A disconnected or intentionally terminated duct delivers concentrated warm moisture to cold attic materials.
Failure path
- Step 1: Shower raises indoor moisture.
- Step 2: Fan moves moisture into the duct.
- Step 3: The duct ends or leaks inside the attic.
- Step 4: Condensation and frost form around the discharge area.
- Step 5: Repeated cycles wet insulation and sheathing.
What makes this pathway plausible
The timing, location and operating or weather trigger should repeat. A diagram shows a mechanism; evidence from the actual house determines whether it applies.
Best next observation
Record the trigger and compare the nearest materials, components and routes before opening finishes or choosing a repair.
Verification after repair
Recreate the original trigger when safe, then confirm the symptom does not return and affected materials are stable or drying.
Trigger→Pathway→Symptom→Verification
Simulation boundaryThis pathway explains a plausible mechanism. It does not establish that the mechanism is active in a specific house without matching evidence.
