Design & DIY

How to check your deck for rot

Man installing new deck boards. Photo by ronstik/

Is rot setting in on your deck boards? Replacing the lumber you walk on is usually an easy repair. You can even upgrade wood to low-maintenance composite lumber if you’re tired of refinishing your deck. But a new deck surface won’t last long unless you check and repair the substructure at the same time.

Remove a few old boards from the edge of the deck to be sure that the existing substructure will be safe and reliable if you reuse it. If you used deck screws, you may be able to unscrew them, but chances are debris and corrosion will frustrate your efforts. Instead, use a reciprocating saw with a hacksaw blade to slice through screws or nails at the joint line between deck boards and the underlying frame. It’s a lot easier than smashing and bashing, and it will leave you with decent scrap lumber you can use for those odd projects around the cottage. 

How does the underlying wood frame look?

Poke the joists with a screwdriver to test for strength, especially along their top edges. Is the wood firm or punky? With the floor frame partially open and visible, are there any other areas of rot? Don’t trust your eyes, but poke here and there to make sure all is solid. Sometimes thoroughly rotten wood can look surprisingly good superficially—until your screwdriver sinks in. The ends of joists, beams, and posts are most likely to develop rot because water wicks into end grain in these parts more than other places. Also, pay particular attention to any parts of the deck frame with large areas of moisture-trapping wood-to-wood contact. 

Small, isolated areas of rot no larger than a toonie are usually okay, but when rot sets in, it’s typically over a large enough area that you’ll need to replace some frame parts. Luckily, once the deck boards are removed, it’s not difficult to install some new joists. Now the deck is ready for new boards on top.

This article was originally published in the May 2022 issue of  Cottage Life magazine.

How to prevent rot and adjust joists. 

Don’t have a deck to repair? Get some inspiration for your next build. 

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