Cost: $100-$300 for a 200-square-foot deck, more for a larger deck.
How often: every one to three years, depending on the amount of traffic, moss and mold.
When: any time in sunny weather.
Power washing gets rid of stains, algae, mold, mildew and moss. Algae and mold can make your deck slippery and dangerous, says Justin Lee of JL Power Washing in Williamsburg, Va. Sealing your deck after it is cleaned helps prevent water damage. Wood soaks up rain like a sponge, expands and then shrinks, Lee says. Sealing makes the water bead up and roll off. And let's not forget -- your deck will look nicer, too.
If you let it go, your deck will warp, nails will pop out and the deck won't last as long.
Potential savings: $4,000 to $20,000 or more to replace your deck, depending on size.
Bottom line: "A properly cleaned and sealed wood deck can last 20 to 30 years," Lee says.