What dry rot really is
The name is misleading. Dry rot is wood decay caused by fungus, and the fungus needs moisture to grow. In our climate, wood that stays damp through a long wet season is an easy target. Once it starts, the wood loses strength and turns soft, crumbly or stringy.
The hard part is that rot often starts behind a coat of paint that still looks fine. By the time you notice it, it may have spread further than you'd guess. Many Oregon homeowners find it only when they go to repaint.
Rot starts where water sits. Find the water and you find the rot.
Where it hides on a house
- Window sill rot, especially on the lower corners where the sill meets the trim
- Door jamb rot at the bottom of the frame, near the threshold
- Siding boards closest to the ground, a deck, or a patio
- Fascia and trim behind gutters that overflow
- Corner boards and the ends of siding boards, where end grain soaks up water
- Walls next to downspouts, sprinklers or planter beds
- Any joint where old caulk has cracked or pulled away
Signs that are easy to miss
Walk around the house on a dry afternoon. Look low and look high. These are the clues that tend to get ignored:
- Peeling paint in one small patch while the rest of the wall looks fine
- Paint that bubbles or blisters near a sill or a corner
- Cracks running across the grain, or wood broken into little cubes
- Dark staining or a musty smell near the bottom of a wall
- Gaps opening at trim joints
- Gutter overflow marks running down the fascia
Try the screwdriver test
Take a flat screwdriver and press the tip into the suspect spot. Sound wood resists and the tip barely sinks in. Soft wood gives way, and the tip may slide in with little effort. Rotted wood often breaks out in short, dull pieces instead of long splinters. Test a few inches around the spot, too. Rot rarely stops at the edge of the stain.
What a proper dry rot repair involves
A good repair is more than filling a hole and painting over it. Paint over rot looks fine for a season and then fails again. Here is the usual order of work:
- Find where the water is coming from and fix that first
- Remove the damaged wood back to solid, dry wood
- Check for rot behind siding, including the sheathing and framing
- Replace rotted wood with new boards cut to match the profile
- Prime all sides and the cut ends before the new wood goes up
- Add or fix flashing where water was getting in
- Caulk the joints that need it and paint to match
For a small, shallow spot on decorative trim, an epoxy filler is sometimes an option. For anything structural, or anything that keeps getting wet, replacing the wood is the safer choice.
How to keep it from coming back
- Keep gutters clean so water runs off the roof, not down the wall
- Keep soil, mulch and bark a few inches below the bottom of the siding
- Aim sprinklers away from the house
- Trim shrubs back so walls can dry out
- Re-caulk open joints and repaint before bare wood shows
Water damage on a house almost always has a cause you can fix. Catching rotted trim early keeps a small repair from turning into a big one.
Questions to ask a contractor
Ask how they'll find the source of the water. Ask how far they expect to open things up, and what happens if the rot goes deeper than it looks. Ask whether new wood will be primed on every side. A good contractor will answer plainly and show you what they find.
Triple SSS Construction repairs dry rot in siding, trim, sills and fascia around Portland and Gresham. We'll show you the bad wood, explain what caused it, and replace rotted wood the right way. Call (503) 781-2093 any time.
Dry Rot Repair
