Step flashing, counterflashing or masonry interfaces allow water to enter during particular wind directions.
Failure path
- Step 1: Rain strikes the upslope or side face.
- Step 2: Water reaches a flashing or mortar defect.
- Step 3: The chimney chase redirects the path.
- Step 4: Staining appears beside or below the chimney.
- Step 5: Calm rain may not reproduce the symptom.
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.
