How Long Does a Deck Last in Oregon? Repair vs Rebuild

A deck in western Oregon usually lasts somewhere between 10 and 30 years. InterNACHI's life-expectancy chart puts deck planks at about 15 years, structural wood at 10 to 30 years, and composite decking at 8 to 25 years. Where yours lands in that range depends mostly on how wet it stays, how it was built, and how it has been looked after. The chart says it plainly: life expectancy "varies with usage, weather, installation, maintenance, and quality of materials."

Why rain shortens a wood deck's life

Wood doesn't rot just because it gets rained on. It rots when it stays wet. The USDA Forest Products Laboratory's Wood Handbook explains that serious decay only happens when wood's moisture content is above the fiber saturation point, about 30%, and that dried wood only gets there when it's hit by rain or condensation or sits in contact with wet ground.

That's the problem with a deck around Sandy, Boring, or up toward Mt. Hood. Long wet seasons, shade from tall firs, and moss all keep the wood damp for months at a time. The parts that suffer first are the ones that never dry out: board ends, the tops of joists under the boards, posts near the ground, and the ledger board where the deck meets the house.

The Wood Handbook's advice for building against that is to use preservative-treated wood or the heartwood of a decay-resistant species for parts that stay above ground, and pressure-treated wood rated for ground contact anywhere wood touches soil.

What to check every year

The North American Deck and Railing Association (NADRA) publishes a short checklist homeowners can run themselves. The main points:

• Probe for soft wood. Push an ice pick or screwdriver into the wood. If it sinks a quarter to half an inch easily, or the wood is soft and spongy, decay may be present. Check board ends, joists, posts, and the ledger.
• Look at the ledger. NADRA calls the ledger board, where the deck attaches to the house, "a common source of deck failure." It should not be fastened with only nails, and it should have flashing to steer water away from the house.
• Check fasteners and connectors. A rusted or corroded fastener can damage the wood around it. Replace it rather than leave it.
• Test for movement. The deck and stairs should look even, without sagging, and should not sway or move when you push on them.
• Shake the railings. They should be firmly held in place.
• Watch for mildew and worn finish. If mildew is present or the coating has worn away, clean it and put a new water-repellent coating on.

Moss and slippery boards

Oregon State University Extension notes that moist, shady patios are ideal for moss, that moss on decks can be slippery, and that pressure washing is effective for cleaning decks. Moss also holds water against the wood, which is exactly what you don't want. Clear it when it shows up, and trim back anything that keeps the deck in constant shade if you can.

Upkeep that adds years

The Forest Products Laboratory's guide to deck finishes says that without proper maintenance, wood decks develop checks, cracks, raised grain, and mildew, which raises the risk of decay. Its guidance on clear water-repellent preservative finishes is that they last about a year on exposed deck surfaces, so plan on recoating more often than you might expect. Pigmented finishes generally last longer than clear ones.

Composite and PVC boards follow their maker's care instructions instead, but the framing under them is usually wood that ages like any other wood deck, so the yearly checks above still apply.

Repair or rebuild?

There's no single rule, but the condition of the structure usually decides it:

• Surface wear, sound framing. Weathered or cracked boards on solid joists, posts, and ledger can often be fixed by replacing boards, cleaning, and refinishing.
• Some soft spots in the framing. A few decayed joist ends or a bad post can sometimes be replaced or reinforced. This depends on how far the rot has spread.
• A failing ledger, widespread rot, or a deck that sways. When the parts holding the deck up are compromised, a rebuild is usually the safer and more sensible path, since new boards on old framing won't last.

If you're replacing the whole deck, check the Clackamas County deck permit rules first. A raised deck more than 30 inches above grade needs a permit.

Composite and PVC lifespans

Manufacturer warranties give a sense of how long the boards themselves are expected to hold up. Trex lists limited residential warranties from 25 to 50 years: 25 years on its Enhance line, 35 years on Select, and 50 years on its top lines. TimberTech says its Advanced PVC decking carries a lifetime limited product warranty and a 50-year fade and stain warranty. These are limited warranties, so read what each one actually covers, and remember the framing underneath is usually still wood.

Not sure what you're looking at?

If you've done the screwdriver test and you're not sure whether you're looking at a weekend repair or a new deck, have someone look at the framing and ledger in person. Anthony builds decks and covered porches around Sandy and the east Portland metro, in Trex, TimberTech, or cedar, whatever the homeowner picks.