What is a skylight leak?
A skylight leak is water getting into the house through or around a roof window. Almost every skylight sits on a curb, a short box frame that raises the unit above the roof surface, and the curb is wrapped in metal flashing that sends water around it. A leak means water has found a way past that flashing, past a seal in the unit, or through a crack in the glazing.
Marin homes have a lot of skylights. Mid-century Eichlers use them to bring light into rooms under flat roofs with no attic, hillside homes in Mill Valley and Larkspur use them under tall redwoods that shade the windows, and remodels across Novato added them to brighten 1960s and 1970s floor plans. Each one is a penetration the roof has to seal.
Not every drip from a skylight is a leak, though. On cold winter mornings, warm indoor air meets the chilly glass and condenses, and the water runs down the frame. Telling the two apart is the first job.
How skylight leaks are repaired
Once the source is clear, the fix is usually one of four repairs.
- Reflashing the curb. The unit is lifted off, old flashing and sealant are removed, and new step or kit flashing is woven into the roofing, with a head piece at the top and an apron at the bottom.
- Rebuilding the curb. If the curb wood is soft from years of slow leaks, it is replaced and raised to the right height before new flashing goes on.
- Replacing the unit. Crazed plastic domes, fogged double glazing and broken frames are replaced, often with a newer insulated unit that cuts condensation too.
- Membrane tie-in on flat roofs. On Eichlers and other low-slope roofs, the curb is wrapped with membrane that bonds to the field of the roof instead of shingle-style flashing.
Surface caulk alone is a stopgap. It can buy a few storms, but it is not a substitute for flashing that sheds water by overlap.
Eight signs your skylight is leaking
- Water stains at the upper corners of the skylight shaft
- Peeling paint or swollen drywall on the shaft walls
- Drips that appear only during rain, not on dry cold mornings
- A cracked, cloudy or yellowed plastic dome
- Fog or moisture trapped between double glass panes
- Dried, cracked sealant around the frame on the roof
- Debris or leaves piled against the uphill side of the curb
- Dark or soft wood at the curb seen from inside the shaft
What makes Marin skylights leak
Debris dams are the most local cause. Oak leaves, bay laurel leaves and redwood needles collect against the uphill side of a curb, especially on the shaded roofs of southern Marin. The pile holds water against the head flashing, and in a long storm the water climbs over it.
Age and sun come next. Many skylights in Marin date from remodels decades ago, and their rubber gaskets and sealants have been through many dry, hot summers. Plastic domes turn brittle and craze. Factory seals in older double-glazed units fail, letting moisture in between the panes.
Installation shortcuts round out the list. Skylights that were sealed with mastic instead of proper step flashing, curbs that sit too low above the roof surface, and flat-roof skylights whose membrane tie-in was never fully bonded all hold up in light rain and fail in a hard, wind-driven storm.
Leak or condensation? Safe checks first
- Note when it drips. Rain-only drips point to a leak; cold, clear mornings point to condensation.
- Feel the frame on a cold morning. Beads of water on the inside of the glass are condensation.
- Look at where the stain starts: upper corners suggest head flashing, sides suggest step flashing.
- Run a bathroom fan or open a window for a few days; condensation drops quickly with ventilation.
- From the ground, use binoculars to look for leaf piles against the skylight.
Tape a paper towel to the shaft wall near the top corner during a storm. A wet towel by morning with a dry glass surface points to the flashing, not condensation.
Skylight types you will find on Marin roofs
Plastic bubble domes are the oldest style still common here, especially on Eichlers and 1970s remodels. They are light and cheap, but the acrylic yellows and crazes after years of sun, and hairline cracks let water through the dome itself. Flat glass units on a site-built curb came next, and the newest are factory units with their own flashing kits and double or laminated glass that cut both heat and condensation.
Tubular skylights, the small round tubes with a dome on the roof, show up in hallways and bathrooms. They leak less often because the opening is small, but their flashing collar still has to sit correctly in the roofing. Knowing which type you have, and roughly how old it is, helps the roofer decide between resetting it and replacing it on the first visit.
The roofer's skylight visit, step by step
- Inside look. They study where the stain starts on the shaft or ceiling and check the glazing and frame.
- Roof inspection. On a dry day, they check the curb height, flashing, sealant and any debris around the unit.
- Water test. If needed, they run water at the bottom of the curb first, then the sides, then the head, to isolate the failure.
- Options. They explain whether the unit can be reflashed and reset or should be replaced.
- Repair. Flashing, curb wood or the unit itself is replaced, tied into the surrounding roofing.
- Follow-up. You check the shaft during the next storm to confirm it stays dry.
What changes the size of a skylight job
| Factor | Effect |
|---|---|
| Unit condition | A sound unit can be reset; a crazed or fogged one is usually replaced. |
| Curb wood | Rotted curbs are rebuilt before flashing. |
| Roof type | Shingle, tile and flat membrane roofs each tie in differently. |
| Interior damage | Long leaks bring drywall and paint repairs on the shaft. |
| Fire-area rules | Replacement units in hazard areas may need tempered glass. |
When a skylight leak is urgent
Treat it as urgent if the glazing is cracked or broken, if a falling branch has hit the unit, or if water is running down the shaft onto floors or near ceiling lights. A broken skylight is an open hole in the roof and needs a cover before the next band of rain.
Never step on a skylight or lean on it from the roof; many are not built to carry weight. If water is near recessed lights around the shaft, switch that circuit off at the panel and keep the area clear.
Skylight questions
Why does my skylight drip on cold mornings when it has not rained?
That is condensation. Warm, humid indoor air meets the cold glass or frame and turns to water, which runs down and drips. Better ventilation and a newer insulated unit reduce it; it is not a roof leak.
Can the old skylight stay if the flashing is replaced?
Sometimes. If the unit itself is sound, a roofer can remove it, reflash the curb and reset it. If the glazing is fogged, cracked or the dome is crazed, replacing the unit during the same visit usually makes more sense.
Do skylights in fire hazard areas have special rules?
Wildland-urban interface building standards generally call for tempered glass in skylights on new work. Ask the roofer and the building division what applies if your skylight is being replaced.
Is caulk around the skylight a real fix?
Caulk can slow a leak for a while, but sun and movement break it down within a season or two. A lasting repair replaces or rebuilds the flashing that sheds water around the curb.
My skylight shaft walls are stained. Where is the leak?
Stains on the shaft usually start at the top corners of the curb, where the head flashing or the upper corners fail. A roofer checks those first, then the side flashing.
Are tubular skylights less likely to leak?
They have a smaller opening and a one-piece flashing, which helps, but they still rely on correct installation. A poorly seated flashing collar leaks like any other penetration.
Related pages
If the skylight sits on an Eichler or another low-slope roof, read about flat roof leaks as well. Leaves piling against the curb are part of a bigger debris problem covered under moss and debris.
Homes in the redwood canyons above Larkspur deal with that debris every winter, as the Larkspur page explains. The Novato roof leak line home page has the full leak checker.