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Rooflight Installation in London: Planning, Types, Costs and What to Expect
Rooflights are one of the most effective and cost-efficient ways to increase natural light in a London home. Whether installed on a flat roof extension, within a pitched roof slope, or as part of a loft conversion, a rooflight can transform a dark internal space with minimal structural intervention compared to a full extension or dormer.
For pitched roof rooflights (roof windows set flush within the slope of an existing pitched roof), the most common brand in the UK market is Velux, though alternative quality manufacturers include Fakro and Keylite. Pitched roof windows set flush within the roof slope are typically within Permitted Development for dwelling houses, provided they do not protrude more than 150mm above the roof plane and do not front the principal elevation (the street-facing slope). This means that rear slope rooflights on London terraced houses are very commonly installed without planning permission.
For flat roof rooflights, the product range includes fixed flat glass units (Velux Modular, RoofLITE, various bespoke suppliers), walk-on glass units (designed for terraces and accessible areas), and frameless flush-mounted units. Flat roof rooflights are installed within or above the flat roof deck and require a curb or upstand to raise the glass above the waterproofing layer and prevent water ingress.
Glazed roof lanterns — a structural pyramid or ridge-and-hip glass roof element — are a premium option for flat-roof extensions. They provide high volumes of natural light and are an architectural feature, but cost significantly more than flat rooflights.
Planning permission for rooflights on pitched roofs (within PD conditions) is generally not required for rear slopes. Front slope rooflights on a principal elevation are typically within PD if they do not project beyond the plane of the roof. In conservation areas, however, any rooflight may require planning permission — many conservation areas have policies against roof windows on front slopes, and some have stricter policies on rear slopes too. Check with the local planning authority before installing in a conservation area.
Building Regulations apply to new rooflights as part of an extension or conversion. The rooflight U-value must comply with Part L (maximum 1.4 W/m²K for the whole unit). Structural support for the rooflight opening in a pitched roof must be provided (a trimmer and header), and for large flat roof rooflights the flat roof structure must be assessed by a structural engineer to confirm it can carry the rooflight frame loads.
Costs for pitched roof windows in London range from five hundred to two thousand five hundred pounds per unit for supply and installation depending on size and specification. Flat roof rooflights range from one thousand five hundred to five thousand per unit. Glazed lanterns cost eight thousand to twenty-five thousand pounds installed.
RCB installs rooflights as part of extension and conversion projects across London. +44 7359 872594 | connect@rcbGroup.co.uk | www.rcbGroup.co.uk
Frequently Asked Questions
Do I need planning permission for a rooflight in London?▼
What is the difference between a Velux window and a flat roof rooflight?▼
How much does a rooflight cost to install in London?▼
Important Note
This guide is for general information only. Building regulations, planning rules, and legal requirements change regularly and vary by local authority. Always seek professional advice specific to your project and location. To talk through your own project, book a project review.
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