The core idea
Stairs, chases and service shafts can act as hidden air highways between floors.
How the mechanism works
Large connected openings reduce resistance and let pressure differences move air through cavities rather than planned ventilation routes.
When it becomes relevant
Typical trigger: Temperature differences, fan operation or open doors between levels.
Evidence that supports this interpretation
- Odor or draft aligns with a vertical chase
- The symptom appears on multiple floors
- Sealing one small gap shifts the exit point
Evidence that weakens it
- The pattern stays confined to one isolated room
- No vertical connection exists
- The trigger is liquid water only
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 seal service shafts or penetrations in ways that compromise fire stopping, drainage or equipment clearances.
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.
