Velux is a brand name, and it has become the everyday word for a roof window, in the way that people say hoover for a vacuum cleaner. When a householder asks what a Velux costs, they usually mean the whole job of putting a window into the roof, not the window alone. Those are different things, and most of the confusion about price comes from mixing them up.
A roof window is a glazed unit set into the slope of a roof, with a frame, flashing to keep the weather out at the edges, and a lining inside to finish the opening. If a window is already there, swapping it for a new one is a contained job. If the roof has no window, a new opening means cutting the covering, trimming the rafters and finishing the room around it. The second job costs more because it is more work.
Below we give the figure the national cost guide publishes, explain what separates a swap from a new opening, and set out the points that move a price on a house in Farnborough or the villages around. Figures are typical UK ranges from a named source and not Fortis Roofing Farnborough prices.
The figure MyJobQuote publishes
In a guide dated September 2026, MyJobQuote prices a standard mid-range Velux at around £1,100 and puts a straightforward swap about £100 lower. These are typical UK figures for the job, and the guide does not say which size, glazing or roof covering it assumed.
Reading the number
The figure is a marker, not a quote. It is the cost of a typical job, and a typical job suits a typical roof. If yours has an awkward pitch, a slate covering, a high roof or an unusual window size, the price will differ. Equally, a plain replacement of an old window of the same size can come in near the lower figure.
What it covers
The guide's figure is for fitting the window and making it weathertight. A finished ceiling opening with lining and decoration, a structural beam, scaffold and the removal of a chimney breast are separate jobs that raise the total wherever they are needed. A chimney breast sitting in the way is a common surprise, because removing one is structural work and Building Regulations approval always applies to it.
Where the figure comes from
It is one cost guide, so treat it as a way to judge whether a quote is in a sensible place, and ask each roofer to explain what is in their figure. A figure far above or below it is not wrong by that fact alone, but it deserves a question about which of the points in this post explains the gap, whether the window size, the roof covering, the access or the work inside the room. Our guide to replacing a Velux window sets out what a swap involves in more detail.
A swap against a new opening
The most important split in roof window pricing is between replacing a window that exists and making one where there was none.
Replacing an existing window
The old unit comes out, and a new one goes into the same opening. The opening is already cut, the rafters are already trimmed, and the lining is already in place. If the new unit is the same size as the old one, the job is mostly a change of unit and a renewal of the flashing. That is the straightforward swap MyJobQuote's lower figure describes.
A change of size is different. A larger window needs the opening widened, and a smaller one needs it infilled. Both are building work and not a swap.
Cutting a new opening
With no window, the roofer strips the covering back, cuts through the underlay and battens, and trims the rafters to form a frame for the unit. That framing carries the weight the rafters would have carried and it must be done properly. The window goes in, the flashing is dressed to the covering, and the covering is made good around it. Inside, the opening is lined and finished.
Why the second costs more
There is more labour, more material and, usually, more access. A new opening also brings the Building Regulations into play, as we explain below. It also affects the room underneath: a ceiling has to be cut, and dust and disruption follow, so the room below should be cleared and the furniture covered before the day.
What changes the price of a roof window job
Beyond the swap and the new opening, several facts about the house and the window set the final figure.
The size and type of window
A larger unit costs more to buy and to fit, and a bigger opening needs more structure. The glazing specification, such as the insulation and noise performance, changes the price of the unit. Opening types differ too, and an electric or rain-sensing unit costs more than a manual one.
The roof covering
The weather seal around a window is a flashing made to suit the covering around it. A kit for plain tiles differs from one for slate or for interlocking tiles. Slate and clay roofs take more care and time than concrete tile. Our guide to the roof window flashing kit explains the options.
Height and access
Work on a high roof needs a scaffold. Scaffold cost comes from the job and not from a table, and scaffold on a public pavement needs a licence from the highway authority. Find out who applies for the licence and whether the quote has the scaffold in it.
Inside the house
The room below needs the ceiling opened and a lining formed. Plastering and decorating can be left out of a roof window price, so check whether the figure includes them and who does the finishing.
The roof frame
A trimmed rafter may need strengthening. If the survey finds soft timber, there will be repairs. Our answer on how long it takes to fit a Velux window shows how the work is organised.
Rules a new roof window must satisfy
A roof window is a building element and it has to meet standards for insulation, structure and, in some rooms, escape. Those requirements shape the specification and so the price.
Insulation
Approved Document L (2021 edition, 2023 amendments) lists targets for new elements in an existing dwelling. The row for windows includes roof windows, and its target is Band B on the energy scale or a U-value of 1.4 W/(m²·K). Rooflights sit in their own row, at 2.2. Windows sit outside what counts as a thermal element, so adding a roof window does not make the job a roof renovation.
Structure
Cutting the rafters is structural work. The building control body can tell you whether an application is needed. For houses in Rushmoor or Hart, ring the Hart and Rushmoor Building Control Partnership on 01252 398715.
Escape
When the window is also the way out of a loft room, it has to meet the escape sizes in Approved Document B. Our post on roof windows for a loft conversion sets those out.
Planning
A roof window on a house is normally permitted development under Class C, with limits. Flats, listed buildings and some conservation areas differ, and our post on planning permission for a skylight goes through them.
Why it matters for cost
A window that must meet a specification and be approved by building control costs more than one that need not. The quote should say which applies.
Reading and comparing roof window quotes
Two quotes for a roof window can differ widely and still be for the same job, or they can look alike and be for different jobs. A few questions make them comparable.
Is it a swap or a new opening?
The quote should say. If it says "fit Velux window" without saying whether there is an opening already, ask. The difference between the two jobs is bigger than the differences between most roofers.
Which window, what size?
Ask for the make, model and size, and the glazing specification. A quote that names the product can be checked against the maker's information, and one that does not cannot.
What flashing and what covering?
Ask which flashing kit is going in and how it suits your roof covering.
What is included inside?
Check whether the lining, plastering and decoration are in the figure.
Scaffold and VAT?
The standard VAT rate is 20%. Ask for the VAT position and for the scaffold to be stated.
One total price
We measure the roof and the opening, photograph the rafters, and send one written total when the survey is complete. Citizens Advice recommends at least 3 written quotes, and a comparison works when each roofer has seen the same roof. Our roof windows and skylights page covers the work we carry out.
Weighing up whether to fit one at all
A roof window can transform a dark loft or landing. It also adds cost, and your decision turns on what the room is used for.
Light and ventilation
A roof window brings daylight into a space that has none and gives a way to ventilate it. Over a stairwell or landing it can cut the need for artificial light through the day, and in a loft room it makes the space feel larger than its floor area suggests. The choice of opening type affects how easily it can be cleaned from inside, which matters on a pitch you cannot reach.
Heat and glare
A south-facing window lets in heat as well as light. Blinds help, and the glazing specification changes how much heat passes. Ask the supplier about options for the room you have in mind.
Loft rooms
In a loft conversion the window may be a requirement, not an extra, because of escape and ventilation. The pitch and headroom also shape where it can go.
Repair rather than replace
If an existing window leaks or will not close, the fault may be a flashing, a seal or a glass unit, and not the whole window. Replacing a part can cost far less than a new unit, and the survey says which you have.
Condensation
Condensation on a window can be a ventilation problem in the room and not a fault in the window. Check before you replace.
Next step
If you are weighing it up, a survey shows what the roof allows. The written price follows.
