Skylight dripping or fogging up
Moisture at a skylight has three different sources and they need three different fixes. Rain coming past the flashing or the frame is a leak. Fog trapped between the panes is a failed glass seal. Beads on the inside face on a cold morning are condensation from the room. Watch when it appears and where it starts, and the source usually names itself.
The symptom
What you are seeing
- Drips running down the light well after rain, a damp patch or stain on the drywall at one corner of the opening, or a skylight that looks permanently misty even on a dry afternoon. Sometimes it is only a few beads of water along the bottom edge of the glass first thing in the morning that are gone by lunch.
- The timing is the clue. Water that shows during or just after rain, and starts at a corner or an edge of the frame, is coming from outside. Haze that sits between the panes and never dries is inside the sealed glass unit and has nothing to do with the roof. Beads on the room-side surface that appear on cold clear mornings, especially above a bathroom or a kitchen, are the room's own moisture meeting cold glass. Take a photo each time it happens and note the weather, because the pattern is worth more to an inspection than any single visit.
Most likely first
Likely causes
Flashing that has lifted or been patched
The metal that laps the skylight frame into the roof covering is where most real leaks start. Sealant applied over it during an earlier repair hides the joint and fails again within a couple of seasons, so a skylight with a history of caulking is a strong suspect.
Debris packed against the uphill side
The raised frame catches leaves and grit on the side facing up the slope. Water held there stays against the flashing for days after a storm and finds its way past laps that would shed a normal flow.
A failed seal in the glass unit
Double glazing is sealed at the factory. When that seal gives out, moist air gets between the panes and condenses there as fog that no amount of cleaning reaches. The unit needs replacing, but the roof around it may be perfectly sound.
Condensation from the room below
Warm damp air rises to the coldest surface it can find, and in winter that is the skylight. Old single-glazed units and unheated light wells make it worse. This is not a leak, and the fix is ventilation and glazing rather than roofing.
A leak in the roof above the skylight
Water entering higher on the slope can run down the underlayment and emerge at the skylight because that is the first opening it meets. The skylight gets blamed for a roof problem. Tracing the path uphill before touching the frame avoids replacing a unit that was never at fault.
The honest rule
Repair or replace
A leak at the flashing on a skylight whose frame and curb are sound is a repair: the covering around it comes up, the flashing is refitted or replaced with a kit made for that unit and the roof is laid back in. Condensation is not roofing work at all. A fogged glass unit is a replacement of the skylight, and it is a good moment to look at the curb and flashing underneath, since the roof is open anyway.
What turns a flashing repair into a full replacement is the frame itself. Old acrylic domes gone brittle, a wooden curb that has been wet for years, or a unit whose manufacturer no longer makes a flashing kit each mean the repair would be fitted to something that is about to fail. We would rather tell you that before the roof is open than find it afterward. And if the roof around the skylight is near the end of its life, the skylight should be replaced with the roof rather than reflashed into covering that will be torn off in two years.
What fixes it
The service for this, and where to read more
Service
Skylight replacement and repair
We inspect the skylight and nearby roofing to find the source of moisture before recommending a repair.
Service
Skylight installation
A new or replacement VELUX skylight, with the surrounding roof work and agreed interior finish included.
Guide
Why skylights leak after a re-roof
A leak that appears after roof replacement needs an inspection of the flashing, the supporting curb and the surrounding roof.
Related problem
Ceiling stain that appears after rain
A stain that darkens or spreads after rain means water is getting through the roof and reaching the drywall.
Related problem
Skylight gone cloudy or yellow
A skylight that has slowly yellowed or gone milky is an acrylic dome that has spent decades in the sun.
Questions
Asked about this problem
How can I tell condensation from a leak without waiting for rain?
Run a shower or boil a kettle in the room and see whether beads form on the inside of the glass within the hour. If they do, the glass is cold enough to condense on and at least some of what you have seen is condensation. A leak needs water from outside, so it will not appear that way.
Will more sealant around the skylight stop the drip?
For a season, sometimes. Sealant over a flashing joint hides the real fault and traps water behind it, and when it fails the leak is worse and harder to trace. If a skylight has already been caulked more than once, the next step is to lift the covering and refit the flashing properly, not to add another bead.
The glass is foggy inside. Does the whole skylight have to come out?
The glass unit has to be replaced, and on most models that means the whole skylight, because the glazing is fixed into the frame at the factory. The good news is that fog between the panes is not a roof leak, so the flashing and curb may only need checking while the unit is out.
Free estimate
Find out what it costs
Tell us what's happening at your property, one step at a time. We'll review your request during business hours and arrange a free inspection.
What happens after you send it
- We call during business hours to set a time.
- A free visit. We measure on site and nothing is signed at the door.
- The proposed work and the price, in writing.
- (925) 555-0100Phone
- Mon–Fri 7:00 AM – 5:00 PMHours
Sat by appointment · Sun closed
100 Example Road, Brentwood, CA 94513 · office@example-roofing.demo
Your property answers are saved in this browser as you go. About saved answers.
Having trouble? Use the short form
Thanks. We will call during business hours to set up the inspection.
That did not send. Call (925) 555-0100 instead and we will take the details over the phone.