Hi, My sunroom has OSB over 2x8 decking (it used to be an outside deck). My husband thinks if we can find long enough staples/nails to install the Mullican Engineered wood over this we'll be ok. From reading messages here, I want to install a layer of plywood over the OSB. What do you all suggest?

Thanks!
Lee

Well, for what its worth, here is my suggestion. The OSB is doing nothing for you, so I would remove it, re-screw the decking to the joists, add 6 mil poly on top, and 3/8th plywood on top of that and then lay the new hardwood.

Well, here's my two cents...

I would re-screw, like Dennis mentioned. But leave the OSB, and screw through the OSB & decking, into the joists. Then 6 mil. poly, and sheet out with 3/8 plywood. IMO, why tear out the OSB? It's supplying a more ridgid subfloor, without the additional labor of tear out.

I just have this undefinable aversion to adding layer after layer of product when is serves no real function. I cant imagine what contribution to stiffness a layer of OSB sandwiched between existing 2 bys and new plywood sheathing would have.
Since this is a sunroom, I am making the assumption that it is about 200-300 sq feet. How hard can it be remove 6 or 8 sheets of that crap.

I'm with you Dennis on adding unesessary layers. I would imagine this would depend on the flatness of the 2bys under the OSB, how the OSB is attached, and affecting transitions. And if tearing up the OSB is opening up another potential problem. We're not getting the full picture. ( OSB is recognized as a suitable subfloor ).I would have to disagree with you on the stiffness. Anytime you add layers, or laminate products together, it aids in strength, such as engineered hardwood. Getting the full picture, if the OSB SHOULD come up, I would advise a stouter plywood thickness than 3/8, for stiffness, and wood floor fastner bite.

Well dont lose sight of the fact that the substrate is 2 by 6, which gives more depth (1 1/2 inches) than any flooring fastener can use. I recommend the additional ply to help create a flat surface, and 3/8th inch should be sufficient, even after sanding (if necessary) any minor high spots out of the 2 bys.
Of course this also makes the assumption that the deck was sturdily constructed and the joists are on 16 inch centres. If not, all bets are off, and I would want 3/4 ply and might even consider leaving the OSB in place, although that would prevent the fasteners from biting into the 2 bys.

You wouldnt want to penetrate the 2 by 6 with the wood floor fasteners. What would be the reason for the poly, if your penetrating the barrier with the fasteners ? It would render it useless. If you go with a thicker subfloor, you wont be penetrating the poly barrier. A thicker subfloor is also more addequate for an engineered product. If you leave the OSB in place, your assured of a sturdier subfloor if the deck is not sturdily constructed ( say that fast 3 times ). Leaving the OSB will not only save labor, as I mentioned,( which saving labor is not always the answer for the best job), but it will also save on flattening of the joists, by spanning the joists & providing a flatter subfloor, for the plywood underlayment.

I think we are both on the same track here, given that we dont have much knowledge of the actual site conditions for this project.
However, regarding the penetration of the poly, we use V-Lok from Armstrong which self seals around the fastener.
It has been a great blessing to us since we switched to this product early this year.
Up here a simple wax coated paper is the norm. (ya I know, I know).
We do a lot of new construction in adverse conditions and the V-Lok has resulted in far greater protection from dampness from below in tract housing that takes about 2-3 months from digging the hole to the moving van pulling into the driveway.