How to Replace a Rotted Deck Board (4 Steps + What to Buy)

TL;DR: A rotted deck board feels spongy underfoot, pulls nails easily, and shows dark staining or soft wood when you press a screwdriver into it. Cut out the damaged section with a circular saw set to the board thickness, check the joist underneath for rot, sister a 2×8 alongside if the joist is compromised, and fasten a new pressure-treated board with two 3" deck screws per joist. The repair costs $15–$40 in lumber and takes 60–90 minutes if the joists are sound.

_Last reviewed: July 2026 · 6 min read_

A single rotted deck board is a red flag: water has breached the finish, the wood has stayed wet, and fungi have moved in. Left alone, rot spreads to the joists below, turning a $30 board swap into a $3,000 structural rebuild. Catching soft boards early—during a walk-through or when you notice a nail popping—saves money and keeps the deck safe.

Okoniq Property Hub logs the replacement date, board count, and lumber grade so you can track which sections age fastest and plan the next round of sealing or staining.

How do you know a deck board is rotted and needs replacement?

Press a flathead screwdriver into the suspect board at a 45-degree angle. Healthy pressure-treated lumber resists; rotted wood yields like cheese, and the screwdriver sinks a quarter-inch or more with light pressure. You'll also see dark brown or black staining, feel a spongy give when you step on the board, or pull a nail out with almost no resistance. If the board was installed before 2003 and has never been resealed, odds are high that capillary action has wicked water into the end grain and started decay from the inside out.

Check the joist directly underneath by reaching between boards or removing a second board temporarily. If the joist surface is soft, flakes apart, or shows the same dark staining, you're looking at structural rot that requires sistering—fastening a new joist alongside the damaged one. Ignoring joist rot voids most homeowner's insurance claims for deck collapse and can drop resale value by 5–10% when an inspector flags it. Document the rot with photos before you start; ceiling water stain diagnosis principles apply here—trace the source, don't just patch the symptom.

What tools and materials do you need to replace one board?

Buy one pressure-treated 2×6 or 5/4×6 deck board (match your existing dimensions) from a big-box store; expect $12–$25 for an 8-foot length depending on grade. Finger-joint boards are fine for replacements under 6 feet; avoid them for longer spans. You'll also need a circular saw, a pry bar, a drill, 3-inch exterior deck screws (two per joist), and a speed square to mark cut lines. If the joist is rotted, add a 2×8 pressure-treated board (the standard joist size) and four 3-inch lag screws with washers.

Rent a reciprocating saw ($25/day) if the rotted board sits tight against the house or under a railing post where a circular saw can't reach. Wear safety glasses and a dust mask—pressure-treated lumber dust contains copper azole preservatives that irritate lungs and eyes. Keep a shop vacuum nearby; sawdust on a damp deck turns into a slip hazard fast.

Set your circular saw blade depth to exactly the board thickness (typically 1 inch for 5/4 decking, 1.5 inches for 2×6) so you don't score the joist underneath. Mark the cut line 1 inch past the last visible rot on each end—cutting into healthy wood ensures you remove all the decay. If you're replacing multiple boards in one session, stage the lumber so each piece acclimates to outdoor humidity for 48 hours; fresh kiln-dried boards can cup or twist as they release moisture.

How do you remove the rotted board without damaging surrounding boards?

Start by removing all fasteners in the rotted section. Use a pry bar or cat's paw to pull nails; for screws, back them out with a drill. If a fastener won't budge, cut the board on both sides of it and pry the middle section out—the fastener will come with it. Once the board is free, lift one end and slide it out perpendicular to the joists. If it's wedged under a post or rail, cut it flush with a reciprocating saw or oscillating multi-tool.

Inspect the gap. If the joists are dry, firm, and free of black staining, you're clear to install the new board. If you see soft spots, sister a new joist: cut a 2×8 the same length as the span between support beams, apply construction adhesive to one face, press it against the damaged joist, and drive four 3-inch lag screws (two near each end) through both joists into the beam. The sistered joist carries the load; the old one stays in place for lateral stability. This is a one-hour add-on that prevents callbacks and liabilities.

