Due to cracks, holes and hills and valleys in our flooring, my wife and I are wanting to replace the old tongue & groove oak flooring in our home with new tongue & groove oak flooring. We discovered that the entire house has no subfloor, including under the outside perimeter walls, and all are sitting on the old tongue and groove flooring. Our delimma is: Can we remove all the t&g flooring right to the outter walls, leaving that small portion under the wall, leveling by glueing and screwing 2x6 planks to each floor joist, and then adding a 3/4" plywood subfloor. OR, leaving the old floor in place, placing some kind of thin pliable material in layers to bring the valleys up to the highest points in the floor which are the perimeter and embedded floor jacks, and add subfloor and new t&g flooring. Any other ideas would be appreciated as well.