Windows and doors are the most concentrated air-leakage paths in most houses, which is why they appear at the top of every air-sealing checklist. The work splits cleanly into two techniques that are easy to mix up: caulking for the stationary joints around a window, and weatherstripping for the moving parts that have to open and close.
Caulk versus weatherstrip
Caulk seals fixed cracks and joints — the gap between the window frame and the surrounding wall, or between trim and finish. It is suited to joints that do not move and that are no more than about a quarter inch wide. Weatherstripping seals the gaps around operable sashes and doors; the ideal weatherstrip compresses when the sash is shut and springs back when it opens.
| Location | Moves? | Technique |
|---|---|---|
| Frame-to-wall perimeter | No | Caulk (exterior-grade) |
| Trim and casing joints | No | Caulk, or seal behind removed trim |
| Operable sash edges | Yes | Weatherstripping / gaskets |
| Window kept shut all season | No | Strippable caulk (removable in spring) |
| Joints 6 mm (1/4 in.) or wider | No | Backer rod, then caulk |
Detailing a joint that lasts
The most common failure is recaulking over old, degraded sealant: new caulk will not bond to a failed bead beneath it. Remove the old material completely, clean and dry the surface, and apply in mild conditions — most sealants need temperatures above roughly 5 °C to cure properly, and direct sun can skin the bead before it sets. For wide joints, pack a backer rod into the gap first so the caulk forms a correctly shaped bead rather than slumping inward.
A window that is not needed for ventilation or emergency escape can be sealed shut with strippable caulk for the heating season and reopened in spring — a low-cost way to close a persistent draft without replacing the unit.
When sealing is not enough
Caulking and weatherstripping reduce air leakage, but they do not add insulation or control solar heat gain. Where a window itself is the weak point, the options move toward storm windows, interior film, or replacement — decisions that belong to the larger envelope upgrade rather than to seasonal maintenance. Air sealing the openings remains worthwhile first because it is inexpensive and addresses the leakage that undermines everything else.
The funding picture in Canada
Sealing and insulation upgrades have historically been supported by federal programs, and the landscape has shifted recently. The Canada Greener Homes Grant, which offered homeowners between $125 and $5,000 toward recommended retrofits, closed to new applicants in February 2024; existing participants had until the end of 2025 to submit documentation. The companion Canada Greener Homes Loan stopped accepting new applications once its funding was fully committed.
In their place, Natural Resources Canada has introduced the Canada Greener Homes Affordability Program, which provides no-cost, direct-install retrofits — including insulation and air sealing — for lower- and median-income households, delivered through provincial and territorial partners. Eligibility and application routes are set by each province rather than applied for centrally, so the current details depend on where a home is located.
Natural Resources Canada notes that it does not authorize unsolicited contact — by phone, email, or door-to-door — to enrol homeowners or inspect, sell or rent heating and cooling products. Home energy evaluations are arranged by the homeowner with a licensed service organization.
Where this connects
Sealing openings is one part of the wider air-control strategy in air and vapour barriers. Once the envelope is sealed, the thermal layer is covered in insulation types and R-value.
References
- Natural Resources Canada. Keeping the Heat In — Section 4: Comprehensive air leakage control.
- Natural Resources Canada. Canada Greener Homes Grant (closed).
- Natural Resources Canada. Canada Greener Homes Affordability Program.