VELUX centre-pivot and top-hung compared

Start with the mechanism, because everything else follows from it. On a centre-pivot window the sash is hung on pivot hinges set roughly halfway up each side. When you open it, the top half tilts outwards over the roof and the bottom half swings inwards into the room. The control is a bar along the top of the sash, so you operate it with a push at the top rather than a reach to the bottom. In the VELUX catalogue these are the GGL, in lacquered pine, and the GGU, in white polyurethane over a timber core.

A top-hung window is hinged along its top edge only. The whole sash swings outwards and upwards from the bottom, the way an awning does, and nothing comes back into the room at all. The handle sits at the bottom of the sash where you can grip it and push the pane away from you. These are the GPL in pine and the GPU in white polyurethane. VELUX also builds a dedicated top-hung escape version, the GTL, which throws the sash open far enough for a person to climb out.

Both types are roof windows in the true sense: they sit in the plane of a pitched roof, flashed into the tiles or slates with the same flashing kits, and they carry the same glazing options and the same size codes. The difference is entirely in how the sash moves, and that single difference decides where each one belongs, how you clean it, whether it can serve as a fire escape, and how well it purges hot air on a south slope. All of that is worth walking through before you pick.

The deciding question is how high the window sits above the floor, because the centre-pivot brings its lower half into the room when it opens.

Picture a centre-pivot fitted low in a loft, with its bottom edge at around waist height. Open it and the lower half of the sash swings in towards your face at exactly the height you are standing. You duck around it, and if there is a desk or a bed pushed up to the wall below, the incoming glass is now hovering over it. Fitted higher up the slope, above head height, the same movement is fine, because the part that swings inwards is above you and out of the way. That is why the centre-pivot is the natural choice for a window set high in a roof, and the reason its top control bar exists: you can reach the bar and work the window without leaning over whatever furniture sits beneath the sill.

The top-hung is the answer when the window sits low, at the kind of height where you want to stand at it and look out, or sit at a desk beneath it. Because the sash swings entirely outwards, nothing intrudes on the room, your head has clear space right up to the glass, and the view is uninterrupted by a pane of glass hanging in the middle of it. Put a top-hung over a window seat on a cliff-top loft in Leigh or Westcliff and you get an open outward view towards the estuary with the whole sash lifted clear above it. That is the layout it is built for.

There is a practical rule of thumb worth carrying into a survey. If the bottom of the window will land below roughly 1.8 metres from the finished floor, lean towards top-hung. Above that, either works, and the centre-pivot’s balance and lighter action on the top bar start to win. It is not an absolute, because the roof pitch and the position of a knee wall change it, but it is the right starting instinct.

These are the figures that actually separate the two. Sizes are given as VELUX size codes with the sash dimensions, since those codes are what you will see on any quote. Treat the opening angles and pitch ranges as the published VELUX ranges rather than a promise for one specific unit, because they vary a little across the size and generation of window.

The pitch range is the line people miss. A centre-pivot works from a shallow 15 degrees right up to a near-vertical 90, which is why it turns up on everything from flat-ish loft slopes to steep mansards and gable-end conversions. The top-hung stops at around 55 degrees, because on a steep pitch the weight of the sash hanging off a top hinge makes it heavy to push open and awkward to hold. Below 15 degrees neither is the right product, and a proper flat-roof unit takes over.

Common sizes are shared between the two families. The MK04 gives a sash of 78 by 98 centimetres, the MK06 is 78 by 118, the MK08 is 78 by 140, and the wider SK06 is 114 by 118. A larger opening does not change the operation logic, but it does make a top-hung heavier to work and a centre-pivot’s balanced action more of an advantage.

If a loft conversion creates a habitable room, Building Regulations usually want an escape window from it, and this is where the two operation types genuinely diverge.

The requirement comes from Approved Document B. An escape window needs an unobstructed openable area of at least 0.33 square metres, with the opening at least 450 millimetres high and at least 450 millimetres wide, and the bottom of that opening no more than 1,100 millimetres above the floor. The phrase that matters is unobstructed. On a centre-pivot, the sash sits across the middle of the opening when it is tilted, so it splits the aperture in two and eats into the clear area a person could climb through. That is why a standard centre-pivot is not accepted as a means of escape.

A top-hung solves it directly. The sash lifts fully clear of the opening, so the whole aperture below it is available to climb out of. VELUX also builds the GTL escape window, a top-hung variant whose sash swings open to around 45 degrees and locks there, giving the clear escape route the regulation is looking for while keeping the window usable day to day. On any loft bedroom that needs an escape route, the top-hung or the dedicated escape unit is the one to specify, and it is worth settling that before the layout is fixed rather than after.

