's OSB (post #194836, reply #4 of 17)

Keep in mind that there's OSB and then there's OSB.  The particular brand/style makes a big difference in how well it holds up.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

hardwoods over osb (post #194836, reply #5 of 17)

I don't think I'll cut out all the current OSB since it's a new construction build and a bigger job than I'd like.  I'm debating between laying it right on top of the OSB vs adding a layer of ply and then going over it.  I'm not opposed to adding ply but I can't add 5/8" but could get away with 3/8".  Getting it under the dishwasher will be challenging.  I don't plan on putting it all the way under but rather under the metal covering or just to/under the first set of wheels. 

DO NOT TRAP your dishwasher........... (post #194836, reply #6 of 17)

It's a nightmare to try to saw off the rear legs to get it out.  Lifting the countertop is the only other way if you impinge on the MINIMUM opening.

The addition of 3/8s ply won't help you that much-I don't think worth the time or effort, unless you glued it to the OSB in attempt to make it "one".

Best of luck.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


to add or not to add... (post #194836, reply #7 of 17)

So then I shouldn't add 3/8???  Or do I need thicker b/c that I think would be too much of a height increase.  If I was going to add 3/8 ply then I'd def glue and screw it into the joists and existing subfloor.  Let me know if I'm making too much work for myself

2 things. (post #194836, reply #8 of 17)

I don't know if you addressed your post to me.  When replying to a specific post, hit the reply button under that post, otherwise we won't know who you are directing it to.  Corn fusing it is.

The idea of adding ply now b/4 you top it off with the hardwood is critical, because once you lay that HW you be screwed if you "shoulda" added the ply.

So, in spite of a whole lotta floors just put down on that 5/8's OSB................

It's still your decision.  I don't think it's that critical, but you don't know me and I don't know you.  If it appeared to me that you were making a grave error I would tell you.  In this case, I don't think so.  BUT, if it makes you feel more confident to add the ply, please do it.  Again, if you don't and wished you had, you'll be one mad puppy.  If you do and have no problems, you'll be one happy guy.

And as far as too much work?  Beats me, you need the floor vacant to lay the hardwood, so moving furniture shouldn't be an issue.  If you have the time and the money for the ply, sounds like a savings vs. paying the shrink.

Best of luck.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


You Bug Me. (post #194836, reply #9 of 17)

People like you really do bug me. You come to this website asking for advice from professionals only to do whatever you want. Granted, it's your house, your money, your time, and your decision to make but it's just irritating to a professional like myself to be asked my opinion then have it neglected (that's why we have to follow building codes now).

Someone already gave you the proper advice - remove the 5/8 OSB and replace with 5/8 plywood - but  you say: that's "a bigger job than I'd like" to do.

Hey, that's why it's my job! 

I get paid to do work that is a bigger job than the average homeowner would like to do. I also get paid to do it the right way the first time. How would you feel if you hired someone to install the floor and they said that they really should replace the subfloor but won't because it's too much work? Maybe you should just paint the OSB and call that a finished floor; It would certainly be easier than laying hardwood. Or just install some floating laminate flooring with a hardwood look; also easier than laying hardwood. Or hire that builder you mentioned who doesn't even use underlayment (also too much work). That would probably piss you off just as much as the cheap builder who laid the 5/8" OSB in the first place - the same sort of too much work / it's good enough attitude that you are displaying now. 

So, when you come here with two choices which are both the wrong choice what do you really expect?

I think it would be a waste of time and money to install 3/8 ply over the 5/8 OSB unless you are willing to go the extra mile and uninstall the cabinetry and hearth.... but still you run into problems with transitions, door sills/thresholds, etc. you'd probably end up with toe stubber or trip hazard somewhere. 

I guess that leaves only one option then.

Just lay the hardwood right on top of the 5/8 OSB

Don't forget the underlayment and don't be stingy with the staples/nails. BTW, I prefer 15# felt instead of rosin paper but I am probably alone in that area.


to OSB or Not to OSB (post #194836, reply #11 of 17)

Well said and an big round of applause.  Don't ask for advice if you can't take it.  Using rosin paper in never a good idea especially if you leave the OSB!  The Felt paper will at lease keep the sub floor drier.  Thanks for letting me know I'm not alone in insisting on felt.


Never look a gift horse in his other end!

hardwood floor over OSB (post #194836, reply #12 of 17)

Dreamcatcher, I fully agree with you

besides: how big is this kitchen? It should not be sooo expensive to replace a few 4x8 sheets osb. At least this way it is done right and if he replaces the kitchen floor then use 3/4" ply as subfloor.

All he needs is a leak in the dishwasher and he faces replacing the whole hardwood floor anyway.

