Repair Deck Stairs

Deck stairs fail in predictable patterns. The treads crack first, usually along the grain where feet wear them down. Then the stringers rot where they meet the ground, starting at the bottom and working upward through the end grain. Finally, the connections loosen — bolts rust, screws pull free, and what was once solid starts to shift underfoot. You notice it as a wobble, then a creak, then a genuine hazard. The good news is that deck stair repair is modular work. You replace what's failed and leave what's sound, and if you match your materials to what's already there, the repair disappears into the structure. Most repairs involve removing one or two treads and addressing the stringer beneath. Sometimes you're just refastening loose boards. Other times you're sistering a new stringer alongside a compromised one, or replacing a bottom section that's rotted through. The critical skill is knowing when to repair and when to rebuild entirely. If more than half your stringers are soft or if the ledger connection at the deck is failing, you're past the repair threshold. But for localized damage — a split tread, a rotted stringer end, a pulled fastener — the fix is straightforward and holds for years if done with the right materials and methods.

1. Remove damaged treads and inspect structure. Pull out the screws or pry up the nails holding the damaged treads. Use a cat's paw or flat bar to avoid splintering adjacent boards. Once the treads are off, inspect every stringer for soft spots by pressing a screwdriver into the wood. Pay special attention to the bottom six inches and anywhere water pools. Mark any soft areas with chalk.
2. Cut out rotted stringer sections. For bottom rot, measure up from the ground to solid wood, usually six to twelve inches. Mark a square cut line across the stringer and cut with a circular saw, finishing the corner with a handsaw. For mid-stringer rot, cut out the entire damaged section. If more than a third of the stringer length is compromised, plan to sister a full-length stringer alongside instead of patching.
3. Install stringer repair or sister board. For bottom repairs, cut a new pressure-treated section to fit the gap, treat all cut ends with wood preservative, and bolt it to the existing stringer with three-eighths-inch galvanized carriage bolts. Drill pilot holes to prevent splitting. For full-length sistering, cut a new stringer to match the existing one and bolt it on every sixteen inches. Use a construction adhesive rated for exterior use between the boards.
4. Treat and seal all repair areas. Brush a copper-based wood preservative onto all fresh cuts, bolt holes, and repair joints. Let it soak for twenty minutes, then apply a second coat. This step prevents new rot from starting at the repair boundaries. If you're reusing existing bolt holes, flood them with preservative before inserting hardware.
5. Cut and fit new treads. Measure the tread width at both ends to account for any stringer irregularity. Cut pressure-treated two-by-twelves to length, rounding the front corners with a half-inch radius to prevent splintering. Sand the cut edges smooth. Position each tread with a quarter-inch overhang past the riser and a slight gap between boards for drainage.
6. Fasten treads with exterior-grade fasteners. Use three-inch galvanized deck screws or stainless screws, two per stringer contact point. Drill pilot holes slightly smaller than the screw shank to prevent splitting while maintaining holding power. Countersink screws just below the surface but not so deep that you weaken the tread. Avoid placing fasteners within two inches of board edges.
7. Reinforce stringer-to-deck connection. Check the bolts or lag screws connecting the top of the stringers to the deck rim joist. Tighten any loose hardware. If bolts spin freely, drill new holes two inches offset from the originals and install fresh three-eighths-inch galvanized bolts with washers on both sides. Add a galvanized angle bracket on each stringer for extra support.
8. Apply finish and install footer protection. Stain or seal the repaired sections to match the existing deck finish. For bottom stringer ends that touch the ground, set them on concrete pier blocks or composite shims to lift them a half-inch off soil. This simple step doubles the life of the repair by preventing ground moisture from wicking into the end grain.