Learn what MyJobQuote's average says, which four things move a roof window price on a real roof, and what a written quote should show before you sign.
Ask what a roof window costs to fit and the first answer is a wide range. The glass is a small part of it. The roof it goes into, the way the builder reaches it and the finish inside the room do the moving.
MyJobQuote's guide to Velux windows and skylights, last updated in September 2026, prices a standard mid-range Velux unit at £1,100 on average. That is a national figure from an outside guide and never a Castle Roofing Margate price, and it covers a standard window in a standard roof. Your window will not be that. Its size, its slope and the roof covering around it will all be different.
Kent is in the South East, and the Which? Trusted Traders guide and HomeBuilding both say that South East prices sit higher than elsewhere, Which? for its trader prices and HomeBuilding for labour rates. So treat the average as the middle of a range, then use the sections below to see where your roof would fall. This guide sits within our roof windows and skylights work, and it ends with what to look for on a written quote.
What the published average tells you
A single average hides a spread. MyJobQuote's figure of £1,100 is for a standard mid-range Velux window, so it assumes a common size, an ordinary roof covering and a window that is not unusual in its position. That is useful for knowing the order of magnitude. It does not say what the job costs on your house.
Three things to keep in mind when you read any published figure:
- It is one guide's range on one date, so name the guide and the month when you quote it.
- It may or may not include the work around the window, and the guide does not state a VAT basis, so it is not safe to add or take away VAT.
- It describes a standard window, and a bigger unit, a more complex roof or a higher specification sits above it.
You will see other numbers online for roof windows. Some are for the unit alone, some for the unit fitted, some with the inside finished. Setting them side by side without checking what each includes leads to false comparisons.
The VAT rate itself is simple: the standard rate is 20 per cent on GOV.UK. A quote should say whether the total includes it. VAT-registered building firms deal with the reverse charge among themselves under the Construction Industry Scheme, and a homeowner never sees it on a bill.
What the average cannot tell you is the shape of your roof, which is why nothing is priced until the roof has been looked at.
What moves the price on a real roof
Four things drive the difference between one roof window job and another, and the table puts them side by side with the reason each one matters. They are the size and type of the window, the way the roof is reached, the flashing that seals the window into the covering, and the finish inside.
| Factor | Why it moves the price |
|---|---|
| Size | A larger sash costs more and needs a wider opening and heavier framing |
| Access | A high or awkward slope needs more equipment and more time |
| Flashing | The kit must suit the roof covering, slate or tile or flat |
| Internal finish | Lining, plaster and decoration depend on the room |
None of these four can be seen from the street, which is why a price given over the phone or from a photo is a guess. The price is firm only once someone has been on the roof and looked at the loft beneath it.
Two other points sit behind the four. Whether a new opening is being cut or an old window is being swapped is a big difference. A swap uses the existing opening, and the surround is already in place, whereas a new opening means cutting rafters, adding a trimmer and making good. Second, building control and planning can add a step: in some places the council must be told before the roof is opened.
Those steps are explained in the sections that follow, one factor at a time.
Size and position of the window
Roof windows come in a range of widths and heights, and the standard sizes fit between rafters at common spacings. A window that matches the gap between two rafters is the simplest to fit, because no rafter needs cutting. A wider unit, or two windows side by side, calls for a structural change, and that adds both materials and time.
Position matters as much as size. A window in the lower part of the slope is easier to reach and to fit than one high near the ridge. A window near a valley, a chimney or the edge of a slope needs a more careful surround. Where two units sit above each other, the flashing must be made to suit the pair.
The type of the window changes the price too. One type is an opening sash that pivots on a central bar. Some units open as a top-hung sash, some are fixed, and some are electric. Electric controls add to the work, and a fixed unit is the other extreme. A fixed unit costs less to make than an opening one, but it cannot ventilate, and a room needing air will not be well served by a fixed pane.
If the window is for a loft room, the escape and energy rules also affect the choice of size and glazing. A new roof window must reach 1.4 or WER Band B under Approved Document L, so the specification is not an open choice. Our guide to roof windows for a loft conversion goes through those rules.
Access and the roof covering
How the roof is reached changes the job. A low roof can be worked from a ladder or a tower. A tall house, a steep slope or a roof above a narrow side passage may need scaffolding, and the scaffold may stand on or over the pavement.
A scaffold on the pavement or the road needs a licence under section 169 of the Highways Act 1980. Kent County Council issues it at £52 per week for 2026 to 2027, and the scaffolding firm applies, giving 5 working days' notice. What the scaffold costs at your house is set once the roof is surveyed, because height, length and time standing all change it.
The roof covering matters in a different way. A window set into slates needs a flashing kit made for slate. One set into plain or interlocking tiles needs a kit made for that profile. A flat roof takes an upstand and a membrane. Fitting the wrong kit to the covering is one way leaks start, so the kit is chosen to suit what is on the roof. Our page on the roof window flashing kit shows what is involved.
If the covering around the window is worn, it is usually sensible to deal with it at the same visit. Re-covering a small area afterwards, once the new window is in, costs more in time because the surround has to be opened up again.
The inside of the room
The work does not stop at the glass. Inside, the opening needs a lining: the sloping and vertical faces that frame the window from the room. The lining is boarded or plastered, then painted. In an unfinished loft that can be a quick job. In a finished bedroom with a plastered slope, every dust sheet and every coat of paint counts.
The size of the lining depends on the thickness of the roof. A deep roof, with insulation between and under the rafters, has a deeper reveal, and that increases the finishing work. The insulation round the window also needs to be right, because a gap there is a cold spot where damp air condenses.
Questions to ask about the inside finish:
- Is the lining plasterboard, timber or a pre-formed kit from the maker?
- Who plasters, who paints, and are they part of the same total?
- Is the existing ceiling being cut, and who makes good?
- Does the insulation around the opening meet the current energy figures?
- How long does the room stay out of use?
The answers change the price and the time on site. A job described as the window only usually means the fitting is done and the finish is left to you, so check which one a quote means. How long a fit takes is covered in our page on how long it takes to fit a roof window.
Reading one written quote
Citizens Advice recommends collecting at least 3 written quotes from different traders. When they come back, read each against the same questions, so you are comparing like with like and not a set of bare numbers.
On a roof window quote, look for these:
- The make, model and size of the window, and the flashing kit named for your covering.
- Whether scaffold or other access is part of the total.
- Whether VAT is included in the total.
- Whether the inside lining and decoration are part of the work.
- Whether waste is taken away and the roof left tidy.
- What happens if the work, once started, shows something the survey could not see.
Our quote is a single written total, given once a person has inspected the roof. The photos you get show what we saw, and anything found on the day that changes the work is raised with you before it is touched.
A contract you sign at home after the survey counts as off-premises, so the Consumer Contracts Regulations give you 14 days to cancel, starting the day after you sign. That right does not apply to an urgent repair you asked the trader to visit for, and any work that starts inside the period does so only on your written request. Citizens Advice runs a consumer helpline on 0808 223 1133 if a dispute arises.
If the roof window is part of a loft conversion, the cost of the window is one part of a larger project, and a registered building control approver or your council's team will want the specification before the roof is opened.
