I need to replace the hardwood floors on the second floor of an old home. A challenge is that the existing floors are nailed directly to the floor joists, with the walls resting on top of the finish floor. There is no subfloor. I know this is a relatively common situation in older homes, but I am wondering how much of a problem this is going to cause me if I try to replace the floors. For walls running perpendicular to the floor joists, it seems like removing the hardwood up to the baseboards will be fine, since the flooring underneath the walls will be left intact and continue holding up the walls. I already know that each 3/4 inch T/G hardwood slat is nailed to every joist with 2.5 inch common nails, so the flooring is very secure.
For walls running parallel to the floor joists, however, I am going to run into issues, especially if the wall lands in between the joists. Once I cut the flooring, there will be nothing holding up the wall anymore. My thought was to cut the floor out in small sections and install cross-blocking as I go to keep the walls supported. I am wondering if this seems reasonable or if I will end up getting into trouble here. The existing floors are in really bad shape, so leaving them be is not a good option.