Anyone comparing a top hung vs centre pivot roof window is really asking how the window will behave when it is open, and what it will be like to stand beside. The two are the common mechanisms in pitched roofs, and they suit different rooms. This guide is part of our roof windows service and covers roof window opening types, so you can choose before the survey.
How a centre-pivot window works
A centre-pivot window turns around a horizontal axis near the middle of the sash. You lift a handle at the top, the sash rotates, and the lower half swings outward while the upper half swings inward. In the fully open position it can be rotated through to let the outside face be cleaned from inside the room, which is useful on a roof you cannot reach safely.
Because the sash pivots in the middle, the handle sits at the top of the frame. That is a good position when the window is set high on the slope, since you reach up to open it. It is the long-established design that comes to mind first when a roof window is mentioned.
How a top-hung window works
A top-hung window is hinged along its top edge and swings outward from the bottom, like a hatch opening upward. It is also called a projection or a view type of window in some ranges, because as it opens it lifts clear of the sill and gives a more open view out. The handle sits at the bottom, which is the right place when the window is set low enough to reach from a bed or a desk.
Opened out, the sash forms a small canopy over the opening. Some top-hung designs allow the sash to stand at an angle and be held there, giving ventilation even in light rain. The headroom at the sill is better than with a pivot, because the sash does not swing inward.
Pivot windows are happiest high on the slope. Top-hung windows are happiest low. The room tells you which one you need.
The key differences, side by side
| Feature | Centre-pivot | Top-hung |
|---|---|---|
| Handle position | Top of the frame | Bottom of the frame |
| How it opens | Rotates on a central axis | Swings out from the bottom |
| Best set | Higher on the slope | Lower, near eye level |
| View when open | Partly blocked by the sash | Clearer, more open |
| Cleaning | Outer face turns inward | Pivots for cleaning on many models |
Choosing by position in the room
Standing height decides most of the choice. In a loft room where the roof is fully lined and the windows sit at the middle of the slope, a centre-pivot handle falls at a comfortable height and the window opens neatly. Where the sill is set low, for instance so you can see out from a bed, the pivot's inward swing can clash with furniture and the top handle becomes an awkward stretch. A top-hung window with a bottom handle opens more naturally there.
Window height also affects safety. A low window at a child's bed height needs to be considered with the opening limit in mind, and we talk through restrictors at the survey. Our page on roof windows for loft conversions covers positioning across a whole loft.
Ventilation in practice
Opening a roof window is the quickest way to clear a hot or humid room, because warm air rises and leaves through the highest opening. A pivot window opens at both ends, with the lower half swinging out and the upper half swinging in, so air can move through the gap in both directions. A top-hung window opens along its bottom edge and lets air pass out through a wider slot across the whole width.
Both can hold a small vented position, which lets in fresh air with the window almost closed. That is handy overnight and when you leave the house. Many units have a trickle vent built into the frame, so you can ventilate without opening the sash. In a bedroom, a vent that works with the sash shut is worth a thought, because it keeps the room fresh without noise or draught.
Cleaning and maintenance
Glass in a roof slope gets dirty from rain, pollen and bird droppings, and being able to reach it matters. The pivot design makes cleaning simple, because the sash turns right around and presents its outer face to the room. You can wipe both sides without leaving the floor. Many top-hung windows also pivot for cleaning, so the outer pane turns inward; check the model, as some are cleaned from outside.
The rest of the care is light. Wipe the seals and the frame, check the drainage slots at the base of the frame stay clear, and keep any blinds running freely on their rails. Moving parts are sealed in the frame, so there is little to oil. If a window sticks or a seal looks tired, we can look at it during a visit and tell you whether it needs attention or a replacement unit.
Blinds, curtains and shading
Blinds are specified to the window, and the type of window decides which ones fit. A pivot window carries its blind on rails fixed to the frame, with the handle at the top so the blind pulls down from the same area. A top-hung window has a handle at the bottom, and its blinds are designed so the controls do not clash with it. Blackout, pleated and roller styles are all available, and electric blinds can pair with an electric window.