Part K is the other regulation in play, and it applies to both types equally. Anything glazed overhead needs a laminated inner pane so that a broken pane holds together rather than falling into the room, and VELUX roof windows are built to that standard as a matter of course. When we install a new or enlarged roof window it is notifiable work, and we make the Building Control notification to Southend-on-Sea City Council, or to the relevant local authority for your address, as part of the job.

Both windows are built to be cleaned from inside, which matters on a roof slope where the outer face is well out of reach of a ladder.

The centre-pivot rotates a full 180 degrees, so the outer pane comes round to face into the room. A barrel bolt at the top holds the sash in the cleaning position while you wipe the outside, then you release it and swing it back. The top-hung has a second pivot lower down that lets you rotate it in a similar way once it is open, bringing the outer face within reach. Neither needs a window cleaner on a ladder, which on a two-storey Southend semi with a rear loft slope is a real saving over the life of the window.

Ventilation is shared too. Both carry a ventilation flap in the top bar that lets a trickle of air in with the window shut and locked, drawn through a filter that keeps insects and the worst of the road dust out. That background airflow is separate from actually opening the window, and it is useful overnight or when the house is empty. On the electric and solar versions of either type, a rain sensor closes the window automatically at the first drops, so an open roof window left unattended is not the gamble it sounds. We fit those electric opening units where a window sits too high to reach a manual control comfortably, which in a tall loft is often the case.

This is where the operation type meets the thing this business is built on. Southend faces south across the Thames Estuary, and a great many loft conversions here put windows into a south-facing slope with an open horizon and no shading above them. On a clear summer afternoon that glass is collecting a serious amount of solar energy, and the room underneath it heats up from the ceiling down.

The glass is what controls how much of that heat gets in, and it is the same choice for both operation types. A south-facing VELUX wants solar-control glazing, with a G-value down around 0.3 or lower, so that most of the sun’s near-infrared is reflected before it ever enters the room, while the visible daylight still comes through. Clear glass at a G-value near 0.6 lets in roughly twice as much heat, and no amount of opening the window afterwards undoes that. Specifying the glass for the aspect is the same discipline whether the sash pivots or hangs, and it is covered properly on our page about the whole VELUX roof window range and in more depth under solar-control glazing.

Where the operation type does earn its keep on a south slope is in getting hot air out once it has built up. Warm air stratifies and sits at the top of the room, right where a roof window is. A top-hung, swung fully outwards, opens the aperture wide and lets that hot layer spill out over the roof with very little to obstruct it. A centre-pivot vents well too, but the tilted sash sits partly across the opening and the airflow has to work around it. On a large south-facing loft where summer purging matters, the wider clear opening of a top-hung is a genuine advantage, and pairing it with an opening window lower in the room, or on a cooler slope, sets up a flow that pulls the heat up and out. Glass controls what arrives. Opening controls what leaves. On a south slope in Southend you want both working for you.

Put the pieces together against the kind of roofs this stretch of coast actually has, and the choice usually settles itself.

The 1930s semi, of which south Essex has an enormous stock, typically converts with a rear slope of moderate pitch, and the escape-window requirement on a new loft bedroom often points straight at a top-hung or the dedicated escape unit. The steeper roofs on Victorian and Edwardian villas along the cliff, and the mansards on some of the older terraces, sit at pitches where the top-hung’s 55 degree limit rules it out and the centre-pivot’s full range is the only option that fits. A window set high in a vaulted loft ceiling, above where anyone stands, is a centre-pivot job for the reach and the balance. A window at desk height in a home office in the eaves is a top-hung, for the clear view and the head room.

Run through this before you commit:

1. How high off the floor does the window sit? Low favours top-hung, high favours centre-pivot.
2. Is this room a habitable loft bedroom? If it needs an escape window, that is a top-hung or a GTL escape unit, not a standard centre-pivot.
3. What is the roof pitch? Above 55 degrees, the centre-pivot is your only VELUX option.
4. Is there furniture directly below the window? A desk or bed under the sill leans towards a centre-pivot, worked from the top bar.
5. Which way does the slope face? South or west means solar-control glass regardless of type, and on a big south slope the wider opening of a top-hung helps clear the heat.
6. Will you reach it? A high window that you will never wind open by hand is a candidate for an electric or solar version with a rain sensor.

None of this is guesswork on a real roof. We survey the slope, measure the pitch, work out how high each window will sit and which way it faces, and pick the operation type and the glass to match, the same way we do on any pitched-roof installation. If you want that worked out for your own loft before you order anything, with the pitch, the sizes and the glass specification set down in writing, ask us for a survey and we will give you the reasoning for each window rather than a single line that treats them all the same.