Skylight Leak Repair

Common Symptoms

• ✓Water dripping or staining directly below the skylight
• ✓Condensation or fogging between skylight panes (failed seal, not a roof leak)
• ✓Dark staining or rot on the wooden curb or light shaft framing
• ✓Visible daylight gap between the skylight frame and the surrounding roofing
• ✓Bubbling or peeling paint on ceiling near the light shaft

What Causes This

Skylight leaks in St. Louis homes fall into three categories, each with a different repair scope and cost. The most common is sealant failure at the skylight curb — the raised wooden frame the unit sits on — where roofing cement or butyl tape has dried and shrunk over 10–15 years of thermal cycling. Second is flashing failure: the step and counter-flashing system surrounding the curb uses the same metal joints as any other roof penetration and fails for the same reasons. Third is a failed insulated glass unit, where the seal between the panes has broken and allows interior condensation — this looks like a leak but is an interior humidity problem, not a roof problem. Correctly identifying which type you have before any repair work begins determines both the scope and cost.

When to Call Immediately

Do not allow a skylight leak to continue without repair. The wooden curb and light shaft framing are extremely vulnerable to rot — sustained moisture intrusion over even one winter can require complete framing replacement as part of what would otherwise be a simple flashing repair. The longer the delay, the higher the scope.

How Revolve Fixes It

1. 1Inspect the skylight from the attic first — trace any water staining to the curb, flashing, or glass seal to identify the leak type.
2. 2For sealant failure: remove all existing sealant from curb-to-flashing joint, clean metal surfaces, apply roofing-grade polyurethane sealant or fresh butyl tape, and re-bed the skylight frame if movement is present.
3. 3For flashing failure: lift surrounding shingles, remove and replace step flashing and counter-flashing around the full skylight perimeter, install self-adhering ice-and-water membrane at the curb base.
4. 4For failed glass unit: the unit requires replacement by a glazing contractor or skylight manufacturer rep — this is not a roofing repair.
5. 5Inspect the wooden curb for rot; replace deteriorated framing before reinstalling flashing.
6. 6Water-test with garden hose after repair and verify interior is dry before closing out.

How to Tell Which Type of Skylight Leak You Have

The most important diagnostic question is: does the water appear during rain, or does it appear regardless of weather? If you see moisture dripping or pooling during or shortly after rain events, you have a roof-side leak — either sealant, flashing, or curb failure. If you see fogging, streaking, or condensation between the glass panes in dry weather, the insulated glass unit has failed and no amount of roofing work will fix it.

A secondary diagnostic is location. Water staining directly at the frame perimeter points to the curb seal or flashing. Water staining further along the light shaft, or appearing at the ceiling some distance from the skylight, suggests water is traveling — a sign of flashing failure that is wicking along the framing before dripping.

Revolve's attic inspection process identifies the type and location of skylight moisture intrusion before any repair scope is written. We do not recommend full skylight replacement for what turns out to be a $400 re-seal job, and we do not re-seal a skylight whose curb framing is rotted through. The scope follows the actual condition.

What Full Skylight Re-Flashing Involves

A complete re-flash is the appropriate repair when the existing flashing metal is corroded, kinked, or installed without proper step flashing legs woven into the shingle courses. This is common in skylights installed during original construction in St. Louis homes built in the 1990s and early 2000s, where the flashing was often sealed with roofing cement rather than properly lapped metal.

The process requires lifting three to four courses of shingles on all four sides of the skylight curb, removing all existing flashing metal, installing new ice-and-water underlayment at the curb base, and weaving new step flashing between each shingle course. The skylight's integral flashing kit — supplied by manufacturers like Velux and Fakro — is the preferred solution when a unit is being upgraded or replaced at the same time.

A properly flashed skylight with intact curb framing should not require repair again for 15–20 years. We back skylight flashing repairs with a Revolve workmanship warranty.

Skylight Replacement — When It Makes Sense

If the skylight glass is fogged, the frame has significant corrosion, or the unit is more than 20 years old, replacement is often the better economic decision. Velux and other manufacturers have made significant improvements in thermal performance and glazing quality in the last decade, and a new unit will outperform a repaired old one in both leak resistance and energy efficiency.

Replacement also makes sense when the existing unit is a non-standard size that would require expensive custom framing work to re-seal. In those cases, the cost delta between a re-flash and a full replacement narrows considerably.

For homes where a skylight is being considered as part of a broader re-roofing project, see our skylights page for installation options. When a re-roof and skylight replacement happen simultaneously, the incremental cost of the skylight installation is lower because the surrounding shingles are already being replaced.