Deck boards rotting or splintering
moderate 2–5 h
Tools: awl or screwdriver, circular saw, drill, pry bar, hammer, tape measure, square · Materials: pressure-treated or composite boards of the same width, stainless or coated deck screws, joist tape (self-adhesive flashing), deck stain or sealer
Steps
- Probe every board and, from underneath, every joist with an awl; soft wood that the point sinks into is rot, and grey splintered wood that stays hard is weathering.
- Check the joists and the ledger where the deck meets the house first: if they are soft, the boards are not the problem.
- Unscrew or pry out the rotten boards, cut new ones to length, and lay them bark-side up with a 3 mm (⅛-inch) gap for drainage.
- Before screwing down, stick joist tape over the top of each joist you exposed; water sitting on the joist tops is what rots the next set of boards.
- Fasten with two coated or stainless screws per joist, set just below the surface, and sand the edges.
- Once the new wood has weathered for a few weeks, clean and stain or seal the whole deck so the old and new boards age together.
Stop and call a pro if
- the joists, beams, posts or the ledger are soft or the fasteners at the ledger are rusted — the structure needs a carpenter
- the deck is more than 75 cm (30 inches) off the ground or the railing moves when pushed
- more than a third of the boards are rotten
Rules in the US: A deck more than 30 inches above grade is a permitted structure in most jurisdictions; ledger and railing repairs must meet current code.
What a pro does that you can't
A deck contractor replaces rotted joists and a failed ledger with proper flashing and hardware, checks the posts and footings, and rebuilds railings to code.
DIY cost: $40–150 in boards, screws and tape