Use this atlas page to organize evidence, not to declare a diagnosis. Below-grade walls and floors where surface water, groundwater, capillary transport and cool-surface condensation can overlap. 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 wall-edge dampness, efflorescence or peeling finishes, odor after rain. 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, below-grade walls and floors where surface water, groundwater, capillary transport and cool-surface condensation can overlap. Compare at least two plausible routes rather than choosing the first familiar explanation. Compare ground drainage, structure foundation, ventilation airflow 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 wall-edge dampness
- Map efflorescence or peeling finishes
- Compare the ground drainage and structure foundation 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 remove structural finishes, enter flooded electrical zones or treat sewage-contaminated water as ordinary dampness. Movement, active flooding and energized water demand prompt professional help.
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.
