To repair a sloping floor, jack up the affected joists, and then install sister joists to support the original joists in the floor. Start by nailing a 4-by-6-inch wooden beam across the affected joints the lowest point of the slope. Make sure that the beam is long enough to reach all the affected joists. Since the beam is temporary, drive the nails at an angle via the side of the beam and into the joists.
Place another 4-by-6 inch wooden beam, directly beneath the beam nailed to the affected joists. On top of each end of the wooden beam, place a 1/4-inch steel plate. Place a 1-ton hydraulic jack on each of the plates, and then measure the distance between the hydraulic jack and the beam attached to the joists. Adjust the threaded adjustable ends of two Lalley columns to a length that allows for a secure placement of columns between the beam and hydraulic jacks.
Use the hydraulic jacks to raise the floor no more than 1/4-inch daily to keep the drywall from cracking. Continue this every day until the floor is level. Measure the length and width of the joists, and then cut sister joists of a similar length as that of the original joists.
Apply adhesive on one side of the board, and then attach the glued side of the board to the affected joists. Drill two evenly place ¼-inch pilot holes, and insert lag bolts into each hole. Tighten the lag bolts using a socket and ratchet. Lower the hydraulic jacks, and remove the support beams and Lalley columns.