Composite or wood decking in a rain climate

Composite and wood decks stand on the same pressure-treated frame, so the choice is only about the surface you walk on. Wood is cheaper to put down but wants a clean, stain and seal every few years, about $550-$1,250 per deck with materials (Portland-area market data, November 2026) . Composite never needs stain, yet in fir shade it still turns green. Here's how we build decks.

What is actually different between a composite deck and a wood deck?

Look under any deck and you'll see the same thing: posts, beams and joists cut from pressure-treated lumber. Composite doesn't change that. What changes is the decking itself, the stair treads, and often the railing.

The surfaces you'll be offered come in four kinds. Pressure-treated softwood is the budget board. Cedar is lighter, smells good and resists decay better than plain softwood. Capped composite is a core of wood fibre and plastic wrapped in a plastic shell. PVC boards are plastic all the way through.

In a long wet season, the part that gives out first is usually the frame, whichever board sits on top .

How does each board handle a long wet season and fir shade?

Wood takes on water wherever it can hold it: in the small cracks along the grain and at the ends where two boards meet. A deck that never gets full sun stays damp for days after a shower. Those spots go grey first, then soft.

Composite boards don't rot, but their surface isn't immune to the weather either. Algae, mildew and moss can grow on a shaded composite deck and make it slippery in winter. So it gets scrubbed or washed too, just without the stain afterward.

Both kinds share one problem. Needles and leaves pack into the gaps between boards, hold water, and keep the tops of the joists wet for weeks. Clearing the gaps a few times a year matters as much as the board you pick.

You see this on Cedar Mill's 1960s and 70s houses, where big firs drop needles on the deck all autumn. On West Slope's hillside lots a deck often stands high on long posts, and the frame underneath sits exposed to the weather and is awkward to reach for cleaning .

Why do the joists matter more than the boards?

A composite board can be sold with a warranty measured in decades. The treated joists it rests on carry no such promise, and in a wet climate they may give out first. That's why keeping water off the joist tops and keeping the board gaps open does more for a deck's life than the brand stamped on the decking .

The second point comes up when someone wants to put new composite boards on an old wood frame. Many composite boards need the joists closer together than an older wood deck was built with. Each board maker publishes a span chart in its install guide. If the existing spacing is wider than that chart allows, the job grows into added joists or a new frame, not just new boards.

This question shows up a lot in Bethany, where houses from the 1990s and 2000s still have their first decks, now 25 to 30 years old. Before anyone quotes boards, the frame needs a look from below. Our deck repair page covers what we check and fix under there .

What does each cost to build and to keep up?

For a new deck of about 300 square feet, Portland-area market data puts the build at $10,000-$30,000 with materials, typically $16,000 (November 2026). That works out to roughly $37-74 per square foot. The figure doesn't separate a wood surface from a composite one, so treat it as a range for any deck, not a price for either material . The full build arithmetic is in our guide to the cost to build a deck.

Upkeep is where the two materials part ways, and here the market figures are clearer.

Portland-area market ranges, November 2026; our own figures will go on the pricing page .

Some simple multiplication: three rounds of staining at those rates come to $1,650, $2,550 or $3,750 (low, typical, high). Five rounds come to $2,750, $4,250 or $6,250. How many rounds a deck needs depends on sun and shade, and Slava will give that number from his jobs .

A composite deck drops the staining line but not the washing. The washing row is labour only and is a ceiling for hiring it out; plenty of owners do it themselves with a scrub brush and a hose.

What is the downside of composite decking?

The price on day one is the obvious one. The rest:

• In shade it grows a green film and gets slick, which is the rain-country version of the complaint.
• A deep scratch or gouge can't be sanded out the way it can on wood.
• If one board gets damaged years later, you need the same brand and colour, and that colour may be discontinued.
• The boards are heavy, and most lines want their maker's own clips or screws.
• In direct summer sun they get hot underfoot. Under tall firs that matters less.

People who say they don't like a particular brand, Trex included, usually list some mix of these, and they apply to most composite lines .

How long does each kind of deck last?

We don't put a number of years on either material, because nobody can promise one for a given yard. What can be checked is the warranty. Trex, for example, says its baseline boards carry a 25-year limited residential warranty. A board warranty covers the board. It doesn't cover the joists, the posts or the workmanship.

Wood's life depends on the species, how much sun the deck gets and how often it's stained. The frame's life applies to both. Composite resists splinters and the cracking that wood gets, but chairs and grit dragged across it will still mark it .

Is composite decking easy to install?

It isn't hard, but it's fussy. Each line goes down with its own hidden clips or screws, and the gaps for expansion follow that maker's chart. Using another company's parts can void the board warranty on some brands. Cut ends usually get covered with a border board around the edge, called a picture frame. For a weekend builder, wood forgives more mistakes .

Which should you pick for your yard?

• Wood (treated or cedar) if the budget is tight, the deck gets sun and dries quickly, and you don't mind staining it.
• Composite if you won't stain, the deck sits in full sun, or the frame is new and built to the board maker's spacing.
• Think twice about composite on an old frame with wide joist spacing, or on a deck in deep fir shade, unless you'll wash it regularly.

If the rot has gone past the deck into the house wall behind it, that's a separate repair. See wood rot and siding repair.