Air Leakage at Windows and Doors
Windows and exterior doors are the most visible transitions between the conditioned interior of a home and the outdoor environment. They are also common sites for air infiltration — not primarily through the glass or the door panel itself, but through the perimeter sealing: the interface between the frame and the rough opening, and the contact surfaces between moving parts of the window or door and their frames.
In an older Canadian home, windows and doors may account for a meaningful share of uncontrolled air infiltration. Cold air entering through gaps at floor level, or warm air exfiltrating at ceiling level through unsealed rough openings, contributes directly to heating demand. Unlike adding insulation, most air sealing work at windows and doors can be done without tools, special equipment, or building permits.
Finding Air Leaks Before You Seal
Identifying the location and severity of air leaks before applying sealants prevents wasted effort and ensures the most significant gaps are addressed first.
Simple Methods
- The hand test: On a cold, windy day, slowly move your hand around the perimeter of window and door frames. Noticeable cold airflow points to gaps that need attention.
- The incense or smoke pencil test: Hold a lit incense stick or smoke pencil near suspected gaps. Movement or deflection of the smoke stream indicates air movement.
- Visual inspection: Check interior window trim for gaps where it meets the wall, look for daylight visible around door frames, and check for deteriorated or missing caulk on the exterior.
Professional Assessment
A blower door test, conducted as part of a home energy assessment, depressurizes the house and measures total air leakage. It can be combined with thermal imaging to show exactly where infiltration is occurring. Natural Resources Canada's EnerGuide home energy assessment program connects homeowners with certified energy advisors who use this equipment.
Caulking: Sealing Static Gaps
Caulking is the appropriate sealant for gaps that do not move — primarily the joint between window and door frames and the surrounding wall surface, both interior and exterior.
Exterior Caulking
The joint between an exterior window or door frame and the siding or cladding is exposed to full weather. Sealants used here need to withstand UV exposure, rain, and the mechanical stress of freeze-thaw cycles. Silicone and siliconized acrylic latex caulks are generally the most durable choices for exterior applications in Canada. Fully silicone products resist UV degradation and remain flexible at very low temperatures but are difficult to paint. Siliconized acrylic latex formulations are paintable and perform well in most climate zones.
Interior Caulking
Interior gaps — between window trim and drywall, or between door casing and the rough opening — are protected from weather. Acrylic latex caulk is sufficient for most interior applications. For gaps behind baseboards and along floor perimeters, acoustical sealant (non-hardening sealant) is preferred in high-performance retrofits because it remains permanently flexible without cracking.
Weatherstripping: Sealing Moving Parts
Where a door or window sash meets its frame, the seal must accommodate repeated opening and closing. Rigid sealants are not suitable here — weatherstripping products are designed for this application.
Door Weatherstripping Types
Durability in Cold Climates
Rubber and silicone weatherstripping products maintain flexibility at low temperatures. EPDM (ethylene propylene diene monomer) rubber is commonly specified for exterior door applications in cold climates because it does not harden or crack at temperatures typical of Canadian winters. Avoid products made from PVC foam or basic polyurethane foam for exterior door installations in cold regions — these materials become stiff and compress poorly when temperatures drop significantly below freezing.
Expanding Foam Sealant: Filling Large Gaps
Low-expansion polyurethane foam in a can is suitable for filling large gaps around window and door rough openings — typically the space between the frame and the framing lumber. Standard expanding foam is not appropriate for application between the frame and the door stop, as the expansion pressure can distort the frame and affect the door's ability to close properly.
Use minimal-expanding or "window and door" formulated foam around frames where distortion is a risk. Standard expanding foam can exert significant pressure as it cures and may bow a window or door jamb out of square if applied in a continuous bead around the full frame perimeter.
Backer Rod and Caulk for Wide Gaps
For gaps wider than approximately 12mm (1/2 inch), it is better to first insert a foam backer rod — a round foam cord available at hardware stores — and then apply caulk over the top. Caulk applied without backing into a wide gap will not cure properly in the centre and will eventually crack.
Interior Window Film
For windows with poor thermal performance, interior window film kits provide a temporary secondary glazing layer. A plastic film is attached to the interior window trim using double-sided tape and then tightened with a heat gun. The sealed air space between the film and the existing glazing adds a layer of insulation and can meaningfully reduce cold radiation from single-pane or poor-quality double-pane windows.
Window film is a seasonal measure rather than a permanent upgrade, but it is inexpensive and can be effective in homes with older glazing that is not yet due for replacement.
When Sealing Is Not Enough
Air sealing addresses infiltration through gaps, but it does not change the thermal performance of the glass or frame itself. In locations with severe winters, single-pane windows or old double-pane units with failed seals — visible as fogging or condensation between panes — may warrant replacement rather than further sealing effort.
When evaluating window replacement in Canada, the key ratings are the U-factor (lower is better for heat retention) and the Energy Rating (ER) — a Canadian standard that combines U-factor, solar heat gain, and air leakage into a single number. Windows with a higher ER are more energy-efficient in cold climates. ENERGY STAR window certifications in Canada use climate-zone-specific thresholds, with different minimums for the zone covering Alberta and the Prairies versus coastal British Columbia.