How Rainy Seattle Weather Causes Dry Rot and How to Stop It

Seattle’s rain is more than a mood, it is a building science problem that never takes a season off. Moist marine air presses in from the Sound, wind-driven rain tests every seam, and overcast days slow drying times. When wood can’t shed moisture, fungi find their moment, then quietly convert framing, sheathing, and trim into soft, friable material you can push a screwdriver into. Dry rot is misnamed, of course, because it thrives in damp, not dry. But the name has stuck, and so has the damage. After twenty years crawling under porches in Ballard, replacing sill plates in Queen Anne, and opening up siding on Beacon Hill, I can tell you the causes are predictable, the warning signs subtle, and the fixes straightforward when you catch them early.

Dry rot is a wood-decay fungus, most often Serpula lacrymans or similar species, that colonizes wood when three conditions line up: moisture, oxygen, and a food source. Wood is the food. Air is everywhere. Moisture is the pivot. Keep wood below roughly 20 percent moisture content and you choke the fungi. Let it sit above that threshold, and you have an active risk window.

Seattle’s climate stacks the deck. Annual precipitation might hover around 35 to 40 inches, but the pattern matters more than the total. It falls over many months. We get long strings of days with intermittent showers and relative humidity moving between 70 and 100 percent. Sun breaks help, but not enough to drive a hard dry-out through thick siding assemblies or shaded north elevations. Add coastal winds that push rain up and under cladding, and you create wetting events that last.

I have opened walls in February and found wet sheathing behind siding that otherwise looked fine. The nails were dark, the OSB had a sweet, mushroom scent, and the studs showed early brown rot cubing. The owners never saw a leak inside because the water was trapped in the wall, not pouring through.

Not all water is equal. Some you can see, some you can’t. Here’s how moisture sneaks in around our houses.

Window and door flashings are the big hitters. In homes built before about 2008, I often find little or no head flashing over windows. Wind-driven rain hits the top trim, runs behind, then settles into the sheathing. Even with modern flanged windows, if the flashing tape was applied backwards or the WRB shingle-lapped the wrong way, water gets in. One Ravenna project comes to mind where a crisp set of new windows had been taped in a reverse lap pattern. It took two winters for the sills to soften, but the sheathing was gone the full width of a 12-foot wall.

Roof-to-wall intersections act like rain catchers. If the kick-out flashing at the end of a roof-to-wall step flashing is missing, Seattle Trim Repair water rides the siding like a waterslide and dumps directly into the wall cavity. I have replaced entire lower gable walls in Magnolia where missing kick-outs fed rot for years. It looks like a siding stain until you open it up and find finger-jointed trim dissolving in your hand.

Deck ledger attachments pierce weather-resistant barriers and often lack adequate flashing. If a contractor lag-bolts a ledger without a fully integrated flashing and counterflashing detail, the ledger becomes a sponge that feeds the rim joist and band. From there, rot marches into floor framing. In older bungalows with cedar decks added later, this is a common point of failure.

Siding and trim end grain are like straws. When exterior trim repair isn’t done with sealed cuts, end-grain primer, and back-priming, water wicks up from the bottom edges. I see this on Hardboard and fiber cement installations too, when installers cut planks and skip edge sealing. It is one reason requests like seattle trim repair or House trim repair spike in late spring after a long wet winter.

Poor grade and drainage around the foundation keep lower walls wet. If the soil or mulch rides high on the siding, capillary action pulls moisture up behind the cladding, and splash-back from hard rain peppers the first course. You can sometimes see a sharp horizontal line where decay starts, exactly at the height of the landscape beds.

Gutters and downspouts concentrate water. If they clog or discharge near the foundation without diverters, water rebounds. The siding repair seattle crews do every fall and winter often starts with a ladder and a handful of wet leaves pulled from a downspout elbow.

Dry rot rarely announces itself indoors until the damage is advanced. Outside, you look for specific tells.

Paint that bubbles or peels near joints can mean trapped moisture trying to escape. Poke the area with an awl. If the tool sinks easily, you have decay. On cedar, decay can show as a brittle, cubed texture that crumbles. On trim, you might see hairline cracks that radiate from nail heads.

Discoloration that doesn’t dry out after a few days of sun signals absorption rather than surface wetting. On fiber cement, look at the cuts and edges. On wood, look at the bottom ends of corner boards and around fasteners. If you see white, cottony mycelium in a crawl or wall cavity, you have active fungal growth and a moisture source nearby.

Indoors, a musty odor near a baseboard on an exterior wall sometimes precedes visible staining. Floors near exterior doors can feel bouncy. A screwdriver test at the door threshold might end in a sinking feeling as you punch through what should be solid wood.

