How to Brace Floors


A sagging and bouncing floor can happen in any home that does not run cross bracing between the joists. A home places a lot of weight on the floor joists, and over time the joists can start to sag. Installing sister joists and cross bracing between the joists will help you brace your floors and eliminate floor sag and bouncing when you walk across a room.

Things You'll Need

  • Miter saw
  • 1-inch thick boards
  • 4-by-6-inch boards
  • Two hydraulic jacks
  • Nails
  • Hammer
  • Pry bar
  • Measure the length and width of your joists with a tape measure. Cut 2 boards that match the length with a miter saw for each joist that you want to brace. Use 1-inch thick boards at a minimum and make sure the boards are the same width as your joists.

  • Cut a 4-by-6-inch beam to length with the miter saw. Make it long enough to span across the joists that are sagging. Nail the beam to the bottom of the joists to hold it in place.

  • Place a hydraulic jack on the ground under each end of the beam you secured to the joists and measure the distance between the bottom of the joists and the top of the beams. Cut additional 4-by-6-inch beams to match those lengths.

  • Place the beams between the joists and the hydraulic jacks. Slowly jack up the joists with the hydraulic jack. Do not lift the joists more than ¼-inch per day. Lifting more could cause the drywall or plaster in your walls to crack.

  • Slide the boards you cut in step two beside the joists. You will have one on each side of the joist. Secure the sister joists to the joist with 3-inch nails. Position evenly spaced rows approximately 1-inch apart.

  • Lower the hydraulic jacks and remove the 4-by-6-boards. You must pry the board you nailed to the bottom of the joists loose with a pry bar.

  • Measure the distance between joists with a tape measure and cut pieces of wood to match those distances. Use the same wood that you used for the sister joists. Cut one board for every 36-inches of joist.

  • Wedge the boards between the joists every 36-inches and tap them upward with a hammer so they rest against the bottom of the floorboards. Secure the braces to the joists by driving nails through the sides of the boards at an angle. This is called a "toe nail."

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