Use this atlas page to organize evidence, not to declare a diagnosis. Drainage geometry, penetrations, flashings, wind exposure and freeze-thaw conditions determine how exterior water reaches hidden layers. The useful starting point is a repeatable pattern tied to location, timing and conditions that changed or stayed normal.
Read the visible pattern
Begin with stains after directional rain, ice or overflow at edges, localized sheathing change. Record the first location, direction, edge or cycle where the symptom becomes noticeable. Photograph from the same position, preserve original timestamps and note comparable areas that remain dry, quiet, cool or odor-free.
Trace the connected mechanism
In this room, drainage geometry, penetrations, flashings, wind exposure and freeze-thaw conditions determine how exterior water reaches hidden layers. Compare at least two plausible routes rather than choosing the first familiar explanation. Compare roof drainage, exterior envelope, insulation airtightness before treating the visible point as the source. A strong hypothesis predicts where the symptom should begin, what trigger should reproduce it and which nearby areas should remain unaffected.
Use safe, non-destructive checks
- Map stains after directional rain
- Map ice or overflow at edges
- Compare the roof drainage and exterior envelope pathways
Pair every reading with its instrument, location, time and environmental condition. One reading can support a pattern but cannot certify a hidden material condition or prove that a repair is complete.
Respect the stop boundary
Do not access unsafe roofs or work near power lines, ice or unstable surfaces. Active leakage, structural deflection or extensive decay needs qualified inspection.
Prepare the next decision
Summarize the trigger, first visible change, rooms or systems involved, checks already completed and what would count as a verified outcome. A useful handoff gives the next person a timeline and competing explanations instead of only a symptom label.
Primary references for this topic family
These references ground the general building-science or safety context. They do not diagnose a specific house, replace local requirements or certify a repair.
