Wood Rot & Houston Humidity

Your trim does not need a leak to rot here. It only needs to stay damp.

Last updated 2026-09-16

Wood rot is a fungus. It needs wood, oxygen and moisture, and it becomes active once the wood moisture content rises above roughly twenty percent. In a climate with our humidity, rainfall and long warm season, exterior wood that is not properly sealed sits close to that threshold for months at a time.

Which is why Houston houses rot in places that would be fine almost anywhere else, and why homeowners here find it much earlier than they expect to.

Where it starts, in order

1. Fascia, behind and below the gutters. Nearly always first, because an overflowing gutter runs water down the back of the board it is screwed to.
2. Soffit, at corners and where it meets the wall.
3. Window sills and the trim below them, where water sits on a horizontal surface.
4. Door frames and thresholds on unprotected elevations.
5. Porch column bases, where the column meets concrete. Concrete wicks moisture and holds it against end grain, which is the most absorbent part of the timber.
6. Garage door jambs, in the bottom six inches, from driveway splash.
7. Deck and porch framing, at joist ends and ledger boards.
8. Siding, at the bottom course and around penetrations.

The two kinds

Dry rot is badly named. The fungus spreads at relatively low moisture and can travel well beyond the original wet spot, which is why damage usually extends past what you can see. It leaves wood dry, cracked into cubes and crumbling.

Wet rot stays where the water is. The wood is soft, dark and spongy, and the damage is more contained.

Either way, the repair rule is the same: cut back past the visible damage to sound wood.

The test

Push a screwdriver into the wood where you can safely reach it. Sound wood resists. If it goes in, the board is gone and paint will not save it. Do this on the fascia behind a gutter joint, at the base of a porch column, and under a window sill, which is where you are most likely to find it first.

Why filler is not a repair

The causes worth fixing this week

• Gutters that overflow, which is the single biggest contributor
• Downspouts discharging against the foundation or next to a column
• Sprinkler heads spraying the siding or the trim
• Soil or mulch piled above the bottom of the siding
• Shrubs grown tight against the wall, holding moisture in
• Any horizontal wooden surface without a slope or a drip detail
• Paint that has started to chalk or dull, because that is the seal going

When you replace, replace properly

The most common reason a rot repair rots again is unprimed end grain. Cut ends absorb water many times faster than face grain, and a board installed without priming every face including the back and the cuts is starting its own countdown. In locations that keep failing, fiber cement or PVC is usually worth the cost difference. How we do it.

Common Questions

Can rotted wood be repaired instead of replaced?

Small contained damage on a piece worth saving can be consolidated with epoxy. Anything structural, anything soft through its thickness, and anything with active fungus needs cutting out back to sound wood.

Is wood rot the same as termite damage?

No, though they look similar from a distance and often appear together, because damp wood attracts termites. If insects are involved, that needs a pest inspection separately.

Should I replace rotted trim with PVC?

In locations that keep failing, it is usually worth it because PVC will never rot. On visible trim with a distinctive profile, matching the original material often matters more, particularly in a historic district.

Read Next

• Wood Rot Repair
• Fascia & Soffit Repair
• Exterior Painting
• When to Replace Your Gutters