Skylight Leaking: Is It the Glass, the Seal, or the Flashing?

Water on the ceiling does not mean the leak is above the stain. That is the first rule of skylight leaks, and it is the reason so many of them get "fixed" two or three times before anyone fixes the right thing. Water that gets in at a skylight travels — along the curb, down a rafter, across the drywall — before it finds a place to drip. The stain shows you where the water landed. The leak is where it started, and on a skylight there are really only four suspects: the glass unit itself, the seals and gaskets around it, the flashing where the skylight meets the roof, or no leak at all — condensation that only looks like one. Each one leaves a different signature, and each one takes a different fix.

Suspect one: the glass unit

Most skylights built in the last few decades are insulated units — two panes sealed together, just like a double-pane window laid on the roof. When that edge seal fails, you usually see it before you feel it: fog, haze, or moisture trapped between the panes that no cleaning on either side will remove. A failed unit mostly hurts clarity and insulation, but it is telling you the unit is at the end of its life — and a cracked pane is different: it lets rain straight into the unit and through any weakness below it. Overhead glass also has a safety rule with no exceptions: it must be laminated on the inner pane, so if anything ever breaks, the glass stays in place instead of coming down. If your skylight is a single sheet of tempered glass with nothing laminated under it, that is worth correcting when the unit is replaced, leak or no leak.

Suspect two: the seals, gaskets, and the curb

A skylight sits on a raised curb, and everything between the glass, the frame, and that curb is a gasket, a seal, or a bead of sealant — all of which bake in Los Angeles sun, shrink, harden, and split. This is the most common true leak we find: water driven under a dried-out gasket at the lower edge, or in at a corner where the sealant has pulled away. The signature is a leak that shows up in wind-driven rain more than in a straight-down rain, and staining that starts tight against the skylight shaft rather than out in the middle of the ceiling.

Here is the part homeowners get sold wrong: a tube of caulk smeared around the outside is not a reseal. Surface caulk peels within a season or two, and worse, it can dam water that was designed to drain. A real repair means opening the assembly, replacing the failed gasket or glazing seal with the right profile, and re-bedding the unit — not decorating the frame with silicone. Our skylight repair and replacement work starts with identifying exactly which seal in the stack has failed, because "the skylight leaks" is not a diagnosis.

Suspect three: the flashing — where the roof and the skylight argue

Flashing is the metal work that ties the curb into the roofing, and it is where a glazing problem turns into a roofing problem. Step flashing up the sides, a head flashing at the top, and a sill at the bottom shed water over the roof surface in sequence, like shingles. When flashing was skipped, nailed through where it should not be, buried under the wrong layer of roofing, or corroded through — common on older Los Angeles homes re-roofed around an original skylight — water enters outside the curb and runs under the roofing. The signature: leaks that appear even though the skylight itself looks sound, staining offset to one side or below the skylight, and a leak that got worse after a re-roof.

Flashing failures are not fixed from inside, and they are not fixed with glass work at all. They need the roofing opened around the curb and the flashing rebuilt in the right order — which is why an honest diagnosis matters before money moves. If the flashing is the problem, we will tell you it is a roofing repair, even though the skylight is what brought us out.

Suspect four: condensation — the leak that isn't

On cool mornings, a skylight over a bathroom or kitchen can drip with no rain in the forecast and no leak at all. Warm, moist indoor air hits the coldest surface in the room — the glass overhead — and the water forms on the inside face, runs to the frame, and drips. The signature is timing: drips in the morning, after showers or cooking, worse in winter, and moisture you can wipe off the inside surface. Old single-pane and cheap plastic-dome skylights are the worst offenders. The fix is not sealant. It is a properly insulated unit, ventilation that actually moves bathroom air out, and sometimes a better skylight. Replacing a unit for condensation without understanding that will buy you a new skylight that still drips.

How to read your leak before you call anyone

• Only leaks in hard, wind-blown rain: suspect seals, gaskets, and the low-side joints first — wind drives water uphill into tired seals.
• Leaks in any rain, even light rain: suspect flashing, a cracked pane, or a joint that is fully open. Light rain should never beat a sound skylight.
• Fog between the panes, no drip: the insulated unit's seal has failed. Not an emergency, but the unit is done — plan replacement, and check the gaskets while it is open.
• Drips with no rain: condensation until proven otherwise. Check whether the moisture starts on the inside face.
• Stain offset from the skylight, or worse since a re-roof: suspect flashing and water traveling from outside the curb.
• Don't let anyone sell you a repair before the source is isolated. A controlled hose test — low sections first, working upward — is how the entry point gets proven instead of guessed. And leave the roof work to a crew: a wet roof around a skylight is no place for a homeowner on a ladder.

Repair it, or replace the skylight?

A sound frame and curb with failed gaskets is a repair. A failed insulated unit in a sound frame is a glass replacement — the unit is fabricated to size, with laminated safety glass on the underside, and swapped into the existing frame. But when the frame itself is corroded, the dome is crazed plastic, the curb was built wrong, or the flashing has failed around a unit that is also at end of life, replacing the whole skylight — curb-mounted or deck-mounted, with a proper flashing kit tied into the roof — is cheaper than paying for two half-fixes in two rainy seasons. Los Angeles gives you long dry stretches to do this work on your schedule instead of the storm's. Use them: a skylight diagnosed in the dry season gets fixed once, in daylight, with the right parts on the truck.