How to Fix a Joist That Bows Downward

Age, damage and improper installation can cause a floor joist to sag, or bow down. This causes the joist to pull away from the floor, reducing the floors strength and causing squeaks to form in the house. Properly repairing a bowed floor joist will increase the strength of a sagging floor and eliminate squeaks. Using the correct method of strengthening a sagging floor will ensure the repaired joist will remain strong and level under the weight of a house.

Cement block
House jack
Tape measure
2 -by-6-inch board
Circular saw
4-foot level
Construction adhesive
Drop-in caulk gun
2-by-10-inch board
4 c-clamps
8d nails
Hammer

Instructions

- 1
  Place a cement block directly below the bowed joist, centered with the lowest point. Set a house jack on top of the block. Measure the distance between the top of the jack and the bottom of the joist.
- 2
  Cut a 2-by-6-inch board to the measured length with a circular saw. Set the board on top of the house jack. Pump the jack until pressure holds the board in place. Hold a 4-foot level on the bottom of the joist as you pump the handle of the house jack. Stop pumping the jack handle when the joist is level.
- 3
  Set an open tube of construction adhesive in a drop-in caulk gun. Apply a zigzag bead of adhesive to one side of the bowed joist. Place a 2-by-10-inch board against the glued side of the joist. Hold the joist in place by placing one c-clamp every 2 to 4 feet.
- 4
  Secure the sister joist to the joist that has bowed by hammering 3 8d nails in a line every 16 inches. Keep the top and bottom nails 1 inch from the top and bottom edge. Place the third nail 5 inches from the bottom edge of the joist.
- 5
  Remove the c-clamps from the two joists. Lower the house jack while holding the 2-by-6-inch board with one hand. Remove the board, house jack and cement block from the area.

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