Even rot-resistant species and treated woods deteriorate some day. Here’s how to protect a couple key areas and keep your deck looking good for a long time.
Wood rots through a combination of soaking up water and drying out. So one of the ways to prevent rot is to make sure the wood doesn’t soak up too much water in the first place.
When a tree is growing, it sucks water up through tubes extending to the roots. These tubes are exposed at the end grain of finished boards, and continue to wick in water forever. So treat the ends of boards with an approved treatment/fungicide before installing, and follow up every couple years. Cap posts with plastic caps or with wood, sealing wooden caps with a good stain or finish top and bottom.
Try and use complete lengths for deckboards whenever possible, but if you need to butt two boards together, bevel-cut them so they meet neatly on the surface, but aren’t touching elsewhere. This allows water to flow through instead of getting trapped and sucked into the wood. You may need to double up a couple of joists to allow for the gap.
Whenever possible, allow air circulation between boards or between boards and another surface. For example, deck builders often nail three 2x6s together to create beams. That large contact area between the boards can trap water, so it’s better to install small spacers between each board at 18″ intervals. Make these out of 1/2″ pressure treated plywood; just cut squares and place them slightly on angle to help them shed water. Do the same thing when you’re attaching a ledger board to a concrete house foundation. (If you’re attaching to a frame structure, install S-shaped flashing over the ledger board to prevent water from getting between the board and the structure.)