Is it possible to install a hardwood floor (2 1/4×3/4) oak strips in the same direction as the floor joists over diagonal planking sub-floor in a 50 year old house? The existing oak floor needs patching because of the original closets and wall that I removed and I would like the floor to match the room adjacent to it so I am willing to rip up the old floor and install a new one in the opposite direction. Room size about 15’x 12′.
No, in you case it is NOT OK to install the floor parallel to the joists. If you step on one of those diagonal boards, you will see how much it flexes. This is because it spans as much as 25-30 ” corner to corner. If you want to install the floor this way you will have to add a layer of 1/2″ plywood nailed to the joists on top of the board subfloor. And even then you have add 1 1/2″ wood screws in between the joists to keep all these layers from squeaking later on.
It is best to install the new floor crossing the joists. And re-nail most of those old subfloor planks in any case, they will cause no end of squeaks later if you don’t.
As always your Most humble servant, Joseph, the Wood Floor Doctor.