Contents
Types of Rooflight
Flat roof rooflights: used in flat-roof single-storey extensions. Available in several systems:
- Fixed flat glass rooflight: a frameless or slim-framed unit that sits just above the flat roof membrane, usually with a kerb upstand. Fixed lights provide light only.
- Opening flat roof lantern: a pitched glazed lantern (pyramid or ridge lantern) sitting on a flat roof, providing both light and ventilation. Popular in London kitchen-diner extensions.
- Walk-on rooflight: a flat unit designed to be flush with the roof surface and strong enough to walk on — used where the rooflight is at terrace level.
- Bespoke structural glass: frameless large-format glass panels — very high-end and expensive, used in premium extensions.
Pitched roof rooflights (roof windows): set into a pitched roof slope, flush with or slightly above the roof covering. The most widely used product is the Velux GGL (fixed) or GGU (white polyurethane, ideal for loft bathrooms) range. Other major manufacturers include Fakro and Keylite.
- Flush-fitting conservation-style rooflights: designed to sit in the same plane as the roof tiles, with a slim profile visible from outside. Preferred in conservation areas and on listed buildings where protruding elements would not be permitted.
- Centre-pivot roof windows: the most common type for accessible roof windows. Open by pivoting about the centre of the sash.
- Top-hung roof windows: hinge at the top, providing a larger clear opening and a better view when open.
- Electric and solar-powered roof windows: suitable for high-level or inaccessible positions.
Planning Rules
Pitched roof rooflights (permitted development): rooflights on a pitched rear roof slope can be installed under permitted development without planning permission provided:
- The rooflight does not project more than 150mm beyond the roof slope
- The highest point of the rooflight is no higher than the highest part of the roof
- It is not on a principal elevation (front of the property) visible from the highway
Front elevation rooflights: most London boroughs require planning permission for rooflights on the front slope of the roof, even under the general householder PD rules, as these change the streetscape.
Conservation areas: in conservation areas, conservation-style flush rooflights (non-protruding, flush with the tile face) are often required rather than the standard Velux or similar box. Check with the local authority's planning team — some London boroughs specifically permit flush conservation rooflights under local householder guidance, while others require planning permission for any front or rear rooflight.
Flat roof rooflights in extensions: where a flat roof extension already has planning permission (or is under permitted development), the rooflight within it is generally not a separate planning issue. However, if the extension itself is subject to a specific planning condition relating to materials or appearance, the rooflight specification should be checked against that condition.
Sizes and Orientation
Rooflights for pitched roofs are available in standard widths to suit standard rafter spacings (typically 550mm internal width for 600mm rafter centres). Common sizes are:
- 550 x 780mm, 550 x 980mm, 660 x 1180mm, 780 x 1400mm
Flat roof rooflights are more flexible in size — they can be designed to a specific dimension to suit the room below, typically from 600mm x 600mm up to 2,000mm x 4,000mm for a large extension lantern.
Orientation: a south-facing rooflight maximises winter solar gain and natural light. For a south-facing pitched roof, solar shading (integral or external blinds) should be specified to manage overheating in summer, particularly in loft bedrooms.
Thermal Performance
All rooflights in new work or work requiring Building Regulations approval must meet minimum thermal performance requirements. Current requirements (England) call for a maximum U-value of 1.6 W/m²K for a rooflight (centre-pane), with better performance achievable with triple glazing or warm-edge spacer bars.
Typical Costs
- Standard Velux GGL pitched roof window (780 x 980mm, supply): £300 to £550
- Conservation flush roof window (supply): £400 to £700
- Flat roof fixed rooflight (600mm x 600mm, supply): £250 to £450
- Flat roof opening lantern (1.5m x 0.75m, supply): £600 to £1,200
- Pitched roof window installation (labour per window): £200 to £400
- Flat roof rooflight installation (labour, inc upstand): £350 to £600
Want advice on your own project?
Pick whatever suits you. We'll look at what you have (drawings, photos or quotes) and tell you honestly what the next step should be.
Prefer to phone? Call +44 7359 872594.
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.
Was this guide helpful? Share it:
Have a question about your project?
Message us on WhatsApp or call — we reply during working hours (Mon–Fri 8am–6pm, Sat 9am–2pm).