I have a 3/4 inch tongue and groove plywood subfloor. I am installing hardwood flooring and the joists run the long length of the room. My hardwood manufacture guide says to run the hardwood flooring the long length of the room. Normally you would want to lay hardwood perpendicular to the joists but that contradicts the manufacturer guide. The manufacturer therefore states to lay the hardwood parallel to the joists to add a 2nd layer of subfloor that is 15/32 inches in thickness and to not attach it to the joists (presuming so the layers of decoupled)

My question, does this 2nd layer have to be tongue and groove? It's over double in price. Second question, can I use osb instead of plywood that's about $10 a sheet less. Third question, is glue and staples suitable to attach to the first layer, since I don't want to attach to the joists?

1 Answer 1


It does not, and yes you can.

By adding a substantial second layer you're increasing total rigidity enough that a second t&g connection isn't warranted. You should try to stagger joints with those below and fasten well.

OSB is every bit as stout as plywood, though it can vary in thickness a bit. That probably isn't a concern with solid hardwood. It makes a nice second layer.


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