Passive Principle # 2 - Airtightness

TARGET: A Passive House construction should perform to an Air Changes per Hour (ACH) rating of 0.6 or less @ 50 Pascals pressure.

Air flow from inside to outside (and vise versa) should be restricted as much as possible. The point is to keep air flow controlled inside the building and prevent air leakage - and especially moisture flow via water vapour - into your assemblies.