Why Is My Skylight Leaking? Flashing, Seals and Condensation in Fort Worth Homes

Water dripping from a skylight is one of the more confusing problems a Fort Worth homeowner can have, because the same drip can come from three different places. Your skylight leaking might mean the flashing around it has let rain in, it might mean the unit itself has a failed seal or a cracked dome, or it might not be a leak at all: on a cold morning, warm indoor air condenses on the glass and runs down the shaft looking exactly like rainwater. Each has a different fix, and the questions below work through them in the order a roofer would, cheapest to rule out first.

Is It a Skylight Leak or Just Condensation?

Timing settles most cases: water that shows up during or right after rain is a leak, while water that appears on a cold, dry morning, especially in a bathroom or kitchen, is usually condensation. Condensation forms when warm, moist indoor air touches a surface colder than its dew point, and a skylight is often the coldest surface in the room.

Households make more moisture than most people expect. An NDSU Extension energy educator notes that each person adds about 3 pints of water vapor to the air every day just by breathing, before showers, cooking and laundry are counted. The same release warns against bath or kitchen fans that dump that air into the attic rather than outdoors, which is worth checking if your skylight sits near a bathroom.

National Weather Service normals for DFW put the average January temperature at 46.3 degrees, and a hard freeze after a mild week is exactly when a closed-up house with a hot shower running fogs and drips at the skylight. If the drip only happens on those mornings, start with ventilation, not the roof.

Quick ways to tell them apart

• Points toward condensation: beads across the whole inner glass, water on cold mornings with no recent rain, drips that follow showers or cooking, and no stains on the attic side of the shaft.
• Points toward a leak: stains that grow after storms, water appearing at one corner or one side of the shaft, drips that start partway through heavy rain, and wet or darkened decking in the attic just above the skylight.

Why Does Water Get Past Skylight Flashing?

Flashing is the most common leak path because it is the place where the roof has to hand water around a box instead of letting it run straight down. A skylight is a deliberate hole in the roof, and the Department of Energy's Energy Saver guidance on skylights is blunt that water leaks are a common problem with improperly installed units, recommending a curb and proper flashing and a professional install.

The installation sequence matters more than the materials. Pacific Northwest National Laboratory's Building America guide to repairing or replacing skylights describes the order: underlayment wrapped up the curb from the bottom, sill flashing laid over the shingles below the unit, step flashing woven in with each shingle course up both sides, and head flashing across the top with shingles lapped over it, so every layer overlaps the one below "in shingle fashion" and sheds water outward. Skip a piece, reverse a lap or reuse tired step flashing during a reroof, and water has a path.

Reading the stain location

Water at the upper corners or along the top of the shaft usually points to the head flashing or the shingles above it, which take the full load of everything running down that slope. Water down one side tends to follow a step flashing that was skipped, bent or nailed through. Water at the lower edge often starts at the sill flashing or the bottom corners, where debris collects and holds moisture against the curb.

Could the Skylight Itself Be the Problem?

Yes, and it is easy to miss because the flashing can be perfect while the unit fails. The PNNL guide lists leak paths that have nothing to do with the roof: the joints in the skylight frame, the gap between an operable sash and its frame, and worn or missing gaskets and weatherstripping. Venting skylights have more of these joints, so more places to fail.

Fog trapped between the panes is the clearest sign of a unit problem. The same PNNL guide says condensation between the panes means the seals of the insulated glass unit have failed, and it names long-term exposure to water as the most common cause. That fog will not cause a drip by itself, but it tells you the unit has been wet for a long time and is near the end of its useful life.

Storms add a third failure. Hail can crack an acrylic or polycarbonate dome outright, and older plastic domes become more brittle after years of North Texas sun. After a hailstorm, look at the skylight as carefully as you look at the shingles, and treat any crack or crazed patch as part of the storm and hail damage record.

Why Does My Skylight Only Leak in Certain Storms?

An intermittent leak usually means a small opening that only takes water under heavy, wind-driven rain. A gentle shower runs past a slightly lifted head flashing without trouble; a squall line pushing water sideways and uphill drives it under the same flashing.

The National Weather Service in Fort Worth puts DFW's normal annual rainfall at 37.01 inches, with May averaging 4.78 inches and October 4.37, the two wettest months of the year. Totals can also arrive all at once: NWS Fort Worth records list 9.19 inches at DFW in 24 hours on August 21-22, 2022, the second-highest on record. When rain comes that hard, debris piled on the uphill side of the curb dams water against the head flashing and pushes it higher than the flashing was designed to handle.

Keep a short log every time the skylight drips: the date, roughly how much rain fell, which way the wind was blowing, and exactly where the water appeared. A few entries turn "it leaks sometimes" into a pattern a roofer can trace in one visit.

What Can You Safely Check From Inside the House?

Most of the useful evidence is under the roof. Stay off a wet or steep roof and work from the attic and the room below:

• Find the skylight shaft in the attic with a flashlight and look at the decking and framing above it. Dark stains or soft wood above the head of the shaft point to flashing or roofing problems upslope.
• Look at the shaft walls themselves. Staining that starts low and has no matching wet decking above is more consistent with condensation running down.
• Check where the nearest bathroom fan duct ends. If it stops in the attic instead of exiting the roof or a wall, you have found a moisture source.
• Look through the glass for fog or haze between the panes, and for cracks or a chalky, crazed surface on a plastic dome.
• Photograph every stain with a date so changes between storms are easy to see.

Resist the tube of caulk. Sealant smeared over flashing tends to trap water behind it and hides the original entry point. Proper roof leak repair traces the entry first and then fixes the flashing itself rather than coating over it.

Should You Re-Flash, Replace the Unit, or Wait for a New Roof?

The right fix depends on the age of the skylight and the age of the roof around it. If the roof is fairly young and the unit is sound, with clear glass and intact gaskets, re-flashing the skylight with the correct pieces is the usual answer, and it is a contained roof repair rather than a project.

If the glass is fogged, the dome is cracked or the frame is failing, the unit is due anyway, and replacing it with a new flashing kit at the same time avoids paying for the flashing work twice. PNNL's guide treats these as one job: the skylight is repaired or replaced and fully flashed, with shingles cut back around the curb so the new pieces can be lapped in correctly.

If the roof itself is close to the end of its life, it usually makes sense to replace the skylight and flashing during the reroof. Every flashing piece then goes in sequence with new underlayment and shingles. Ask whoever quotes your roof replacement to price the skylight separately so you can see what it adds.

Narrow It Down Before Anyone Opens the Roof

Start with timing, because it costs nothing: if the water only appears on cold mornings or after showers, fix the ventilation and watch the glass before you spend money on the roof. If it follows rain, your storm log and the location of the stain will already point to the head, side or sill of the curb, and that shortens the visit and the bill. Fogged glass or a cracked dome changes the question from repair to replacement, so check for both before getting quotes.

When the clues point outside, Fort Worth Roofing Texas can trace the entry point and photograph what it finds through a roof inspection, and you can read more about the company on the Fort Worth Roofing Texas homepage.