I want to install 4” walnut in a 12 x 11 room. The floor joists are 16” on center but due to a bay window, 50% of the joists run one way, the other run 90 degrees to the bay window. The builder used ¾” wafer (chip) plywood. The main floors in the house have 2 ¼” oak flooring and seem solid after 17 years of use. When I install the 4” walnut, will I have to add another layer of plywood to the ¾” already down? Guess I am concerned with a plank almost twice as wide, will the 4” floor be as sound as a 2 ¼” floor? I plan on running a chalk line to make sure a staple hits as many joists as I can and probably nail every 8” or so. Also, the resin paper is in the plans as well. Finally, the floor has a 2-foot crawl space under it.

Thanks for the advice!

Your staples will not hit the joists. The angle of the fastener comes into play.

Also, you want to choose a fastener, that does not blow through the subfloor. As soon as it blows through the bottom, you loose a lot of holding power. This was discussed in some detail at the Wood Flooring Summit I attended in August. They called it withdraw, tension.

Thanks for the help. I was concerned about the wider plank across a 3/4" sub-floor so I scrap the staple idea and nail away.