Guide · Electric and Opening Rooflights
Fixed, manual and electric compared
Every rooflight decision comes down to three options, and the right one is decided by the room rather than by the budget. A fixed unit is glass in a frame that never moves. A manual unit opens by handle, winder or pole. An electric unit opens on a motor. They cost different amounts, but they also perform differently in ways that have nothing to do with price: thermal behaviour, sightlines, air tightness, ventilation rate and what each one asks of you in twenty years.
This page compares them on those terms. It is the specification conversation rather than the sales one, and it assumes you already know roughly where the glass is going. The motorised option in detail sits under electric and opening rooflights.
The three options, stated plainly
A fixed rooflight is a sealed unit bonded or clamped into a frame with no moving part anywhere in the assembly. A manual opening rooflight has a sash on hinges, held and moved by a mechanical operator that a person drives. An electric unit is the same sash with a drive in place of the hand.
That is the whole taxonomy. Everything else, solar power, rain sensing, app control, blinds, is a variation on the third. Which matters, because it means the fundamental fork is between glass that moves and glass that does not, and only then between how it is moved.
What a fixed unit does better than either opener
A fixed rooflight is quieter, cheaper, thermally better, more air tight, lighter and has nothing in it to wear out. Given a room where ventilation is genuinely covered by other openings, it is the correct answer and not a compromise.
It also gives more glass for a given hole in the roof, which is the point people underestimate. It has no sash frame inside the outer frame, so the visible glass area for the same structural opening is meaningfully larger. On a modest rooflight over a hallway or a landing, that difference is visible from the floor.
Frame depth, sightlines and the glass you get for the opening
An opening unit needs a sash section, a gasket, hinges and clearance, and all of that lives inside the outer frame. The result is a doubled frame line and a deeper visible edge.
On a typical one metre by one metre unit, the fixed version can show sixty to ninety millimetres more glass in each direction than the opening version of the same range. In percentage terms on the glazed area that is not trivial. Where a rooflight is being specified for daylight rather than for air, this is a real argument for fixed, and it is why a run of fixed panels with one opener among them is a common and sensible arrangement.
Thermal behaviour, and the joint an opener has to seal
A fixed unit’s only thermal weakness is the frame perimeter, which is designed once and stays put. An opening unit adds a second perimeter, the gasket line between sash and frame, and that joint is the harder one to keep performing.
Manufacturers publish whole-unit U-values for both versions and the fixed unit is usually a little better. The gap is not dramatic on a good modern range, but the direction is consistent, and it widens with age because a gasket is a wearing component and a bonded frame joint is not.
Air tightness and the draught test a fixed unit never takes
Air leakage is measured separately from thermal transmittance and it is the metric where the three options separate most clearly. A fixed rooflight has no leakage path through the unit at all. An opening rooflight has a gasket that is doing the work, and its performance is a class rating rather than an absolute.
Between manual and electric there is a real difference here, and it favours the motor. A drive closes to a calibrated position every time, at the same force, in the same place. A hand closes to wherever the person stopped pushing, which on a cold evening with a stiff gasket is often a millimetre short of full compression.
Manual operation, and the ranges that offer it
Manual opening rooflights are widely available on pitched roof windows and much less so on flat rooflights. That imbalance surprises people and it has a mechanical reason.
A roof window in a slope has its sash within reach and gravity partly assists the movement, so a handle at the bottom rail works. A flat rooflight sash lifts vertically against its own full weight on a kerb, usually above head height, with no convenient point to grip. Several ranges therefore offer flat rooflights as fixed or electric with no manual option in between, which settles the question before it is asked.
Winders, poles and the reach a hand can cover
Where manual operation is offered, it takes one of three forms. A handle on the sash, reached directly. A geared winder on the frame, turned by hand or by a hooked rod. Or an eyelet operated by a telescopic pole.
Each has a working envelope. A handle wants the sash within about two point two metres of where you stand. A winder extends that a little. A pole reaches three metres or so on paper and rather less in practice, because holding a pole overhead while turning a rod against a friction hinge is genuinely awkward. Beyond that range the manual option exists on the order form and stops existing in the house.
Electric operation, and what it adds beyond convenience
The motor buys three things that a hand cannot. Consistent closing force, which is the air tightness point above. Operation from a distance, which makes a high unit usable. And the ability to respond to a rule rather than to a person, which is where sensors and schedules come in.
That third one is the underrated argument. A manual rooflight only ventilates when somebody remembers. An electric one can vent a bathroom on humidity, purge a kitchen on temperature and shut itself on the first drops of rain, none of which requires anybody to be in the room or awake.
Ventilation performance compared by free area
Fixed contributes nothing to ventilation, by definition. Between manual and electric the difference in free area at full open is usually small but real, and it runs in both directions depending on the unit.
