Decking · Cold, hard freeze–thaw

How long does a pressure-treated deck last in Denver, CO?

THE SHORT ANSWER

In Denver, freeze–thaw is the defining stress: about 135 days a year cross the freezing point (#1 of 25 cities we cover). Water in checks and fastener holes freezes and expands, so splits widen and fasteners loosen faster than sun or rot alone would explain. Model estimate: 9–11 years unsealed, 12–15 years sealed on schedule.

Main threat

Freeze–thaw

Climate profile

Cold, hard freeze–thaw

Expected life (unsealed)

9–11 yrs

Fully gray by

Year 2

Best seal window

Sep – Oct

Sealed on schedule

12–15 yrs

Simulated pressure-treated deck in Denver, CO after 10 years

Year 10Soft spots — probe for rot, mildew in shade, deep checks

MODEL SIMULATION

Denver, CO · treated southern pine boards, south-facing, full sun, no sealant

Drag through time 0 — 20 years

Color lossSevere

Surface checkingSevere

Mildew / rotSevere

Fails first hereSplits around fasteners and board ends

Storyboard

20 years in Denver, unsealed

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

Pressure-treated deck in Denver, year 1: Sun-bleached silver — **Year 1**Sun-bleached silver

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

Pressure-treated deck in Denver, year 5: Deep checks — **Year 5**Deep checks

Pressure-treated deck in Denver, year 10: Soft spots — probe for rot, mildew in shade, deep checks — **Year 10**Soft spots — probe for rot, mildew in shade, deep checks

Pressure-treated deck in Denver, 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 Denver, year 20: Soft spots — probe for rot, mildew in shade, deep checks — **Year 20**Soft spots — probe for rot, mildew in shade, deep checks

Denver’s wear fingerprint

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

Rainy days / yr84.4 · Low

Avg humidity49.9% · Low

Decay index34.2 · Low

UV index (avg)1.3 · Typical

Freeze–thaw days135.1 · High

Days ≥ 90 °F42.1 · Typical

NOAA station DENVER-STAPLETON (USW00023062, 10.6 km away), 1991–2020 normals · humidity & UV: NASA POWER.

What fails first here

1Checks, splits and warpingAbout 135 freeze–thaw days a year work water into cracks and pry them open.
2Sun bleaching & raised grainSurface fibers break down under strong sun and wash away, leaving a pale, fuzzy texture.
3Mildew & algaeMostly a shady-corner issue here: 84 rainy days a year is moderate, but sun dries boards between storms.
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

Denver 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

Mar

AprInspect ends & fasteners

May

Jun

Jul

Aug

SepSeal / stain

OctSeal / stain

Nov

Dec

Same city, other materials

How the alternatives age in Denver

Cedar deck

Expected life here: 14–19 yrs · main threat: freeze–thaw

See it age in Denver →

Composite deck

Expected life here: 23–30 yrs · main threat: sun and UV

See it age in Denver →

Wood fence

Expected life here: 13–17 yrs · main threat: freeze–thaw

See it age in Denver →

Vinyl fence

Expected life here: 20–26 yrs · main threat: freeze–thaw

See it age in Denver →

Pin-ready

Save it for when you build.

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

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Pinterest storyboard: pressure-treated deck in Denver, CO, new to year 20

Pressure-treated decks in similar climates

…and in very different ones

Miami, FL

New Orleans, LA

Tampa, FL All 25 cities →

Questions Denver owners ask

How long does a pressure-treated deck last in Denver?

Our model puts it at 9–11 years unsealed and 12–15 years if it is sealed every 2–3 years. The national typical range is 10–15 yrs; Denver’s freeze–thaw profile is why the local number differs.

When is the best time to seal a pressure-treated deck in Denver?

September and October: 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 Denver?

Our model gives an unsealed pressure-treated deck 9–11 years here and untreated cedar 14–19 years. Where rot is slow, cedar’s stability wins: treated pine checks and warps faster in sun and frost.

Why does wood turn gray or black in Denver?

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.