Wood Rot Repair on San Juan Island

This is the most common structural-adjacent problem on San Juan Island and the one most often left too long. Cedar siding, fir trim, eight months of wet, salt in the air, and a lot of houses that nobody looks at between October and June. That combination produces soft wood faster than most owners expect.

Rot is not really a wood problem. It’s a fungus that needs food, warmth, and water, and the only one of those three you get to control is the water. Wood-decay fungi stop working below roughly 20 percent moisture content and get genuinely active once wood is up around fiber saturation, near 28 to 30 percent, which is a condition our climate supplies for most of the winter wherever a detail lets water sit. That single fact drives how I work: if I replace a rotted sill and don’t fix what wet it, I’ve sold you the same repair again in three or four years.

So the first thing that happens is a diagnosis, not a demolition. I probe with an awl to find where sound wood starts, use a moisture meter on the surrounding material, and follow the water uphill. Nine times out of ten it’s one of a short list of things, and after enough houses out here the list is predictable: a gutter that has been overflowing behind the fascia for two winters, a downspout dumping against a skirt board, siding that sits too close to grade or hard down onto a deck surface, a horizontal trim board installed flat with no bevel and no drip edge, failed caulk at a window head, a deck ledger without proper flashing, or a post sitting directly on soil or on a slab that stays wet.

There is an island-specific pattern on top of that. Southwest-facing walls take wind-driven rain straight off the water and get soaked in a way a sheltered mainland lot never does. North-facing walls have the opposite problem: they never get enough sun to dry out, so they hold green film and moss and stay damp into May. Salt air keeps surfaces slightly hygroscopic and is hard on fasteners, so electroplated nails corrode, heads bleed, and every corroded nail hole becomes a path for water into end grain. Houses close to the water age their trim noticeably faster than houses a half mile inland, and I’ve seen the difference on the same road.

The places I find it, roughly in order: the bottoms of exterior door jambs and the casing beside them, window sills and the lower corners of window trim, the bottom course of siding, fascia behind a gutter, deck rim joists and ledgers, the base of posts and stair stringers, skirt boards, and the underside of bay windows and cantilevers. Interior rot shows up under exterior doors, at the perimeter of an unvented bathroom, and in crawlspaces where the vapor barrier has been dragged aside and never put back.

The repair itself is unglamorous and specific. I cut back to sound wood, generally six to twelve inches past anything that still feels soft, because the fungus runs ahead of the visible damage. I replace like with like — cedar for exterior trim and siding, pressure-treated where anything is within reach of ground contact — and I back-prime every piece on all six sides with particular attention to cut ends, because end grain is where the next round of water gets in. Fasteners are stainless or hot-dip galvanized, never electroplated, which is not a preference out here so much as a requirement. Joints get caulked where caulk belongs and deliberately left open where they need to drain, which is the detail most often gotten backward.

Epoxy consolidant has a place and I use it honestly: a small area of an original sill you want to keep, or a milled profile that can no longer be bought. It is not a substitute for replacing a rotted member, and anybody troweling epoxy into a soft jamb bottom and calling it done is selling you two years.

Matching material is the part that takes local knowledge. Browne’s in Friday Harbor stocks common cedar trim and dimensional stock, but an original 1970s profile usually has to be milled or run over on the ferry, and that changes the schedule more than the labor does. For outer-island work by skiff, 20-foot boards are the hard ceiling on a 16-foot boat, and anything longer or heavier goes by hauler or chartered boat at cost.

What I don’t do, plainly: roof replacement, roof-level flashing, and structural repair that changes how a building carries load. Replacing a rotted trim board, sill, siding run, fascia, or a rotted post base with like-for-like is inside a general contractor registration and inside my competence. If an awl sinks into a beam, a bearing post, or a floor joist carrying real load, that needs a permit and probably an engineer, and I will tell you that on the first visit rather than the third. If the water is coming from a supply line or a drain, a licensed plumber fixes that part before I touch the carpentry.