The short answer
The cost of fitting a roof window is made up of the window, its flashing kit, the work to the roof covering and rafters, access to the roof, and the lined opening inside. A like-for-like swap of an existing window leaves out the structural and lining work, so it usually costs less than a new opening. Your written quote prices each part.
The window itself
Size is the first thing that moves the price. A larger window costs more, and the code on a VELUX unit tells you the size: in a code such as MK04, the letter marks the width and the digits mark the height. Other makers use their own codes, and we convert them on the quote so the sizes can be compared fairly.
Glazing is the next step. Double glazing is the starting point, and laminated or toughened inner panes, triple glazing and solar control coatings each add cost. Part L 2021 holds a roof window in an existing dwelling to 1.4 W/m²K, the ordinary window figure, with WER Band B as the other route, and the units we fit meet it.
The opening type changes the price as well. A centre pivot window is the usual choice, a top hung window gives a clearer view and more headroom, and an electric opening one with a rain sensor costs more than a manual one. Our guide to roof window makes compared sets the makers and ranges out side by side.
Flashing, covering and the roof around it
Every roof window sits in a flashing kit that is matched to the roof covering: slate, plain tile, pantile or flat profile. The kit is a separate line, and the covering decides which one is needed. Some coverings are quick to cut back and re-lay, and others take longer, so the labour moves with the roof.
A window in an old roof with brittle tiles or slates may need replacement tiles around it, and the quote lists this separately. If the roof is low in pitch, the window must suit it, and our answer on roof windows on a low pitch explains what changes.
New opening or like-for-like swap
The biggest difference in price is between cutting a new opening and swapping an existing window. A swap uses the opening that is already there, so there is no structural work and no new lining.
| Item | Like-for-like swap | New opening |
|---|---|---|
| Rafters | Left as they are | Cut, with a header and trimmers |
| Lining inside | Usually kept | Built, insulated and plastered |
| Building Control | Notifiable when the whole window is replaced | Notifiable, as building work |
| Flashing and covering | New kit, covering dressed around it | New kit, covering cut back and re-laid |
| Price | Usually lower | Usually higher |
Taking out and replacing a whole roof window or rooflight, glazing and frame included, is a controlled fitting job that must be notified, while a sealed glass unit renewed alone is not. Where notification is required, we send it to Building Control on your behalf. Our page on replacing an old VELUX window covers the swap in more detail.
Access, scaffold and the finish inside
How the roof is reached changes the price. A window on a low roof can be fitted from a ladder or a tower. A window on a high or steep roof needs scaffold or an edge protection system, which is priced as its own line, and a roof next to a neighbour or a public path may need more planning for access.
Inside, a new opening is lined with insulation and plasterboard, and the plaster is finished so that the splays look like part of the room. The quote states how the splays are left, and if you would like them painted as part of the job, ask at the survey and it is priced as its own line.
If the room below is a loft conversion, the windows serve a specific purpose, and our answer on roof windows for a loft conversion explains it.
Why a roof window price needs a survey
Once glazing, opening type, flashing, covering, access and lining are counted, two windows of the same size can end up well apart on price, and much of that comes down to the roof. Any figure quoted without seeing the roof would be a guess, so no charge is made for the survey, and the quote itemises every part of the price for each option.
- Window, flashing kit and lining priced as separate lines
- Access and scaffold shown on their own
- Maker lead times stated for each option
Each quote shows more than one suitable window next to the others, drawn from a range of makers, where the roof permits. Book a free survey and we will price the windows that suit your roof. You can also read our page on roof windows for the full range.
Related questions
Is a roof window cheaper than a flat rooflight to fit?
They suit different roofs, so the comparison depends on the project. A pitched roof window needs a flashing kit matched to the covering, while a flat rooflight needs a kerb, and the quote prices whichever suits.
Does the quote include the Building Control fee?
Where the work is notifiable, we handle the notification and the quote shows what that line covers.
Does a bigger window always cost proportionately more?
Not exactly. A larger window needs a larger opening, which can mean more rafter work, so a small step up in size can bring a larger step up in cost.
Can I choose the make myself?
Yes. No single manufacturer holds us, so we price the makes that suit your roof together, and the choice is yours, made on glazing, frame, opening type, lead time and cost, side by side.