Beneath the roof, only slope remains where a wall would hold a window. That is why the loft roof window is the workhorse of a conversion: it takes light straight from the sky into a room that would otherwise be dim. A good one turns a storage space into somewhere you want to be, whether that is a bedroom, a study, a playroom or a quiet corner with a chair and a book.
The choices are less obvious than they look. Where the window sits sets what you see and where you can stand. Its type sets how it opens and how it feels in summer. And the building rules around escape and head height decide what is allowed in the first place. This guide takes them in turn, so you walk into a survey knowing what to ask.
Costs are covered separately in what moves the price of a roof window, and the full range sits on the roof windows page.
Why the sky is the better view from a loft
A dormer or a gable window looks sideways. In a loft, sideways can mean a neighbour's roof, a fence line or the top of a tree. A roof window looks up and out, and the sky is the one view that nothing blocks. Straight up is clear.
That is also a practical point. A window set in the slope brings daylight deep into the room, because the light arrives from above and spreads across the ceiling and floor. A skylight in a bedroom lets you see clouds at night and weather in the morning. In a study it gives even light on a desk without a glare on the screen.
Those benefits are real, but they depend on placing the window well, and on picking a size that suits the rafters you have. The next sections cover how.
Head height decides where the window goes
A loft roof slopes, so the floor area where you can stand upright is limited. The part of the room with full head height is the useful part, and it is where you want the light to land. A window placed too low in the slope lights the part of the room you cannot use. A window placed too high can look out at nothing but sky when you are seated.
The way to test it is to stand where the bed, desk or sofa will go and look at where the window will be. The aim is a view out from near the middle of the room, with the bottom edge at a height that lets you reach the handle without stretching. For a top-hung window the handle sits at the bottom, which suits low positions. For a centre-pivot window the handle is at the top, which suits higher ones.
Head height also feeds into the wider conversion. The room needs enough clear height for the stair and the floor, and that is a matter for your designer and Building Control, not for the window alone.
Pivot, top-hung or conservation
Three types cover almost every loft. They differ in how they open, how they look from outside and what they ask of the room.
A centre-pivot window turns on a horizontal bar. It is the classic loft window, with a handle at the top, a wide view and a sash that can rotate to clean the outer glass from inside. A top-hung window is hinged along its upper edge and swings outward, giving more clear height at the bottom and a view over furniture. A conservation roof window sits close to the covering with a slimmer frame, and suits a roof that needs a lighter touch.
The table compares them side by side.
| Type | Suits | Know |
|---|---|---|
| Centre-pivot | Rooms with space under the window | Handle sits high on the frame |
| Top-hung | Beds and desks below the sill | More headroom at the bottom edge |
| Conservation | Sensitive or protected roofs | Slim frame, sits flat to tiles |
Escape windows and the 4.5 metre line
In a loft conversion, a window can be a way out in a fire. the rules accept an escape window only where the storey's floor sits no more than 4.5 metres above the ground. Inside that line, a roof window large enough to climb through, with the right clear opening and a sill at a reachable height, can be the escape route.
Convert the loft of a two-storey house and you are above that line, because the floor of the new storey is higher than 4.5 metres. In that case a roof window cannot serve as the escape. The conversion needs a protected stair instead, which is a fire-resisting route down to the front door. Your designer and Building Control will confirm which applies to your house.
A roof window can still be an escape window on a lower, single-storey roof, such as a bungalow loft. If that is your house, tell us at the survey, because the size and height of the opening then matter.
Pitch, and what the roof allows
Every roof window is rated for a range of roof pitches. A window designed for a shallower roof sits differently from one for a steep roof, and the flashing differs too. Plenty of lofts sit inside the standard range, but a low-pitched roof can need a particular window or an extended flashing kit.
The pitch is easy to check. Measure the angle with a phone app or a spirit level and a tape. The limits are set out in what pitch a roof window needs.
Roof structure is the other limit. Rafters set the possible widths, and a trussed roof, where the timbers form a fixed frame, cannot be cut at will. If the loft has been converted already, the structure has been altered once and the layout is known. If it has not, the survey looks at which rafters or trusses sit where.
