How to Raise a Floor Joist

You may notice that the second or third floors in your home are sagging or leaning. Finding the solution doesn't have to be expensive. Fortunately, you can raise the floor joists in the basement of your home by using a jack. This is a slow process, but you'll be able to raise your sagging floors with some effort.

Measure the section of sagging floor joists that you need to raise. Cut a 4-by-6-inch beam to this measurement.

Attach the 4-by-6-inch beam across the underside of the floor joists so it runs perpendicular to the joists. Use rafter ties and screws to hold the beam in place. This beam spreads the lifting force to the entire floor. Then place another beam of the same length on the floor directly under the first beam.

Place an adjustable jack under each side of the crossbeam to shore up the sagging floor and raise the floor evenly.

Use thin steel plates between the jacks and floor joists to avoid damaging the floor. If you're using a hydraulic jack, use a 1-inch steel plate to distribute the load between jacks. However, if you're using threaded adjustable jacks, the thin plates are included.

Lift the floor approximately 1/8 inch every day. Use a wrench to adjust the height of the jack. You don't want to lift the floor too fast and risk damaging the house.


Be sure to use adjustable jacks so you can raise the floors slowly. Ask a home improvement store representative whether a hydraulic jack or a threaded adjustable jack best suits your needs.

Things You'll Need

  • 4-by-6-inch board
  • Circular saw
  • Rafter ties
  • Screws
  • Drill with bit
  • 2 jacks
  • Metal plates
  • Wrench
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