How to Repair a Floor Truss

Floor trusses, or joists, can start to sag or bow over time, particularly in older homes. When this happens, the floor can also start to sag, resulting in an unlevel floor. Completely replacing a joist can be complicated and time consuming; however, repairing one can often be accomplished by sistering the joist alongside the problem joist. The result is a reinforced joist, making the floor stronger and level.

Lumber
Tape measure
Circular saw
Common nails
Hammer
Hydraulic jack
Construction adhesive
Caulk gun
16d Nails

Instructions

- 1
  Measure the existing truss using a tape measure.
- 2
  Cut your new sister truss, or joist, using a circular saw. Your sister joist must be the exact same length and width as the existing joist. In most cases, you will install more than one to strengthen the floor. Install sister joists at least 3 feet from where the floor is sagging.
- 3
  Remove all electrical wires and plumbing pipes. When this is not feasible, you can make notches in the sister joists for the wires or plumbing to pass through; however, it reduces the strength of the joist.
- 4
  Nail two, two-by-fours together to create a beam. Tack the beam under the joist where it is sagging. A small nail will work for this as the beam will be removed eventually.
- 5
  Maneuver a hydraulic jack into place under the beam. Set the post on the jack directly under the beam and jack the beam up 1/8-inch per day until it is level with the other joists.
- 6
  Apply a liberal amount of construction adhesive to the sister joist. Attach the sister joist to the existing joist by nailing in 16d common nails every 16 inches.
- 7
  Remove the hydraulic jack once all the sister joists have been installed.

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