What is the difference between centre-pivot and top-hung?

The two styles solve the same problem, getting daylight and air through a sloping roof, but the sash moves in a completely different way and that is what you feel day to day.

A centre-pivot window is balanced on two pivots set roughly halfway up each side. When you open it, the sash rotates about that line. The top edge tips into the loft and the bottom edge lifts outwards. On the common VELUX pattern the control bar sits along the top of the frame, so you reach up and over rather than leaning down to the sill. That top bar is deliberate: it means you never have to stretch across an open sash, and it works whether the window is at head height or higher up the slope.

A top-hung window keeps the hinge at the top and lets the whole sash swing outwards from the bottom, up to around 45 degrees on most units. The handle is at the bottom of the sash, so you push it away from you and it holds open on a stay. Both types still rotate a full 180 degrees and lock in place for cleaning, so the outer glass can be washed from inside without leaning out over the roof. The everyday opening action is the real difference, not the cleaning position.

The choice usually comes down to how high the window sits and what is directly beneath it. Because a centre-pivot sash swings the top half into the room, you do not want to stand tight against it with your head in the opening arc. That is no problem when the window is set higher up the roof plane, above where anyone stands, which is exactly where centre-pivot units tend to go.

Top-hung units come into their own lower down the slope, where the sill is near waist or chest height and you naturally walk up to the glass to look out. Nothing swings back into your face, so you can put a desk, a bed head or a kitchen worktop directly under the window and still open it fully. If the roof is a loft conversion with a low knee wall, a top-hung window set at the eaves gives you a proper view down to the garden or the estuary rather than straight up at the sky.

Pitch matters too. Centre-pivot windows are happy across a wide range of roof angles and stay easy to reach on a steep pitched roof. Top-hung units prefer the shallower end of the range, because on a very steep pitch the outward swing carries the sash a long way out and it can catch the wind.

Stand at a top-hung window and the glass is above and in front of you with nothing crossing your eyeline, so the outward view is clean. At a centre-pivot window the pivot bar and the open top edge sit across the middle of the opening, which barely matters when the window is above head height but is more noticeable if you are looking out from close up. If the view is the point of the window, that alone often settles it.

Ventilation works differently between the two. A centre-pivot lets air in low at the bottom and out high at the top through the same opening, which moves stale air well and can be left on a small night-vent latch without releasing the whole sash. A top-hung opening acts more like a single wide flap, good for shifting a lot of air quickly on a warm day when you want the room to dump heat fast.

For cleaning they are level. Both rotate right round and lock, so the outside face turns to meet you indoors. The practical point is safety: neither style should ever mean climbing onto the roof, and any window we fit is set up so the outer pane can be reached from a firm footing inside the room.

If the window is the designated means of escape from a habitable loft room, the opening style is not a free choice. An escape rooflight needs a clear unobstructed opening, generally at least 450mm high and 450mm wide, giving a clear area of at least 0.33 square metres, with the bottom of the opening set no more than 1.1 metres above the floor. A top-hung sash, or a dedicated top-hung escape unit that swings almost fully clear, gives that clear route far more easily than a centre-pivot, whose sash sits across the middle of the hole and eats into the usable opening.

Whether an escape window is required at all depends on the storey, the room use and the rest of the layout, and it is a Building Control question rather than a rule of thumb. New and enlarged rooflights are notifiable under the Building Regulations in any case, with Part L covering thermal performance and Part K the safety glazing. We handle that notification to Southend-on-Sea City Council, or to the relevant authority for your address, as part of the job, so the escape sizing is checked before anything is ordered rather than after it is fitted.

As a working guide: pick top-hung when the window is low, when you want the clearest view, or when it doubles as an escape route. Pick centre-pivot when the window sits higher up the slope, when furniture goes underneath it, or when you want simple trickle ventilation you can leave on overnight. Plenty of roofs end up with a mix, a top-hung unit at the eaves for the view and a centre-pivot higher up for light and air.

Here is the part the opening style does not touch. Neither a centre-pivot nor a top-hung window changes how much summer heat comes through the glass. That is set entirely by the glazing, and on a roof facing south across the estuary it is the question that decides whether the room is pleasant in July. A south-facing rooflight wants solar-control glazing with a G-value around 0.3 or below, whichever way the sash happens to hinge. Both styles are offered in the same glass specifications, so choose the mechanism for how you will live with the window, then specify the glass for the orientation. Our work on solar-control glazing covers that side in full.

When you are ready, the next step is to look at the actual roof: which way it faces, where the window sits on the slope and what goes under it. That is what our VELUX window installation service is built around, and you can see where the money goes on the costs page first. Ring 01702 898232 or request a quote, and we will match the opening style and the glass to the room rather than sell you a standard unit.