Composite vs Cedar Decking in the Pacific Northwest
Most composite-versus-cedar advice is written for places where the problem is sun. In Puget Sound the problem is water that does not leave: eight months of drizzle, yards shaded by firs, decks built low over damp ground. That changes how each material ages, which is why the right answer here depends less on budget than on where the deck sits and who will look after it. This guide explains what happens to each material in our climate; the Composite vs Cedar tool runs the costs for your deck.
What cedar is good at
Western red cedar is a native wood with natural oils that resist decay and insects. It is light, stable for a wood, smells good and feels warm underfoot. Freshly finished, nothing looks better on a Northwest house. It is easy to cut, repair and refinish, and a damaged board can be replaced and blended in an afternoon.
Its decay resistance comes from extractives in the heartwood. Those extractives leach out over years of wetting and drying, which is why a cedar deck's life depends so much on how often it gets wet and how fast it dries.
What happens to cedar in our climate
On a sunny, raised deck, cedar wets in the rain and dries within hours. It greys on the surface if left unfinished, checks slightly, and lasts fifteen to twenty-five years with periodic oiling.
On a low deck in shade, the story changes. The underside of the boards stays damp through the winter. Algae and moss colonize the surface and the gaps fill with needles and soil, which hold more water. Boards cup as the top and bottom dry at different rates. Fastener holes soften. Within eight to twelve years, boards on the shaded side of such a deck are often soft enough to replace.
Film-forming stains make it worse in this climate: they trap moisture under the film and peel. Penetrating oils that soak in and leave the surface breathable perform far better.
What composite is good at
Capped composite boards are a core of wood fiber and plastic wrapped in a polymer shell. The shell resists water, stains and fading. The boards do not rot, do not need staining and do not splinter. In damp shade, they hold up where cedar would not, and maintenance is reduced to washing.
Capped PVC boards go further: no wood fiber at all, lighter, cooler in sun and more stain resistant, at a higher price.
What happens to composite in our climate
Composite does not absorb water, but water still sits on it and on whatever collects on it. In deep shade, a mildew or algae film can form on the surface, especially on darker, textured boards. It washes off with a deck cleaner and a soft brush and does not damage the board, but it does come back each season in the same places.
In full sun, dark composite gets hot. On most Eastside decks, trees and the house shade it for part of the day, and lighter colors reduce the issue.
Composite boards expand and contract with temperature more than wood does. Correct end gaps and fastening, following the manufacturer's tables, prevent buckling and gaps opening too wide. Installation outside the manufacturer's specification usually voids the warranty.
The framing is the same either way
Under both materials sits pressure-treated framing, and that framing decides how long the deck really lasts. The details that matter in a wet climate:
- Ground-contact-rated lumber for posts, beams and joists.
- Butyl joist tape on the top of every joist and beam, so water from the gaps does not sit in the wood.
- A flashed ledger spaced off the house so the rim joist behind it stays dry.
- Footings on undisturbed soil below the frost line, with posts on standoff bases.
- Airflow under the deck: the higher the deck and the more open its sides, the faster everything dries.
A composite deck on untaped framing with an unflashed ledger will outlive its boards' warranty in appearance and fail underneath. A cedar deck on well-built framing in the right spot can last decades.
How to read your own yard
Stand where the deck will go and ask:
- How many hours of direct sun does it get in summer? In winter?
- Are there trees overhead dropping needles, leaves or cones?
- How high will the deck be? Will air move under it?
- Does the ground there stay soft and wet after rain?
- Will someone oil cedar every two to three years?
Mostly sun, raised, open and maintained points to cedar. Mostly shade, low, under trees, or no one to maintain it points to composite. Anything in between is a judgment call where cost and look decide.
Combinations that work
- Composite decking with a cedar cap rail: wood where hands touch, composite where feet and rain land.
- Cedar decking on a sunny upper level and composite on a shaded lower level.
- Composite decking with cedar fascia and a cedar pergola above: the look of wood without the board maintenance.
- PVC around hot tubs and along the shaded edge, composite elsewhere.
What each material costs over time
Cedar costs less to build, roughly 20% to 35% less than mid-line composite on the same deck. Over five years it usually stays cheaper. Over fifteen, refinishing and board replacement often bring the totals together, sooner in shade. The Composite vs Cedar tool calculates both for your size, exposure and ownership horizon.
A builder's bottom line
We build both, and we recommend against cedar more often than for it on low, shaded Eastside decks, because we see those decks again when they fail. On a sunny, raised deck with an owner who likes caring for wood, cedar is still the deck we would build for ourselves.
Want a second opinion on your yard? We will look at the sun and the shade with you.