Had exactly the same job recently. DW leaked, floor swelled up, could not get the same color replacement floor, ended up ripping everything out. If it happens again he said he will take the HW floor out and get ceramic tile. There it paid off having a good subfloor otherwise he would have to replace that also

Re: You Bug Me (post #194836, reply #16 of 17)

Hey Dreamcatcher, your response is (among other things that can't be said here) offensive.  Wildcard585 simply asked a question.  No need to bite his head off.  Your comment gives proof this forum is NOT exclusive to professionals.

Richie, that was three and a (post #194836, reply #17 of 17)

Richie, that was three and a half years ago.  Give it a rest.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

5/8 OSB for a floor (post #194836, reply #10 of 17)

This is not very common, it is usually 3/4 T&G OSB that being said are you joist 16" oc, I hope so. I have to agree with Calvin if everything is in good shape it should be fine, try to get nailing into the joist if you have to use longer nails to do so then so be it. also screwing the OSB to the joist is a good idea at hardwood, squeaks at hardwood are very difficult to fix. Other than that refer back to Calvin. Dreamcatcher I also agree with your recommendations even though you were a little hard on the guy.

Good Luck!!

Update? Same issue (post #194836, reply #13 of 17)

I have the same issue and was about ready to get hardwood when I learned my subfloor is 5/8 aspenite. Curious how this turned out in the end? Did you put down the ply? has anyone laid hardwood (nail/staple) over 5/8 aspenite and had good success (it sounds like yes from the above post, but the ply is some degree of extra insurance). I get opinions ranging from "it should be ok" to big box store comments..."if I was going it I'd put down I'd put 1/4 ply ontop".

I can see why 5/8 ply is better, it holds nails better and if wet, returns to its original shape.

The other varying opinion I get is whether to glue down the layer of ply...that glueing it can cause more problems, so many don't glue it, just screw it. what is a good technique to glue zig zag beads and notch trowl them?

Also, everyone recommends felt, but it does have an oder to it when you are close to it. Does anyone have issues with that odor permeating the house or causing other ill effects?

Greetings (post #194836, reply #14 of 17)

Like has been said, ply used to be the norm and for a while-the hardwood association didn't recommend nailing down to osb.  You say you have aspenite-which in the 70's around here was vertical sheeting only-no structural properties to speak of.  If you mean osb, then fine.

I have, as well as countless others, nailed to osb with no noticeable least no call backs because of it.  However, the movement from heating seasons changing could possibly give it the opportunity to loosen up over time-then maybe a squeek or two.  The slip sheet between will help, but shrinking hardwood will allow the t's and g's to rub against each other.  If it loosens up from fasteners pulling-the squeek is more pronounced.

Never had anyone complain of felt as the slip sheet-tho some have the nose of a bloodhound.  Don't want to use it-try rosin paper, a perfectly good substitute.  The beauty of felt is when placed over sheeting over a crawl, you get the help of a marginal moisture barrier-further protecting your installation.

Glueing the ply over (if you add it) makes it one with what it's stuck to..................presumably a clean subfloor.  For tile on top, a must.  For the guy tearing it out later-a major headache.  When we've done it, we have used PL Premium, a urethane adhesive that really works well.  Cheap subfloor adhesive, maybe not so much.  The deal is-if both sides are clean, most will work well to bond the sheets.  The drag is tube dispensing.   You need enough to bond most of the sheet-trowell grade would be better, tho I don't know if PL comes like that.  I'd think there's trowel grade urethane, tho can't give you a brand.  Bostik would be a place to start your search.

Have used (not sparingly) tube dispensing PL concentrating between the joist layout (easy to watch your layout from screwing the sub).  Good results, tho no one has asked me to tear out my work down the road (thank you jesus).

Have also spread wood glue-when gluing ply to diagonal board sheathing.  Wood to wood.  With screws, makes for a good bond.

It's not a sin to staple the heck out of an underlay to subfloor either, if they hold till the glue sets, should be fine.  Concerned-screw it.

FIRST, screw down the subfloor (not with drywall screws)

Last, 1/4" isn't usually a full qtr (Arauco ply is pretty close-most lino underlays are a full qtr.).   Adding a 1/4 isn't worth the effort in my mind-too thin.   Staples will shoot through it.  3/8's or nothing.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


OSB subflooring is the norm (post #194836, reply #15 of 17)

OSB subflooring is the norm today but it's usually thicker than 5/8". It's a different product than your father's OSB. Nailed down strip hardwood flooring is commonly used over OSB. If you are installing perpendicular to the joists, you nail in the joists and you should be fine, not ideal but you have what you have. If installing with the joists, that's different since you have to rely on just the OSB holding the nails.

Beat it to fit / Paint it to match