Control of airflow is important to several aspects of building enclosure performance. For example:

• Pressure moderation as a part of water penetration control is highly dependent on the existence of an effective air barrier.
• An effective air barrier limits the amount of moisture that can be deposited within assemblies due to condensation.

For deep stud assemblies, or those without exterior insulation, an effective interior air barrier is crucial to reduce the amount of warm humid air that is allowed to enter the framing cavity and deposit moisture on the cold sheathing surface.

Condensation through interior air leakage is more severe than condensation through vapour flow and should be treated as a greater threat to enclosure durability.