What’s Causing That Leak Around Your Skylight — and How to Fix It
A leak around skylight openings is one of the most common — and most frustrating — problems homeowners face. Here’s a quick overview of what’s likely happening and what to do about it:
Most common causes of a leak around a skylight:
- Cracked or dried-out sealant or caulk
- Damaged, corroded, or improperly installed flashing
- Clogged weep holes or drainage channels
- Worn weatherstripping or rubber gaskets
- Cracked glass or dome
- Damaged shingles near the skylight
Quick action steps:
- Place a bucket under the drip to protect your floors
- Check whether it’s a true leak or just condensation (more on this below)
- Inspect the flashing, sealant, and surrounding shingles
- Apply a temporary patch if needed
- Call a professional if the source is unclear or damage is extensive
Skylights are, according to industry experts, the most leak-prone windows in any home. And here in Wisconsin, harsh winters, ice dams, and heavy storms put them under serious stress year after year. The good news? About 70% of skylight leaks are tied to maintenance gaps — meaning most are preventable and fixable.
I’m Matt Smith, owner of Smith Roofing & Exteriors, and over the years I’ve diagnosed and repaired countless cases of a leak around skylight on homes just like yours across rural Wisconsin. In this guide, I’ll walk you through exactly how to find the source of the leak and what to do about it.
Basic leak around skylight terms:
Common Causes of a Leak Around Skylight
When we get a call about a leak around skylight fixtures in Jefferson or Fort Atkinson, the culprit is usually one of a few “usual suspects.” Because skylights are essentially a hole cut into your roof, they rely heavily on a complex system of layers to stay watertight.
Flashing Failure
Flashing is the metal shielding that directs water away from the skylight and onto the shingles. Over time, flashing can develop cracks or corrosion. In our Southeastern Wisconsin climate, the constant expansion and contraction from freezing and thawing can pull flashing away from the frame. If the flashing was “site-made” (hand-bent by a roofer rather than a factory kit), it often relies on caulk that fails within 5 to 10 years.
Sealant Degradation and Weatherstripping
The sealant between the glass and the frame is subjected to intense UV rays and extreme temperatures. Eventually, it becomes brittle, shrinks, and loses its grip. Similarly, the rubber gaskets or weatherstripping can dry out. Once these barriers fail, water seeps through the frame itself. This is one of the primary 5-reasons-to-fix-roof-leaks-asap, as a small seep can quickly turn into rotted roof decking.
Clogged Weep Holes
Most modern skylights have tiny internal drainage channels called weep holes. These are designed to let moisture from condensation escape. However, leaves, pine needles, and roof granules can clog these channels. When they’re blocked, water backs up and overflows into your home, making it look like the roof is failing when it’s really just a “plumbing” issue.
Identifying a Leak Around Skylight vs. Condensation
Before you climb onto the roof, we always recommend checking if you actually have a leak. In humid rooms like bathrooms or kitchens, warm air hits the cold glass of the skylight and turns into water droplets. If you notice a musty or moldy smell, it could be either, but condensation usually appears as a uniform fog or small drips across the entire pane, whereas a leak typically creates localized staining or a steady stream during rain.
You should never ignore a residential roof leak, but if the “leak” only happens when someone is taking a hot shower and disappears during a rainstorm, you likely have a ventilation problem rather than a roofing one. Single-pane or older acrylic dome skylights are particularly prone to this “sweating” effect.
External Factors and Roof Age
Sometimes the leak around skylight isn’t the skylight’s fault at all. Water is sneaky; it can enter through a damaged shingle three feet above the window and travel down the roof deck until it hits the skylight opening.
Sealing your shingles is a great preventative measure, but if your roof is over 15-20 years old, the materials may simply be at the end of their lifespan. In Lake Mills and Elkhorn, we also see a lot of damage from ice dams. When snow melts and refreezes at the eaves, it forces water under the shingles and flashing. Understanding the difference that a timely roof repair can make can save you thousands in interior drywall repairs.
How to Diagnose and Fix a Leak Around Skylight
Ready to play detective? Finding the exact source of a leak around skylight requires a bit of patience and a dry day.
The Hose Test
The best way to find a leak is to recreate a rainstorm. Have a partner stand inside with a flashlight while you go onto the roof with a garden hose. Start at the bottom of the skylight and spray water slowly. Work your way up the sides and finally the top. If the water starts dripping inside when you hit the bottom edge, you know the issue is likely the lower flashing or weep holes. If it only drips when you spray the top, the problem is further up the roof.
Safety First!
We can’t stress this enough: roof work is dangerous. Always use a sturdy ladder on level ground and wear non-slip shoes. If your roof pitch is steep (over 35 degrees), do not attempt this yourself. Professional roofers use a safety harness and specialized anchors to stay safe. If you’re tackling a simple roof leak fix, make sure the roof is completely dry.
Step-by-Step Guide to Fixing a Leak Around Skylight
If you’ve identified a minor gap in the sealant or flashing, here is how to address it:
- Clear Debris: Use a soft broom to remove leaves and dirt from the channels around the skylight.
