The short answer: A well-made opening rooflight (the skylight that opens, in everyday speech) that is fitted correctly and weathered properly should not leak when it is shut. When one does, the cause is usually the seals, the way it was fitted into the roof, or the kerb and flashings around it, not the fact that it opens. We assess the unit and the roof on a free survey and tell you in writing whether it should be replaced.
This page sits within our guide to electric and opening rooflights. It explains why an opening rooflight might let water in, and how to tell a leak from something that looks like one.
Why an opening unit is a fair thing to worry about
A fixed rooflight has a sealed glass unit set into a frame, and nothing moves. An opening one has all of that plus a sash that lifts away from the frame, a seal that has to close tightly each time, and hinges or an actuator that must keep the sash square. More moving parts means more places for wear to show up, which is why the question is reasonable.
It does not follow that opening rooflights leak as a rule. A well-engineered unit is tested to resist water when shut, and the seal is designed to compress evenly around the whole perimeter. The weak points are the ones that appear over time or through poor installation.
The usual causes of water getting in
| Cause | What it looks like |
|---|---|
| Worn or displaced seal | Drips along one edge after heavy rain. |
| Sash not closing square | A gap you can see or feel when shut. |
| Failing flashing or upstand | Stains on the ceiling or reveal around the frame. |
| Blocked or poorly detailed drainage | Standing water at the base of the frame. |
| Left open in rain | Water on the floor below, with no fault in the unit. |
Notice that only the first two relate to the opening mechanism. The rest could happen to a fixed rooflight just as easily. Water around a frame is often a weathering problem at the roof, where the flashing, the kerb and the surrounding membrane or tiles meet the unit.
Is it really a leak?
Before blaming the rooflight, it is worth checking for condensation. Warm, moist air from a kitchen, bathroom or busy room can condense on a cold surface, and a rooflight pane or frame is often the coldest surface in the room. The result is a film of water, or drips from the frame, that looks like a leak but is not coming through the roof.
The signs differ. Condensation tends to appear on cold mornings, after cooking or showering, and it fades as the room warms. A leak appears during or after rain, and often in the same place each time. Water between the panes is neither. It means the sealed unit has failed, and our page on misted and failed rooflights covers what that involves. For condensation that comes from the room, our page on reducing condensation on rooflights is the place to start.
Installation matters as much as the product
A good unit in a poorly weathered opening will still let water in. The weathering is the junction between the rooflight and the roof: the kerb or upstand, the flashing, the membrane and the way they lap. On a flat roof, the upstand has to be tall enough, the membrane has to turn up and over it, and the frame has to sit on it with the sash clear of any standing water.
On a pitched roof, the flashing kit has to suit the roof covering. A flashing designed for slate does not work on a plain tile, and a kit for a thin covering may not work on a deep one. The right flashing, correctly lapped, is what keeps a roof window dry.
How you can help the survey
If you have noticed water, note where and when. A stain that appears only after wind-driven rain from one direction points to a flashing or an exposed edge. A drip that follows any rain at all suggests a seal or a kerb. Photographs of the ceiling and the frame help, and so does a note of whether the rooflight was open or shut at the time.
Please do not seal around the frame with a tube of mastic in the meantime. It can trap water inside the junction and hide the true path, which makes the later assessment harder.
What about electric units?
An electric opening rooflight uses the same sash and seal as a manual one, and the motor does not change how water is shed. What it adds is a cable entry, which has to be detailed so that water cannot follow the cable in, and a rain sensor if you choose one. A sensor closes the unit when it detects wet, which reduces the chance of rain entering through an open sash. See rain sensors and smart rooflight controls for more.
What we do when we find a problem
When we survey a rooflight that lets water in, we look at the unit, the kerb, the flashing and the surrounding roof covering, and we tell you what we find. If the unit has reached the end of its life, or the weathering around it needs rebuilding, the answer is a new rooflight set on a correctly formed upstand. That is a replacement job with a fixed written quote, and it comes with our 10-year workmanship guarantee. See the guarantee page for details.
If a leaking opener means the whole unit comes out, the replacement is building work, so it must meet current energy rules and be notified. The notice to Building Control is ours to send, and our Building Regulations guide has more. The access plan in your quote sets out how we reach the roof, including any scaffold licence we apply for.
If you are comparing opening types, our page on opening rooflights for ventilation and summer heat explains what they are good at. To get yours looked at, book a free survey, or return to the electric and opening rooflights hub.
