Dry Rot Siding Repair in Portland: Signs & Fixes
A screwdriver that sinks into a sill or corner board is the classic sign. The question that decides the repair is how far the rot goes behind the siding.
Dry rot siding repair in Portland, Oregon starts with finding out how far the decay goes. On most houses the rot shows up first where water sits on wood: window sills, the ends of lap boards at trim, the bottom of corner boards and the lowest course of siding. If it has stayed in those pieces, the repair is replacing the rotted wood and fixing the caulk or flashing that let water in. If it has reached the sheathing or framing behind, the repair becomes part wall rebuild.
Portland’s climate gives rot a long season. The city averages about 37 inches of rain a year, with November, December and January each bringing about five inches or more, so a spot that takes on water in autumn often stays damp until spring.
Surface rot or rotten wall?
Probe the soft area and the wood around it. Rot confined to one trim piece or a few board ends, with firm siding around it, is usually a surface repair. Signs that it has gone further:
- soft spots along the length of several boards, not just at ends;
- stains or bubbling paint on the inside of the same wall;
- siding that flexes when pushed, as if nothing solid is behind it;
- rot below a roof-to-wall corner or window, where water runs behind the siding (see water behind siding).
What an inspection involves
A contractor will usually probe the suspect boards and trim, check the caulk, flashing and clearances above the damage, and remove one or two boards to look at the house wrap and sheathing. On a house built before 1978 they should treat the paint as possibly containing lead: if the repair disturbs 20 square feet or more of exterior paint, Oregon requires lead-safe work by a contractor with a CCB lead-based paint renovation license.
How dry rot gets repaired
- Fix the water source. Flashing, caulk, clearance to grade or roofing, a sprinkler or downspout.
- Remove the decayed wood back to sound material.
- Repair sheathing or framing if rot has reached it.
- Patch the house wrap and flash openings properly.
- Install new boards and trim, primed on all faces; many contractors use fiber cement or PVC trim at sills and corners where wood keeps failing.
- Caulk and paint to match.
Small decay in otherwise sound wood, common on older houses, can be consolidated and filled with epoxy instead; see historic wood siding repair.
When rot means a re-side
Rot on one or two walls is a siding repair. Rot that turns up on every side, especially on houses with hardboard siding or T1-11, is a sign the siding and the layers behind it have reached the end, and siding replacement is worth pricing alongside the repair.
Pricing a rot repair
It depends almost entirely on what is behind the boards. Portland repair figures and per-square-foot material costs are on the siding cost page, with their sources. Ask for any sheathing repair to be priced per sheet or per hour in the quote, since nobody knows how much there is until the wall is open.
What you may notice
A screwdriver or awl sinks into the wood with little pressure, especially at board ends, window sills and the bottom of corner trim.
Wood that has darkened, cracked across the grain into small cubes, or crumbles when pressed.
Paint bubbling or flaking in one area while the rest of the wall is fine.
Caulk joints that have split or pulled away at trim and window edges.
Mushroom-like growth, or a musty smell near the wall inside the house.
What causes it
Despite the name, dry rot is fungal decay in wood that stays wet: behind failed caulk, along the tops of trim with no drip cap, and where boards sit close to soil, decks or roofing. Portland averages about 37 inches of rain a year, most of it from November to January, so the same spots stay damp for months.
Failed caulk and paint at joints, trim edges and nail holes, letting rain into end grain.
Window and door trim with no drip cap or head flashing, so water sits on the top edge.
Siding too close to soil, bark mulch, patios, decks or roofing, so the bottom edge stays wet.
Sprinklers and downspouts that wet the same wall over and over.
Missing kickout flashing where a roof edge meets a wall, sending water down the siding.
How soon it needs attention
Rot spreads while wood stays wet, so in a Portland winter it keeps advancing until the water source is fixed. Soft trim and a few boards are a routine repair. Once decay reaches the sheathing or framing, the job becomes wall work, so it is worth an inspection before the rainy season rather than after it.
Services that fix it
Siding Repair
Targeted work on part of a wall: rotted boards and trim cut out, torn or missing flashing fixed, storm and ice damage patched, and matching boards woven in.
Siding Replacement
Tear-off to the sheathing and a complete new wall skin: rot repair, house wrap, flashed windows, a drainage gap where it is required, new trim and new siding.
Cedar Siding
Cedar bevel and lap boards, board-and-batten, and sawn shingles: replacing split or rotted pieces, re-siding in cedar, and keeping the finish ahead of the rain.
Historic Wood Siding Repair
Repairing original lap and shingle siding on older Portland-area houses: consolidating and patching sound boards, milling matches for missing ones, and working lead-safe.
Common questions
Is dry rot actually dry?
No. Dry rot is a common name for fungal decay in wood. The fungi need moisture to grow; the wood only looks dry and crumbly once they have broken it down. Stopping the water stops the rot.
How do I tell if rot has gone past the siding?
A contractor removes a board or two at the worst spot and probes the sheathing behind. Stains or soft spots on interior walls near the damage, or rot that extends across several boards, suggest it has reached the wall. You cannot tell from the outside of the board alone.
Is epoxy filler enough for rotted siding?
Small areas of decay in otherwise sound wood, such as a sill corner or the end of a trim board, can be dug out, consolidated and filled with epoxy. Boards that are soft through, or where rot has spread along their length, are replaced. Either way, the water source needs fixing first.
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