- Remove Old Caulk: Use a utility knife to carefully score and pull up old, cracked sealant. Clean the area with mineral spirits to ensure the new bond is strong.
- Reseal the Flashing: If you find gaps between the flashing and the shingles, you can seal up the holes with caulking cement. Lift the shingle edge slightly, apply the cement underneath, and press back down.
- Apply New Sealant: Apply a continuous bead of high-quality sealant along the joint where the glass meets the frame.
- Clear Weep Holes: Use a small wire or compressed air to ensure the drainage holes are clear of obstructions.
| Feature | Silicone Sealant | Polyurethane Sealant |
|---|---|---|
| Flexibility | Extremely high (Great for glass) | Moderate (Great for flashing) |
| Lifespan | 20+ years | 10-15 years |
| Paintable? | No | Yes |
| Best Use | Glass-to-frame seals | Shingle-to-flashing gaps |
Essential Tools and Materials for DIY Repair
Before you head up, make sure you have your “skylight first aid kit” ready:
- Caulk Gun: For precise application.
- Utility Knife: To remove old materials.
- Roofing Cement: For shingle-level repairs.
- Sealant: We recommend a high-quality product like Loctite Roof & Flashing Sealant or a GE Supreme Silicone.
- Soft Broom: To clear the area without scratching the glazing.
- Safety Gear: Non-slip boots and, ideally, a harness.
Professional Repair vs. Full Replacement
Sometimes, a tube of caulk isn’t going to cut it. If your skylight is more than 15 years old, or if the frame itself is rotting, it’s time to talk about replacement.
The Benefits of Replacement
While a repair might cost $300 to $800, a full replacement usually runs between $1,000 and $3,000. However, there are great benefits to adding new skylights to your roof. Modern units are significantly more energy-efficient, often reducing energy bills by 10-20%. Newer models also come with “No Leak” warranties that can last 10 years or more, giving you peace of mind that a DIY patch simply can’t provide.
When to Call a Professional
For 95% of people, it’s better to let a professional handle skylight issues. You should definitely call a roof repair contractor if:
- The glass or acrylic dome is cracked (this cannot be “sealed”).
- The leak persists after you’ve tried to reseal it.
- You see rotting wood or mold in the attic or around the interior casing.
- The roof is too steep or high for you to access safely.
- The leak started right after a new roof installation (which often happens when old, brittle skylights are disturbed).
Long-Term Maintenance and Prevention
The best way to deal with a leak around skylight is to make sure it never starts. Here in Wisconsin, a little proactive care goes a long way.
- Annual Inspections: Twice a year, once in the spring and once before the first snow, take a look at your skylights. Look for cracking sealant or loose shingles.
- Quarterly Cleaning: Keep the “valleys” around the skylight clear of debris. If water can’t flow around the window, it will eventually find its way into it.
- Improve Attic Ventilation: This reduces the temperature difference that causes condensation, making it easier to spot a real leak if one occurs.
- Tree Trimming: Keep branches at least 10 feet away from your roof to prevent physical damage to the glass and to reduce the amount of leaf litter clogging your drainage channels.
- Gutter Maintenance: Believe it or not, clogged gutters can cause water to back up under the roofline, eventually affecting the area around your skylight.
Frequently Asked Questions about Skylight Leaks
How much does it cost to fix a leak around a skylight?
For a professional repair, expect to pay between $300 and $800. This usually covers resealing the unit and fixing minor flashing issues. If the flashing needs to be completely replaced or the roof deck is rotted, costs can exceed $1,000. A full replacement typically costs between $1,500 and $3,000 depending on the size and type of skylight.
Can I use Flex Seal to stop a skylight leak?
Flex Seal can be a decent temporary fix if you’re in the middle of a storm and need to stop the bleeding immediately. However, it is not a permanent solution. It can last anywhere from 6 months to 2 years, but it often masks deeper issues and can make a professional repair more difficult later by trapping moisture against the wood frame.
How do I know if my skylight needs to be replaced?
If your skylight is over 20 years old, it’s likely reached the end of its life. Other signs include cracked glass, a frame that is warped or rotting, or a “foggy” appearance between the panes of glass (which indicates the gas seal has failed). If you are getting a new roof, most manufacturers and contractors recommend replacing the skylight at the same time, as the process of tearing off shingles often breaks the old, brittle seals of an aged unit.
Conclusion
A leak around skylight doesn’t have to mean a disaster for your home, but it does require prompt attention. Whether it’s a simple matter of clearing out some leaves or a more complex flashing repair, addressing the issue early will save you from mold, rot, and expensive structural repairs.
At Smith Roofing & Exteriors, we’ve been the local experts in Fort Atkinson and the surrounding areas for years. We pride ourselves on transparent pricing and high-quality materials that stand up to the Wisconsin weather. Whether you’re in Lake Geneva, Walworth, or right here in Fort Atkinson, our team is ready to help.
Don’t let a drip turn into a downpour. Schedule your professional skylight inspection and repair today with the team at Smith Roofing & Exteriors. We’ll make sure your home stays bright, beautiful, and—most importantly—dry.
