Why Most Skylight Leaks Are the Flashing, Not the Glass

Why homeowners blame the glass when it is usually the flashing

When you see water around a skylight, the glass is the obvious suspect because it is the part you can see from inside. But modern skylights use sealed, tempered, double-pane glass set into a factory-built frame, and that assembly is one of the most weather-tight pieces of the whole roof. Actual glass failure, a cracked pane or a blown seal that fogs the glass, does happen, but it is the exception, not the rule. The water that ends up on your ceiling almost always traveled there from somewhere along the edges.

The real leak point is the transition: the line where the skylight meets the roofing material around it. That joint is sealed by flashing, the layered metal and underlayment that channels water around the unit and back onto the roof surface. Flashing is where the craft lives. It is also where shortcuts hide, because once shingles or membrane go over it, nobody can see whether it was done right until water proves otherwise.

There is one more reason people misread skylight leaks. Water rarely drips straight down from where it enters. It can run along the underside of the deck, follow a rafter, and surface a foot or more away from the skylight before it ever stains the ceiling. So a leak that looks like it is coming from the glass may actually be entering at a corner of the flashing several feet uphill. That is why guessing leads to repeated, frustrating repairs, and why finding the true entry point matters more than the symptom on your ceiling.

How skylight flashing should be detailed

Good skylight flashing is not a single piece and it is not a tube of caulk. It is a system of overlapping layers, each one shedding water onto the layer below it so gravity does the work instead of relying on sealant to hold a joint forever. When that system is built correctly, the skylight sheds water the same way the rest of the roof does. When even one layer is missing or reversed, you get a leak.

• Self-adhered underlayment, sometimes called ice-and-water membrane, wrapped up onto the skylight curb so the wood framing is protected even if water gets past the metal.
• Sill or apron flashing at the bottom edge, the downhill side, so water coming down the roof is carried out and over the shingles below.
• Step flashing up both sides, woven in piece by piece with each course of shingles so every overlap sheds onto the next, not behind it.
• Head or saddle flashing at the top, the uphill side, that diverts water around the skylight instead of letting it pile up against the curb.
• A counter-flashing or cap, often part of a manufacturer flashing kit, that covers the top edges of the step flashing and keeps wind-driven water out.

The most common failure we find is not exotic. It is a skylight that was face-nailed and caulked in instead of properly stepped and layered, or one where the flashing kit was skipped to save time. Caulk has its place as a backup at terminations, but a skylight that depends on caulk to stay dry will leak the day that caulk cracks, and on the coast, sun and salt air shorten that day. Flashing done as overlapping layers is what lasts.

Wind-driven rain and skylights on the Oregon coast

A skylight that would stay dry in a calm climate can leak here, because our weather does not play fair. On the coast from Newport down to Coos Bay, and inland through the wetter stretches of the valley, rain does not just fall straight down. Strong coastal gusts drive it sideways and even upward, pushing water under edges and into laps that a gentle rain would never reach. A skylight is a raised obstacle sitting in the middle of that flow, and wind-driven rain finds a poorly flashed one fast.

Salt air adds a second pressure. It is hard on fasteners and metal, so coastal skylight flashing should use corrosion-resistant components, the same reason we use stainless components on our PVC membrane work near the water. A galvanized fastener that rusts out is a leak in waiting, and you will not see it happening up there until the stain appears below.

Marine climate also means moss and constant moisture, which keep the roof surface around a skylight damp long after the rain stops. That standing dampness works on any marginal seal. A skylight installed on a sunny day with no thought to how coastal storms actually behave is the one that calls you back in January. This is the part of the job where genuine coastal experience matters more than a generic install. We flash skylights for the weather we actually get out here, not the weather in a manufacturer's brochure.

Repair and reflash vs full skylight replacement

When we find a leaking skylight, the honest first question is not how fast can we sell you a new one. It is what is actually wrong. A lot of skylight leaks are a flashing problem on a perfectly good unit, and the right fix is to reflash it: lift the surrounding roofing, rebuild the layered flashing correctly, and tie it back in. That solves the leak without the cost of a new skylight.

Reflashing usually makes sense when the glass and frame are sound, the unit is not very old, and the curb and surrounding deck are still solid. Replacement starts to make sense when the picture is worse.

• The glass seal has failed, meaning the panes fog up with condensation that you cannot wipe away.
• The frame or curb is cracked, warped, or rotted, so there is nothing sound to flash to.
• Water has been getting in long enough that the deck and framing around the opening are soft or rotted and need to be rebuilt.
• The skylight is an old, single-pane or builder-grade unit at the end of its life, where a new one will seal and insulate far better than a patched old one.
• You are reroofing anyway, which is the moment a replacement costs the least extra labor.

If rot has reached the deck or framing, that work comes first no matter which path you choose, because flashing over soft wood just buys a few months. We will show you what we find, explain it in plain terms, and put it in a written, itemized estimate so you can see exactly what you are paying for and decide with the facts in front of you.

When to add or replace a skylight during a reroof

The smartest time to deal with a skylight is when the roof is already coming off. During a reroof, the roofing around the skylight is removed anyway, so reflashing it correctly, or swapping in a new unit, adds far less labor than doing it as a standalone job later. If you have an aging skylight, a reroof is the natural moment to retire it and start fresh with new glass, a new frame, and brand-new flashing tied cleanly into the new roof.

It is also the right time to think about whether you want a skylight at all, or want one in a different spot. Some homeowners add a skylight to a dark hallway or bathroom during a reroof; others retire one that has always been trouble and patch the deck closed. Either way, doing it as part of the larger job means one crew, one tie-in, and one warranty covering the work, instead of cutting into a finished roof down the road and hoping the seam holds.

However we handle it, we manage the whole job and every crew on your roof is held to our standards and overseen by us, and our installation is backed by our own written 10-year workmanship warranty. That covers our labor and how the skylight is tied into your roof. The skylight manufacturer's warranty on the unit itself is separate and runs on the manufacturer's terms, two different things that are easy to confuse. We will walk you through both so you know exactly who stands behind what.

Common questions about skylight leaks