The cost of 1/2" OSB vs 1/2" CDX plywood is about half. Is it acceptable the use 1/2" OSB on top of 5/8" subfloor and run the planks parallel to the joists. At first I was planning to use 3/8" plywood but the cost of 1/2" OSB is about 2/3 0f the 3/8" struc 1. Please advice.

Also, is it a good idea to glue the undelayment to the subfloor? if so what type and where to apply?

We need to know what the finished floor is going to be , and, is it a glue down or mechanically fastened?

How is the 5/8" subfloor constructed... plywood, OSB ... T&G or square edge?

Jerry,

The existing subfloor is 5/8" T&G plywood nailed down @ 2" OC. On another post, Gary has recommended to use 1/2" plywood on top of the existing subfloor as would like to nail down the new 3/4" hardwood running parallel to the joists. I am wondering if the 1/2" plywood is that much better than the 1/2" OSB for my purpose as the 1/2" ply is more than twice the cost of the OSB. It is an old house with limited budget. Am I asking for trouble if I go with OSB due to the poor holding power of fasteners. I will be using 2" staples to nail down the new 3/4". Comments and suggestions will be appreciated.[/quote]

I recommended 1/2" plywood because that is what NOFMA, the NWFA and most manufacturers recommend. I stand behind the recommendation.

Gary,

I am not second guessing your suggestion, I am sorry if I sounded that way. I was trying to find out if I can substitute OSB to plywood in this case due to my budget.

The question is: should you? Of course you can and you may. OSB does not have the nail holding capacity that plywood does. That has been established. If you substitute the plywood for OSB, you do so at your own risk. Will your floor fail? Probably not. It MAY move a little more than it would of if you had used plywood.

You should be using plywood in your situation. I realize there is a price differential but that justs part of the deal. Plywood will hold fasteners better than 1/2" OSB wall sheathing. Floating a floor I would have no problem using OSB, but not on a nail down.

Not to be a liar... on very few occasions I have installed over 1/2" OSB, but the client was buying all the materials and I was hired to install the job. It's still there without any problems so far.

I squiggle out yellow wood glue as I am laying underlayments. If i were laying a 1/4" plywood underlayment with a thin glue-down engineered on top.. I would not glue the 1/4 to the subfloor in case you ever wanted to rip it out one day.