A manual top hung sash can often be pushed to a wider angle than a drive’s stroke allows, so the manual version may have more free area at maximum. Against that, a motorised unit reaches its useful angle every time it is asked, while a manual unit at maximum angle is a position most people never use because it is hard to reach. Designed free area and used free area are different numbers, and the second one is the one that ventilates the room.
| Fixed | Manual | Electric | |
|---|---|---|---|
| Visible glass for the same opening | Most | Less | Less |
| Whole-unit U-value | Best of the three | Slightly behind | Slightly behind |
| Air tightness over twenty years | No leakage path | Depends on how it is closed | Calibrated every cycle |
| Ventilation | None | When someone is there | On demand or on a rule |
| Useful height above floor | Any | Up to about 2.6m | Any |
| Can serve an escape opening | No | Yes, with the right sash | Yes, with a hand release |
| Weight on the kerb | Lightest | Heavier | Heaviest |
| Yearly attention | Wash the glass | Seal and hardware | Seal, hardware and a test cycle |
The ventilation duty, split between background and purge
Building Regulations treat ventilation as two separate duties. Background ventilation is the small continuous air exchange that runs all the time, usually delivered by trickle vents. Purge ventilation is the large, occasional exchange that clears cooking, moisture or overheating quickly.
A fixed rooflight satisfies neither, though many fixed units can be ordered with a trickle vent in the frame to cover the first. Only an opening unit delivers purge, and there the question is simply whether the opening is large enough and whether it will actually be opened. In a room where the rooflight is the purge provision and it sits four metres up, the honest answer is that it needs a motor.
Escape openings, and which of the three can serve one
Where a rooflight is the means of escape from a loft conversion or an inner room, Part B sets a clear opening area and a sill height, and only a unit that opens can meet it.
Manual units meet it directly. Electric units meet it provided there is a way of opening the sash without power that a person in the room can operate, which on most ranges means a release at the bracket or a hand winder. Fixed units cannot serve, which is why an escape rooflight and a daylight rooflight in the same loft are often two different products in the same slope.
Rain, and the option that closes itself
This is the practical difference that people notice most in the first year of ownership. A fixed unit does not care about rain. A manual unit left open in a shower puts water into the room. An electric unit with a sensor closes on the first drops, typically within seconds.
On a rooflight you can see and reach, the sensor is a convenience. On one above a stairwell, or in a house that is empty from eight until six, it is what makes an opening unit at that position a sensible idea at all. What the sensor can and cannot do is set out under rain sensors and what they actually do.
A manual rooflight opens when you remember; an electric one closes when you have forgotten, which is the more valuable half.
Weight, structure and what each option puts on the kerb
An opening unit weighs more than a fixed one of the same size, because it has a second frame, hinges and hardware. An electric one adds a drive and its bracket on top of that.
On a domestic timber kerb the difference rarely changes the structure, but it does change the fixings and the number of them, and on a large lantern or a wide flat rooflight it can move the specification of the trimming timbers. It is also a dynamic load rather than a static one, since an opening pane in wind imposes forces the fixed version never sees. This is one of the things a survey establishes before an order goes in.
Maintenance over twenty years, option by option
A fixed rooflight wants its glass washed and its perimeter looked at every few years, and that is the complete list. A manual unit adds the gasket, the hinges and the operator hardware, all of which want an annual look and occasional adjustment.
An electric unit adds the drive, its bracket and the control, plus a test cycle and any batteries. That is more items but not more time; the yearly routine on a motorised unit still fits inside twenty minutes. The difference is that it has to actually be done, because a drive working against a neglected seal wears faster than one that is not.
Mixing the three across one roof
The best specifications on larger jobs are rarely all one thing. A run of three flat rooflights over a kitchen extension works well as two fixed panels and one electric opener, positioned at the high end of the fall and towards the back of the room where the warm air collects.
The logic is that ventilation is a whole-room requirement rather than a per-unit one. You need enough free area somewhere in the ceiling, and you buy it once, in the position where it does the most work. The remaining units are then specified purely for daylight, which means more glass, better numbers and less to look after.
Choosing between them for an Essex extension
The pattern that recurs across the county is straightforward. On the interwar semis and Victorian terraces of Chelmsford and Colchester, loft conversions take a manual roof window where it is reachable over a floor, because the reach is genuine and the escape duty often sits on the same unit.
On the vaulted rear extensions going onto houses at Great Notley, Beaulieu Park and South Woodham Ferrers, the ceiling height and the flat roof kerb push it the other way, and the sensible arrangement is fixed glass for light with one motorised opener for air. Where the roof is a heritage slope in Thaxted, Coggeshall or Saffron Walden, the frame profile of a conservation rooflight often settles it before any of the above, because the section decides what a drive can be hidden in.
Keep reading
More on electric and opening rooflights
Rain sensors and what they actually do
Read the guide →Wiring an electric rooflight at first fix
Read the guide →Solar powered rooflights without a mains run
Read the guide →Remote controls, wall switches and smart home links
Read the guide →Electric blinds fitted inside the rooflight
Read the guide →
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