A skylight is a hole in your roof. Everything depends on how it’s flashed.
Why most skylight leaks aren’t coming from the skylight, and why this work belongs to a roofing contractor.
Why skylight work belongs to a roofer
The glass almost never fails. The integration with the roof around it is what leaks.
The most common search that brings homeowners to this page is some version of "roofing contractor for skylight installation." That phrasing is telling, and it is correct. A skylight is not a window. It is a deliberate opening cut through the one continuous surface on your house whose entire job is to shed water. A window installer treats the unit as a window and seals around it. A roofer treats it as a penetration detail and builds the surrounding roof so water is directed over it.
In the field, the glass unit is rarely the failure. What fails is the flashing kit, the sealant on a site-built curb, or the way the shingle courses were run around the head of the unit. Manufacturer flashing kits are model-specific and pitch-specific. They are not interchangeable between units, and they are not a thing you improvise with step flashing and a tube of caulk.
Two consequences follow from that. First, reusing an old flashing kit on a new roof is a future leak with a delay timer on it — the kit is consumed by its original installation and was never designed to be lifted and re-set. Second, installing a brand-new skylight into an aging roof means you will be disturbing that same detail again in a few years when the roof is replaced.
So the rule we give homeowners is simple: if the roof is within about five years of the end of its service life, skylight replacement and roof replacement should happen at the same time. One opening, one flashing detail, one date on the assembly.
Is it a leak, or is it condensation?
The single most useful diagnostic on this page, and the one that most often saves a homeowner money.
Shows up on cold mornings and through the winter. Water forms on the interior glass and frame and runs down fairly evenly on all four sides. Worst in kitchens and bathrooms. It happens whether or not it rained.
The cause is humid indoor air meeting cold glass, made worse by poor attic ventilation and by single-glazed or aging units. That is a ventilation and glazing problem, not a flashing problem.
Shows up during or shortly after rain. Staining concentrates at one corner or along one side rather than all around. Drywall and paint on the shaft carry water marks, and the timing tracks the weather.
The cause is failed flashing, failed sealant on a curb, or a cracked acrylic dome. This one is ours to fix.
We get called out for skylight "leaks" that turn out to be condensation on a regular basis. Telling a homeowner they need ventilation work rather than a new skylight is the cheaper answer, and it is one we are happy to give.
How attic ventilation actually controls interior moistureTypes, and which one fits
Four categories cover essentially everything on San Antonio roofs.
- Deck-mounted (curb-less)
- Sits low against the roof plane with an integrated, model-specific flashing kit. On adequate pitch and installed correctly, this is the best water performer available and the modern default on a shingle roof.
- Curb-mounted
- Sits on a built-up wooden curb above the deck. Common on low-slope roofs and on older installations, and easier to retrofit into an existing opening. Its performance depends entirely on the curb being built square and flashed properly — a poorly built curb is a permanent leak.
- Tubular (sun tunnels)
- A small dome feeding a reflective tube that delivers daylight into hallways, closets, and interior bathrooms with no framing changes. Far less heat gain and far fewer leak paths than a conventional unit. Frequently the right answer when the goal is light rather than a view.
- Acrylic domes
- The standard on San Antonio homes built in the 1980s and 1990s. UV degrades acrylic, so these yellow, craze, and eventually crack. Nearly all original domes from that era are now at or past end of life whether or not they are leaking today.
Repair or replace?
Repair makes sense in a fairly narrow set of conditions: the unit is under roughly ten years old, the glass seal is intact, and the problem is isolated to flashing or sealant. Under those conditions a targeted repair restores the detail without touching the unit at all.
Replacement is the right answer when the insulated glass seal has failed and you can see permanent fogging between the panes, when an acrylic dome is crazed or cracked, when the unit is more than about twenty years old, or when the roof itself is being replaced anyway.
It is worth being clear about how large the gap is between old and new units. A 1990s acrylic dome is a single layer of degrading plastic with site-built flashing and no meaningful warranty. A current unit is laminated low-E glass in a factory frame with a model-matched flashing kit behind it. That difference means replacement frequently solves the heat-gain complaint and the condensation complaint at the same time as the leak, which is not something a repair can do. If condensation is your primary issue, read how attic ventilation drives it before you spend anything.
What good skylight installation actually includes
Six steps, in order. Skipping any of them is how a skylight becomes a leak.
- 1. Verify pitch against the manufacturer's minimumEvery unit has a minimum roof slope. Installing below it voids the warranty and guarantees standing water at the head of the unit. This gets checked before anything is ordered.
- 2. Use the model-specific factory flashing kitFlashing kits are matched to the unit model and to the roofing material and pitch. They are not interchangeable between models, and generic step flashing plus sealant is not a substitute.
- 3. Ice-and-water membrane around the full openingA self-adhering membrane wraps the entire perimeter of the deck opening before the unit sets, so the second line of defense exists before the first one is installed.
- 4. Integrate the shingle courses correctlyHead flashing weaves under the courses above the unit, side flashing interleaves with each course as it runs up the slope, and the apron sheds onto the courses below. Water should run over every joint, never into one.
- 5. Finish and insulate the interior shaftAn uninsulated shaft passing through a hot or cold attic becomes a condensation trap, and the homeowner reads that condensation as a leak. Insulation and an air seal at the ceiling plane prevent it.
- 6. Verify attic ventilation around the shaftA shaft can block a rafter bay and interrupt soffit-to-ridge airflow. We confirm the path is still open, adding baffles where the shaft narrows it.
One principle sits behind all six: sealant is a supplement to correct flashing, never a substitute for it. A skylight that depends on caulk to stay dry will leak, because caulk has a service life measured in a handful of Texas summers and flashing does not.
Skylight FAQs
We inspect the unit, the flashing, and the roof around it, then tell you plainly which one needs work — including when the answer is neither.