The dining room floor in my 175 year old house sags toward the center of the house. I have tried to jack up the 2 or 3 joists that are responsible, but they don't want to move much. There is no rot or structural damage, just settling I guess. I have the joists well-supported now by basement posts. The floor is the original hardwood, which will look great when it is sanded and refinished -- and leveled! But how? I was thinking I could cut the subfloor loose from the joists (run a reciprocating saw between the joist and subfloor to cut the nails) and then push up the floor from the basement off the joists until it's level and nail sister joists onto the joists to support the subfloor. Crazy?