1. Stop at the safety boundary
Do not vent moist air into the attic or detach a powered fan without isolation.
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
Bath use during cold weather or rain at the roof cap.
4. Compare, do not assume
Supports this pathway
- The symptom follows showers in cold weather
- The duct sags or lacks insulation
- Moisture is inside the duct or at a joint
Weakens this pathway
- Rain alone reproduces the leak
- The fan does not operate
- The duct is dry while roofing around the cap is wet
5. Repeat only safe checks
- Run the fan and verify airflow at the exterior outlet if safely accessible
- Record shower duration and outdoor temperature
- Inspect visible duct slope and joint condition from a safe platform
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. A ventilation or roofing professional may be needed when the duct route and roof termination both require correction.
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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