Skylight Leaks on Flat Roofs in Toronto — Causes and Solutions

Skylights are a great feature on flat roofs—they bring in natural light, improve energy efficiency, and enhance aesthetics. But when installed or maintained poorly, skylights become one of the most common sources of leaks in Toronto homes and buildings with flat roofs. Knowing what causes skylight leaks and how to fix them can save you from expensive water damage and tenant complaints.

The most frequent cause of skylight leaks is faulty flashing. Flashing is the material used to seal the connection between the skylight frame and the roofing membrane. On a flat roof, where water tends to pool and flow slower than on sloped surfaces, any weakness in the flashing creates a direct path for water to enter. Over time, the sealant can crack or separate from UV exposure, freeze-thaw cycles, or simple aging.

Another issue is improper installation. If the skylight wasn’t leveled properly or lacks adequate upstands (the curb that raises it above the roof surface), water can collect around the edges and force its way inside. This is especially risky in Toronto, where snow accumulation followed by a sudden thaw creates pressure around the base of skylights.

Cracked glass or damaged frames are also potential leak sources. Hailstorms, falling debris, or thermal expansion can stress the glass or cause the frame to warp. Even a hairline crack can let moisture through during heavy rain.

In some cases, the leak doesn’t come from the skylight at all but from surrounding roof areas. Water can enter a few feet away and travel along the roof deck or insulation before dripping down through the skylight opening. That’s why professional leak detection is essential to determine the true entry point.

Fixing skylight leaks starts with a detailed inspection. A roofing specialist will examine the sealant, flashing, and membrane around the skylight, as well as inspect the glazing and frame.

Preventative maintenance can go a long way. Clear debris buildup from around the skylight regularly, especially after storms or fall leaf drops. Check seals for cracking or lifting, and have the entire area professionally inspected every year or two—particularly if your flat roof is more than a decade old.

Avoid DIY sealants or quick fixes that don’t address the full flashing system. These temporary solutions often trap moisture inside and worsen the damage.

For expert detection and repair of skylight leaks on flat roofs, trust Flat Roof Repair Toronto. Their experienced team also offers flat roof flashing repair and urgent flat roof leak repair across the GTA.