Roofing
Why Skylights Leak and How They Are Fixed
Most skylight "leaks" come from one of three things: flashing around the skylight that lets rain in, a failed seal on the glass or frame, or condensation that only looks like a leak. Flashing problems are a roof repair. A failed glass seal or an old skylight usually means a new unit. If your roof is close to replacement, VELUX, a major skylight maker, says that is the best time to replace the skylight too.
A water spot near a skylight does not always mean you need a new one. Here is how to narrow it down before anyone climbs a ladder.
Is my skylight leaking, or is it condensation?
Start with when and where you see water.
| What you notice | Likely cause |
|---|---|
| Water after rain, dripping from the sides or top of the frame | Flashing or frame seal problem |
| Stains on the drywall around the skylight that grow after storms | Flashing or frame seal problem |
| Droplets all over the inside of the glass on cold or humid mornings, with no rain | Condensation from indoor moisture |
| Fog or streaks between the two panes that do not wipe off | The glass seal has failed |
| Water only after snow, at the lower edge | Snow or ice backing water up at the skylight |
VELUX's article on when to replace skylights explains that condensation forms when warm, moist indoor air meets cold glass. It lists "dripping from the sides around your skylight or water accumulating beneath it" and "yellow stains around your skylight" as signs of a real problem. It also says that if streaks stay between the panes after cleaning, "the sealant has failed."
If you think it is condensation, lower the humidity in the room. Run the bath fan, and do not dry laundry nearby. If the water stops, you likely never had a roof leak.
What causes skylight leaks?
Flashing. Flashing is the metal and membrane that turns water away from the skylight and back onto the roof. Ohio's residential code, in Section 903.2.1, requires flashing "around roof openings." When it is bent, rusted, lapped the wrong way, or missing, water runs under the shingles and into the shaft.
Caulk instead of flashing. Some skylights were installed, or later "fixed," with a bead of caulk or roof cement doing the job flashing should do. Caulk dries and cracks in the sun. It may work for a season or two, then leak again.
A failed seal on the glass or frame. Glass units and frames have seals that wear out with age and sun.
Debris on the uphill side. Leaves and dirt collect above a skylight and hold water there. VELUX's FAQ says to clean around the flashing "so rainwater will continue to flow freely."
Snow and ice. In a Cincinnati winter, snow can pile up against the top of a skylight. Melt water can back up behind it.
Hail. Old plastic dome skylights crack. IBHS suggests impact-resistant skylights for homes in hail-prone areas.
How is a leaking skylight fixed?
When we check a skylight leak, we start on the roof at the uphill side of the frame. That is where water and debris collect, and where flashing problems usually show first. Then we look at the sides, the glass, and the shaft inside.
The fix depends on what we find:
- Clearing debris and resealing small gaps. This is the smallest job. It only helps if the flashing itself is sound.
- Reflashing. The shingles around the skylight come up. New underlayment and a flashing kit go in, and the shingles go back down or are replaced. This is the right repair when the skylight is fine but the flashing is not.
- Replacing the glass or sash. VELUX's FAQ says it offers replacement sashes with glass for its venting skylights made in 2010 and newer. Older models and other brands vary.
- Replacing the whole skylight. This makes sense when the unit is old, the frame is damaged, or the seal has failed and parts are not available.
A tube of roof cement smeared around the frame is a stopgap, not a repair. If someone offers that as the full fix, ask why.
Should I repair or replace my skylight?
Use these questions:
- How old is it? VELUX says many of its skylights "can last 20 years or more" and suggests upgrading "after about 30 years."
- Is there fog between the panes? That means the glass seal has failed.
- Is it a plastic dome? VELUX lists leaks and condensation around the panes as signs an old bubble or dome skylight is due for replacement.
- How old is the roof? VELUX's FAQ says "the best time to replace old skylights is when you reroof your home." The roofers are already up there, and the new flashing ties into the new shingles.
When a roof is replaced, Ohio's residential code says "flashings shall be reconstructed in accordance with approved manufacturer's installation instructions." Keeping a 25-year-old skylight under a brand-new roof means the oldest part of the roof sits in the middle of the newest.
VELUX also notes that improper installation "may void the warranty," and suggests coordinating skylight work with your roofer in writing. Our guide to roof warranties explains how those warranties fit together.
What to do while you wait for a repair
- Catch the water. Put a bucket or towels under the drip.
- Photograph it. Take photos of the stain, the drip, and the date. Note whether it was raining.
- Check the ceiling and walls around the shaft. Soft drywall or a spreading stain means water has been getting in for a while. Our guide to ceiling water stains covers what to do next.
- Stay off the roof. Skylights are glass. Never step on one or lean on it.
If you are wondering whether insurance will help, it depends on the cause. A sudden storm loss is treated differently than a slow leak from wear. Our guide to roof leak water damage and insurance in Ohio explains the difference.
How Shamrock can help
We repair roofs, flashing, and the water damage a leak leaves behind. We will tell you whether your skylight needs new flashing, a new unit, or just a cleaning, and whether it makes sense to wait for your next roof. Request a free roof inspection or read about our roofing services. If water has already damaged the ceiling, see our water damage restoration page.
FAQ
Why does my skylight leak only in heavy rain? Heavy or wind-driven rain pushes water past weak spots in the flashing that light rain does not reach. That points to the flashing, not the glass.
Can I seal a leaking skylight myself? You can lower indoor humidity and keep the area around it clear from the ground. Roof work around glass is risky. Caulk on the outside rarely holds for long.
Should I remove my skylight instead of fixing it? Some homeowners do, especially with old dome skylights. The opening is framed in and roofed over. It is a bigger job than reflashing, but it ends the upkeep.
Do new skylights need new flashing? Yes. A new skylight should get the flashing made for it. Reusing old flashing defeats the purpose.