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A skylight leak often shows up after a hard rain or a spring thaw: a brown ceiling stain, damp drywall, or water tracking down the inside of the frame. Knowing how to repair skylight flashing starts with identifying where water enters, because the stain below is rarely the exact point of failure. On homes across Toronto, Mississauga, and the GTA, freeze-thaw cycles can open small gaps around older skylights and turn a minor defect into hidden water damage.
Flashing is the layered metal or membrane system that directs roof water around the skylight curb and back onto the shingles. It works alongside the skylight’s glazing seals, frame gaskets, roofing underlayment, and drainage paths. A leak can come from any of these parts.
Check the inside first during or shortly after rain. Look for moisture at the glass edge, water near the interior trim, staining at the top corners, or drips from one side of the frame. Condensation can also collect on cold glass, but condensation usually appears as widespread moisture rather than a water path that worsens during rainfall.
From the roof, a technician checks for lifted or cracked shingles, exposed fasteners, gaps in step flashing, damaged counterflashing, dried-out sealant, and cracked skylight cladding. On older sunrooms and solariums, the problem may be where a skylight meets a glass roof system rather than a standard shingle roof.
A lasting repair normally requires removing enough roofing material to inspect the full flashing assembly. Applying caulk over a visible gap may slow a leak for a short time, but it does not restore the water-shedding layers beneath the shingles.
The proper approach depends on the roof and skylight design. On an asphalt-shingle roof, the work usually involves lifting shingles around the skylight, removing failed flashing, checking the roof deck and curb for rot, and installing new underlayment and correctly lapped flashing. Side pieces must overlap in the direction water travels, while the top flashing must direct water over the side pieces, not behind them.
For a curb-mounted skylight, the curb itself must be sound, level, and properly sealed to the roof. A warped curb, loose fasteners, or decayed wood can allow water behind otherwise good flashing. For deck-mounted units, damaged factory cladding, a failed perimeter gasket, or an incorrect installation detail may call for skylight replacement rather than flashing work alone.
Do not rely on roofing cement as the primary fix. It can crack as temperatures change, hide a more serious problem, and make future repairs harder. In Burlington, Oakville, and Milton, where exposed roof areas see sharp seasonal swings, flexible but properly installed waterproofing materials matter far more than a heavy bead of sealant.
A complete flashing repair generally includes these connected steps:
If the roof is nearing the end of its life, repairing flashing alone may not be the best value. Coordinating the skylight work with reroofing can prevent the same area from being opened twice.
Many homeowners assume every skylight leak comes from flashing. That is understandable, but it can lead to a repair that misses the actual failure.
Water between panes, a foggy appearance, or permanent cloudiness usually points to a failed insulated glass unit, not roof flashing. Water entering at the glass-to-frame joint may come from worn gaskets or failed glazing seals. A cracked dome, damaged glass panel, corroded aluminum frame, or blocked drainage channel can create similar symptoms.
This is especially common on aging solariums and conservatories in Vaughan, Richmond Hill, Markham, Kitchener, Waterloo, Cambridge, and Hamilton. These structures often combine custom glazing, aluminum framing, roof panels, and complex transitions. The visible leak may be at a skylight, while the source is a failed joint farther uphill or a drainage route blocked by debris.
Roof work carries fall risk, and a skylight opening is not a safe place to experiment. Professional assessment is the sensible choice when water is entering the home, the roof pitch is steep, the flashing is concealed beneath roofing, or there are signs of structural damage.
Call for help if you notice soft drywall, sagging interior trim, moldy odor, rot around the opening, repeated leaks after caulking, cracked glass, or fog between panes. These signs indicate that water may have been present longer than expected.
Alumwave Glazing Inc. assesses the full assembly – glass, frames, seals, drainage, roof connection, and surrounding structure – rather than treating every leak as a sealant problem. For homeowners with older skylights attached to sunrooms or solariums, this can mean a targeted repair, replacement of failed glass, frame restoration, or a broader restoration plan when the system has reached the end of its serviceable life.
A repaired skylight still needs basic seasonal attention. Keep leaves, branches, and roof debris from collecting above the unit, especially after fall storms. Debris holds moisture and can block designed drainage paths.
Inspect the interior after major storms and again after winter. In North York, Scarborough, Ajax, and Pickering, ice buildup and repeated thawing can expose weak roof transitions that were not obvious in dry weather. Address loose shingles, cracked sealant, and small roof defects before water reaches the roof deck.
Avoid pressure washing around skylights or applying coatings that block drainage channels. If the glass is old, cloudy, or inefficient, replacing the insulated glass at the same time as a repair may improve comfort and reduce condensation, but only if the frame and roof connection are still sound.
Caulk can seal a small exposed joint temporarily, but it cannot replace missing or incorrectly layered flashing. If water is getting under shingles or behind the curb, the roof layers need repair.
Condensation tends to form on the interior glass surface during cold weather. A roof or flashing leak usually follows rain, leaves staining around trim, or creates a defined wet path.
Usually, yes. Reusing old flashing can compromise a new skylight installation, particularly when the existing metal is bent, corroded, or incompatible with the replacement unit.
Wind can force water into gaps that normal rainfall does not reach. This often points to a failed side flashing detail, damaged cladding, or a gap in the upper roof transition.
No. Fog between glass panes is generally a failed insulated glass seal. The glass unit may need replacement even if the flashing is also repaired.
Freeze-thaw movement, aging sealants, wind exposure, roof wear, ice buildup, and past installation errors are common causes. Older homes can also have deteriorated roof decking around the opening.
Yes. Slow water entry can soak the roof deck, curb, interior framing, and trim. Rot is often hidden until shingles or interior finishes are removed.
Not always. A sound skylight may only need corrected flashing or new seals. Replacement is more likely when the glass, frame, curb, or factory cladding is damaged or outdated.
Often, yes. Sunrooms and solariums may use custom glass panels, aluminum roof systems, internal drainage, and nonstandard transitions. The repair must match the original system rather than follow a standard shingle-roof detail.
Some urgent repairs can be completed in winter if conditions are safe and materials can be properly installed. Permanent work may need to wait for dry weather and suitable temperatures.
As soon as possible. Even a small leak can wet insulation and framing before the ceiling shows obvious damage. Early repair is usually less disruptive than restoring water-damaged materials later.
A skylight should bring daylight into a room, not repeated worry every time rain starts. Whether the issue is flashing, glass, seals, or the roof structure around it, a careful diagnosis and properly layered repair will protect the home far better than another surface patch.