What causes air leaks around windows?

Air leaks around windows are primarily caused by deteriorated weatherstripping, failed caulking, poor installation, or settling of the home over time. In Toronto's climate with extreme temperature swings from -20°C to +35°C, these sealing materials expand and contract repeatedly, leading to gaps that allow drafts and energy loss.

Weatherstripping breakdown is the most common culprit, especially in homes over 10-15 years old. The rubber, foam, or vinyl strips that seal the moving parts of windows become compressed, cracked, or brittle from Toronto's harsh winters and humid summers. You'll notice this most around the sash where the window opens and closes, or where the window meets the frame.

Caulking failure around the exterior window frame is equally problematic. The caulk that seals the gap between your window frame and the house structure can shrink, crack, or pull away over time. This is particularly common in Toronto's older homes where settling occurs, or in newer builds where the caulk wasn't properly applied during construction. Look for visible gaps or cracks in the caulk line around the outside of your windows.

Installation issues from the original window installation can create persistent air leaks. If windows weren't properly shimmed and sealed during installation, or if the rough opening was cut too large, gaps can develop that no amount of weatherstripping will fix. This is common in Toronto's century homes where window replacements may not have been done to current standards.

Structural settling affects many Toronto homes, especially those built on clay soil common throughout the GTA. As homes settle, window frames can shift slightly, creating gaps in previously tight seals. This is normal but requires periodic maintenance to address new air leaks as they develop.

Window hardware problems can also contribute to air leaks. Loose or worn window locks, hinges, or operators prevent windows from closing tightly against their weatherstripping, creating gaps even when the window appears closed.

To identify air leaks, perform a simple test on a windy day by holding a lit incense stick or candle around window edges - the flame will flicker or smoke will move where air is infiltrating. Focus on the corners of the frame, where the sash meets the frame, and around any window hardware.

Professional assessment is recommended if you're losing significant energy or experiencing persistent drafts despite basic weatherstripping replacement. A qualified contractor can determine whether the issue requires simple maintenance, window adjustments, or more extensive repairs to the installation. Browse contractors in our directory at Toronto Construction Network who specialize in window maintenance and energy efficiency improvements.