Size codes and how many windows
Window size is often written as a code. In the VELUX system a code such as MK04 names one shape and UK04 a wider one, with width in the letter and height in the digits. The code helps you compare windows between suppliers.
How many windows a loft room needs is a question of floor area and use. A small bedroom may be well lit by one window placed centrally. A long room, or one used as a studio, may need two in a line to light the length evenly. Two windows also give cross-ventilation, which helps in summer.
One caution on size: a very large window in a loft can make the room hot in summer if it faces south. Solar control glass and a blind take care of that. We talk through it at the survey.
Loft window words
Head height
The clear height from floor to ceiling where you can stand upright.
Sill
The lower edge of the window opening, inside the room.
Pitch
Roof slope angle, measured up from the horizontal.
Splay
The angled lining that opens the light out into the room.
Protected stair
A fire-resisting route from the loft down to the front door.
Semi-detached and detached roofs offer different positions
The shape of the house decides where windows can go. A semi-detached house has a party wall on one side, so the roof slope facing the garden and the slope facing the street are the two you can use. A detached house has a free slope on every side, and sometimes a hipped end as well, which gives more choice about where the light enters and which way the room faces.
On a gable-ended roof the two long slopes are the natural place for windows, one on each side of the ridge if the room is wide. The rear slope is the simplest to plan, because it looks over the garden and is not seen from the road. A window on the front slope shapes how the house looks to the street, so it deserves a little more thought about size and alignment with the windows below.
Where houses sit close together. A roof window looks upward, so it keeps the room private in a way a side or dormer window cannot. Nobody in the next garden can see in through the sky.
Bring to the survey a few photos taken from the garden and from the road that show the roof, and a note of which room you want lit. They help us talk through the options with you before anyone climbs a ladder.
Glass, ventilation and blinds in a loft
A loft gets warmer than the rooms below it, because heat rises and the roof catches the sun. The glass and the opening are how you manage that.
Double glazing with a low-emissivity coating keeps heat in during winter. Solar control glass keeps some of the summer sun out. Triple glazing adds insulation and takes the edge off rain noise. All of it has to meet the thermal limit in Part L, Approved Document L, Table 4.2 for existing dwellings: 1.4 W/m²K for a roof window, or WER band B.
Ventilation matters for comfort and for damp. A loft bedroom needs a way to let stale air out. Roof windows come with a vent flap in the frame that allows a trickle of air with the sash closed, which helps prevent condensation on the glass. Blinds finish the job. Blackout blinds make a bedroom dark enough to sleep in summer, and a pleated or roller blind softens glare in a study. Blinds are made to fit the window's code, so choose them when you choose the window.
Planning, Building Control and the finish
Roof windows on a house can be covered by permitted development, subject to conditions, but a listed building, a flat or an Article 4 direction can change that. Our planning permission guide sets it out, and the planning answer deals with the question directly. A call to Milton Keynes City Council's planning team will tell you if your street carries extra rules, and it is worth making before you order. Ask about the front slope in particular, since that is where any extra rule is likely to bite.
Because a loft conversion is notifiable work, we make the Building Control notification wherever one is needed. That can go through the council or through a registered building control approver. Everything we fit meets the current Building Regulations.
A standard rooflight goes in over one or two days, and the inside is finished tidily, the lining formed and made good. If you wonder whether the work can be done without scaffold in the room, can a roof window be fitted from inside explains how it is approached.
Before you book a loft survey
- Where the bed, desk or seating will go
- How high the floor will sit in the finished room
- Whether the house is two storey or lower
- Whether you want blinds or electric opening
- Any thoughts on how the room will be used in summer
Loft window questions
Can I use a roof window as my fire escape?
Only where the storey's floor is no higher than 4.5 metres above the ground. With a two-storey house, the loft needs a protected stair instead. Building Control confirms which applies to you.
Is a loft roof window the same as a skylight?
Yes. Skylight is the everyday word and rooflight is the trade word. For a loft on a pitched roof, the product is a roof window.
Do I need one window or two?
It depends on the room's length and use. A compact bedroom can be lit by a single window, while a longer room is better lit by two in a line. We talk it through at a free survey.
