The design of an airtight assembly requires the use of appropriate materials, components, and accessories that can be combined to create an effective air barrier system. Ensuring continuity of the air barrier at interfaces and penetrations of the building enclosure is challenging and critical to its performance.

An effective air barrier should have the following features:

• Air impermeability - All materials, components, and accessories used
  to create the air barrier must be able to prevent airflow. This is typically
  defined in industry standards referenced by the BC Building Code as an air
  permeability of less than 0.02 L/s·m² (0.004 cfm/f²) at 75 Pa.
• Continuity - The air barrier system must completely enclose the conditioned
  space without any gaps or interruptions. Continuity is the most important
  criteria for an effective air barrier and also one of the most challenging.
  Designers and contractors must ensure continuity of the air barrier around
  penetrations, transitions, and interfaces in the enclosure. This can be done
  through proper detailing and diligent construction practices.
• Durability - The air barrier system must be designed to last for the entire
  service life of the building or of the materials that cover it. The system should
  resist mechanical forces, UV exposure, moisture, chemicals, and other
  contaminants, throughout its expected service life. Interfaces in particular
  should be designed to be resilient and able to accommodate expected
  deflections, for example at floor slabs.
• Strength and stiffness - From construction to occupancy, the air barrier
  system must resist forces acting on it. The design should account for mechanical forces created by wind and stack effect pressures and allow for dimensional changes in the structure caused by thermal expansion and moisture absorption.