In This Guide
Skylights bring beautiful natural light into a home, and they also bring one of the highest leak risks on the entire roof. A skylight is essentially a large hole cut into your roofing system, sealed with flashing, gaskets, and sealant that all age at different rates. In Lynnwood's wet climate, skylight leak causes range from simple condensation to failed flashing that soaks the surrounding framing.
Before you assume the worst, know this: many "skylight leaks" are not roof failures at all. This guide helps you tell the difference and fix the real problem.
Why Skylights Are Leak-Prone
Unlike a chimney, which is solid masonry, a skylight combines glass, operable parts, rubber gaskets, and multiple flashing pieces in one assembly. Water naturally collects on the uphill side of the curb, snow piles against it in winter, and every component expands and contracts with temperature. The skylight shaft inside the house also creates a long path where condensation can form and drip, looking exactly like a leak from above.
7 Common Skylight Leak Causes
- Failed step flashing. The most common true leak source. Flashing pieces around the skylight curb corrode, lift, or separate from the roofing.
- Deteriorated sealant. Caulk and sealant around the frame dry out and crack, especially on the sun-exposed uphill side.
- Worn gaskets. The rubber gasket between the glass and frame shrinks and cracks with UV exposure.
- Improper installation. Skylights installed without proper flashing kits, or flashed after the roofing instead of integrated with it, leak early.
- Clogged weep holes. Many skylights have small drainage channels that clog with debris, forcing water inward.
- Ice dams. Ice backing up behind the skylight curb forces water under the flashing.
- Condensation. Warm indoor air condensing on cold glass drips down and mimics a leak perfectly.
Skylight Leak or Condensation? How to Tell
| Clue | True Leak | Condensation |
|---|---|---|
| Timing | During or after rain | Cold mornings, even when dry outside |
| Location | Edges of the frame, shaft walls | On the glass itself, dripping from the frame |
| Amount | Can be steady dripping or streaming | Usually light droplets or fogging |
| Roof condition | Flashing or seals visibly damaged | Flashing looks intact |
If condensation is the issue, improving ventilation and controlling indoor humidity often solves it. Our indoor humidity guide covers healthy targets. If the flashing looks suspect, read our roof flashing leak detection guide.
Pro tip: on a dry, cold morning, condensation is at its worst. If the "leak" only appears then, you likely have a humidity problem, not a roofing problem.
How to Fix Skylight Leaks
For condensation, ventilate the room, run exhaust fans, and consider a dehumidifier. For failed sealant, carefully remove old caulk and apply fresh sealant rated for roofing. For worn gaskets, replacement gasket kits are available for many skylight models. For flashing failures, the surrounding shingles must be lifted and the flashing rebuilt or replaced, which is professional work. Never just smear roofing tar over the problem; it traps moisture and makes proper repair harder later.
When to Replace Instead of Repair
Consider replacement when the skylight is more than 15 to 20 years old, when the frame is warped or the glass seal has failed (fogging between panes), when flashing repairs have already been attempted more than once, or when you are re-roofing anyway. A new skylight installed with a proper flashing kit during a re-roof is the most reliable long-term solution.
Skylight Types and Their Leak Risks
Not all skylights leak equally. Fixed curb-mounted skylights, the most common type, rely on step flashing around a site-built curb; their weak point is almost always the flashing or the seal between the unit and the curb. Deck-mounted skylights sit lower on the roof and use a factory flashing kit, which performs well when installed correctly but is unforgiving of shortcuts. Venting skylights add moving parts, gaskets, and operators that wear out, creating leak paths fixed units never have. Plastic dome skylights yellow and crack with UV exposure, while glass units last longer but cost more. Knowing your type helps you focus maintenance where it matters most.
Maintaining Skylights Year Round
A simple seasonal routine keeps skylights dry. Each fall, clear leaves and debris from around the skylight, check the flashing and seals, and make sure weep holes are open. In winter, watch for interior condensation and wipe it away before it damages the frame; persistent condensation may mean the unit needs better insulation or a humidity fix inside the home. Each spring, inspect for cracked glazing and reseal any gaps in the exterior sealant. Every few years, have the flashing inspected up close, especially after major storms. Skylights reward this attention with decades of leak-free light.
Choosing a Contractor for Skylight Work
Skylight flashing ties into both the roofing and the window trades, so choose a contractor comfortable with both. Ask how they will integrate the new flashing with your existing shingles, what underlayment they use at the curb, and whether they follow the skylight manufacturer's flashing kit instructions exactly. A proper installer removes surrounding shingles, installs step flashing course by course, and reinstalls the roofing, never just caulks around the old unit. Get the scope in writing, including who handles interior trim repair if the opening needs reframing. Good skylight work is quiet and dry for decades; rushed work leaks by the second rainy season.
Skylights deserve an annual look: check flashing, seals, and gaskets each fall, keep weep holes clear, and watch for condensation in winter. Catch problems at this stage and the fix stays small. If water has already marked your ceiling, ProLine Leak Fix Pros can trace it to the source. Call (425) 380-0028.
