How to Replace Rotted Deck Boards

Rotted deck boards announce themselves in stages: first a soft spot under your boot, then spongey wood that holds a screwdriver's impression, finally a plank that's genuinely unsafe to walk on. Catching rot early—when it's localized to one or two boards—means you can pull them without dismantling the deck structure. The real work isn't the removal; it's finding boards that match your existing deck in species, width, and profile, then understanding why that particular board rotted in the first place. A single rotten board usually points to a drainage or ventilation problem. Fix the board and you fix the symptom. Find the cause and you prevent the next one. The job itself is straightforward: remove fasteners, pry out the old board, insert the new one, and fasten it down. You'll need basic tools and a replacement board that matches your deck. Most homeowners finish one or two boards in an afternoon. The work is methodical, not difficult, but it demands care during removal so you don't damage the joists or adjacent planks.

1. Inspect and locate all fasteners. Walk the damaged board and mark every nail, screw, or fastener holding it down. Use a stud finder or simply probe with a screwdriver to feel where fasteners sit. Most deck boards are fastened every 16 inches along each joist—typically two fasteners per joist. Mark each one with chalk or a marker so you don't miss any when prying.
2. Remove fasteners with a cat's paw or pry bar. Slide the cat's paw under each fastener head and lever it out. Work from one end of the board toward the other. If nails are corroded or stubborn, tap the pry bar handle downward with a hammer to get leverage underneath. For screws, use a screwdriver in reverse or a screw extractor if the head is stripped. Set fasteners aside—you'll replace them with new corrosion-resistant ones.
3. Pry the board free without damaging joists. Once fasteners are out, position a pry bar perpendicular to the board's length and work along the joist lines. Push downward steadily; rotted wood usually pops free easily. If the board resists, check for missed fasteners. Once it lifts, slide it out lengthwise. If the board is severely rotted, it may break during removal—that's fine; pull out pieces carefully and inspect the joist for rot damage.
4. Inspect joists for rot and clean the deck surface. With the board gone, examine the joist tops where the old board sat. Probe the joist with a screwdriver; it should be hard and resistant. If the joist is soft or spongy, mark it and plan for joist repair (a more involved job). Clean the joist tops with a wire brush to remove algae, debris, and any remaining rot fragments. A clean surface ensures good contact with the new board.
5. Position and fit the new board. Slide the new board into place, matching the existing board's width and alignment. The board should sit flush against joists with even gaps on either side (typically 1/8 inch) for seasonal expansion. If it binds or sits high, check that no fasteners remain below the surface and that joists are level. Don't force it—a properly sized board should settle into place with light hand pressure.
6. Fasten the new board with corrosion-resistant fasteners. Drive fasteners in the same pattern as the original board—typically two per joist, spaced evenly. Use stainless steel or hot-dipped galvanized fasteners (never bare steel or standard nails, which will rust). For nails, use ring-shank or spiral nails, which grip better than smooth shanks. For screws, use deck screws long enough to penetrate at least 1.5 inches into the joist. Set fasteners flush but not recessed; over-driving splits the wood and weakens the connection.
7. Identify and address the cause of rot. Before you finish, think about why this board rotted. Check drainage underneath the deck—water pooling below accelerates rot. Look for low spots or debris blocking water runoff. Inspect the deck's trim and flashing; rotted boards often sit where water collects at deck edges or where the deck meets the house. Poor ventilation under the deck traps moisture; clearing debris and ensuring airflow helps. If rot recurs, a more comprehensive drainage or ventilation fix will be needed.
8. Finish and seal the new board. New pressure-treated boards need time to dry before sealing (typically 3-6 months). However, you can apply wood stain or sealer immediately to the joist tops that are now exposed. If your deck is sealed, match the existing color and finish on the new board once it's dry. Regular sealing every 2-3 years dramatically extends deck life and prevents future rot.