How to Fix a Leaking Skylight: Leak or Condensation?

How to fix a leaking skylight: first decide whether it is a leak or condensation, then trace the water to the flashing, the sealant, the glazing seal or a roof leak above. A bead of compatible sealant fixes some leaks, but failed flashing needs to be rebuilt and a skylight with a broken glass seal may need replacing.

Do not climb a wet roof.

How to fix a leaking skylight: leak or condensation?

Condensation forms on the inside glass in cold, humid conditions and drips or runs down the frame, even when it is not raining. A true leak appears during or after rain or snowmelt, and shows as stains on the frame, the shaft or the ceiling around the skylight. Wipe the glass dry and check again the next time it rains.

Quick facts: how to fix a leaking skylight
Time needed	1 hour to inspect; 2 to 6 hours to reflash
Tools	Ladder, flashlight, caulk gun, compatible sealant, flashing kit
Difficulty	Moderate to hard; work at height
Safety	Never work on a wet, icy or steep roof without proper equipment

Common causes

Cause	Sign	Fix
Failed flashing	Leak around the edges during rain	Reflash the skylight
Dried or cracked sealant	Gaps at the curb, glass or frame	Remove old sealant, reseal
Failed glazing seal	Fog or water between panes	Replace the glass or unit
Condensation	Dripping with no rain	Improve ventilation, insulate
Roof leak upslope	Water tracks to the skylight	Find and fix the source
Cracked glass or frame	Visible damage	Replace parts
Ice dam	Winter leaks after snow	Fix attic heat loss

Inspection steps

1. From inside, look for stains, wetness and mould on the skylight frame and the light well. Note where water first appears.
2. From the ground or a ladder at the eaves, look at the skylight with binoculars for lifted flashing, cracked sealant, debris and moss.
3. Check the attic around the shaft for wet insulation or stained wood.
4. Test with a hose on a dry day: wet the area below the skylight first and work upward, with a helper inside watching for water.

Temporary fixes

• Place a bucket and towels, and a plastic sheet in the light well if water is running.
• Apply exterior-grade sealant to small cracks in dry weather, as a stopgap.
• On a larger leak, a roofer can cover the skylight with a tarp. Do not climb in bad weather.

Lasting repairs

Resealing: remove loose old sealant, clean and dry the surfaces, and apply a sealant that is compatible with the skylight and roofing materials. Fit it carefully without blocking drainage channels.

Reflashing: this is the most reliable cure for a leaking skylight. A roofer removes shingles around it, installs a flashing kit made for your model, overlaps layers properly, and replaces the shingles. It needs skill, because flashing must be layered so water always runs over, not under.

Replacing the unit: if the glazing is fogged, the frame is rotted or the skylight is old, replacement is often better than repair. Choose a unit with the right flashing kit for your roof.

Condensation fixes

Reduce indoor humidity with extractor fans, keep the light well insulated, and open the skylight to ventilate where possible. If you learned how to fix a leaking skylight that turned out to be condensation, ventilation and insulation are the cure.

Prevention

Inspect annually, clear debris and leaves, keep the roof around it clear of moss, and have flashing checked when the roof is replaced.

When to call a professional

Call a roofer for reflashing, glazing replacement or leaks you cannot trace, especially on steep or high roofs.

How to fix a leaking skylight: find the entry point

Water that enters around a skylight usually comes through the flashing, the seal between the frame and the glass, or a crack in the glazing. Start by watching the skylight during rain, then check the flashing for lifted shingles, cracked sealant or rust. Learning how to fix a leaking skylight often means resealing the flashing or replacing a damaged gasket, not replacing the whole unit. Clean the area before applying sealant, and use a product made for the skylight material. If the leak comes from condensation between panes, the seal has failed and the unit needs replacing. Because roof work can be dangerous, have a roofer confirm the source before you start.

A small leak is often easier to stop when you know how to fix a leaking skylight early. If the first repair fails, call a roofer rather than repeating how to fix a leaking skylight with more sealant.

Related reading

• Chimney Flashing Leak: How to Spot It and What Fixes It
• Practical Guide: How to Find Where a Roof Is Leaking
• How to Repair a Flat Roof Leak: Find It, Patch It, Prevent Ponding
• Roof Inspection After Storm: Safe Checks, Evidence and Next Steps

Browse all roofing guides, or find a roofer in your city from the roofing directory.