DIY Joist Repair

Prep

• 1

  Inspect the joist to determine how severe the damage is. Look for cracks running all the way through the board. Place a long level along the bottom edge of the joist to determine how much, if any, the joist is sagging.

• 2

  Position a piece of two-by-four along the bottom edge of a joist that is sagging more than 1/2 inch. Position screw type post jacks, with four-by-fours cut to fit on top of the jacks, with their tops against the bottom of the two-by-four. Raise the jacks slowly until the joist is lifted back into position to remove any sag.

• 3

  Measure the damaged area and add 12 inches. Cut a piece of lumber the same width and thickness as the original joist, and 12 inches longer than the damaged section using a miter saw set to 90 degrees.

Repair

• 4

  Position the "cripple" you just cut centered on the damaged section, alongside the joist, sitting on the edge of the two-by-four on top of the jacks. Fit the cripple alongside a joist that has less than a 1/2-inch sag without the jacks.

• 5

  Drill through the cripple into the joist with a 1/4-inch bit, one hole every 6 inches, 2 inches deep. Drive a 2 1/2-inch lag bolt, 5/16 inch thick with a socket wrench until the head of the bolt is flush with the face of the cripple.

• 6

  Let the jacks back down to allow the cripple to take the weight of the joist. Remove the 2-by-4 brace and the two 4-by-4 columns underneath the joist to complete the project.