Skylights are a cut in the roof, and every cut is a place water can get in. When a skylight leaks, people often assume the glass or dome has failed. In our experience it is usually the flashing around the outside, or something the roof is doing near the opening. The good news is that most skylight leaks can be fixed without replacing the skylight.
Is it a leak or condensation?
Check this first, because the fixes are completely different. Condensation forms when warm, moist air inside the house meets the cold glass. It shows up as droplets or a film on the inside of the skylight, often on cold mornings, and in bathrooms and kitchens. A leak shows up during or after rain, often as drips at one edge or corner, or staining on the shaft lining.
- Water appears during or soon after rain: likely a leak.
- Water appears on cold, dry mornings: likely condensation.
- Drips come from one corner or side, often the top: likely a leak at the flashing.
- The whole inside surface of the glass is fogged or beaded: likely condensation.
What causes a skylight to leak?
- Flashing that was not fitted properly in the first place, often sealed with silicone instead of being properly lapped under and over the roof covering.
- Old seals and gaskets around the glass or dome that have perished in the sun.
- Leaves and debris building up on the upslope side, damming water so it rises over the flashing.
- Cracked or slipped tiles around the skylight, letting water under the roof next to the opening.
- A cracked dome or failed glazing seal, more common on older acrylic domes.
- A skylight fitted on a pitch it was not designed for, so water does not run off it the way it should.
Are some skylights more likely to leak than others?
Yes. Older acrylic domes, skylights fitted on low-pitch roofs, and units installed without a flashing kit made for the roof type all leak more often. So do skylights fitted by someone who sealed them in with silicone and mortar rather than flashing them into the roof. On tile roofs, the tiles around the skylight need to be cut and laid properly so water runs around the opening, not into it. On metal roofs, the sheet above the skylight needs to direct water around the frame.
Silicone around a skylight is a temporary measure, not flashing. If the only thing keeping water out is a bead of sealant, the leak will come back.
Why does the water show up away from the skylight?
Because water that gets in at the top of the skylight can run down the outside of the shaft, along a rafter or across the sarking before it drops. It might show on the ceiling a metre away, or run down a wall. That is why we look at the roof space around the shaft as well as the skylight itself.
Repair or replace the skylight?
If the skylight unit is sound and the problem is flashing, seals or debris, a repair makes sense. We remove the old flashing or sealant, fit flashing designed for the roof type, and make sure the tiles or sheets around the opening sit properly. If the dome is cracked, the frame has failed, or the unit is old enough that parts cannot be found, replacement is usually the better use of money, and it is a chance to fit a unit with a proper flashing kit for your roof.
What can I do until it is fixed?
- Put a bucket or towel under the drip, and protect flooring and furniture.
- If there is a light fitting in or near the shaft, turn the power off to that circuit until it is checked.
- If you can see the skylight from a safe spot, check whether leaves are piled against it. Do not climb onto the roof to clear it.
- Take photos of where the water appears and when, which helps us find the entry point.
We repair, reflash and replace skylights on tile, slate and metal roofs across central Sydney, and trace the leak first so the fix goes where the water actually gets in. If the leak turns out to be elsewhere on the roof, our roof leak repairs cover that too.
