Short answer: neither opening type is approved or banned across the board. What a conservation officer reads is the roof window when it is shut: how flat it lies, how slim its frame is and how much it stands above the slates. Choose the type that gives you the slimmest, flattest closed profile, then check it with the planning authority for your street.
How the two types open
A top-hung roof window is hinged along its top edge. The bottom of the sash swings outward and upward, rather like a hatch lifted from below. A centre-pivot window turns on a horizontal axis through the middle of the sash. The lower half swings into the room while the upper half goes out over the roof, and the sash can turn right round for cleaning.
Both can be made with a slim frame. Both can also be fixed, with no opening at all, which is a third option in a conservation area and the quietest of the three.
What matters to a conservation officer
Planning officers do not rate hinge types. They look at the finished roof. The points that come up again and again are these:
- how far the window sits above the plane of the slates or tiles;
- the thickness of the frame and the glazing bars, since slim steel or a thin metal-framed unit reads closer to a historic cast-iron light;
- whether the window looks onto the street or the back garden;
- how many windows there are, and whether they line up with the openings below;
- the colour and finish of the frame against the roof covering.
An opening type matters only where it changes one of those. A conservation skylight opening that leaves a deep hood or a chunky side casing on a street slope is harder to defend than a fixed light with the same glass.
Where each type has the edge
| Question | Top-hung | Centre-pivot |
|---|---|---|
| Closed profile | Can be made low and flush | Can be made low and flush |
| Open position | Sash rises at the bottom, out over the slates | Sash turns, upper half stands above the roof |
| Cleaning | Varies by model; some swing round so the outer face is reached from inside | Sash turns so the outer face is reached from inside |
| Parts that wear | Hinges, stay, seals | Pivot, friction arm, seals |
For a steep stone-slate roof where the window is mostly shut, a top-hung unit keeps its outward movement to the bottom edge. For a window the owner wants to clean from a bedroom or a landing, check that the model turns for cleaning; every centre-pivot does. Neither is a reason in itself to be refused.
The planning side
For a house, permitted development allows a rooflight that projects 150 mm or less from the slope and stays below the roof's top edge. Flats do not have these rights. A conservation area does not remove them by itself, but a listed building needs consent and an Article 4 direction, which many conservation areas carry, can remove them, so you may need to apply.
The authority also differs by address. Most of Sheffield is dealt with by Sheffield City Council. Where the address falls inside the National Park, out towards the moors, the Peak District National Park Authority takes over. We check which applies and look at the conservation map at the survey. For the national rules, read our planning guide.
Listed buildings are different
On a listed building the question is not permitted development. Changing a roof window usually needs listed building consent, and the officer will want to see the detail. That is a separate subject, and we deal with it in do I need listed building consent for a rooflight. If the opening you are replacing is original cast iron, see replacing a cast-iron rooflight.
Energy and ventilation
Part L 2021 holds roof windows going into an existing house to 1.4 W/m²K, or WER Band B on the energy label. A rooflight, which in the regulations means glazing in a flat or low-pitch roof, is held to 2.2 W/m²K. For a heritage roof you can sometimes agree some flexibility with building control, but we start from the standard figures. Our page on conservation rooflight energy efficiency explains the trade-offs in a thin frame.
Opening windows also matter for air. A roof window you can open gives control of damp and stale air in a loft room, and a fixed light does not. Where the room needs fresh air, a different opening in the wall or an extractor may be the answer.
Wear and the life plan
The frame is built to last, but the hinges, stay or pivot, and the seals can all wear. In the quote we name the opening gear and say how each is swapped later, and if that means lifting slates. A slim frame often means a hardware part that is hard to find years later, so we ask the maker about spares before you commit. At year 5 we suggest checking the seals and moving parts together.
Where the work is notifiable, the notification is ours to make, whoever signs it off. See our conservation rooflights hub for the rest of the range.
A practical way to choose
Start with the room. If you want the window to open for air, decide how high it will sit and whether you can reach it. Then look at the roof slope: the steeper and more visible it is, the stronger the case for a fixed light or a very slim unit.
Finally, put the choice to the planning authority early. A drawing that shows the frame section and the height above the slates answers most of the questions an officer will have.
