Q imported from our old site, Face Lift Floors: Is it good to put a new oak floor over an old one, or is it better to tear up the old one and put new plywood boards and then install the new oak floor?
A: It is far better, and never advisable to install a new hardwood floor over an existing one. I would never recommend such a thing. It is always better to remove the old hardwood floor and screw down at least 3/8 plywood into the joists, on top of the original subfloor, which in an old home will be pine boards, often installed diagonally across the joists, but sometimes at right angles.
One doesn’t really “wear out” hardwood flooring. Usually, due to neglect or poor maintenance, the floor ends up being sanded beyond its wear surface and the edges of the boards begin to break off. In this case, if the existing floor is an oak strip, 3/8 thick X 1 3/4 wide, in a room 15 feet across, you will have over 100 rows of such boards installed. That is over 100 boards that probably have movement to them and are no longer stable.
A good part of having a “solid” wood floor is determined by what your new floor is sitting on. If the subfloor is quite unleveled and has movement in it, then your new floor that you spent so much money on will also move.
Original / moved link https://faceliftfloors.com/q-and-a/over.php