Because the symptoms can be slight, a Seattle dry rot inspection is less about gadgets and more about pattern recognition. Moisture meters help, infrared cameras can suggest temperature differences, but experience knows to start at kick-out locations, ledger lines, window heads, and lower courses. A good dry rot repair contractor will map the likely intake points and then open only what is needed to verify.

Treat exterior assemblies like layered raincoats that have to overlap in the right order. If a single piece is tucked out of sequence, it directs water inward. Common examples:

Builders are not careless so much as rushed, and many houses in the region passed inspection with details that work in drier climates but fail here. That is why siding contractors in seattle build rain screen cavities more often now, even when not required by code. A rain screen, which is just a small drainage and ventilation gap between the siding and the WRB, changes the whole moisture equation. It lets incidental water drain and air move, which shortens wetting cycles and starves the fungi of the sustained damp they need.

Owners often ask if we can inject something, seal the outside, and call it good. If the wood has lost strength, topical fixes don’t cut it. Dry rot repair is invasive by necessity. The rule is simple: remove all compromised material until you reach sound wood, correct the water entry point, then rebuild with better detailing.

On a typical mid-century house in West Seattle with decayed window sills, a sensible scope goes like this. We remove the exterior trim and a band of siding above and below the window. We cut back sheathing to the nearest studs, inspect, and keep cutting until every cubic inch of rot is out. We check the stud ends, sill plate, and any king/jack studs for compression or loss. If the framing is gone, we sister or replace. Only then do we re-sheath, properly flash the opening, and reinstall siding with adequate clearances. If the homeowner wants to keep the original trim profile, we mill new pieces with back-primed ends and seal the cuts with high-quality primer and paint. When the issue is widespread, Siding replacement services seattle wa might be more cost effective than chasing spot repairs for years.

Where the damage traces to a deck ledger, we detach the deck, remove the ledger and the affected rim, treat adjacent wood with a borate preservative, and rebuild with a continuous, layered ledger flashing that kicks water out and down. In every case, the water management detail is as important as the replacement wood.

Seattle homeowners love the look of cedar. It moves with humidity, it takes stain beautifully, and it is abundant in older neighborhoods. But it needs thick coats of quality finish, well-ventilated assemblies, and overhangs to protect it. Without those, it is work. Fiber cement siding behaves better in persistent wet, and when installed with a rain screen, it is remarkably resilient. It still needs a disciplined trim and flashing package, because fiber cement does not make a wall waterproof on its own.

For trim, PVC and fiber cement trim boards shrug off moisture, but they expand and contract differently than wood. They want proper fastening and allowances for movement. On historic homes, I sometimes mix materials: cedar for visible wide casings and PVC for ground-contact skirt boards that take the brunt of splash-back. Metal flashings, particularly at horizontal transitions and window heads, should be formed with hemmed edges and kick-outs that throw water clear.

Paint and sealants are part of the system, not the system. A perfect bead of caulk will fail if applied to a wet surface or if it is the only defense against water entering a joint. Backer rods, proper joint sizing, and high-grade urethane or silyl-terminated polyether sealants extend service lives. In trim and siding repair, rushing the paint and sealant steps is one of the most common ways a job fails early.

You don’t have to rebuild your whole exterior to keep rot at bay. Focus on keeping assemblies dry more often than they are wet, and make water paths predictable.

These are low-cost moves. They buy time and reduce the need for larger interventions. When you see a stain that persists after dry weather, or paint that blisters in the same spot each spring, call for a Seattle dry rot inspection. Verified early, the repair area stays small.

Not every crew is built for wet-climate forensic work. When you interview siding contractors seattle wa has to offer, ask to see photos of open-wall repairs and flashing details. You want installers who can describe sequencing, not just brand names. A veteran dry rot repair contractor should talk about kick-out flashings, head flashings, end-grain sealing, and rain screens in the first five minutes. If the pitch leans heavy on caulks and paints and light on water-shedding layers, keep looking.

Permits matter when framing is affected, and not all exterior trim repair is as simple as it looks. For decks, ask about ledger load paths and approved fasteners for treated lumber. For windows, ask how they protect the rough opening and whether they will integrate with the WRB you have, not just the one they prefer. If your house needs targeted siding repair seattle specialists should be frank about when spot fixes make sense and when to consider phased siding replacement.

Cost is not just the number at the bottom of the estimate. Fast, cheap patch jobs can trap water more effectively than the original failure. I have returned to homes where a low bid meant new trim was pinned over rotten substrate without removing decay. The surface looked clean for six months, then everything beneath collapsed. Pay for the disassembly and the sequencing. That is where the value lies.

