Supply and installation of roof windows and rooflights
Roof Window Installation (Velux and Equivalent)
Roof window installation is the supply and fitting of a pitched-roof window — commonly known by the Velux brand name regardless of manufacturer — into an existing or new roof structure, including trimming the rafters, fitting the flashing kit, and making the surrounding roof covering weathertight.
Definition
What Roof Windows covers
Roof windows are fitted directly into a pitched roof slope rather than a vertical wall, most often to bring natural light into a loft conversion, but also as a straightforward upgrade to an existing loft or roof space. Installation involves trimming or reinforcing the roof structure to form the opening, fitting the window unit itself, and installing the manufacturer's flashing kit to keep the surrounding tiles or slates weathertight — a step that's critical to get right, as flashing failure is a common cause of roof window leaks.
Suitable for
- Bringing natural light into a loft conversion or existing roof space
- Replacing an old, draughty or leaking roof window with a new unit
- Adding ventilation to a roof space via an opening roof window
- New roof window openings as part of a wider loft conversion or re-roof
Not suitable for
- Flat roof rooflights, which use a different product and installation approach — see our flat roof service
- Openings requiring significant structural alteration to rafters without the relevant Building Regulations sign-off
Process
How the work is carried out
- 01
Survey
Confirming the proposed window position, size and whether the rafter spacing needs trimming or reinforcing.
- 02
Structural opening
Cutting and trimming the roof structure to form the opening, with additional support where needed.
- 03
Installation
Fitting the window unit and the manufacturer's flashing kit, matched to the existing roof covering.
- 04
Completion
Checking the installation is weathertight and, internally, plastering back around the reveal.
Typical timescale
A single roof window is typically installed within a day; multiple units or those requiring structural reinforcement take longer.
Cost guidance
Roof window installation typically costs £900–£2,000 per unit installed in our area, with window size, opening or venting mechanism and the amount of structural trimming required pushing the price toward the top of that range. We provide an itemised quotation after a site survey rather than a fixed headline price.
Limitations and exclusions
- Internal plastering and decoration around the reveal is priced as part of the installation unless otherwise agreed
- Blinds and internal trim kits are typically quoted as optional extras alongside the window itself
- Structural reinforcement beyond standard rafter trimming is priced separately if identified at survey
Areas we cover
Roof Windows across Sussex, Surrey, Kent and South London
Local property styles, planning authorities and neighbourhood coverage for roof windows in each town we work in.
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FAQs
Roof Windows FAQs
Is "Velux" the only brand of roof window you fit?
Velux is the best-known brand and the term people commonly use for any pitched roof window, but we fit from a range of manufacturers depending on your budget and specification. We advise on the right product at survey.
Do roof windows need planning permission?
Most roof windows fall under permitted development, provided they don't project significantly beyond the roof plane and meet other standard criteria, but conservation areas and listed buildings can have additional restrictions. We confirm the position for your specific property before ordering.
Why do roof windows sometimes leak?
The most common cause is flashing failure — the flashing kit around the window is what keeps the surrounding roof covering weathertight, and it needs to be correctly matched to the roof covering and fitted precisely. We use the manufacturer's specified flashing kit for the installation rather than improvising a fix.
Discuss your roof windows project
Tell us about the property and what you have in mind, and we'll arrange a site visit.
Last reviewed 2026-07-28.