Air-Barrier Materials

Requirements for Air-Barrier Systems

The air-barrier system is an important part of any retrofit job. It is the main means of protecting the building structure and the insulation from moisture damage. In order to be effective, the air-barrier system must be:

• resistant to air movement
• continuous, completely surrounding the envelope of the house and properly supported by rigid surfaces on both the interior and exterior (to prevent movement in high winds)
• strong and durable

A variety of materials are used throughout the envelope to act as the air barrier. In some cases, building materials such as drywall, baseboards or structural members are incorporated into the air barrier by sealing them to adjoining materials.

Air-Barrier System Components

The most common components of an air-barrier system are:

• sheet or rigid materials for large surfaces
• caulking and gaskets for joints between materials that do not move
• weather stripping for joints that do move

Choosing Air-Barrier Materials

If the material offers resistance to airflow, strength and durability, consider the following installation factors:

• Is it easy to install?
• If installed in a concealed location, will it last the life of the building or will it be accessible and easily repaired?
• Is it compatible with other materials in the system? Can it be successfully sealed to adjacent materials?
• Is the choice of material appropriate for the other work being done on the home? Some renovation work will permit the installation of a new sheet-material air barrier, while other jobs may require comprehensive air-sealing work instead.
• Does it serve other functions such as acting as insulation or as a vapour barrier?

Sheet Materials

Polyethylene Sheeting

• Available in wide sheets, minimizing the number of seams required.
• Seams and edges should be supported on both sides to maintain the seal.
• A thickness of 0.15 mm (6 mil) now commonly installed as an air barrier.
• Should be protected from exposure to sunlight. When exposed to sunlight over extended periods, a UV-stabilized polyethylene should be used.
• Should be clear, made from virgin material and labelled. Should conform to the Canadian General Standards Board standard for polyethylene.
• Can also function as a vapour barrier.

Housewrap

• Available in wide sheets, minimizing the number of seams required.
• Acts solely as an air barrier; does not function as a vapour barrier.
• Used to wrap the exterior of a house; often bonded to exterior glass-fibre sheathing.
• When installed on the exterior, acts as a wind barrier, preventing wind from reducing the effective RSI value of insulation.
• Should be protected from extended exposure to sunlight.

Rigid Materials

Most solid building components will act as barriers to air. These components include drywall, plaster, plywood, glass, wood and poured concrete (not concrete blocks). Insulating materials such as rigid foam boards also act as air barriers. To be effective, the seams between these various materials must be sealed with caulking, weatherstripping or gasket.

• For example, caulking can be used between the baseboard and a wall as well as between the baseboard and the floor, linking the air-sealing qualities of three different building components.