Flat Roof Skylights and Rooflights: A Complete Guide

Adding a rooflight to a flat roof is one of the most impactful upgrades you can make to a single-storey extension or bungalow. Natural light transforms spaces that would otherwise feel dark and pokey.

Types of Flat Roof Rooflight

• Fixed flat rooflights: the most common type, sit in a kerb above the roof level
• Opening flat rooflights: can be opened for ventilation, either manually or electrically
• Walk-on rooflights: toughened glass suitable for foot traffic, for roof terraces above habitable space
• Dome rooflights: older style, common on commercial buildings, increasingly replaced by flat profiles
• Lantern rooflights: architectural feature lights with multiple glazed faces, often on extensions

Rooflight Kerbs

The kerb is the upstand frame on which the rooflight sits. For flat rooflights, the kerb must be a minimum of 150mm above the finished roof surface to prevent water ingress. The waterproofing membrane must be dressed up the kerb face and terminated correctly.

Thermal Performance

Building regulations require rooflights to meet minimum thermal performance standards. Specify triple-glazed or high-performance double-glazed units to minimise heat loss. A thermally broken frame is essential to prevent condensation.

Costs

Fixed flat rooflights start from approximately £200–£400 for a basic unit (600mm × 600mm). Quality lantern rooflights can cost £3,000–£10,000+. Installation is additional — the opening in the deck and structural support must be properly formed, and the waterproofing around the kerb must be done correctly.