Homeowners want a sense of scale. Ballpark figures vary with access, materials, and scope, but some useful ranges in Seattle:

These numbers reflect doing it right: removal to sound material, proper flashing, good materials, and finish restoration. Siding replacement services seattle wa offer will quote per square, but decay repair is rarely a clean square count. Contingency allowances with transparent unit rates for additional rot discovered once open are a sign you’re dealing with pros.

A craftsman in Phinney Ridge had charming tapered columns wrapped in cedar with a small belly band detail. Water stood on the horizontal ledge, the paint failed, and the band wicked moisture into the column wraps. By the time we were called, the bottom 18 inches of each column crumbled. We rebuilt the bases with PVC for the lowest 8 inches, cut a slight slope on the new band, added a concealed metal flashing with a hemmed drip edge, and sealed all end grain. Ten years on, the paint still looks fresh, and moisture meter readings stay in the teens.

A modern townhouse cluster in Capitol Hill had fiber cement siding with no rain screen and very tight clearances to metal decks. Condensation from the metal poured into the wall during cool nights. We removed narrow vertical strips at suspect points, installed furring to create a drainage gap, corrected the deck-to-wall flashing with larger kick-outs, and reinstalled siding with sealed cuts. The owners expected wholesale replacement, but targeted work preserved most of the skin and prevented future decay.

A mid-century rambler in Shoreline suffered from a missing gutter over a 20-foot wall section. Repeated splash-back rotted the sheathing behind painted T1-11. We replaced the sheathing, installed a robust gutter system, added a rain screen, and converted to horizontal fiber cement with quality trim. The owner wanted wood aesthetics, so we used cedar at the eye-level details and PVC at ground-contact zones. That mix kept the look and solved the problem.

The decision point is structural integrity, spread, and age of the exterior. If more than about 20 to 30 percent of a given elevation shows decay or water intrusion, wholesale replacement with a modern assembly often beats piecemeal spending. You get a unified WRB, consistent flashing, and a warranty that means something. If the home’s siding is nearing the end of its service life, siding contractors in seattle will recommend replacing entire elevations or the full perimeter in phases, starting with the worst side. Phasing lets you prioritize south and west exposures that weather harder and often dry less because of shading from adjacent features.

When the siding is relatively young, isolated failures at penetrations or transitions justify focused repair. That is where a skilled Dry rot repair contractor earns their keep. They should document each step with photos, from the first piece removed to the last flashing installed, so you know what you paid for and have a record for resale.

Set reminders keyed to our climate, not the calendar on the label. After the first big fall storm, walk the perimeter. Look up at kick-outs and down at the grade. Clear drains. In the quiet week between Christmas and New Year’s, check for persistent damp spots that never dried after earlier storms. In early spring, as temperatures climb but rain still visits often, look for paint that bubbled during cold snaps and failed. Late summer is your window for exterior painting and sealing because the dry stretch gives coatings time to cure.

Treat exterior checkups like dental cleanings. Small problems, handled early, cost time and hundreds. Left alone, they turn into thousands and a renovation you didn’t plan.

Rot is a strength issue before it is a smell or a stain. A garage door jamb that has lost bearing can drop the header. A deck ledger on the edge of failure is a safety hazard. Window sills that rot invite pests that compound the damage. Preventing rot preserves structure, improves indoor air quality, and saves energy because wet assemblies conduct heat differently and draw moisture through capillary action.

There is also a softer benefit. When a house sheds water predictably, it is quieter. Windows close properly, doors don’t stick seasonally, and paint lasts longer. It is the difference between maintenance that feels constant and maintenance that feels routine.

Some tasks are weekend-friendly. You can trim back shrubs, clean gutters, add splash blocks, and reseal a bit of end grain. Once you suspect decay beneath the skin, call in a pro. Seattle dry rot repair often involves removing structural elements and re-establishing the water barrier, which is not a first-time DIY project. The right team will tell you where you can save by prepping, painting, or handling simple re-installations, and where it is wiser to leave the envelope intact. Trim and siding repair done carefully pays for itself by preventing a second round of problems.

If you are interviewing teams, look for clear scopes, photo documentation, and an explanation of how they will handle unknowns behind the wall. Ask whether they provide both targeted repair and full siding replacement services seattle wa homes sometimes need. A contractor who is comfortable with both is less likely to force you into one option.

Seattle’s rain is not going anywhere. Your house does not have to suffer because of it. Build with layers, let assemblies breathe, keep water moving away from the structure, and repair with an eye toward how the next storm will behave. Do that, and dry rot becomes an occasional fix, not an annual fight.

Seattle Trim Repair
8338 20th Ave NW, Seattle, WA 98117
(425) 517-1751