Velux roof window installation in Southampton costs £600 to £1,200 supply-and-fit per window, or £300 to £500 fit-only. Rear-elevation windows are permitted development; conservation areas and front elevations may need consent. Correct flashing kits for slate, clay or concrete tile are essential — a poorly flashed window leaks in the first wet winter.
Velux roof windows are one of the most popular home improvements in Southampton — particularly on the Victorian terraces and 1930s semis where loft conversions are now common. A correctly installed Velux window transforms a dark loft or top-floor room into a bright, usable space. This guide covers everything from costs and planning to the critical flashing detail that determines whether the installation stays watertight.
Types of Velux Windows
Velux's Centre-Pivot range (GGL) is the standard choice for habitable loft conversions — the window tilts inward on a central axis for easy cleaning and good ventilation. The Top-Hung range (GGU) opens from the top and gives a cleaner internal finish but slightly less ventilation. For roof terraces and areas where opening is not required, the Fixed range (GGG) is the simplest and cheapest option. All are available in a range of standard sizes and can be motorised if required.
Permitted development rights under the Town and Country Planning (GPD) Order allow most rear roof windows without a planning application.
Source: Town and Country Planning (GPD) Order
Flat Roof Skylights
For flat-roofed extensions across Southampton's 1950s to 1970s housing stock, fixed-light roof skylights are the most common specification. Double-glazed glass or polycarbonate on a GRP or EPDM upstand, integrated into the flat roof during installation. The most important detail is the upstand height — minimum 150mm above the finished roof level to prevent water entry. We always integrate skylights into new flat roof installations rather than adding them to existing roofs where possible.
The Critical Flashing Detail
The single biggest cause of Velux window failure is incorrect flashing. A roof window installed without a proprietary flashing kit — or with an incorrect flashing kit for the tile or slate profile — will leak within the first wet winter. On Welsh slate, clay plain tile and concrete interlocking tile, Velux produce specific approved flashing kits. We use the correct kit for every installation. We have seen too many callbacks on windows installed by non-specialists with generic flashings that do not integrate properly with the specific tile profile.
Costs in Southampton 2025
Planning a Velux Installation?
We survey the roof and advise on position, size, planning implications and the correct flashing specification before quoting. Free survey across Southampton and Hampshire.
Call 0238 184 9628Planning Permission for Velux Windows in Southampton
Non-principal elevation installations that do not protrude more than 150mm above the roof pitch are permitted development. This covers the vast majority of loft conversion installations on the rear slope. Front elevation and conservation area installations need planning consideration. We advise on this during the free survey.
Last reviewed: 20 July 2026 by Southampton Roofing Experts