Detecting and sealing air leaks in a home

Air infiltration in a home greatly reduces occupant comfort and increases heating and cooling costs.

Warm-air exfiltration—that is, warm indoor air leaking outward—carries moisture with it. This can lead to hidden condensation inside the building envelope, degrading the insulation, promoting mould growth, and causing wooden structural components to rot.

In a poorly sealed home, air leaks can be numerous and well hidden. If all the gaps letting air through were combined, they would be equivalent to a hole as large as a cooking pot.

This explains why poor air sealing can raise a home’s energy bill by up to 15 %.

Here are two ways to detect air leaks in a home.

If you participate in the Rénoclimat program, you will receive a blower-door test during the home energy evaluation, covering everything from the foundation to the attic.

Once you have listed the locations to be sealed, follow these recommendations:

• Install the air barrier material continuously to prevent air from passing through the exterior envelope. Any gap in the air barrier allows cold air to penetrate the insulation, reducing its insulating capacity.
• Install the vapour barrier material continuously on the warm side of the insulation. The vapour barrier prevents moisture from migrating toward colder areas. Without this barrier, moisture could condense and cause mould problems.
• Seal around every object (ceiling fixture, electrical outlet, switch, fan, dryer vent, fresh-air intake, electrical or plumbing pipe, etc.) that penetrates the air-barrier or vapour-barrier membranes to maintain their continuity.
• Choose the sealant based on the area to be caulked and the surrounding conditions. Also consider cost, durability, adhesion, elasticity and ease of application.
• Thoroughly clean the joint before applying the caulking product. Remove paint, dust and old compound with a putty knife or screwdriver. For best results, the joint to be sealed must be clean.
• Start sealing on the interior side to first control leaks of moist indoor air. Then proceed to seal the exterior side to prevent rainwater infiltration into the walls.
• Apply caulking from top to bottom. Exfiltration can cause condensation problems and deterioration of insulation and wooden structures. Since most leaks occur upward, begin sealing the upper levels of your home and humid rooms such as bathrooms.
• Install weatherstripping around doors and windows.

A poor joint between the concrete foundation wall and the wooden framing is often the cause of air infiltration. During construction, it is relatively easy and inexpensive to place a compressible gasket under the sill plate to prevent cold air from entering under the ground-floor subfloor. In an existing home, this defect can still be corrected, though it requires care and attention.

Work can be done from the inside by sealing each joint with acoustic sealant. If the exterior cladding is being replaced, it is advisable to seal the gaps between concrete and wood with the same product before installing the new siding.

Once airtightness is ensured, insulate the top of the concrete wall and the rim joist to prevent direct contact between cold air and the wooden structure.

Various materials can achieve good results. Batt mineral wool is the easiest to use: cut the batts precisely and insert them without compression. Cover the assembly with a polyethylene vapour-barrier membrane and seal the joints with appropriate adhesive tape. Spray polyurethane foam can also be used, but it must be covered with a fire-resistant coating.