I may be opening Pandora's box with this question, but here it is.

Can a 3/4" solid wood floor be considered "properly" installed if it is over a 1/2" plywood subfloor?

My professional advice is to avoid installing hardwood over 1/2" at all costs. If you must install over 1/2", at least try to take the following precautions.

Technically, according to NWFA guidelines, you should have a minimum of 5/8" plywood for proper installation of hardwood flooring. Do not add "luan" to make up the difference; this will not help. You should add a proper 1/4" CDX or OSB plywood. You will notice that 1/2" plywood directly over the joists seems somewhat weak, or have a give to it, especially if the house is much older.

If your framing is over 16" on center, such as 19.2" on center, I do not recommend installing hardwood on 1/2" plywood. NWFA also requires you add additional layer of 1/2" plywood run perpendicular to the existing plywood if your framing is over 16" on center.

Adding additional screws throughout the entire sub-floor will be necessary to be sure to strengthen and secure the 1/2" plywood prior to installing the hardwood. If the space you are installing is over a Garage or large area that is not heated or insulated during winter, you could also have problems down the road. Be sure to nail the hardwood with a good staple nailer every 6"-8" to be sure to secure the flooring properly to the sub-floor. Use a heavy duty liquid nail or PL for your areas close to the walls and doorways.

Best of luck!

Dustin
EverWood Flooring LLC.

Dustin nailed that so to speak.

Yeah it all depends on joist spacing. Min 5/8, and then on up ad the joist spacing gets wider.

I used to have the Installation guidelines on my pc but deleted it cus it was taking up too much space. Beside you can pull it up with any search engine rather easily if you look. The newest one ya gots to pay for.

Here's one I found rather quickly; http://www.oldewoodltd.com/getting-star ... uidelines/ Go down to part IV Panels

Thanks guys!

I thought as much. I frequently run into houses that have existing oak floors over 1/2" ply, and the homeowners want an adjoining carpeted section with particle board underlayment removed and hardwood installed.

Typically, I remove the particle board and then screw the exiting 1/2" plywood down to secure it to the joists and then install new hardwood over the top. I don't insist on additional ply because of their desire to have a smooth transition from the existing to the new.