Ask what a roof window costs and the honest first answer is a question: which roof, which room, which window? A skylight is a small piece of glass in a large piece of building, and most of the effort goes into the building. The frame, the flashing, the roof covering around it and the finish inside all count towards the final figure.
So this guide does not hand you a number to hold up against a quote. It explains the parts that move the price, in the order they usually come up at a survey, so you can read a written quote line by line and see why it says what it says. The same thinking applies if you are searching for the cost to fit a roof window in a loft, a landing or a kitchen.
For the bigger picture, start with the roof windows page covers the types, the glass and the way we fit them.
A quote is several jobs, not one
A rooflight or roof window quote is really a short list of separate tasks that happen to be done by one team. There is the window itself, with its frame and glass. There is the flashing kit that seals it to the roof. There is the opening: cutting the roof structure, trimming rafters where needed and forming the lining. Then there is the access to do all of that safely, and the finishing inside.
Any one of these can be simple on one house and awkward on the next. That is why two neighbours with the same window in the same street can be quoted differently, and why a figure given over the phone without a look at the roof is only a guess. A free survey turns the guess into a fixed written quote.
Size and the code on the box
Bigger windows need more of everything: more glass, a larger flashing kit, a wider opening in the roof and more careful handling on the day. Size is the first thing a quote reflects, and it is also the first choice you make.
Many roof windows carry a size code. In the VELUX system, for example, width sits in the letter and height in the digits, so MK04 is a different shape from MK08 or CK02. The code tells you the window's footprint, but it does not tell you the whole story. A taller window can sit awkwardly between rafters. A wider one may mean cutting and trimming a rafter, which adds structural work.
The neat trick is to choose the size that lines up with the rafters you already have. When the opening fits the existing spacing, the roof needs less alteration, and that shows in the quote. Measuring the gap between rafters in the loft is the quickest way to see what is possible before anyone arrives.
The roof covering decides the flashing
Every roof window is sealed to the roof with a flashing kit, and the kit is chosen for the covering it sits in. A concrete interlocking tile, a plain clay tile and a natural slate each lap and shed water differently. A profiled tile needs a flashing that follows its profile. A flat plain tile is thin and needs a different approach. Slate is cut and dressed to suit the window.
This is why the first thing a surveyor looks at, from the ground or from a ladder, is what is on the roof. The covering sets the flashing, the flashing sets the labour, and the labour is a large share of the price. A watertight finish at the edges of the window matters more than any other detail, because that is where a leak would start.
If the covering is old, brittle or slipping, that is worth knowing before the window goes in. Opening the roof next to tired tiles can disturb them, and it is much simpler to plan for that in the quote than to meet it halfway through the day.
| Factor | What changes | Settled at |
|---|---|---|
| Window size | Glass, frame and opening width | Survey, from rafters |
| Roof covering | Flashing kit and labour | Survey, from the roof |
| Glass choice | Insulation, noise and solar control | Your choice |
| Opening type | Pivot, top-hung or electric | Your choice |
| Access | Ladder, tower or scaffold | Survey |
| Inside finish | Lining, plaster and decoration | Survey, with you |
Glass, and the figures it has to meet
The glass is where you decide how the window behaves. Double glazing is the starting point. Triple glazing adds insulation and takes down some outside noise, which can matter on a roof where rain lands directly on the pane. Laminated glass on the outer or inner pane adds strength and a quieter feel in rain. Solar control coatings help a south-facing loft room stay comfortable in summer.
Whatever you choose has to meet the thermal limits in the Building Regulations. Part L, Approved Document L, Table 4.2 for existing dwellings sets the limits shown below. A roof window must achieve 1.4 W/m²K or sit in WER band B. A rooflight, meaning the flat or rooflight-style glazing on a flat roof, is held to 2.2 W/m²K. These are the numbers the glass specification is checked against, so they shape what can be offered.
Better glass costs more to make and often carries a heavier pane, which can affect handling. In return it pays you back in comfort, and in how well the room holds heat in winter. It is a trade between budget and the room's use, and you do not need to decide until you have seen the options at the survey.
Two thermal limits in Part L
- 1.4 W/m²K
- upper limit for pitched-roof windows, or reach WER band B
- 2.2 W/m²K
- upper limit for flat-roof glazing in a home that already stands
Pivot, top-hung, fixed or electric
How the window opens is a design choice with a cost attached. A centre-pivot window turns on a bar across its middle, so the top swings out and the bottom swings in. It is the familiar shape and it sits well in most loft rooms. A top-hung window is hinged along its upper edge and swings outward, which gives a clear view and more headroom at the bottom edge, useful where furniture sits below. A conservation roof window sits flatter to the covering and has a slim bar, which is why it suits older, listed or protected roofs.
