What causes basement windows to leak during storms?

Basement window leaks during storms are typically caused by poor drainage around the window well, deteriorated sealing, or inadequate grading that allows water to pool against the foundation. The combination of Toronto's heavy rainfall and aging window installations creates perfect conditions for water infiltration.

The most common culprit is window well drainage failure. Many Toronto homes, especially those built before the 1980s, have window wells that weren't properly designed with drainage systems. When storm water accumulates faster than it can drain away, hydrostatic pressure forces water through any available opening. This is particularly problematic in Toronto's clay soil, which doesn't drain well naturally and can become saturated during heavy rains.

Deteriorated window sealing is another major factor. The caulking and weatherstripping around basement windows breaks down over time due to Toronto's freeze-thaw cycles. Winter temperatures can drop to -20°C or lower, causing materials to contract, while summer heat causes expansion. This constant movement creates gaps where water can penetrate. Additionally, many older Toronto homes have original steel or aluminum basement windows that may have developed rust or corrosion, compromising their water-tight seal.

Grading and surface water management plays a crucial role in basement window leaks. Toronto's building standards require ground to slope away from foundations at a minimum 5% grade for the first 6 feet. However, settling over time, landscaping changes, or improper initial grading can create low spots that direct water toward window wells instead of away from the house.

In Toronto's climate, seasonal factors compound these issues. Spring snowmelt combined with April showers can overwhelm drainage systems. The city's aging infrastructure in neighborhoods like Riverdale, High Park, and parts of North York means storm sewers may back up during heavy rainfall, preventing proper drainage from window wells.

Professional assessment is essential for persistent leaks, as water damage can lead to mold, foundation issues, and expensive repairs. A waterproofing contractor should evaluate the window well drainage, inspect sealing integrity, and assess grading around the foundation.

Immediate steps include clearing debris from window wells, checking that weeping tile systems are functioning, and ensuring gutters direct water well away from the foundation. However, proper repairs often require excavation, new drainage installation, and professional window resealing - work that typically requires permits through the City of Toronto Building Division when structural modifications are involved.

For reliable waterproofing contractors experienced with Toronto's unique drainage challenges, browse verified professionals in our Toronto Construction Network directory.