How to Replace Rotted Deck Boards

Rotted deck boards are a structural and safety problem that won't heal themselves—they'll only spread. The wood has lost its integrity, and the deck is now a liability. The good news is that replacing them is straightforward work that any homeowner with basic tools can handle. You'll need to identify which boards have failed, understand why they failed (usually poor drainage or deferred maintenance), and swap them out with new pressure-treated lumber before the rot compromises the joists underneath. Done right, your repaired deck will last another 15–20 years.

1. Identify and mark all rotted boards. Walk the deck surface and probe boards with a screwdriver or awl. Rotted wood will be soft and the tool will sink in easily. Mark affected boards with chalk or a pencil. Check the underside too—rot often starts on the bottom where water sits. Pay attention to boards near edges, valleys, or gutters where water drains poorly.
2. Remove fasteners from the rotted board. Use a reciprocating saw with a metal-cutting blade to cut through screws, or carefully pry up fastener heads with a flat pry bar and pull them out one by one. Work from one end of the board toward the other. If fasteners are seized, spray them with penetrating oil 15 minutes before attempting removal. Don't rush this—a stuck fastener can split adjacent boards when forced.
3. Pry out the old board. Once all fasteners are removed, slide a flat pry bar under the board at each joist and carefully lift. The board should release cleanly. If it's stuck (because of old paint or swelling), use a reciprocating saw to make relief cuts along the joist tops, then pry again. Remove any old fasteners, nails, or debris left behind on the joists.
4. Inspect joists for rot. Before installing the new board, check the joists it sits on. Probe with your awl. If the joist is soft or has soft spots, that rot must be addressed—usually by replacing the joist or having a contractor reinforce it. If joists are sound, move forward. Clean away any debris, old fastener holes, or lichen on the joist tops.
5. Cut the replacement board to length. Measure the opening where the old board came out. Cut your new pressure-treated board 1/4 inch shorter than the span between the joists—this allows for thermal expansion and contraction. Use a circular saw or miter saw. Sand any splinters or rough edges with 80-grit sandpaper.
6. Install the new board. Set the new board into place, ensuring it sits flat and flush with adjacent boards. Drive stainless steel deck screws (or hot-dipped galvanized) at each joist, using 2.5-inch or 3-inch fasteners depending on joist thickness. Space screws 12 inches apart along each joist. Countersink screw heads slightly below the surface to prevent tripping and water pooling.
7. Seal the new board. Once all fasteners are in place, apply a deck stain or sealer to the new board. Match the color and product type of the surrounding deck. This protects the fresh wood and prevents premature rot. Allow the sealer to dry per manufacturer instructions (usually 24–48 hours) before allowing foot traffic.