Replace Deck Joists in 6 Steps

Lead Image
  • 6 hours
  • Beginner
  • 50-200
What You'll Need
Framing hammer
Measuring tape
Galvanized #8 nails
Galvanized #16 nails
Circular saw
Joist hangers
Nail puller
Power drill w/ Phillips bit
Eye Protection

It is sometimes necessary to replace old deck joists that have become time-worn or damaged due to exposure to the elements. Decks that endure wide-ranging seasonal temperature extremes, as well as large amounts of precipitation, will eventually become susceptible to weathering and decay that even pressure-treated lumber cannot prevent. The joists are a major component of the framework and rotting joists can affect the structural integrity of the deck. If replacing one or more joists, you will want to do so without rebuilding the entire deck. This article will explain how to go about replacing deck joists in 6 easy steps.

Obtain the Replacement Joists

Select new joists that are equal in nominal dimensions (width and thickness) to the existing adjacent joists. Use the straightest boards available with little or no bow or twist. Cut the new joist to length with a circular saw; use a measuring square to make a square cut.

Determine the Best Way to Gain Access to the Joist

If possible, you will want to avoid dismantling much of the decking to gain access to the joist or joists to be replaced. If there is sufficient room, you may be able to remove the joist from below. Remove the fasteners and joist hangers from the joist and remove the joist. Do so without leaving any visible scarring on members that are to remain, such as the band joists or decking. Maneuver the new joist into position. Use a measuring tape to make sure that it is 16 inches on center from the adjacent joists. If necessary, use a hammer to knock it into a vertical upright position. Secure the joist by replacing all fasteners and hangers.

Remove the Decking

If there is insufficient room to replace the joist from below, you will have to remove the decking to access the joist from above. Decking typically comes as 5/4 x 6-inch boards that run perpendicular to the joists. Using a nail puller or a power drill set in reverse with a Phillips bit, remove only enough decking to expose the joists to be removed. Take care not to damage the decking so that it can be re-installed. Remove the decking in full lengths; do not cut back or shorten the boards. Decking is installed in a regular pattern so that the joints of alternating courses are aligned.

Remove the Damaged Joist (or Joists)

Remove the fasteners from the joist hangers and any that might be attached to a crossbeam. You can leave the joist hangers in place if they are undamaged. Remove the damaged joist.

Install the New Joist (or Joists)

Drop the new joist into the hangers with the crown (if there is one) pointing up. Secure the new joist with fasteners as before. If the joist is supported by a crossbeam, toe-nail through the joist into the beam.

Replace the Decking

Replace the decking in the same order as it was removed. Place the nails or screws into the existing holes - do not make new ones. Set the nails or screws at a depth slightly below the surface.