Why does my skylight leak every time it rains?
Short answer. If a skylight leaks every time it rains, even lightly, there is a direct path for water rather than flashing that gets overwhelmed: missing or rusted-through flashing, a cracked acrylic dome, a failed glass or frame seal, or cracked shingles and exposed nails right beside the unit. That kind of leak gets worse quickly and should be fixed before the curb and decking rot.
Likely causes of an every-rain leak
- Failed or missing flashing: step flashing that was never woven in, a sill apron tucked under the shingles below instead of over them, or metal that has corroded through.
- Sealant-only installation: some older skylights were set with roof cement instead of flashing, and once the cement cracks, water comes in with every rain.
- Cracked dome or glass: older acrylic domes go brittle and crack, and hail or falling limbs can break glass or domes outright.
- Frame or glazing seal failure: the gasket between glass and frame, or the frame corners themselves, let water into the unit.
- Damage above it: cracked shingles, popped nails or a lifted shingle just above the skylight route water straight to the curb.
Clues from inside
- Water on the glass or dripping from the frame points to the unit itself.
- Water running down the shaft walls or staining the drywall around the opening points to the flashing or the roof above.
- Rust streaks or soft, dark wood at the curb mean the leak has been going on for a while.
What to do now
Catch the water, protect the room and photograph the damage. If a storm or falling limb broke the skylight, report it to your insurer. For the repair, expect either a reflash with new membrane and a flashing kit, or a new unit if the glass, dome or frame has failed; on an older skylight, replacement usually makes more sense. See replacing skylights with a new roof and common roof leak causes.