Decking · Cool & damp

How a cedar deck ages in San Francisco, CA

THE SHORT ANSWER

San Francisco is easy on wood: a decay index of 26.7 means rot is slow, and there is almost no freezing weather. What remains is ordinary sun and weathering, so untreated boards mostly gray and develop fine surface checks over time. Model estimate: 17–22 years untreated, 23–30 years sealed on schedule.

Main threat

Sun & UV

Climate profile

Cool & damp

Expected life (untreated)

17–22 yrs

Fully gray by

Year 2

Best seal window

Jul – Aug

Sealed on schedule

23–30 yrs

Simulated cedar deck in San Francisco, CA after 10 years

Year 10Mildew in shade, deep checks

MODEL SIMULATION

San Francisco, CA · south-facing deck, full sun, no sealant

Drag through time 0 — 20 years

Color lossSevere

Surface checkingHigh

Mildew / rotModerate

Fails first hereSun-facing board ends and surface fibers

Storyboard

20 years in San Francisco, untreated

Cedar deck in San Francisco, install: Fresh boards — **Install**Fresh boards

Cedar deck in San Francisco, year 1: Silvering begins — **Year 1**Silvering begins

Cedar deck in San Francisco, year 3: Sun-bleached silver — **Year 3**Sun-bleached silver

Cedar deck in San Francisco, year 5: Surface checks — **Year 5**Surface checks

Cedar deck in San Francisco, year 10: Mildew in shade, deep checks — **Year 10**Mildew in shade, deep checks

Cedar deck in San Francisco, year 15: Decay starting at board ends, mildew in shade, deep checks — **Year 15**Decay starting at board ends, mildew in shade, deep checks

Cedar deck in San Francisco, year 20: Soft spots — probe for rot, mildew in shade, deep checks — **Year 20**Soft spots — probe for rot, mildew in shade, deep checks

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

1Mildew & algaeMostly a shady-corner issue here: 71 rainy days a year is moderate, but sun dries boards between storms.
2Rot at board ends & joistsSlow here (decay index 26.7), but ends and joists under planters still fail first.
3GrayingCosmetic, and fast: our model has the surface fully silver by year 2. Not damage on its own, but it means the protective surface is gone.
4Surface checkingMild here: limited UV and only 0 freeze–thaw days a year keep cracks shallow.

Upkeep

San Francisco maintenance calendar

Built from local normals: bar width is the share of days with rain; sealant needs 2–3 dry days between 50 and 88 °F.

Jan

Feb

MarInspect ends & fasteners

Apr

May

Jun

JulSeal / stain

AugSeal / stain

Sep

Oct

Nov

Dec

Same city, other materials

How the alternatives age in San Francisco

Composite deck

Expected life here: 24–31 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 →

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

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

Cedar 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 cedar deck last in San Francisco?

Our model puts it at 17–22 years untreated and 23–30 years if it is sealed every 2–3 years. The national typical range is 15–20 yrs; San Francisco’s sun & uv profile is why the local number differs.

When is the best time to seal a cedar deck in San Francisco?

July and August: the months with the fewest rainy days while average temperatures sit between 50 and 88 °F. Most sealants need 2–3 dry days to cure.

Is composite better than cedar in San Francisco?

It depends: composite won’t check or bleach, but it fades and gets hot in strong sun. Our model gives composite 24–31 years here versus 17–22 for untreated cedar.

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.