In the UK, the words "roof window" and "skylight" get used almost interchangeably, which makes shopping for glazing more confusing than it needs to be. Strictly speaking, a roof window is a framed unit that sits flush within the pitch of a sloping roof and usually opens. It is the classic choice for a loft conversion, set into the slope above your head as you climb the stairs or beside your new bed. A skylight, more often called a rooflight in the trade, tends to be a larger, fixed pane — or one with a small opening section — and is commonly used on flat roofs, extensions and boxy dormers. Both bring daylight into a dark loft, but they behave very differently when it comes to ventilation, cleaning and how the room feels once it is finished.
Knowing which one suits your roof is the first decision. If your loft has a pitched roof with slates or tiles, you are almost certainly looking at roof windows. If you have a flat roof section, or you are building a dormer with a vertical face, a rooflight on a kerb is usually the neater answer.
Light is the whole point of the exercise, so it pays to think about quantity and placement before you choose a model. As a rule of thumb, aim for glazing that covers roughly 15 to 20 per cent of the floor area of the loft room. A 12 square metre bedroom, for instance, benefits from around 2 to 2.4 square metres of glass. Less than that and the room can feel gloomy on a grey February afternoon; much more and you risk overheating in July.
Where you put the window matters as much as how big it is. Setting roof windows higher up the slope throws light deeper into the room and gives you a better view over neighbouring rooftops, which is a real bonus in a terraced street. Positioning them lower gives you a closer look at the garden but can leave the back of the room in shadow. Many loft conversions work best with a pair of windows side by side, or one above the other, rather than a single small unit.
On the glazing itself, look for:
Also check whether the window can serve as an escape window. Building Regulations require a safe route out of habitable loft rooms, and a roof window can often do the job if it opens far enough and the clear opening meets the minimum size.
Lofts get stuffy. Warm air rises, and a well-insulated loft can turn into a greenhouse without decent airflow. The two main opening mechanisms are centre-pivot and top-hung, and each has its place.
Centre-pivot windows rotate around a horizontal axis near the middle of the frame. They are brilliant for ventilation because the top half swings inward, scooping air into the room, and you can reach the outer pane from inside for cleaning. The trade-off is that the open sash takes up headroom in the middle of the window, so they suit walls where you are not standing right up against the glass.
Top-hung windows hinge at the top and open outwards, giving you a clear opening and full headroom below. They are ideal above a desk, a kitchen counter or anywhere you might stand close to the window. They also shed rain well, so you can leave them open during a shower.
Whichever you choose, consider background ventilation. Trickle vents, a small opening section, or a mechanical ventilation system with heat recovery will keep moisture down and reduce condensation on cold mornings — a common complaint in newly converted lofts.
Nobody wants to balance on a ladder to clean a window. This is where roof windows win hands down over fixed rooflights. A centre-pivot window that rotates a full 180 degrees lets you clean both panes from the comfort of the room. Many top-hung models also allow the sash to be cleaned from inside, though you may need to check the manufacturer's specification.
Blinds are worth planning for at the same time. Integrated blinds sealed between the panes stay dust-free and are ideal for bathrooms and kitchens, while blackout blinds are essential in a bedroom where you want a lie-in past sunrise. Thermal or anti-heat blinds can noticeably reduce summer overheating. If you fit blinds later, choose ones designed specifically for your window model, as generic roller blinds rarely sit neatly against a sloping frame.
Frame choice affects maintenance as much as looks. Timber frames with an aluminium cladding on the outside give you the warmth of wood indoors with a weatherproof shell that needs little more than an occasional wipe. PVCu is cheaper and easy to clean, but the frames tend to be chunkier and can look bulky in a slim roof pitch. Whatever you pick, check the warranty on both the glazing unit and the seals, and make sure the installer is familiar with your roof covering — a poorly flashed window is the most common source of leaks in loft conversions.
Finally, take your time over the specification. A roof window is difficult and expensive to change once the plaster is up and the tiles are back on, so getting the size, position and opening style right at the design stage is time very well spent. Get it right, and your loft will feel bright, airy and used all year round rather than a spare room you avoid in winter.
Nimble Spaces shares practical, down-to-earth guidance on loft conversions, attic storage and small-space home improvement for readers across the UK.
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