OSB And Hardwood Floors

I have a situation in a 13yo townhouse (I own this one) where the first floor has about 325 sq ft of 1/2" hardwood laminate coverage and about 600 sq ft of carpet. Both rest directly on an OSB subfloor.
I want to replace the entire floor with 3/4" hardwood planks. This is do-able because it will only raise the floor a net 1/4". However, some of the contractors I've talked to insist that I need to lay a 3/8" layer of plywood on top of the OSB before the new floor is installed. Others say it's not important and that OSB is the recommended subfloor for hardwood anyway.
I'd obviously like to avoid both the cost and pain of raising the floor an additional 3/8" if I don't have to. But ... I also want this done rights. So ... what is the wisdom of the Wreck on this one?
TIA,
P.S. There are some floor creaks, but at least one contractor told me this was primarily an artifact of the floor joists and that adding the additional layer of plywood would make little or no difference. I wonder ...
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On Fri, 19 Oct 2007 22:46:57 -0500, Tim Daneliuk

With 3/4" solid wood, across the joists, I'd go over the OSB. Parallel to the joists, I'd probably add the ply. Other times I'd add any sort of extra layer might be under linoleum, to prevent the OSB texture from embossing, or tile, to remove some bounce.
Try to catch as many joists with the HW flooring nails as you can. I usually shoot for the joists, with another nail midway between, using 2" nails in a PortaNails air nailer.

An extra layer could actually add more creaks, or eliminate them, I've seen both results.
When you install the HW, be sure to drive home any popped subfloor nails before you lay the paper. You can also tighten up any creaking areas with a few drywall screws.
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"Tim Daneliuk" wrote

Assuming that it is indeed tongue and groove "OSB subflooring", properly installed and level, there should be no need to add an additional layer of plywood subfloor prior to installing nailed down HW flooring.
Most of the houses I build are HW floors throughout, and the above is a common practice on all second story HW floor installations.
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Contact the manufacturer of the wood floor that you intend to purchase and ask their advice.

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Folks, Leon is REALLY correct. I had selected a flooring to put down, only to find out from the manufacturer, that my choice would be disastrous. ( Radiant Heat floor) The point is the manufacturer is the one holding the guarantee on the flooring. They have a vested interest in telling you what will go wrong. BTW, most manufacturers have a web site you can post the question to them. Then you have the reply in writing !!
Paul

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On Fri, 19 Oct 2007 22:46:57 -0500, Tim Daneliuk

I've seen hardwood floor installers install wood flooring on top of OSB since OSB has been around. I've never seen them put anything on top of the OSB (for wood flooring) except felt or that funny looking foam paper. That doesn't make it right but that's all I've ever seen done.
Mike O.
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snipped-for-privacy@anywhere.net says...

plywood, swallowing a significant extra cost because I thought it was the right way to go. I have since seen more than a few installations using osb.
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