Air leakage carries indoor moisture into a cold attic where it freezes on roof sheathing and later melts.
Failure path
- Step 1: Warm humid room air reaches ceiling penetrations.
- Step 2: Pressure and buoyancy move air into the attic.
- Step 3: Cold roof sheathing drops below freezing.
- Step 4: Moisture deposits as frost.
- Step 5: A thaw releases stored water into wood and insulation.
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.