If the window is going into a south-facing slope, think about shading at the same time as opening type. External shading cuts heat before it enters the glass and works better than anything inside. Whatever you choose, tell us at the survey so the frame and flashing are chosen with the accessories in mind.
Other opening types you may meet
Centre-pivot and top-hung are not the only choices. Several others suit particular jobs.
- Fixed windows do not open at all. They give the lowest-cost route to daylight and suit places where ventilation comes from elsewhere.
- Electric and solar-powered windows open at the press of a button or from a rain-sensing control, which suits windows set out of reach.
- Vertical combinations pair a roof window with a vertical window beneath it, to bring in more light and a view at standing height.
- Balcony and cabrio designs open to form a small balcony or a door-like opening, where the roof allows it.
- Conservation windows have a slim, flush profile for sensitive roofs and are covered in our conservation rooflights pages.
Electric operation is worth a thought for any window beyond arm's reach. A mains-wired window needs a qualified electrician to connect it, and a solar one runs from its own panel.
Frames, materials and finish
Frames are made in timber with a protective coating, or in a material such as PVC that needs less upkeep. White is the usual finish, but darker and natural tones are available. A timber frame suits a bedroom or study where the warmth of the material is part of the look. A coated, maintenance-light frame suits a bathroom or kitchen where moisture is greater. The choice affects how the window looks from inside more than outside, since most of the frame is hidden by the roof covering.
The rules that apply to both
Opening type does not change the rules. A replacement or new roof window is building work, and the unit must meet Part L. Both mechanisms can be supplied to reach the figure Part L expects of a roof window in an existing home. The same applies to a unit in a pitched roof that is described as a rooflight. We cover the figure in our answer on what U-value a roof window needs.
Planning follows the usual Class C test on projection from the slope and on height against the ridge. Neither opening type projects significantly when closed. Our planning guide explains the exceptions.
Safety around opening windows
A window that opens is also a gap that needs thought. In a child's room, a restrictor stops the sash opening beyond a safe distance, and a lock on the handle keeps small hands from forcing it. Windows set low in the slope are most at risk, which is another reason to talk about height before the survey is finished. Roof windows also need to be secure from outside, and the locks and laminated glass in modern units are chosen with that in mind.
Where a window is above a stair or in a room used by someone with limited reach, electric operation can be safer than a pole. We would rather plan these things in advance than add them later, because the frame, the wiring and the opening all depend on the decision.
Escape and ventilation
A roof window is sometimes chosen with fire escape in mind. An escape window is only accepted for low storeys, so a loft above a two-storey house relies on a protected stair instead. In that case the opening type is chosen for comfort, light and air. Both mechanisms ventilate well. A top-hung window can be left slightly open with the sash angled, and a pivot can be locked in a vented position.
Replacing an existing window with the other type
If you already have a roof window and want a different opening style, the first question is the size. Roof windows are made in standard sizes, and our guide to VELUX window sizes explains how to read them. A new unit of the same size usually drops into the existing opening, and the flashing is renewed around it. A change of type can move the handle or the sash, which may affect your blinds, so we plan the swap with those in mind. Tell us about any blinds, shutters or window seats you want to keep, and we will measure around them before we specify the new unit. Photographs of the existing window, taken from inside and out, help us arrive at the survey prepared.
Where the opening has to change size, the rafters and the reveal inside are altered, and the job becomes a little larger. We say so in the quote, and the finish inside is made good, plastered and ready for decorating.
How we help you choose
At the free survey we look at the slope, the room, the height of the sill and how you use the space. We mark on the slope the height it would sit. The window you select is priced in a fixed written quote, flashed and sealed on the roof, with the lining shaped where the roof allows, plastered and made good inside. Our fitting is backed by a 10-year workmanship guarantee, and we handle the Building Control notification where the work needs it. If two opening types would both suit the room, we explain the difference in plain terms and leave the choice with you.
