Replacing a few rotten or cracked deck boards extends a deck's life and restores safety. Before you start, check whether the problem is just the surface boards or something more serious underneath.
Check the structure first
Probe soft boards and the joists beneath them with a screwdriver. If the joists or the ledger are rotten or the framing is failing, that's a structural issue beyond a board swap — address it before re-decking, since the structure carries the load.
Remove and replace
Unscrew or pry up the damaged boards, taking care not to damage good neighbours. Cut replacement boards to length, matching the thickness and ideally the wood type. Let new pressure-treated boards acclimate, and leave a small gap between boards for drainage and expansion.
Fasten and finish
Fasten with exterior-rated screws into the joists, pre-drilling near board ends to prevent splitting. New boards often look different from weathered ones until they age; cleaning and re-staining or sealing the whole deck blends them and protects the wood.