The short answer comes from MyBuilder's guide to Velux window costs (updated 21/08/2026). Installation typically runs from £350 to £600 for a standard job, and that range covers both labour and fitting. The guide lists a standard centre-pivot window separately, at £305. Where scaffold has to go up to reach the roof, MyBuilder puts it at approximately £500.
Those are typical UK ranges for a plain job, not Watertight prices. Each of the three can shift, and the hub page on skylights and roof windows sets the wider scene. A new opening in the slope, a bigger window, several windows for a loft room, a hard-to-reach roof or an awkward covering all raise the figure, and fitting a replacement into an existing opening tends to be the simplest case.
This guide takes the parts in turn: what the fitting covers, the difference between a swap and a new opening, the window and the standard it has to meet, the flashing, the scaffold, and how to read the number you are given. Our quote comes in writing after a survey, together with pictures of the slope in question.
What the fitting figure covers
When MyBuilder quotes £350 to £600 for a standard installation, it means the labour of taking out the old window or cutting in the new one, setting the unit in the roof and making it weathertight. The guide prices the window separately, at £305 for a standard centre-pivot model, and the scaffold is extra where needed. Add the three pieces together and you have the usual shape of the job: a unit, a fitter and some way of reaching the roof.
A standard job means a like-for-like replacement or a clean new opening in a simple slope, with ordinary access. Take any of those away and the labour changes. Windows set high on a steep roof take longer to reach and handle. Two openings fitted in one visit save on the second trip, since the tools, the access and the clearing up are already in place.
Branded and other windows
Velux is the name most people use for the whole category, and £305 is MyBuilder's figure for a standard centre-pivot window. Other manufacturers make roof windows to similar sizes, and our page on roof window flashing kits explains why the flashing has to match the window and the covering, whichever make you choose.
What the unit price leaves out
Blinds, electric opening, trim kits and special glazing are all extras, and the usual advice applies: decide what you want in the room before you settle on a model. A plain centre-pivot window is the baseline, and every upgrade is priced on top. Ask for the exact model in writing, since two windows of the same size can differ by a good deal.
Swapping a window or cutting a new opening
Replacing a window in an existing opening is the easiest job to price, because the hole, the framing and the internal lining are already there. The fitter removes the old unit and its flashing, checks the timbers and the batten line around the opening, and sets the new window in. The surrounding tiles are lifted and relaid, so the new flashing sits properly in the covering.
A new opening is a bigger operation. A rafter is cut and the gap is framed with trimmers, so the load is carried around it, and the plasterboard and finishing inside have to be made good. Structural alterations need approval, according to the Planning Portal, so a new opening brings the council or a registered building control approver into the job. We say what applies, and where notification is due we take care of it.
Planning for a new opening
Under the General Permitted Development Order, a roof window in a house roof is often permitted development, subject to conditions. Any window in a side-facing roof slope has to be obscure-glazed, and non-opening as well unless its openable part sits more than 1.7 metres above the floor. Article 4 directions at Old Shoreham, Kingston Buci and Warwick Place take the right away for some slopes facing a road, and listed buildings need consent. Our guide to skylight planning permission goes through all of it.
Making good inside
The finishing round a new opening is plastering and decorating, which a roofer may not include. Ask what the figure stops at, so you are not surprised by a bare plasterboard reveal on the day.
The window, its performance and its size
Size is the first price driver. A bigger pane needs a wider opening, more cutting, a bigger flashing kit and more hands to lift it. The £305 unit price describes a standard model, not a large one.
The window also has to meet the energy standard. Approved Document L, in Table 4.2, puts the limit for windows (roof windows are named) at a U-value of 1.4, with a Band B rating on the Window Energy Rating scale as the alternative. A rooflight, the glazed unit that sits proud of the slope on a kerb, has a limit of 2.2, with 0.35 as the ceiling for a site-built upstand. A like-for-like swap is held to the performance of what came out, at least. Choosing a unit that meets the standard from the start avoids having to explain a poor rating later.