A fixed window, with no opening sash, is simpler. It is a good choice for a stairwell or landing where you want the daylight but not the airflow.
Then come the controls. An electric or remote opening window needs power run to it, and a rain sensor that closes the sash when it starts to drizzle needs the same. They add convenience for a window you cannot reach, such as one high over a stair, and they add to the quote because of the cabling and the more complex unit.
Blinds and the finish indoors
A roof window with no blind can be glaring in summer and bare at night. Blinds made for the window slot into channels on the frame, so they sit close to the glass. Blackout, pleated and roller styles are all available. Adding them at the time of fitting is simpler than retrofitting, and the quote can show them as their own line.
Then there is the inside. When a new window goes into a roof, a lined opening, or splay, is formed so the light spreads into the room. The lining is plastered or boarded and decorated. Tidy work with the inside finished is part of how we fit, but the amount of finishing depends on the room. A bare loft with open rafters needs one kind of finish; a bedroom with a decorated sloped ceiling needs another.
Say at the survey how you want the inside left, and it goes into the written quote.
Access and structure
Getting to the roof safely is a real part of the cost. A ladder is enough for a low roof with easy ground. A steep or high roof, or a roof above a conservatory or extension, may need a tower or scaffold. The survey notes which, and it is written into the quote.
Structure is the other quiet factor. If a window sits between two rafters, the opening is simple. If it is wider, a rafter is cut and the load is carried by new timbers, called trimmers, around the opening. If the roof is a trussed one, as some modern roofs are, the trusses cannot simply be cut, and the layout needs careful thought or a different approach. We settle it at the survey, standing under the roof itself.
Words you will hear on a quote
Flashing
The set of metal and rubber pieces that seals the window frame to the roof covering.
Trimmer
A timber that frames the opening and carries the load of a cut rafter.
Splay
The angled lining inside, which opens the light out into the room.
Sash
The opening leaf of the window, glass and frame as one.
WER band
A rating of a window's overall energy performance, from A down.
Replacing a window, or cutting a new opening
Swapping an existing roof window for a new one in the same place is a different job from making a new opening. A like-for-like replacement can reuse the structure, so there is no cutting of rafters. The old window and its flashing come out, the new ones go in, and the lining is made good. That is the simplest case, and it is why a replacement quote can look quite different from a new-opening quote.
A new opening adds the structural work, a fresh hole through the covering and a new lining from scratch. It also brings Building Control into the picture where the work is notifiable, and we handle that notification for you. For the planning side, see our planning permission guide.
If the old unit has misted, blown or stopped sealing, say so. Sometimes a replacement sash or sealed unit is all the old frame needs, and a new full window is a better use of the money when the frame itself has failed.
How to read the quote when it arrives
A good quote shows its working. Look for the window size and code, the glass specification, the opening type, the flashing for your roof covering, the access method, any structural work, the inside finish and any blinds. Each line has a reason. If one has none, ask.
Our quotes are fixed and written, so the figure you agree is the figure you pay. The work comes with a 10-year workmanship guarantee in writing, and it is installed to current Building Regulations. Putting the window in is a one- or two-day task for a standard rooflight, and the finishing is planned around the room.
If you are weighing up a loft room, read roof windows for loft conversions next. If you are wondering what the roof needs, what pitch a roof window needs answers it, and our costs page sets out how we price a job. Then book a free survey and we will measure, look and write it down.
Have these ready for the survey
- Which room, and what you want from the light
- A photo of the roof from outside
- Whether you want blinds or electric opening
- How you want the inside finished
- Any old windows that have misted or leaked
Cost questions, answered plainly
Why can't you give a figure without visiting?
Because the roof sets the work. The covering, the rafter layout and the access are all things we need to see. Once the free survey is done you hold a fixed written quote, and its figure does not move.
Does a bigger window always cost more?
A bigger window means more glass and a larger opening, so it moves the figure up. But a larger window that lines up with your existing rafters can need less structural work than a smaller one that does not.
Is a skylight the same as a rooflight when it comes to cost?
The words overlap. Homeowners say skylight; the trade says rooflight. A roof window on a pitched roof and a flat rooflight on a flat one are priced by the same logic: size, glass, flashing or upstand, access and finish.
