The second floor floors were squeaky and uneven. The floorboards (less than 1/2 inch thick) were nailed directly to the beams. The beams are being reinforced, the tops of said beams being shimmed to level, and one inch plywood is forming the support for 2/3-inch floorboards. But the process involves leaving the floors open while reinforcing and leveling. The carpenters walk along the beams quite blithely.