The core idea
A tighter house still needs controlled replacement air when exhaust, combustion or occupancy removes or changes indoor air.
How the mechanism works
When planned air paths are insufficient, the building draws air through whichever cracks offer the least resistance.
When it becomes relevant
Typical trigger: Range hoods, dryers, fireplaces, multiple exhaust fans or high occupancy.
Evidence that supports this interpretation
- Pressure symptoms appear only under high exhaust
- Opening a safe exterior window changes the pattern
- Ventilation commissioning is absent or outdated
Evidence that weakens it
- No exhaust source is operating
- The building is highly leaky everywhere
- The symptom is caused by a direct spill
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 improvise permanent openings or disable alarms; makeup-air design must respect climate, fire and combustion safety.
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.
