In a climate that rains eight months a year, exteriors don't fail all at once — they fail at one unsealed joint, quietly, for three winters. By the time paint bubbles, the damage is usually behind the board.
Why our climate is hard on siding
Dry rot is a fungus, not a drying defect. It needs wood, oxygen, and sustained moisture. SW Washington supplies the moisture for most of the year, so anything that lets water sit — a failed caulk joint, missing kick-out flashing, a downspout dumping against a wall, siding too close to grade — becomes a rot site instead of drying out between storms.
The five places to check first
- Below window corners — the classic failure point when flashing was skipped
- Bottom courses and the water table — splash-back and grade contact
- Trim ends and butt joints — end grain drinks water once caulk opens
- Deck and railing ledger connections — where fasteners penetrate the wall
- Under gutters and behind downspouts — overflow runs down the siding all winter
The screwdriver test settles most arguments. Firm pressure into painted trim: if the tip sinks a quarter inch with no resistance, you have rot, not just weathered paint.
Patch vs. open the wall
| Patch is reasonable when… | Open the wall when… |
|---|---|
| Rot is confined to trim or one or two boards | Sheathing behind the siding is soft or stained |
| Sheathing behind reads dry on a meter | Rot shows in several spots on the same elevation |
| The water source is obvious and correctable | You can't identify where the water is entering |
| Framing is sound at the perimeter of the cut | Framing or a sill plate is affected |
What a proper repair includes
- Remove all affected material back to sound wood — not to the edge of the stain
- Find and correct the water path: flashing, kick-outs, gutters, grade clearance
- Verify sheathing and framing are dry before anything closes up
- Repair or replace sheathing, then integrate weather-resistive barrier correctly with flashing laps
- Install matched siding and trim with proper end-grain sealing and fastener placement
- Prime all cut ends, then finish paint — not paint over bare cuts
Our Vancouver siding repair project in the gallery shows this sequence on a real wall, including what was found behind the boards.
Prevention that actually pays
- Keep siding at least six inches above grade and clear of soil and bark dust
- Clean gutters twice a year — fall and late winter here, not just fall
- Re-caulk trim joints and penetrations before they open, roughly every few years
- Trim vegetation back so walls get airflow and sun
- Walk the exterior each spring and press-test the five spots above
Frequently asked questions
What causes dry rot in Pacific Northwest homes?
A fungus that digests wood once moisture content stays above roughly 20 percent. In SW Washington, months of steady rain plus failed caulk, missing flashing, ground contact, or splash-back keep siding and trim wet long enough for it to take hold.
How do I know if my siding has dry rot?
Press a screwdriver into suspect trim — sound wood resists, rotted wood sinks. Look for soft or crumbling corners, paint that bubbles and flakes in one spot, dark staining below windows, and separated joints at trim and butt seams.
Can dry rot be patched, or does the siding need replacing?
Isolated trim or a couple of boards can be cut out and replaced. Once rot has reached sheathing or framing, or shows up in several locations on the same wall, the whole assembly needs to be opened and the water path corrected.
How much does dry rot repair cost?
Small trim and single-board repairs are often in the high hundreds to low thousands. Wall sections involving sheathing, flashing, wrap, and repainting scale up quickly. The honest answer requires opening one spot to see how far it traveled.
Will paint stop dry rot?
No. Paint over rot hides it and traps moisture. The rotted material has to be removed and the water source corrected first — flashing, caulk joints, gutters, and grade clearance — then prime and paint.
Keep reading
RestorationRepublic repairs rot, siding, flashing, and the framing behind it across SW Washington — one licensed contractor, one written scope.
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