The crawl space held damp-earth odor
The odor source and the room where it was noticed were different places.
↓House Autopsy · ventilation-and-airflow
The musty odor pulled from the crawl space
House pressure changed when extract equipment operated and drew crawl-space air through floor openings.
Trigger conditionexhaust fan operation
Four layers, one connected story.
Exhaust operation lowered indoor pressure
The signal appeared within minutes of fan operation.
↓Floor and service penetrations supplied replacement air
Airflow direction, not diffusion, explained the rapid change.
↓Pressure and smoke-pencil checks found the route
Air sealing and balanced makeup air reduced the odor transfer.
Canonical connection
The symptom and cause are separate objects.
The autopsy preserves how evidence connected them without collapsing uncertainty into one magic answer.
House pressure changed when extract equipment operated and drew crawl-space air through floor openings.
The visible symptom was the final chapter
The investigation followed the source, transport path, affected material and verification step separately.
What changed the direction
Timing and location evidence ruled out attractive but weaker explanations before repair work began.
The durable lesson
Repair the controlling source and then verify the outcome under the conditions that previously triggered the symptom.
Source→Path→Damage→Verify
