Rooflights and Skylights: PD Rules and Building Regulations
Rooflights (also called skylights or roof windows) are one of the simplest ways to bring natural light into a room — and one of the few roof alterations that are almost always permitted development.
Last updated: April 2026
Do you need planning permission?
Usually not. Rooflights are permitted development under Class C of Part 1 of the GPDO, provided they meet two conditions:
- The rooflight must not project more than 150mm beyond the plane of the existing roof slope. Most standard rooflights (Velux-style) sit almost flush with the roof and easily meet this. Only raised or glazed-dome rooflights may breach the 150mm limit.
- The rooflight must not be higher than the highest part of the existing roof. This is straightforward — your rooflight sits within the roof slope, so it will be below the ridge.
Conservation areas, AONBs, National Parks, the Broads, and World Heritage Sites: On designated land, rooflights facing a highway are not PD. Rear-facing rooflights on designated land are still PD.
Listed buildings: Any alteration to a listed building, including adding a rooflight, requires listed building consent. This is separate from planning permission and there are no PD rights for listed building alterations.
Building regulations
Rooflights on their own do not always need a building regulations application. However, they must comply with relevant standards:
Thermal performance (Part L): Rooflights must achieve a U-value of 1.4 W/m²K or better. Most modern double-glazed rooflights meet this. Older or budget rooflights may not — check the specification before purchasing.
Fire escape (Part B): If a rooflight is relied upon as a means of escape in a fire (common in loft conversions), it must have a clear opening of at least 450mm x 450mm, with the bottom of the opening no more than 1100mm above the floor. The rooflight must be openable from inside without a key.
Structural (Part A): Cutting a hole in the roof to install a rooflight may require trimming rafters. If the rooflight is wider than the gap between rafters, a structural opening must be formed. For large rooflights or multiple rooflights, your builder may need to install additional structural support.
Safety glazing: Rooflights in areas at risk of impact must use safety glass (toughened or laminated).
If the rooflight is being installed as part of a larger project (a loft conversion or extension), it will be covered by the building regulations application for that project. If you are adding a rooflight to an existing room, a separate building regulations application is usually not required — but the installation must still comply with the standards above.
Flat roof rooflights and lantern roofs
Rooflights on flat roofs (common on single-storey extensions) and lantern roofs follow the same PD rules — they must not project more than 150mm above the roof surface.
Lantern roofs (raised glazed structures on flat roofs) can easily exceed the 150mm limit. Check the product specification before assuming PD applies. If the lantern projects more than 150mm, you need planning permission.
How much do rooflights cost?
| Type | Supply cost | Installed cost |
|---|---|---|
| Centre-pivot (Velux-style) | £250–£600 | £500–£1,200 |
| Top-hung | £300–£700 | £600–£1,300 |
| Electric opening | £500–£1,200 | £800–£1,800 |
| Flat roof rooflight | £400–£1,200 | £700–£1,800 |
| Roof lantern (1m x 1m) | £800–£2,000 | £1,500–£3,000 |
| Roof lantern (2m x 1m) | £1,500–£3,500 | £2,500–£5,000 |
Installation costs include cutting the roof opening, forming the structural trimming, fitting the rooflight, flashing, and making good internally.
Next steps
- Check your PD rights — start with our free checker
- Choose your rooflight — consider size, opening type, and U-value
- Check if your property is on designated land — conservation areas and AONBs have restrictions on highway-facing rooflights
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