A wet spot under a skylight sends a lot of people straight to a roofer, but the first question is not who fixes it, it is what it actually is. A large share of so-called skylight leaks are not leaks at all, they are condensation. Getting that diagnosis right is the difference between a simple fix and paying for roof work you never needed.
Is it a leak or condensation?
This matters enough to lead with. One veteran home inspection firm reports finding only a handful of skylights that genuinely leaked against hundreds with condensation problems. Condensation forms when warm, humid indoor air hits the cold glass of the skylight, and it is often really an insulation problem in the skylight shaft, not a defect in the skylight.
You can usually tell them apart:
- Condensation shows up as uniform fog or droplets on the interior glass and frame, appears in cold or humid conditions or during big temperature swings, and is not tied to rain.
- A real leak traces to a specific entry point, streaks down a rafter, leaves yellow-brown stains, or softens the drywall, and it appears or worsens after rain, snow, or ice melt.
The fix is completely different. Condensation is solved with ventilation and insulation, not roofing. A true leak needs roof work. Our guide on roof leak versus condensation walks through the whole diagnosis.
Why skylights actually leak
When it is a real leak, a skylight is just a penetration through the roof that depends on flashing and seals. The usual causes:
- Failed or corroded flashing, the leading cause.
- Degraded seals and gaskets around the glass, which go brittle and crack from years of UV and temperature cycling.
- Cracked or fogged glazing, where the seal between panes has failed.
- Improper installation, or old flashing reused on a new roof.
- Debris damming above the skylight, forcing water sideways under the frame.
- Simple age, because a skylight has a lifespan and eventually reaches it.
Skylights wear out before your roof does
Here is the fact that drives most skylight decisions: a skylight typically lasts about 15 to 20 years, and its seals usually fail well before a modern roof does. That creates a very common situation, an old skylight sitting on a new roof, quietly leaking around a unit that is simply past its life.
Skylights come curb-mounted, sitting on a raised frame, or deck-mounted, low and flush to the roof. Either way, the glass and seals age on their own clock, independent of the shingles around them. So a skylight’s age matters as much as the roof’s.
Repair or replace?
The rule of thumb roofers use is straightforward. If the unit is newer and in good shape and only the flashing is tired, reseal or re-flash it. If the seals are shot, the glazing has fogged, or the skylight is past about 15 to 20 years, replace the whole unit, which is the more reliable and warranty-backed route.
Rough cost ranges, all contractor and aggregator estimates, so treat them as ranges:
- Minor flashing repair or reseal: often 150 to 500 dollars.
- A general leaking-skylight repair: commonly a few hundred dollars, up around 800.
- Replacing the skylight in its existing opening: often 800 to 2,400 dollars depending on the unit.
- A full like-for-like replacement with finishing work: can run into the low thousands.
- A tubular skylight or sun tunnel is the cheapest daylighting option, often under about 1,100 dollars.
The reroof rule: replace the old skylight now
This is the practical heart of the post. Roofers strongly and near-unanimously recommend replacing an aging skylight, or at least installing a fresh manufacturer flashing kit, when you reroof. The Department of Energy’s building science guidance likewise directs contractors to inspect and fully flash skylights at reroof time.
The logic is hard to argue with:
- Tear-off can weaken old flashing, and removing and reinstalling an aged unit can break UV-damaged seals, creating new leaks.
- Old flashing rarely seals correctly against new shingles, and an old skylight may not even fit a current flashing kit.
- Re-flashing an existing skylight can void its warranty, and many roofers exclude reused old units from their workmanship warranty.
- Doing it later means cutting into your brand-new roof to reach the skylight.
The cheapest time to deal with a skylight is while the roof is already open
If your skylight is anywhere near 15 to 20 years old and you are reroofing, replace it now. The incremental cost while the roof is off is far lower than re-opening a fresh roof in a few years to chase a leak.
This is one of the decisions worth settling before the crew arrives, which we cover in what to expect during a roof replacement.
A note on the solar skylight tax credit
Solar-powered venting skylights and sun tunnels were long marketed with a 30 percent federal tax credit, under the Section 25D Residential Clean Energy Credit. That credit ended. Under the 2025 federal budget law, 25D was repealed for expenditures made after December 31, 2025, and an expenditure counts as made when the installation is completed.
So for a skylight installed in 2026, there is no federal residential clean energy credit, whatever an older manufacturer or retailer page still claims. Many of those pages are simply out of date. Check for any state or local incentives, and talk to a tax professional about your own situation. This is general information, not tax advice.
The types, briefly
Skylights come fixed, meaning they do not open, vented, which open manually or by electric or solar motor, and tubular, the small sun tunnels that pipe daylight into a hallway or bath. Vented units add fresh air but add seals and moving parts that can eventually leak. Fixed units have the fewest failure points. Match the type to the room and to how much maintenance you want to sign up for.
“Before you pay to fix a skylight leak, make sure it is a leak. Most are condensation, and the two problems have nothing in common but a wet ceiling.”
The bottom line
Diagnose first: condensation and a true leak look similar and need opposite fixes. If it is a real leak, the flashing or the aging seals are the usual cause, and a skylight past 15 to 20 years is often better replaced than repaired. Above all, if you are reroofing and your skylight is getting old, replace it while the roof is open. It is the one skylight decision almost every roofer agrees on.
With Hommy you post your job once and get quotes from vetted local roofers with real ratings from other homeowners, so you can find one who diagnoses the skylight before selling you a repair.
