Decking · Cool & damp

How a composite deck ages in San Francisco, CA

THE SHORT ANSWER

In San Francisco, sun is the main stress on a composite deck: UV ranks #17 of 25 cities we cover. Capped boards lighten noticeably in the first two years, then stabilize; dark colors also get hot underfoot. Model estimate: 24–31 years of service.

Main threat

Sun & UV

Climate profile

Cool & damp

Expected life

24–31 yrs

Wash

Spring & fall

Rainy days / yr

Days ≥ 90 °F

Simulated composite deck in San Francisco, CA after 10 years

Year 10Color has lightened, then stabilizes

MODEL SIMULATION

San Francisco, CA · capped composite boards, south-facing, full sun

Drag through time 0 — 20 years

Color lossModerate

Surface wearModerate

Mildew / rotModerate

Fails first hereColor on full-sun boards

Storyboard

20 years in San Francisco, washed yearly

Composite deck in San Francisco, install: Install day — **Install**Install day

Composite deck in San Francisco, year 1: Slight early fade — **Year 1**Slight early fade

Composite deck in San Francisco, year 3: Slight early fade — **Year 3**Slight early fade

Composite deck in San Francisco, year 5: Color has lightened, then stabilizes — **Year 5**Color has lightened, then stabilizes

Composite deck in San Francisco, year 10: Color has lightened, then stabilizes — **Year 10**Color has lightened, then stabilizes

Composite deck in San Francisco, year 15: Color has lightened, then stabilizes — **Year 15**Color has lightened, then stabilizes

Composite deck in San Francisco, year 20: Color has lightened, then stabilizes — **Year 20**Color has lightened, then stabilizes

San Francisco’s wear fingerprint

Each bar is scaled to the highest of the 25 cities we cover; the black line marks the median.

Rainy days / yr71.2 · Low

Avg humidity77% · Typical

Decay index26.7 · Low

UV index (avg)1.2 · Low

Freeze–thaw days0 · Low

Days ≥ 90 °F3.3 · Low

NOAA station SAN FRANCISCO DWTN (USW00023272, 0.6 km away), 1991–2020 normals · humidity & UV: NASA POWER.

What fails first here

1Early color fadeCapped boards lighten in the first 2–3 years, then level off. Stronger here than average: UV rank #17 of 25.
2Surface mildewComposite does not rot, but pollen and dirt on shaded boards feed mildew. A wash in spring and fall prevents it.
3Heat underfootOnly about 3 days a year top 90 °F, so surface heat is rarely an issue.
4Gaps & fastenersBoards expand and contract with temperature; check hidden clips and end gaps every few years.

Upkeep

San Francisco maintenance calendar

Built from local normals: bar width is the share of days with rain; composite mainly needs washing.

Jan

Feb

MarWash & check for mildew

Apr

May

Jun

Jul

Aug

Sep

OctWash, clear gaps

Nov

Dec

Same city, other materials

How the alternatives age in San Francisco

Cedar deck

Expected life here: 17–22 yrs · main threat: sun & uv

See it age in San Francisco →

Wood fence

Expected life here: 15–20 yrs · main threat: sun & uv

See it age in San Francisco →

Pin-ready

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The 20-year storyboard as a tall pin, linking back to this page.

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Pinterest storyboard: composite deck in San Francisco, CA, new to year 20

Composite decks in similar climates

…and in very different ones

Phoenix, AZ

Las Vegas, NV

Denver, CO All 25 cities →

Questions San Francisco owners ask

How long does a composite deck last in San Francisco?

Our model puts a capped composite deck at 24–31 years in San Francisco, 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 San Francisco?

Twice a year — in spring and fall. Dirt and pollen are the main thing to wash off.

Is composite worth it over cedar in San Francisco?

In San Francisco our model gives untreated cedar 17–22 years and composite 24–31. The gap is smaller where rot is slow, so upkeep preference decides.

Why does wood turn white or pale in San Francisco?

UV breaks down lignin at the surface; rain and wind wash the loose fibers away, leaving a bleached, silvery layer. It is cosmetic until checks open up.

Model simulation, not a guarantee: south-facing, full sun, no shade or ground-contact surprises. How it works.