How do you fix a sagging second floor?

Measure the length of the damaged area by locating the floor joist. You can shorten one of your beams to be six inches longer than your measurement. Measure the length of the beam on the sagging beam. The second beam should be equal to the length of the first.Place the damaged joint of the floor and measure the length of the damaged area. Cut one of your 6-inch beams to a length of approximately 6 inches more than the size. Cut the length of the beam to the left of the decadeduus beams. Cut the second 6-inch beams to match the length of the beam.