Do electric rooflights leak more?
No, not because there is a motor on them. An electric rooflight sits on the same kerb, takes the same flashing and is weathered exactly as its fixed twin, and the motor has no bearing on any of that. What is genuinely different is that an opening unit relies on a moving joint closing onto a gasket with the right force, every cycle, for twenty years. That joint is the only additional risk, and it is a risk that is managed by setting up rather than by hoping.
The useful way to think about it is that a fixed rooflight has one line of defence around its perimeter and an opening one has two: the same perimeter, plus the seal between sash and frame. Both are ordinary to get right. Both are unforgiving if they are not. The wider mechanics of motorised units sit on the electric and opening rooflight page.
Where an opening unit actually differs from a fixed one
A fixed rooflight is glazed into its frame at the factory with tape and a bead, and the assembly is effectively one component from then on. Nothing in it moves. An opening unit has a sash that lifts away several hundred times a year and returns to a rubber seal that has to deform by the correct amount to close the path.
Every other part of the installation is identical. The kerb height above the finished surface, the covering dressed up the sides, the flashing laps, the terminations. Those four details decide whether water gets in around the unit, and they are the same whether or not a chain is fitted, which is why an electric unit fitted properly is no wetter than a fixed one fitted properly.
Compression, and the force the motor has to deliver
Gasket seals work by squeeze. The manufacturer specifies a closing force and a resulting deflection, typically compressing the section by a third to a half of its free height, and the actuator has to supply that at the end of its travel with something in hand.
Choose a drive rated close to the weight of the sash and it will open and close perfectly well while looking entirely normal, and it will still be a few newtons short at the moment it matters. The seal is then in contact but not compressed, which holds against ordinary rain falling vertically and fails against rain arriving horizontally at thirty miles an hour. Margin on the drive rating is not a luxury.
Limit switches, and the millimetre that drifts
An actuator knows where to stop because a limit is set, either by a mechanical switch or by the controller sensing current rise as load increases. Both drift. A mechanical limit can shift with vibration over years, and a current-sensing controller reads a chain that has stiffened slightly as though it has reached the sash.
The symptom is a unit that looks shut from the ground and is a millimetre or two proud along one edge. Nobody notices in a normal week. It shows up on the first evening of driven rain from a particular direction, and it produces the classic pattern of a rooflight that is dry through most of a winter and wet three times. Running the unit through a full cycle once a year and watching the last inch of travel catches it before the weather does.
Drainage channels inside an opening frame
Opening rooflights are not designed to be perfectly airtight rectangles. They are designed to manage the small amount of water that gets past the outer line, which is why the frame carries a drainage channel around its perimeter and weep holes that let that channel discharge outward above the kerb.
Those weeps are the size of a pencil and they close up with moss, silt and the fine grit that washes off a tiled roof. A blocked channel fills, and once it is full the water finds the next lowest path, which is inward. A large share of what gets reported as a failed seal on an opening unit is a drainage channel that quietly closed itself over four autumns.
A kerb out of level, and what a twist does to a seal
This is the one that separates a good installation from an average one. Under a fixed unit, a kerb that is out of level by three or four millimetres across its length is invisible and harmless. Under an opening unit it is neither.
A frame set on a twisted kerb takes up that twist, and the sash then meets its gasket harder on one corner and lighter on the diagonally opposite one. The motor still closes it, the limit still trips, and one corner is under-compressed for the life of the unit. Setting the kerb true, checking it across both diagonals before the frame lands, is why the same trade building the kerb and setting the unit tends to produce a better result. The kerb detailing itself is covered on the flat roof rooflight page.
Driven rain from one direction only
Water on a roof does not arrive uniformly. Essex weather that matters for this comes off the estuary and the North Sea, and an exposed site around Maldon, Burnham or Canvey sees rain driven at a low angle across a flat roof rather than falling onto it.
An under-compressed gasket on the windward edge of a unit will hold against everything except that condition. It is why the reported pattern is so often seasonal and directional, and why the honest diagnostic question is which way the wind was blowing rather than how heavy the rain was. On exposed sites the sensible specification is a stronger drive and a shorter stroke, so the sash closes harder and presents less to the wind when open.
Water that came in because the unit was open
Worth separating out, because it is common and it is not a failure of anything. A rooflight open at twenty three degrees on a flat roof is a funnel pointed at the sky, and a shower arriving while nobody is home puts water on the floor.
A rain sensor takes ten to thirty seconds to close a unit from the first drops, so a squall that arrives as a wall of water will still put some inside. That is the argument for siting a purge opener over a hard floor rather than directly above a dining table, and for pairing any automated opening with a sensor. Sensors are covered on the automatic closing page.
Condensation mistaken for water getting in
The first thing to establish about any wet mark near a rooflight is whether it is rain at all. Surface condensation forms on the room side of cold glass and cold frame sections when warm moist air reaches them, and on an opening unit the frame carries more metal and more junctions than a fixed one, so there is more cold surface for it to form on.
The tells are consistent. Condensation appears in cold weather regardless of rain, it is worst first thing in the morning, and it forms as an even film rather than as a run from one point. Water getting in follows the weather, follows a direction, and marks in the same place every time. Establishing which one you have decides everything about what happens next.
Commissioning, and what a survey checks before any of this
An electric unit is not finished when the glass is in. It is finished when the limits are set, the sash is confirmed to be compressing evenly all the way round, the weeps are clear and the unit has been run through several full cycles with somebody watching the closing edge.
Before that, the survey has already asked the four questions that decide the outcome: what the sash will weigh once the glazing is settled, whether the drive is rated for it with margin, whether the kerb can be set true, and how exposed the roof is. Sunspire carries a ten year workmanship guarantee precisely because those decisions are invisible once the job is finished, and every one of them is cheap on the day and expensive later.
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