How do I Repair the Sagging Floors on an Old Two-Story House?


Before beginning any repairs, first determine what has caused the floor to sag in the first place. If the sagging is due to rotten wood, this must be fixed before attempting any other repairs. If the sagging is due to an old and insufficient footing, a new footing should be installed. Jacking up beams before repairs are made can cause one floor to compress into another, or lead to other, more severe structural problems. Start your repairs from the bottom and work up to each floor. Many sagging floors are due to framing members that cannot support their load. In such cases, additional framing is the solution.

Things You'll Need

  • Adjustable metal column
  • 6-inch-by-6-inch wood post
  • Hydraulic jack
  • Lag bolts
  • 16d sinkers
  • Construction glue (optional)
  • Three 2-by-12 boards

Adding a Support Column to a Sagging Beam

  • Lay three 2-by-12 blocks about 16 inches long on the floor below for the hydraulic jack.

  • Cut a 6-by-6 post to fit between the jack and the crossbeam.

  • Jack up the post slowly. If you must significantly raise the beam, in some cases, it is good to spread the jacking over a few days. Watch closely what is happening to the rooms above the jacking to see how it is affecting millwork and walls. Jacking may cause walls to crack and gaps to form in moldings.

  • Place the adjustable column in place under the beam and turn the adjustable foot until it presses up against the beam. Drill pilot holes a little smaller than the lag bolt and install two 3/8-inch lag bolts at the top.

  • Lower the jack and remove the wooden post.

Doubling up Floor Joists

  • Move wires or loosen plumbing brackets with a flat bar and a hammer that can be moved.

  • Cut floor joists that are as wide as the existing floor joists. Cut them as long as possible so they will sit on the same support members as the existing ones. In some cases, you will not be able to cut them to sit on each supporting member. Even so, the new joists will add support and help prevent further sagging.

  • Slide the joists into place and nail them to the existing joists with 16d sinkers. Nail the joists with three or four nails placed vertically every 16 inches on center. Add construction glue for additional support.

Tips & Warnings

  • A more permanent fix to adding an adjustable post is to also install a footing. Doubling up floor joists is not always possible due to plumbing fixtures or electrical wiring. If structurally sound, add a cross beam under the current joists. This works in basements where clearance is not an issue, but not so well in upper floors. If the sagging is extensive, through bolts are a better option than nailing two joists together.

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  • Photo Credit old house image by Tom Oliveira from
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