1. Stop at the safety boundary
Do not use smoke, combustion products or chemical tracers indoors.
2. Capture the baseline
Take one context photo, one close view and a short note describing location, date, weather, recent water use, equipment state and occupancy.
3. Track the trigger
Exhaust fans, heating equipment, wind or closed interior doors.
4. Compare, do not assume
Supports this pathway
- Odor changes with fans
- The crawlspace has a similar odor
- Floor penetrations or return leaks are present
Weakens this pathway
- The crawlspace is odor-free
- The smell follows a drain trap
- Outdoor sources explain the pattern
5. Repeat only safe checks
- Compare fan-on and fan-off conditions
- Close crawlspace access and note change
- Inspect accessible duct and floor penetrations
6. Decide the next step
If the pattern is active, expanding, safety-related or requires opening inaccessible construction, stop self-help testing and prepare an evidence-based handoff. An HVAC or building-envelope professional can test pressure and duct leakage safely.
7. Verify the outcome
After any action, repeat the same observation under a comparable trigger. A dry surface immediately after work is not sufficient proof when the original symptom was intermittent.
Observe→Compare triggers→Repair source→Verify outcome
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