Subfloor over subfloor?

[Spanky8n]

Hello,
I am currently drywalling and have passed all of my inspections so far both offical and unoffical  . I have a 3/4 osb t&g subfloor and my neighbor suggested(during one of his unoffical inspections... )that I put down a 3/4 sanded plywood subfloor over this before I put down the carpet & hardwood. To be honest I have not given this much thought. Do I need to do this? I am building over a conditioned crawlspace if that matters. I plan on contracting out the finshed floors when I am close to finishing. What does everyone think?
Thanks in advance-  Dan

[MountainDon]

Is the existing osb in good shape? No water damaged raised edges or anything? Is the hardwood you mentioned real wood, plank style flooring?

If you were laying vinyl floor I could see overlaying the osb with 3/8" sanded plywood. I've done that myself. But I don't understand why you'd have to do that for carpet.

Ask some of the installers what they recommend.

[Spanky8n]

Hello-
Thanks for the quick response Don. The osb only got rained on 3 times and I used the shop vac to get any standing water off of it fairly fast so it is in good shape. There is some raised spots here and there but nothing too bad. Planning on using real wood plank style flooring.
Dan