Decking · Hot & humid

How long does a pressure-treated deck last in Mobile, AL?

THE SHORT ANSWER

In Mobile, moisture — not sun — is the main enemy of a pressure-treated deck. The city sees about 133 days with rain a year, mostly from February to February, and its Scheffer decay index of 110.2 is high (#2 of 25 cities we cover). Unsealed boards gray within the first year, then mildew and soft board ends become the real problem. Model estimate: 9–11 years unsealed, 12–15 years sealed on schedule.

Main threat

Moisture & decay

Climate profile

Hot & humid

Expected life (unsealed)

9–11 yrs

Fully gray by

Month 11

Best seal window

May – Sep

Sealed on schedule

12–15 yrs

Simulated pressure-treated deck in Mobile, AL after 10 years

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

MODEL SIMULATION

Mobile, AL · treated southern pine boards, south-facing, full sun, no sealant

Drag through time 0 — 20 years

Color lossSevere

Surface checkingSevere

Mildew / rotSevere

Fails first hereCut ends that lost their treatment, and joists

Storyboard

20 years in Mobile, unsealed

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

Pressure-treated deck in Mobile, year 1: Fully gray — **Year 1**Fully gray

Pressure-treated deck in Mobile, year 3: Mildew in shade, checks and some warping — **Year 3**Mildew in shade, checks and some warping

Pressure-treated deck in Mobile, year 5: Heavy mildew, checks and some warping — **Year 5**Heavy mildew, checks and some warping

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

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

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

Mobile’s wear fingerprint

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

Rainy days / yr133.4 · High

Avg humidity79.2% · High

Decay index110.2 · High

UV index (avg)1.5 · High

Freeze–thaw days15.1 · Typical

Days ≥ 90 °F73 · Typical

NOAA station MOBILE DWTN AP (USW00013838, 8.7 km away), 1991–2020 normals · humidity & UV: NASA POWER.

What fails first here

1Mildew & algaeA wet season from February to February and 79% average humidity keep shaded boards damp; dark spots start near walls, planters and gaps.
2Checks, splits and warpingStrong UV (rank #8 of 25) dries and shrinks the surface faster than the core, opening fine cracks.
3Rot at board ends & joistsThe real lifespan limiter in Mobile: decay index 110.2. Treatment protects the wood, but cut ends and drilled holes lose it — brush end-cut preservative on during building.
4GrayingCosmetic, and fast: our model has the surface fully silver by month 11. Not damage on its own, but it means the protective surface is gone.

Upkeep

Mobile 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

AprWash off mildew

MaySeal / stain

Jun

Jul

Aug

SepSeal / stain

Oct

Nov

Dec

Same city, other materials

How the alternatives age in Mobile

Cedar deck

Expected life here: 9–12 yrs · main threat: moisture and decay

See it age in Mobile →

Composite deck

Expected life here: 23–30 yrs · main threat: moisture and decay

See it age in Mobile →

Wood fence

Expected life here: 10–13 yrs · main threat: moisture and decay

See it age in Mobile →

Vinyl fence

Expected life here: 22–29 yrs · main threat: moisture and decay

See it age in Mobile →

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 Mobile, AL, new to year 20

Pressure-treated decks in similar climates

…and in very different ones

Las Vegas, NV

Phoenix, AZ

Denver, CO All 25 cities →

Questions Mobile owners ask

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

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; Mobile’s moisture and decay profile is why the local number differs.

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

May and September: 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 Mobile?

Our model gives an unsealed pressure-treated deck 9–11 years here and untreated cedar 9–12 years. Treated pine resists rot better than cedar in damp climates, but it checks, splits and warps more, so surface wear usually decides when boards get replaced.

Why does wood turn gray or black in Mobile?

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.