Now that I know the best solution I’ll take up the OSB and put down 3/4″ plywood fastened with 3″ spiral nails. Thank you for your prompt response.
Based on what I’ve read from others who put hardwood on any thickness OSB or had a new house with hardwood floors over OSB, you are just asking for trouble. One person (on this site or another one) moved into a custom built house with hardwood floors placed over OSB. A few months later (not even years) the floor was squeaking.
One last question, I discovered that there are different grades of plywood. Should I go with BC or is CDX okay?
As far as the plywood, BC grade Douglas Fir would be best, but I’m sure that a good brand of spruce CDX would be just fine, that’s what I just used for a floor repair in my own house just last week.
Oh, and be sure to use a good urethane construction adhesive on all the joists as you are applying the new plywood. And put in the nails every 8″. The hardwood will need to be nailed also with the special flooring cleats, read my new article on this available in the search box at the top of this web page.