OSB/plywood on top of planks or remove planks

[isaacrapelje]

I live in the Washington state and am remodeling a 1950's house that has 1/2 oatmeal particle board on top of 3/4 x 12 wide fir subflooring that is spaced about 1 inch apart. I want to install 3/4 hardwood and know the particle board needs to be removed but my question is do I rip up the 3/4 x 12 plank subfloor and install 3/4 osb/plywood or leave the planks and install the osb plywood on top of the planks and screw into the floor joists? The floor joists are on 17.5 inch centers... yes 17.5 centers, unusual I know. Should I use 1/2 osb, 3/4 osb or plywood? I know plywood is better but it is also more expensive. What size plywood? I have no experience with this so any help is greatly appreciated.

 

[Dan]

Leave the plank subfloor. Your walls are sitting on top of it.