The core idea
Porous masonry, timber and finishes can pull water sideways or upward, so the visible edge may not identify where water entered.
How the mechanism works
Small pores create capillary suction that can move liquid against gravity until evaporation, drainage or a less absorbent layer interrupts the path.
When it becomes relevant
Typical trigger: Ground contact, repeated splashback, a wet joint or a persistent reservoir.
Evidence that supports this interpretation
- A tide-like edge or salt line
- Moisture decreases with distance from a reservoir
- Absorbent materials are connected continuously
Evidence that weakens it
- A single overhead event explains the pattern better
- The material is isolated by a continuous break
- The symptom appears only with indoor humidity
What this concept cannot prove alone
A single observation, image or meter reading cannot confirm the complete failure pathway. Use this concept to form better questions, compare alternatives and decide which safe observation would be most informative next.
Safety and professional boundary
Do not install an impermeable finish over a capillary path before drainage and drying are evaluated.
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.
