Toronto's winter is the single hardest season for a skylight. Ice dams, snow accumulation, freeze-thaw cycles, and the indoor-outdoor temperature differential all stress every joint, gasket, and flashing detail. The skylight problems that show up between December and March almost always trace back to maintenance that was skipped in October. This checklist covers the moves that matter.
Ice dams — the biggest winter risk
An ice dam forms when heat escaping from the attic melts snow on the warm part of the roof, the meltwater runs down to the cold eave, and refreezes. The growing ice ridge backs water up under the shingles — and into the skylight curb if you have one on a lower part of the roof.
Prevention checklist:
- Verify attic insulation is at code (R-60 minimum for Toronto). Inadequate insulation lets heat escape to the roof deck
- Check that soffit intake vents aren't blocked by insulation jammed against them — common in older homes
- Confirm ridge vents are clear and unobstructed
- Have eavestroughs cleared of leaves before the first freeze — clogged gutters trap meltwater right at the eave
- If your skylight is in the lower roof zone, check that the ice-and-water shield extends past it (required by code in the eave 36" but worth confirming around lower skylights)
If you've had ice dam issues in past winters, get an attic ventilation assessment from Toronto Skylight Installers before the snow flies. The fix is usually a $400–1,500 ventilation upgrade, far cheaper than emergency leak repair in January.
Condensation control
Interior glass condensation in winter is the most-common skylight concern. A little is normal on cold mornings. Heavy or persistent condensation means one of three things:
- Indoor humidity too high — over 40% in winter overwhelms most skylight glass. Run bathroom fans, fix any chronic moisture sources, lower humidifier output
- Attic ventilation inadequate — warm moist air collecting at the skylight from below. Fix the ventilation, not the skylight
- Old IGU failure — if condensation is BETWEEN the panes, the seal has failed. Glass replacement needed, not whole-unit replacement
Snow load management
Toronto's snow load rating is 1.0 kPa (21 lbs/sq ft). Modern skylights handle this without issue. Concerns:
- Never climb on a snow-loaded roof to clear a skylight. The unit is not rated for foot loads, especially with snow on top
- If you have an oversized skylight on a flat roof, watch for excessive accumulation — flat-roof drainage can clog with ice. See flat-roof skylight notes
- After major snowfalls, glance at the unit from inside — any visible deflection of the glass means an issue (extremely rare on quality units)
The October checklist (do these every fall)
- Visual inspection of exterior glass, flashing, and curb from a safe vantage point
- Eavestrough cleanout across the whole roof, not just near the skylight
- Attic check — look at the underside of the skylight shaft, the surrounding insulation, and ventilation paths
- Test vented units — open and close once, verify the seal closes properly
- Clear debris from around the curb (leaves, twigs, shingle granules)
- Test interior gasket — feel for drafts around the frame on a cool morning
- Book the emergency repair number in your phone before winter starts: (416) 365-7557 or see emergency skylight repairs
When to call a professional before winter
- Any visible flashing damage, curl, or lift
- Any new ceiling stain near the skylight shaft
- Any sign of moisture in the attic around the skylight
- Heavy condensation on interior glass that didn't happen last winter
- Difficulty operating a vented unit
- Past history of ice dam issues
An October service visit from Toronto Skylight Installers typically runs $200–500 with any minor repairs included. Compare that to a $1,500+ emergency repair in February.