Air Sealing

Illustration Source: CHBA Manual, Fig.2.9,Pg.24

Air sealing is done to control the unwanted movement of air into and out of the home. The above diagram shows the main leakage areas of a home, not including any cracks in the building envelope or leakage due to poor workmanship.

Air flow accounts for almost all of the moisture movement into the wall. Rate of flow is a function of:

  • Size and number of cracks and holes
    • Influenced by the air barrier system
  • Pressure difference across the envelope
    • Influenced by air flow effects such as wind, stack effect, and unbalanced ventilation systems
  • Indoor/outdoor temperature difference

An air barrier must be continuous throughout the building, including:

  • Corners
  • Walls
  • Floors
  • Ceilings
  • Windows
  • Doors
  • Shared areas between the garage and the house
  • Any other opening in the building such as piping and electrical services

Controlling air leakage is a major factor in having a high performing building. It reduces energy costs and reduces moisture build up in the building envelope due to moisture laden air movement. The air barrier of a building can be thought of as an air leakage control layer.

There are two ways to seal the building envelope:

INTERNAL SEALING EXTERNAL SEALING

Approaches

Sealed Polyethylene Approach (SPA)

  • Polyethylene is a common interior air barrier
  • Used with sealants and header wraps (house wraps)

Airtight Drywall Approach (ADA)

  • Drywall used with sealants, gaskets, framing members and other rigid materials is another way to control air leakage

Approaches

Exterior Insulation Approach (EIA)

  • Rigid foam board placed on the exterior wall under the siding creates an air barrier

House Wrap Approach (HWA)

  • Uses a flexible sheathing membrane on the external wall to create an air barrier

Advantages:

  • Located in a stable warm environment
  • Good performance record
  • Prevent particles, fibres, mould, and gases emitted from building materials from entering the home

Advantages:

  • Labour and material costs are lower. There are less connections, joints and penetrations to seal
  • An airtightness test can be performed before drywall is completed. This allows for last minute sealing and insulating to improve airtightness



To be effective, all air barrier systems should have a low air leakage rate, be continuous through the entire building envelope, be durable during and after construction, and last as long as the building.

Additional benefits to properly air sealing a home:

  • Reduces wind-driven rain penetration in walls
  • Reduces heating loads in the winter
  • Helps the ventilation system maintain healthy indoor relative humidity levels
  • Reduces cooling loads in summer
  • Reduces outdoor noise penetration
  • Reduces or eliminates drafts
  • Increases comfort

During renovation, if any work is done where the air barrier exists, great care must be taken to ensure that it remains continuous throughout the house. The Building Code states that an air barrier must be continuous.

Before renovating, determine if the air barrier is located in the interior or exterior. Consider what work is going to be done and how it will effect the air barrier. If new light fixtures or services are going to be installed consider what types and how they are going to be installed and then sealed.

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