The air barrier protects the entire building from air infiltration and exfiltration through the building envelope.

The air control layer tries to stop inside air from escaping through the building envelope and tries to stop outside air from entering through the building envelope.

• Air movement = moisture movement
• Air movement = heat movement and energy loss
• Air movement = noise movement (important in attached buildings)

The air control layer restricts air from entering or exiting the building, making the indoor environment of the home much easier to control. The heating and cooling systems will need to work less to control temperature and moisture/humidity levels in a tighter home. However, when a home is very tight, the mechanical ventilation (usually an HRV) may need to work a little more often to ensure fresh air supply and removal of moisture produced within the building.

Air Barrier Criteria:

• Can be installed anywhere in building envelope assembly
• IMPERMEABLE to air flow
• CONTINUOUS, by sealing all seams, edges, gaps, holes, tears and penetrations
• Not necessarily impermeable to moisture flow
• Rigid and strong enough to withstand air-pressure differences
• DURABLE during construction and for the expected life of the building

Materials:

• Polyethylene
• House wrap system
• Drywall
• Wood and concrete
• Many wood sheathing/plywood products
• Rigid foam board. (must have air barrier properties as described in the OBC…code does not recognize EPS as an air barrier)

Sealants used with materials:

• Acoustical and approved tapes
• Special tape designed for house wraps
• Neoprene gaskets
• Foam, caulking, backer rod

Placement/Location:

Exterior or interior of the entire building envelope. The key is to make it continuous.

If an air barrier is damaged, penetrated, or not completely sealed around the entire building envelope, this can allow outside air to enter and inside air to exit. This will greatly increase heat loss and cause the home to be less energy efficient, reducing the airtightness, and making the house drafty, and possibly causing moisture damage as air carries moisture with it.