Vacuum out sawdust and debris from the joist tops before you set the new board. Water pools in sawdust, accelerating the next round of rot. If the gap between boards was originally 1/8 inch (the standard for drainage), use a 16d nail as a spacer when you position the replacement—slide it between the new board and its neighbor at each joist, then fasten.

How do you fasten the new board so it lasts another 15 years?

Lay the new board across the joists, aligning the ends with adjacent boards for a clean sight line. Predrill pilot holes—1/8 inch smaller than the screw shank—two per joist, about 3/4 inch from each edge. Skipping pilots splits the board ends, especially in cold weather when lumber is brittle. Drive 3-inch coated deck screws (GRK or Spax are the go-to brands) until the heads sit flush; countersinking them 1/16 inch below the surface prevents toe-stub but invites water pooling if you go deeper.

Space fasteners 16 inches on center if your joists run that spacing, 12 inches if they're on 12-inch centers. Never use drywall screws or untreated fasteners—they rust out in 3–5 years and leave the board loose. If you're replacing boards near a railing post, add a third screw in the middle of the board where it crosses the post's blocking for extra pull-out resistance.

Seal the cut ends of the new board with a brush-on wood preservative (Copper Green or equivalent) within 24 hours of installation. Factory-treated lumber is protected on all six faces, but saw cuts expose raw wood that wicks water like a sponge. One coat on each cut end adds 5 years to the board's life. Plan to seal or stain the entire deck within 12 months—the new board will stand out until the finish evens out. Basement waterproofing logic applies here: stop water before it enters, don't just manage it after.

When should you call a contractor instead of doing it yourself?

Call a pro if more than 20% of the deck boards show rot, if the ledger board (where the deck attaches to the house) is pulling away or spongy, or if you see diagonal cracks in the support posts. These are structural red flags that require a building permit, engineering review, and often a tear-down to replace the frame. Ledger failure caused 3,200 deck collapses in the US between 2010 and 2022, most during gatherings of 8+ people—if you suspect ledger rot, stay off the deck and get three bids from licensed contractors.

Also call help if the deck is above 8 feet off the ground, if you've never used a circular saw, or if the joists run at an angle (a herringbone or picture-frame pattern). Angled cuts and complex layouts double the time and error rate for first-timers. A handyman charges $150–$300 to replace 2–4 boards; a full board-replacement job (same joists, all new decking) runs $8–$15 per square foot installed. Get the work inspected if your municipality requires it—most do for structural repairs, and skipping inspection can void insurance and complicate resale.

FAQ

How long does a pressure-treated deck board last before it rots?

Properly sealed pressure-treated boards last 15–25 years in most climates. Boards installed before 2003 (CCA-treated) often hit 30+ years, but post-2003 ACQ and CA-B treatments are less rot-resistant and require resealing every 3–5 years. Ground contact accelerates decay—boards within 6 inches of soil or mulch typically rot in 8–12 years even with treatment.

Can you sister a joist without removing the deck boards above it?

Yes, if you have access from below (a walk-out basement or crawl space under the deck). Slide the new joist into place, apply adhesive, and drive lag screws up through the bottom. If you can't reach from below, you'll need to remove at least two boards on either side of the damaged joist to get a drill in at the right angle.

Do you need to match the exact board width when replacing one deck board?

Match the width within 1/8 inch—a 5.5-inch board can replace a 5.625-inch board without a visible gap, but a 5-inch board in a 6-inch field will leave a noticeable stripe. Most lumber yards carry 5/4×6 (actual 1"×5.5") and 2×6 (1.5"×5.5") as standard stock. If your deck uses an oddball dimension, rip a wider board to fit on a table saw rather than leaving a gap.

Should you seal the new board before or after installation?

Seal cut ends before installation, seal the top surface after. Brush preservative on any saw cuts within 24 hours—once the board is fastened, you won't be able to reach the underside of the ends easily. Wait 48 hours after installation to stain or seal the top; fresh screws need time to set, and foot traffic during curing can smear the finish.

This is educational information, not professional construction advice. Consult a licensed contractor if you're unsure about structural integrity, and check local building codes—many jurisdictions require permits for deck repairs exceeding 50 square feet or any work involving ledger boards.