Rotted deck boards: how to tell if it's three boards or the whole deck
By Jeff Rabkin, JustFix Wood · Published September 28, 2026
Most calls I get start the same way: "I think my deck is shot." Most of the time it isn't. Rot tends to start in a few predictable places, and if you catch it there, the fix is a few boards and some hardware.
Where rot starts
Wood rots when it stays wet. On a deck, water sits longest in a few spots:
- Board ends and butt joints, where end grain soaks up water.
- Boards under planters, grills and doormats.
- Along the house, where the deck meets the siding.
- The tops of joists, right under the gaps between boards.
- Stair treads and the bottoms of stair stringers near the ground.
The screwdriver test
Take a flat screwdriver and push the tip into the wood at those spots. Sound wood resists and splinters in long fibers. Rotted wood lets the tip sink in easily and breaks off in short, crumbly pieces.
Do the same from underneath if you can get there: the tops and sides of the joists, and the post bottoms. Boards are cheap to replace. Joists and posts are where a repair gets bigger.
What the results usually mean
- Soft spots on a handful of boards, framing solid: replace the boards. This is the most common outcome.
- Soft tops on a few joists: the joists can often be reinforced or partly replaced while the boards are up.
- Soft framing across most of the deck, or rot at the ledger where it attaches to the house: that's when replacement becomes a real conversation. I'll tell you if I think you're there.
Slowing it down
Keep the gaps between boards clear of leaves and debris, move planters and mats around, and keep the surface sealed. Water that drains and dries doesn't cause rot.
Not sure what you're looking at? Send three photos: the soft spot, a wider shot, and one from underneath if you can.
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