A roof lantern is a raised, glazed framework that sits on a flat or near-flat roof to flood a room with natural light. Unlike a simple flat rooflight, a lantern has a pitched profile, typically a ridge running along its centre, which sheds rainwater effectively and creates more headroom beneath. They are most commonly installed on single-storey rear extensions, kitchen-dining rooms, and orangeries.
Supplied and fitted, expect to pay £1,500–£8,000+ depending on size, frame material, and glazing specification. Budget aluminium units for a modest 1.0 m × 1.5 m opening start around £1,500–£2,500; a larger 2.0 m × 3.0 m triple-glazed aluminium lantern with a quality installer can easily reach £5,000–£8,000 or more.
Types of Roof Lantern
By Frame Material
| Material | Typical Cost (supply only) | Lifespan | Thermal Performance | Notes |
|---|---|---|---|---|
| uPVC | £600–£2,000 | 20–30 yrs | Moderate | Bulkier sightlines, limited colours |
| Aluminium (powder-coated) | £1,000–£5,000 | 35–50+ yrs | Good (thermally broken) | Slim profiles, huge colour range via RAL |
| Timber | £1,500–£6,000 | 30–60 yrs (with maintenance) | Excellent | Classic look, needs repainting every 5–10 yrs |
| Aluminium-timber composite | £2,500–£7,000 | 40–60 yrs | Excellent | Timber interior, alu exterior, best of both |
Thermally broken aluminium is by far the most popular choice: slim sightlines maximise the glazed area, it is low-maintenance, and modern sections achieve U-values of 1.4–1.6 W/m²K for the frame alone.
By Glazing
- Double glazing, standard; typically 24–28 mm units, U-value around 1.1–1.4 W/m²K (whole unit)
- Triple glazing, adds £200–£800 to supply cost; U-value 0.6–0.8 W/m²K; worthwhile in an exposed or north-facing position
- Self-cleaning glass, titanium dioxide coating breaks down grime in UV light; adds £100–£300 per unit; recommended for most roofs where cleaning is difficult
- Solar control glass, reduces summer heat gain; useful if the room faces south or south-west; adds £80–£200
All glazing in a roof lantern must comply with Building Regulations Approved Document K (protection from falling), overhead glazing must be laminated safety glass (minimum 6.4 mm PVB laminate on the inner pane) so that broken shards do not fall on occupants.
Typical Sizes and Costs
Manufacturers generally quote in external frame size. Opening sizes (the structural hole in the roof) are typically 50–100 mm smaller on each dimension.
| External Size | Frame Material | Glazing | Typical Fitted Cost |
|---|---|---|---|
| 1.0 m × 1.5 m | uPVC | Double | £1,500–£2,200 |
| 1.0 m × 1.5 m | Aluminium | Double | £2,000–£3,000 |
| 1.5 m × 2.5 m | Aluminium | Double | £3,000–£4,500 |
| 2.0 m × 3.0 m | Aluminium | Double | £4,500–£6,500 |
| 2.0 m × 3.0 m | Aluminium | Triple | £5,500–£8,000 |
| 2.5 m × 4.0 m | Aluminium-timber | Triple | £7,000–£12,000+ |
Prices include VAT at 20%, supply of the unit, and a typical installation on an accessible flat roof with an existing structural opening. They exclude making good the ceiling, any structural alterations to the opening, or scaffolding if access is difficult.
What Drives the Price
Size is the dominant factor. Glass and frame cost scale roughly with area; the installation labour (typically one to two days for a pair of fitters) scales much more slowly.
Frame material affects both supply cost and long-term value. Aluminium costs more than uPVC upfront but commands a better resale impression and lasts significantly longer.
Glazing specification adds cost incrementally. Triple glazing and solar control are genuine upgrades; self-cleaning glass is worth it almost everywhere given the difficulty of cleaning overhead glass.
Structural work, if the roof structure needs a lintel or trimmer joists to create or enlarge the opening, add £300–£1,500 for a carpenter and possibly a structural engineer’s calculation (£250–£600).
Access and scaffolding, most lantern installs on single-storey extensions are done from ladders or a small tower scaffold. On a two-storey structure or awkward pitch, scaffolding can add £500–£2,000.
Planning and Building Regulations
Most roof lanterns on existing extensions are permitted development, they do not need planning permission provided:1
- The dwelling is not in a Conservation Area or a Listed Building
- The lantern does not raise the overall roof height of the extension beyond limits (usually the ridge height of the main house)
- No more than 50% of the original house curtilage is covered by extensions/outbuildings in total
Building Regulations (Approved Document L, Volume 1) apply to the thermal performance. The limiting U-value for a rooflight in an existing dwelling is 2.2 W/m²K, which most quality double-glazed lanterns beat comfortably.2 Note that Part L treats a rooflight, which sits out of the plane of the roof on a kerb or upstand, differently from a roof window set in the plane of the roof: a roof window has to reach 1.4 W/m²K. If the lantern makes up more than 25% of the total roof area of the extension, a whole-dwelling carbon calculation may be required.
