The roof window is sticking, the blind has seen better days and the room never quite feels finished. Before turning a replacement into a larger renovation, separate two questions: does the window need replacing, and do you want the opening to change?
That distinction does more for a sensible budget than collecting three prices headed simply “new roof window”.
The number, with its boundaries
VELUX’s UK replacement service gives a broad average of £1,200–£1,600 for the supply and installation of one roof window. The company says the actual price depends on size and specification. This is its published indication, checked on 29 September 2026, not a fixed quote for every property or a whole-market average.
The headline range does not explicitly state its VAT treatment. Ask for a total quotation that clearly says whether VAT is included, rather than quietly adding an assumption to your budget.
VELUX also gives separate product and labour indications on its budgeting pages. Those are alternative ways of describing costs. Do not add a labour allowance on top of a supply-and-install total and count the installation twice.
Keep the first quote deliberately simple
Ask initially for the closest suitable replacement in the existing opening. Give the installer the identification code from the window if accessible, photographs of the interior and roof context, and a description of the problem.
A stiff handle, misting between panes and staining around the opening do not necessarily point to the same remedy. Have the cause assessed. Paying for a new window will be a frustrating answer if water is coming from something else in the roof.
For a same-size replacement, VELUX says its windows can fit existing roof openings without structural alterations and that most replacements can be completed from inside in around four hours. That is a service expectation, not a promise about your house. Access, the existing installation and any damage found when work begins can change the job.
Where the brief becomes a bigger project
Making the opening larger or adding another window changes the scope. So can switching to a different arrangement, repairing damaged surrounding fabric or requiring specialist access.
Decide what the room needs before discussing upgrades. Is the handle difficult to reach? Is glare the real irritation? Do you want an easier way to ventilate, or simply to replace a failing unit? A more expensive operating system may be worthwhile in one room and unnecessary in another.
Ask the installer to price the basic replacement and each optional change separately. That gives you a choice you can understand instead of one attractive but indivisible total.
What should be written into the price?
The quotation should make clear:
The exact window, size, glazing and opening method.
The installation materials and weatherproofing details, including the appropriate flashing, which forms the junction with the roof covering.
Access equipment if required, protection of the room and disposal of the old unit.
The extent of internal making good, decoration and any replacement blind.
VAT, payment stages, guarantees and how additional work would be agreed.
VELUX’s cost guidance identifies access, specification and unexpected damage as things that can affect the bill. Keep some budget available for discoveries, but do not let an unspecified “contingency” substitute for a clear description of the planned work.
If the property is listed, in a designated area or subject to other restrictions, check consent requirements before choosing a different external appearance. Roof-window permission and building-control rules depend on the project and UK nation; use the relevant authority’s advice for your home.
Spend on the problem you actually have
We would prioritise a sound installation and an operating method that suits the room before adding extras. In a bedroom, a well-chosen blind may matter every day. In a high stairwell, reachable control may be the bigger improvement.
A replacement need not become a roof redesign. Start with a clear, like-for-like scope, then add only the changes you can explain in terms of how the room will work.