Decking · Cool & damp

How long does a pressure-treated deck last 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 unsealed boards mostly gray and develop fine surface checks over time. Model estimate: 12–15 years unsealed, 16–21 years sealed on schedule.

Main threat

Sun & UV

Climate profile

Cool & damp

Expected life (unsealed)

12–15 yrs

Fully gray by

Year 2

Best seal window

Jul – Aug

Sealed on schedule

16–21 yrs

Simulated pressure-treated deck in San Francisco, CA after 10 years

Year 10Decay starting at board ends, mildew in shade, deep checks

MODEL SIMULATION

San Francisco, CA · treated southern pine boards, south-facing, full sun, no sealant

Drag through time 0 — 20 years

Color lossSevere

Surface checkingSevere

Mildew / rotModerate

Fails first hereBoard surfaces: checks, splits and cupping

Storyboard

20 years in San Francisco, unsealed

Pressure-treated deck in San Francisco, install: Fresh, green-tinted boards — **Install**Fresh, green-tinted boards

Pressure-treated deck in San Francisco, year 1: Silvering begins — **Year 1**Silvering begins

Pressure-treated deck in San Francisco, year 3: Checks and some warping — **Year 3**Checks and some warping

Pressure-treated deck in San Francisco, year 5: Checks and some warping — **Year 5**Checks and some warping

Pressure-treated deck in San Francisco, year 10: Decay starting at board ends, mildew in shade, deep checks — **Year 10**Decay starting at board ends, mildew in shade, deep checks

Pressure-treated deck in San Francisco, year 15: Soft spots — probe for rot, mildew in shade, deep checks — **Year 15**Soft spots — probe for rot, mildew in shade, deep checks

Pressure-treated 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

1Checks, splits and warpingMild here: limited UV and only 0 freeze–thaw days a year keep cracks shallow.
2Mildew & algaeMostly a shady-corner issue here: 71 rainy days a year is moderate, but sun dries boards between storms.
3Rot at board ends & joistsSlow here (decay index 26.7), but ends and joists under planters still fail first.
4GrayingCosmetic, 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.

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

Cedar deck

Expected life here: 17–22 yrs · main threat: sun and UV

See it age in San Francisco →

Composite deck

Expected life here: 24–31 yrs · main threat: sun and UV

See it age in San Francisco →

Wood fence

Expected life here: 15–20 yrs · main threat: sun and UV

See it age in San Francisco →

Vinyl fence

Expected life here: 24–31 yrs · main threat: sun and UV

See it age in San Francisco →

Pin-ready

Save it for when you build.

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

Save to Pinterest Download pin

Pinterest storyboard: pressure-treated deck in San Francisco, CA, new to year 20

Pressure-treated 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 pressure-treated deck last in San Francisco?

Our model puts it at 12–15 years unsealed and 16–21 years if it is sealed every 2–3 years. The national typical range is 10–15 yrs; San Francisco’s sun and UV profile is why the local number differs.

When is the best time to seal a pressure-treated 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.

Cedar or pressure-treated: which lasts longer in San Francisco?

Our model gives an unsealed pressure-treated deck 12–15 years here and untreated cedar 17–22 years. Where rot is slow, cedar’s stability wins: treated pine checks and warps faster in sun and frost.

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.