Decking · Cool & damp
How a composite deck ages in Portland, OR
In Portland, composite won’t rot, but the damp still matters: about 157 rainy days and 82% average humidity mean shaded boards grow surface mildew unless they are washed once or twice a year. Model estimate: 25–32 years of service.
Storyboard
20 years in Portland, washed yearly
Portland’s wear fingerprint
Each bar is scaled to the highest of the 25 cities we cover; the black line marks the median.
NOAA station PORTLAND INTL AP (USW00024229, 10.1 km away), 1991–2020 normals · humidity & UV: NASA POWER.
What fails first here
- 1Surface mildewComposite does not rot, but pollen and dirt on shaded boards feed mildew — common in Portland’s damp climate. A wash in spring and fall prevents it.
- 2Early color fadeCapped boards lighten in the first 2–3 years, then level off. Stronger here than average: UV rank #23 of 25.
- 3Gaps & fastenersBoards expand and contract with temperature; check hidden clips and end gaps every few years.
- 4Heat underfootOnly about 15 days a year top 90 °F, so surface heat is rarely an issue.
Upkeep
Portland maintenance calendar
Built from local normals: bar width is the share of days with rain; composite mainly needs washing.
Same city, other materials
How the alternatives age in Portland
Pin-ready
Save it for when you build.
The 20-year storyboard as a tall pin, linking back to this page.
Composite decks in similar climates
Seattle, WA
New York, NY
Chicago, IL
Boston, MA
Buffalo, NY…and in very different ones
Phoenix, AZ
Las Vegas, NV
Albuquerque, NMQuestions Portland owners ask
How long does a composite deck last in Portland?
Our model puts a capped composite deck at 25–32 years in Portland, close to typical warranty terms. The boards outlast the look: expect some early fading and surface mildew in shade.
How often should you clean a composite deck in Portland?
Twice a year — in spring and fall. Portland’s damp climate makes mildew on shaded boards the most common complaint.
Is composite worth it over cedar in Portland?
In Portland our model gives untreated cedar 15–19 years and composite 25–32. In a damp climate that gap is mostly rot you avoid.
Why does wood turn gray or black in Portland?
Graying is UV plus weathering of the surface; black spots are usually mildew or algae feeding on that grayed layer in damp weather, not rot. A cleaner and a dry-season seal stop it.
Model simulation, not a guarantee: south-facing, full sun, no shade or ground-contact surprises. How it works.