Waterfront Home:
Dry Rot Through Sill Plate,
Rim Joist & Subfloor
Representative project. This case study is based on work Realty Repair Co. completed on a similar home in a nearby community. The location and identifying details have been changed to protect the owner’s privacy; figures are representative.
A Tacoma waterfront property with years of undetected moisture intrusion. By the time the owner called, dry rot had consumed the south-facing mudsill, 28 linear feet of rim joist, and compromised subfloor framing in two rooms. This is what a complete dry rot repair in Tacoma looks like — from forensic diagnostic to permanent structural rebuild.
The Problem:
Splash-Back Rot on a Waterfront Foundation
The owner had noticed soft flooring near the south wall of the living room and a persistent musty smell in the crawl space. A home inspector flagged "possible wood damage at foundation" but could not quantify scope. The owner's concern: a deal was pending and the buyer's agent was asking for a contractor letter within five days.
Waterfront properties in Tacoma face an accelerated dry rot exposure pattern. Grade-level splash-back from hard surfaces, combined with the narrow drying window the PNW winter provides, keeps mudsill and rim joist moisture content elevated for months at a time. On this property, failed kick-out flashing at a roofline above the south wall had been directing roof runoff directly onto the foundation siding for several seasons. The moisture source was not visible from grade — it required a crawl space entry and moisture meter survey to locate.
The Diagnostic:
$350 Forensic Assessment, Not a Visual Guess
Crawl Space Entry & Moisture Survey
Full crawl space access with moisture meter readings at 6-inch intervals along all foundation walls. South wall readings came in at 28–34% MC — well above the 19% threshold where fungal activity sustains. North and east walls were dry. This told us immediately: one concentrated moisture source, not a systemic drainage problem.
Root Cause Identified: Failed Kick-Out Flashing
Exterior inspection from a ladder confirmed the source. A kick-out flashing at the south roofline junction had separated from the wall, allowing roof runoff to track behind the siding and pool at the mudsill for an estimated 3–5 seasons. Rot was not random — it mapped exactly to the moisture delivery zone.
Scope Defined Before Any Material Was Ordered
Full excision mapping completed in the crawl space: 28 linear feet of rim joist with active decay, the full south-wall mudsill run (22 LF), and two floor joist bays where subfloor sheathing had delaminated. Written findings delivered to the owner and their agent within three days of the diagnostic visit.
The Repair:
Full Excision, Fungicide, Structural Rebuild
Dry rot repair in Tacoma is not patch work. Fungi travel through wood fiber well beyond the visibly discolored zone. Our standard is to excise to clean wood confirmed by probe and moisture meter, treat all adjacent framing with a borate-based fungicide, and rebuild with pressure-treated lumber where ongoing moisture exposure is possible.
- Mudsill replacement — 22 LF: Full removal and replacement with PT mudsill. New sill seal installed. Anchor bolt schedule maintained per original layout.
- Rim joist replacement — 28 LF: Full south-wall rim joist run removed, replaced with PT lumber. All adjacent floor joist ends inspected and probed. Two joist ends sistered where decay had migrated.
- Subfloor sheathing — 2 bays: Delaminated OSB removed and replaced with 3/4" tongue-and-groove plywood, glued and fastened to repaired framing below.
- Fungicide treatment: Borate solution applied to all remaining framing within 4 feet of the repair zone — crawl space posts, blocking, adjacent joist bays.
- Kick-out flashing correction: Failed flashing removed and replaced with properly sealed kick-out at the roofline junction. Siding below the repair zone re-caulked at all penetrations.
- Drainage regrading at south foundation: 6 inches of finish grade re-sloped away from foundation to provide positive drainage. This is the step most contractors skip — we don't.
Outcome
Repair completed in 7 working days from diagnostic. Contractor letter delivered to the listing agent on day 2 after scope confirmation — the buyer's lender required it and the deal stayed on track. Post-repair moisture readings on the south wall came in at 11–13% MC — well within safe range.
The owner received a 5-year written structural guarantee covering all replaced framing. The moisture source — the kick-out flashing failure — was corrected as part of the repair scope. The rot cannot return unless a new moisture source develops, and the owner now knows what to watch for.
Total project value: $11,400 lump sum, all-in. The $350 diagnostic fee was credited in full toward the repair.
Dry Rot Repair in Tacoma:
What You Need to Know
Dry Rot Doesn't
Wait for Spring.
Every wet season it advances further into your framing. A $350 diagnostic tells you exactly what you have, exactly what it costs to fix, and whether it's urgent. No free estimates. No guessing.
253-891-9622