How to Repair Joist Rot

Joists, or lengths of timber sheathed within walls and floors, support a home’s structure. Joists suffer damage for many reasons, including water saturation and termites, which weaken the integrity of the wood and result in rotting. Repairing rotted joists can be done through sistering, a technique that involves bracing the rotted joist piece with additional lengths of wood. Sistering is a two-man job, but requires only basic do-it-yourself skills to perform.

Treated lumber
Tape measure
Circular saw
16d nails
Hammer

Instructions

- 1
  Measure the length and width of the rotted joist. Copy the side and angle measurements and any angles on the rotten joists onto two treated boards.
- 2
  Cut the boards with a circular saw. Hold the two boards against the rotted joist and check the measurements to ensure they match.
- 3
  Enlist the help of an assistant to hold each rotted board among the damaged joists in its original position. Have him hold one board on the outside of one of the joists. Drive 16d framing nails though the new treated board and into the damaged joist with your hammer to attach them. Space the nails 12 inches apart along the length of the boards.
- 4
  Position the second cut board on the opposite side of the rotted joist. Repeat the technique outlined in step 3 to attach the second board to the joist.

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