1920s Craftsman:
Crawl Space Post Rot
& Floor Joist Failure
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 Proctor District homeowner noticed a floor drop of nearly an inch near the center of the main living space — sudden enough to feel when walking. This is what structural repair in Tacoma looks like when the failure involves compromised load-bearing posts, floor joist deflection, and a drainage problem that had been feeding moisture into the crawl space for years.
The Problem:
Sudden Floor Drop in a 100-Year-Old Home
The owner had noticed soft spots in the living room floor for about a year — gradual enough to dismiss as settling. Then over a single wet winter, a section near the center beam dropped noticeably. Doors in the adjacent hallway began sticking. Another contractor told him it was "probably just the foundation" and quoted a concrete repair that turned out to be irrelevant.
Tacoma's Craftsman-era housing stock — much of it built 1905–1930 — uses a common post-and-beam crawl space structure. Wood posts bear directly on concrete piers or pads at grade. When those posts hold moisture for years, decay starts at the base and works upward. The beam or girder they support begins to deflect, and the floor system above follows. This is not a foundation problem. It is a structural repair problem — and it is completely fixable.
The Diagnostic:
Root Cause Before Any Work Begins
Crawl Space Structural Survey
Full crawl space entry with moisture meter readings, visual post inspection, and load-path tracing from floor to beam to post to pad. Four posts along the center girder line showed active decay at their bases — two had lost more than 40% of their cross-section. The girder above showed 1.5 inches of sag at mid-span. Floor joists in the affected bay were deflecting well beyond acceptable limits.
Moisture Source Located: Failed Perimeter Drain
Crawl space moisture readings were elevated across the entire west side — 24–31% MC at post bases. Exterior inspection revealed a collapsed perimeter drain at the west foundation that had been directing surface runoff under the house for at least two seasons. The crawl space floor was visibly damp. Vapor barrier had degraded. This was not a framing problem caused by a one-time event — it was a slow-feed moisture problem that had been running for years.
Temporary Shoring Installed at the Diagnostic Visit
Two of the four compromised posts were carrying live load with insufficient remaining section. Temporary screw-jack shoring was installed under the center girder during the diagnostic visit to arrest further deflection before the owner's family slept in the house that night.
The Repair:
Structural Rebuild — Posts, Joists, Drainage
Structural repair in Tacoma's older housing stock requires understanding how the original framing system was designed to work — and what it needs to work correctly for another century. This job involved four discrete scopes that had to be sequenced correctly: drainage correction first, then post replacement, then joist repair, then floor leveling.
- Perimeter drain restoration: Collapsed drain excavated and replaced with new 4" perforated pipe in clean drain rock, daylighted to grade 12 feet from the foundation. French drain installed along the west wall interior. Crawl space allowed to dry before structural work began — 5 days with ventilation fans running.
- Post replacement — 4 posts: All four decayed posts removed after temporary shoring verified holding. Replaced with 4x6 pressure-treated posts on new adjustable steel post bases — allowing for future leveling adjustments without removing posts. Existing concrete pads inspected and confirmed sound.
- Center girder re-leveling: Girder raised to correct elevation using screw jacks, then permanently supported on new posts. 1.5-inch sag at mid-span corrected to within 1/8 inch across the 22-foot run.
- Floor joist sistering — 6 joists: Six floor joists with deflection exceeding L/360 sistered with full-length pressure-treated dimensional lumber, glued and fastened to original joists. Two joists with active decay at ends replaced entirely.
- Vapor barrier replacement: Full crawl space 20-mil vapor barrier installed, lapped and taped at seams, extending up foundation walls. Crawl space vents inspected — two blocked vents cleared.
- Subfloor correction: Subfloor sheathing in one bay had delaminated from joist deflection. Replaced with 3/4" T&G plywood glued to repaired framing. Finish floor re-fastened from above.
Outcome
Total repair time: 11 working days from diagnostic to final walkthrough. The floor drop was fully corrected — post-repair measurement showed less than 3/16" variation across the entire living room floor. The sticking doors opened freely again within two days of re-leveling as the framing relaxed to its corrected position.
The drainage correction — the step most contractors skip entirely — eliminated the moisture feed that caused the failure. Without correcting the perimeter drain, replacement posts would have repeated the same decay cycle within 5–8 years. The owner received a written explanation of what to monitor annually.
Total project value: $18,200 lump sum. Five-year written structural guarantee on all replaced framing. Diagnostic fee of $350 credited in full.
Structural Repair in Tacoma:
What You Need to Know
Structural Problems
Don't Stabilize on Their Own.
Every month of moisture exposure advances the decay further. A $350 diagnostic tells you what you have, what's causing it, and exactly what it costs to fix permanently — including whether it needs shoring today.
253-891-9622