Always check with your local planning authority if you are in a designated area.
Roof Lantern vs Flat Rooflight
| Feature | Roof Lantern | Flat Rooflight (flush) |
|---|---|---|
| Profile | Raised/pitched ridge | Flush or slightly proud |
| Light quality | Diffused from multiple angles | More direct, overhead |
| Drainage | Self-draining via pitch | Requires fall in roof deck |
| Visual impact | Statement feature | Discreet |
| Cost (1.5 m × 2.5 m) | £3,000–£5,000 fitted | £1,200–£2,800 fitted |
| Cleaning | Harder, steeper glass | Easier with long-handled tool |
The right choice depends on the architectural language of the extension. A lantern suits orangery-style or classical buildings; a flush rooflight suits a contemporary flat-roof extension where a low profile is desired.
How to Choose a Supplier
- Check fabrication quality, look for thermally broken sections (no metal bridge connecting interior and exterior of the frame) and argon-filled sealed units.
- Ask for U-value documentation, a reputable supplier will provide a BFRC (British Fenestration Rating Council) certificate or a BRFC-equivalent third-party test report.
- Verify the warranty, frame warranties of 10 years and glazing sealed-unit warranties of 5–10 years are standard from quality manufacturers.
- Use FENSA or Certass-registered installers, they self-certify compliance with Building Regulations and notify the local authority on your behalf, saving you from applying for a Building Regulations certificate separately.
- Get three quotes, fitting quality varies; the cheapest quote is not always the best value if the installer uses inferior sealant or omits flashing details.
A well-installed roof lantern with a quality frame and double or triple glazing will transform a dark extension and add genuine appeal to a home. Spending an extra £500–£1,000 on a thermally broken aluminium unit over a uPVC equivalent almost always proves worthwhile over a 20-year horizon.
The rules in this note are those that apply in England. Scotland, Wales and Northern Ireland have their own building standards and permitted development rights.
References (2)
Figures in this note were checked against the sources below on 13 September 2026. Superscript numbers in the text point to them. Every source the site cites, by topic.
- 1technicalvery strongThe National Archives (legislation.gov.uk), legislation.RN-5QRXP7Class C permits any other alteration to the roof of a dwellinghouse, which is the right rooflight and Velux loft conversions rely on. Paragraph C.1(b) makes development not permitted if the alteration would protrude more than 0.15 metres beyond the plane of the roof slope, measured perpendicular to the original roof plane, and C.1(c) if the highest part of the alteration would be higher than the highest part of the original roof. C.1(d) excludes chimneys, flues, soil and vent pipes and solar equipment from the class, and condition C.2 requires any window in a roof slope forming a side elevation to be obscure-glazed and non-opening below 1.7 metres above the floor of the room.
- 2technicalvery strongMinistry of Housing, Communities and Local Government.RN-L0FCJXThe in-force U-value tables a DIY insulation or door note must quote, with the exact numbers. Table 4.2, limiting U-values for new fabric elements in existing dwellings, sets roof 0.15, wall 0.18, floor 0.18, swimming pool basin 0.25, window 1.4 or Window Energy Rating Band B minimum, rooflight 2.2, doors with more than 60 per cent of the internal face glazed 1.4 or Doorset Energy Rating Band C minimum, and other doors 1.4 or Doorset Energy Rating Band B minimum. Table 4.3, for existing elements, gives a roof threshold of 0.35 and an improved value of 0.16, which is the figure a loft insulation note needs: paragraph 4.12 says a retained element whose U-value is higher than the column (a) threshold, for example through a loft or garage conversion, should be upgraded to the column (b) value. Paragraph 4.13 allows a lesser upgrade only where the improved value is not technically or functionally feasible or would not achieve a simple payback of 15 years or less. Paragraph 4.8 requires a replacement element to be no worse than the one it replaces as well as meeting Table 4.2. Paragraph 4.10 gives the heritage exception: where character must be maintained, a centre pane U-value of no more than 1.2 or low-emissivity secondary glazing. Note 9 records that the timber window concession of 1.6 or Band C ended on 14 June 2023. The 2021 edition came into force on 15 June 2022; a 2026 edition exists at https://assets.publishing.service.gov.uk/media/69c122a6cfa346b9d4704a55/ADL1_2026.pdf.
-
The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, Class C, legislation.gov.uk, accessed 14 September 2026. legislation.gov.uk
-
Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments, Ministry of Housing, Communities and Local Government, accessed 13 September 2026. assets.publishing.service.gov.uk