Roof windows for loft rooms
If the window serves a bedroom in the loft, the rules add a size condition. Approved Document B covers a loft bedroom up to 4.5 m above ground by asking for an escape window: openable area 0.33m² or more, no smaller than 450mm by 450mm, and the lowest edge of the opening within 1100mm of the floor. A window that is too small, or set too high up the slope, can fail that test whatever its price. Our page on roof window Building Regulations shows the figures in detail.
Flat rooflights
A flat roof takes a rooflight in place of a roof window, with an upstand and a different price pattern. Rooflight prices follow their own pattern and are worth reading about separately.
Flashing, tiles and the roof covering around the window
A roof window is only as watertight as the flashing around it. The flashing is the set of metal pieces, often a kit made for the window and the type of covering, that carries water over and past the frame. A kit for plain tiles differs from one for interlocking tiles or slate, so the covering decides which kit goes in. MyBuilder's figure covers labour and fitting for a standard job, and the kit is chosen to suit what is on your roof.
The detail on the roof is where leaks usually start. Water that reaches the sides of the frame is carried away by the gutters built into the flashing, and the tiles must lap over them correctly. Lead, where it is used in the surround, is priced by the metre. Checkatrade gives code 5 lead flashing at £50 to £70 per metre and stepped flashing at £80 to £120 per metre, excluding VAT, which gives a feel for the cost where a surround needs lead.
Condition of the roof beside the window
Fitting a new window into old tiles that are cracked, slipped or mossy invites trouble. A roofer opening the slope will see the battens and underlay, and if they are tired, the quote has to say so. Sometimes the right advice is to renew the area around the window, or to wait for a re-roof, and the window is fitted into new work.
Leaks after fitting
When a roof window leaks, the cause is often the flashing or a tile lapped wrongly beside it rather than the glass. If a window you already have drips, the flashing is the first thing we check.
Scaffold, access and the days on site
Scaffold is the cost that most often surprises people. MyBuilder puts it at approximately £500 for a roof window job, and its separate scaffolding guide gives around £850 to £1,200 for a house of two storeys, with a chimney at £400 to £900. The difference is the amount of work the scaffold has to protect and reach. A single window on a low roof may need only a tower, while a high slope on a tall house needs a full lift.
Some windows can be fitted from inside the loft, with the roof reached through the hole, and that can remove the scaffold from the bill. It suits a replacement in an existing opening, and it depends on the pitch, the covering and the fitter's judgement on safety.
Licences
If the scaffold will block a pavement or a road, section 169 of the Highways Act 1980 requires a licence, and the scaffolders arrange it. In our area that means the county council, which wants 10 working days' notice, and so the date depends on the licence as well as on the fitter.
Time, weather and a tidy finish
A like-for-like replacement is normally a short job, but the opening is exposed while the work is under way, so the weather matters. If rain is forecast, a roofer will leave the old window in place, not strip the roof and gamble. Afterwards the old window and packaging go with us, and the roof is left clean.
Roosting bats are legally protected, and the opening of a roof can disturb them, so tell us if you have seen any in the loft.
Reading the figure you are given
When a price arrives, check three things. Is VAT in it? Is scaffolding in it? A figure without it will look lower than one that carries it. And which window does it include: the model, the size and the glazing? Two quotes that look alike can describe different windows.
Our quote is one total price, written once the survey is done, and you see photographs of the roof beside it. The price reflects the window, the covering, the access and whatever turns up around the opening. A window that is letting water in now goes to the front of the queue and is made safe first, with the replacement planned afterwards.
What moves the figure
The things that raise it are a new opening, a larger or specialist unit, a steep or high slope, scaffold, a hard covering such as slate, and extra work found around the window. The things that lower it are a like-for-like swap, reachable access from inside, a standard size and a second window fitted in the same visit.
The extras beyond the window itself
Ask what the fitter's paperwork covers, whether the fitting, the flashing kit or both. Everything beyond that, such as blinds and finishing inside, is agreed before the day.
Choosing between types of daylight, or checking the planning picture, comes before the quote. When you are ready, send us the size and position of the window you want, a photograph of the slope from outside, and one from inside the loft if you can. With those we can say whether a swap, a new opening or a wait for a re-roof is the sensible route, and which of the cost drivers in this guide apply to your roof. A survey then confirms it with photographs of what is under the tiles.
