The main signs of dry rot in siding are wood that is soft, spongy or crumbly, paint that bubbles or peels in patches, trim that swells or cracks, and dark stains or moss near windows and the bottom of the wall. If a screwdriver sinks into the wood, the rot is real. Many spots can be repaired; widespread rot behind the siding usually means a re-side.
What “dry rot” really means
The name is misleading. Wood rot is caused by fungi, and fungi need moisture to grow. The wood may look dry when you find it, because the fungus has already broken down the fibers and left it cracked and crumbly, but a leak or constant dampness started it. Fixing rot without fixing the water source just means the same repair next winter.
Oregon makes this a local concern. Months of rain, wind-driven spray off the Gorge, shaded north walls and old 1950s to 1970s siding on T1-11 or cedar lap give water plenty of ways in.
Where to look first
Rot rarely starts in the middle of a wall. Check these spots:
- Bottom courses and trim near the ground. Splash-back from soil, bark and concrete wets the lower edge. Siding that touches grade is a classic problem.
- Under and around windows and doors. Sills, corners and the head trim. A failed seal or missing flashing sends water into the framing.
- Where roof meets wall. Without kick-out flashing, roof runoff pours down the wall at the end of a roof edge.
- Under deck ledgers and at deck posts. Our decks page covers deck rot, which often travels into the wall.
- Outside corners and board ends. Unsealed end grain soaks up water.
- Soffits and fascia. Look for stained, sagging or soft boards. See trim, soffit and fascia.
- Behind gutters, around hose bibs, vents and light fixtures.
Signs you can see from the yard
- Paint bubbling, peeling or flaking in the same place year after year
- Boards or trim that are swollen, cupped or split
- Dark streaks or stains running from a window corner or roof edge
- Moss, algae or mildew that stays on a wall
- Siding that has gaps, curled edges or loose boards
- Caulk that has split or pulled away
- Mushroom-like growth or a musty smell near a wall
Signs you can check by hand
Try a gentle probe test on a few suspect spots. Press a screwdriver or awl into the wood. Sound wood resists. Rotted wood is soft, spongy or comes up in crumbly pieces. Test on a hidden spot first, since probing leaves a small mark. Tap lightly: a hollow sound can mean the board behind is weak.
Inside, look at the wall under windows for stained drywall, peeling paint, warped baseboards or a musty smell. Those suggest water is inside the wall assembly.
If you cannot reach it safely, do not climb. Stay on the ground and call.
Can rotted siding be repaired?
Often, yes. If the rot is limited to a few boards, a trim piece or a window corner, Dave can cut out the damaged section, fix the underlying cause, flash it correctly, and replace the material. That is the idea of siding repair: fix the actual failure, not just paint over it.
Repair is not enough when:
- Rot has spread through multiple walls or runs up the lower half of a wall
- Sheathing or framing behind the siding is wet or soft in many places
- The siding has no water-resistive barrier or drainage gap and keeps failing
- Repairs have been patched several times without lasting
- The siding is at the end of its life anyway
In those cases, it is usually cheaper and more honest to re-side with new flashing and a proper wall system. Dave will tell you which side of the line your house is on. See James Hardie or cedar replacement.
Why fixing the cause matters
Rot is a symptom. Common causes in this area:
- Missing or poorly done flashing at windows, doors and rooflines
- No gap for drainage behind the siding (see our rainscreen and house wrap guide)
- Siding too close to roofs, decks or the ground
- Failed caulk used as the only defense
- Gutter overflows (Dave does not install gutters, but he can point out when they are the cause)
Older homes: a caution
Houses built before 1978 may have lead paint. Oregon’s Health Authority and CCB oversee the federal lead-safe renovation rule, which applies to work that disturbs painted surfaces on pre-1978 homes. Oregon DEQ also notes siding can contain asbestos in older homes. Do not sand, scrape or tear off old siding yourself until you know what is on it.
Quick answers
- Is rot an emergency? Not usually, but it spreads. Small repairs cost much less than big ones.
- Can I just paint over it? No. Paint hides rot; it does not stop it.
- Does insurance cover rot? Policies vary, and many exclude damage from long-term moisture or lack of maintenance. Read yours and ask your agent.
- Does fiber cement rot? The board itself does not, but the wood behind it can if water gets in.
- What does a repair or re-side cost? See our cost guide.
- What season is best? See the best time to replace siding in Oregon.
Get it looked at
Dave Shaffer has about 40 years of hands-on siding experience and is on every Six-Point job. He serves the Portland metro and East County, including Gresham, Troutdale and Sandy. CCB #153635, licensed, bonded and insured.
Call or text Dave: 503-260-7647. Free estimates.