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Water around a skylight does not always mean the skylight itself has failed. The source can be the roof flashing, underlayment, nearby shingles, condensation on the glazing, a failed insulated-glass seal or water travelling from somewhere upslope.
Why do skylights leak?
The most common categories are flashing defects, incorrect roof-pitch or flashing-system compatibility, damaged surrounding roofing, blocked drainage around the skylight, failed seals or glazing components, and condensation mistaken for a leak.
When is a “skylight leak” actually condensation?
VELUX Canada treats condensation as a separate issue from rain leakage. Condensation forms when warm, humid indoor air reaches a cold glass or frame surface. It may drip from the skylight even when the exterior roofing and flashing are watertight.
Useful clues include:
- moisture appears during cold weather without recent rain;
- water forms directly on the inside glass or frame;
- bathroom, kitchen or indoor humidity is high;
- the pattern improves when indoor humidity is reduced or ventilation increases.
If attic or whole-house moisture is also present, review how attic ventilation affects roof life.
How do flashing and roof pitch cause skylight leaks?
Skylights rely on a flashing system that integrates the unit with the roof covering. VELUX Canada notes that roof pitch is important because flashing kits are engineered for specific slope ranges and roofing materials so water can drain off the flashing and skylight correctly.
Problems can occur when:
- the wrong flashing kit was used for the roof material;
- step flashing or head flashing was omitted or installed incorrectly;
- underlayment was not integrated correctly around the opening;
- shingles or metal around the skylight were later modified;
- sealant was used as the primary waterproofing method instead of proper flashing.
GAF's current flashing guidance also identifies skylights as roof penetrations that require properly integrated flashing to keep water moving down and off the roof.
Can leaves, snow or ice make a skylight leak?
Yes, indirectly. VELUX Canada recommends removing leaves and debris from skylight flashing so rainwater can flow freely. In cold regions, snow and ice can remain around a skylight for long periods and melt quickly as temperatures rise.
Blocked drainage can push water into flashing details that normally shed it successfully. The surrounding roof, valleys and gutters should therefore be part of the inspection rather than focusing only on the glass unit.
What skylight-unit problems can cause moisture?
Fogging or condensation between glass panes indicates a failed insulated-glass seal rather than a roof leak. Cracked glazing, damaged gaskets or a problem with an operable sash can also allow water where it should not be.
The age and model of the skylight matter because parts, flashing kits and replacement options vary. Record the manufacturer and serial number if available before planning repair.
How do roofers diagnose a leaking skylight?
A professional roof inspection should avoid assuming that the stain location identifies the exact exterior entry point. Water can travel before it becomes visible inside.
Can a leaking skylight be repaired, or should it be replaced?
Repair is reasonable when the skylight unit is still serviceable and the problem is localized to surrounding roofing, flashing, debris or a replaceable component. Replacement becomes more attractive when the insulated glass has failed, the frame is deteriorated, parts are obsolete, repeated repairs have not solved the problem or the roof is already being replaced.
If the roof around the skylight is also aging, use the roof repair or replacement decision guide so the skylight work is coordinated with the broader roof plan.
Frequently asked questions
Why does my skylight drip when it is not raining?
Condensation is a common possibility, especially in cold weather or humid rooms. Check whether moisture is forming on the interior glass or frame.
Can caulking stop a skylight leak?
It may temporarily stop a small surface opening, but caulk should not replace a correctly installed flashing system. If the flashing sequence is wrong, sealant-only repairs often return.
Why does the skylight leak only in wind-driven rain?
Wind can push water into vulnerable head, side or roof-to-unit transitions that shed vertical rainfall without trouble.
Does fog between the glass panes mean the roof leaks?
No. Fogging between panes generally indicates failure of the insulated-glass seal rather than water entering through the roof.
Should an old skylight be replaced during reroofing?
It is worth evaluating because reroofing provides access to the full flashing system. Age, glass condition, parts availability and remaining expected life should guide the choice.
Research basis: VELUX Canada distinguishes condensation from water leakage, recommends annual debris removal around skylight flashing, and states that flashing kits are designed around specific roof pitches and roofing materials. GAF likewise identifies skylight flashing as a critical penetration detail.
Diagnose the moisture before sealing the frame.
A lasting skylight repair starts by separating roof water entry from condensation and glass-unit failure, then rebuilding the detail that actually failed.
Contact Watershed Roofing