Skylight Leak and Flashing Repair

Skylights have a reputation for leaking that is only half deserved. The units themselves are generally well made. What fails is the junction between a factory-built object and a field-built roof — and, often enough, nothing fails at all and the water was never rain.

Four Problems That Look Identical Indoors

A wet patch at the head of a skylight shaft tells you almost nothing on its own. Four quite different faults produce it.

Failed flashing. The most common by a distance. Head flashing that pushes water sideways instead of over the courses below, step flashing that was sealed to the roofing rather than woven between the courses, or a flashing kit that never matched the roofing material in the first place.

A debris dam. Skylights interrupt the roof plane, so they catch things. On lots overhung by Douglas fir and Garry oak, needles pile against the upslope side of the curb and hold water there permanently. That standing water finds its way under a detail that would otherwise have been fine.

A leak from further up. Water entering at a chimney, a wall junction or a lifted course above travels down the underside of the sheathing and emerges at the first obstruction it meets. A skylight shaft is a very effective obstruction. The unit is where the water appears, not where it entered.

Condensation. Glass is the coldest surface in the room. Moist indoor air condenses on it and on the frame, runs down and collects at the ceiling edge. The giveaway is that it happens in cold dry weather as readily as during rain, and shows evenly around the whole frame rather than at one corner.

Only the first two are repairs to the skylight. The third is a roof repair somewhere else entirely, and the fourth is a ventilation and humidity problem that no amount of roofing work will fix.

Why Diagnosis Comes First

This matters because the fixes are not interchangeable and the wrong one is expensive. A new unit installed to cure a leak that originated at a chimney fifteen feet upslope will leak exactly as much as the old one did, and the homeowner has paid for a skylight they did not need.

So the assessment covers the unit and its glazing, the flashing on all four sides, the roofing courses above it, the state of the curb and deck, and the shaft below — along with the pattern of the staining, which usually tells the story before anything is lifted.

What Repair Actually Involves

Where flashing has failed, the fix is to rebuild it as layered metal in correct sequence with the roofing: head flashing diverting water around the unit, step flashing woven one piece per course down both sides, sill flashing returning water onto the surface below. Every lap oriented so water crosses it rather than enters it.

The alternative is re-caulking, and it is worth being clear about what that buys. Sealant over a failed detail is a season, maybe two, in coastal sun. It is a legitimate short-term measure when a proper repair has to wait, but it should be described as what it is rather than sold as a repair.

Where a debris dam caused it, clearing above the unit is half the job and keeping it clear is the other half — which is why the area above a skylight belongs in routine roof maintenance rather than being revisited only when it leaks again.

When the Unit Itself Is Finished

Some skylights are genuinely past it. Fogging or haze between the panes means the sealed glazing unit has lost its seal and moisture is in the cavity; that pane is not serviceable in place. Perished or distorted frames, particularly on older acrylic domes that have spent decades in UV, are similar.

In those cases the honest answer is replacement rather than another repair, and the best time to do it is alongside roofing work if any is planned. A unit older than the roofing around it is worth dealing with while the roof is open.

Quotes are free and detailed. Crews are licensed, insured and covered by WorkSafeBC.