Quick answer: A standard roof lantern on a flat roof costs £1,500–£5,000 fitted in 2026. A roof window (like a Velux) in a pitched roof costs £400–£1,500 fitted. A flat skylight (flush in a flat roof) costs £800–£3,000 fitted. They look similar in marketing photos but they’re three different products with different installation requirements, different building regs, and different price brackets. This guide explains which is which, what they cost in 2026, and what to verify before signing.
The 3 categories explained
| Roof lantern | Roof window (Velux) | Flat skylight | |
|---|---|---|---|
| Roof type | Flat roof only | Pitched roof only | Flat roof only |
| Profile | Pyramid / hipped frame above roof | Flush with roof slope | Flush with flat roof |
| Typical size | 1m × 1m to 4m × 2m | ~50cm × 80cm to 1.4m × 1.6m | 50cm × 50cm to 3m × 1m |
| Opens? | Optional, premium spec | Standard (manual or electric) | Optional, electric only |
| Cost (typical) | £1,500–£5,000 | £400–£1,500 | £800–£3,000 |
| Best for | Single-storey extensions; statement design | Loft conversions; retrofit lofts | Modern flat-roof extensions; minimal aesthetic |
Your roof type is the deciding factor. You can’t put a roof lantern on a pitched roof or a roof window on a flat roof — match the product to the structure first, then optimise on style and price.
Roof lanterns — cost breakdown
- 1m × 1m uPVC lantern, fitted: £1,500–£2,500
- 2m × 1m uPVC lantern, fitted: £2,000–£3,200
- 2m × 1m aluminium lantern, fitted: £2,800–£4,200
- 3m × 2m premium aluminium (e.g. Korniche, Atlas): £4,000–£6,500
- 4m × 2m or larger premium aluminium: £6,000–£10,000+
- Self-cleaning glass upgrade: +£150–£400
- Electric opening vent: +£600–£1,200
- Solar-control glass: +£200–£500 (south-facing rooms benefit; reduces overheating)
The price gap between uPVC and aluminium is real on lanterns — aluminium achieves much slimmer sightlines (15–25mm bars vs 40–60mm in uPVC), making the lantern look more like a glass roof and less like a structural pyramid. For 2m+ lanterns where the visual matters, aluminium is usually worth the premium.
Key brands worth knowing
- Korniche — UK premium aluminium, slim sightlines, self-supporting (no internal tie bars). 10-year guarantee.
- Atlas Roof Lantern — Korniche’s main competitor. Similar spec.
- Ultraframe Skypod — sectional uPVC; competitive on price, slightly chunkier sightlines.
- Stratus, Eurocell Skyline — mass-market uPVC alternatives at the budget end.
Roof windows (Velux-style) — cost breakdown
- Standard 78cm × 98cm Velux GGL, manual, fitted: £400–£700
- Standard 114cm × 118cm Velux GGL, manual, fitted: £600–£950
- Same size electric (Velux Integra): +£300–£500 over manual
- Conservation-style (with glazing bar): +£100–£250
- Sun-tunnel (rigid, ~35cm diameter): £450–£800 fitted — adds light to a windowless room via a reflective tube through the roof void
- Roof window blind (built-in or retrofit): £80–£250 per window
Velux dominates the UK market but Fakro and Keylite offer near-identical products at 15–25% lower cost. The aftermarket for blinds and accessories is broader for Velux, which matters if you want easy replacements down the line.
Flat skylights — cost breakdown
- 1m × 1m fixed flat skylight, fitted: £800–£1,500
- 2m × 1m fixed flat skylight: £1,400–£2,500
- 3m × 1m fixed flat skylight: £2,000–£3,500
- Electric opening flat skylight (1m × 1m): £1,600–£2,800
- Walk-on glass skylight: £2,500–£5,000 (used as transparent floor in upper-storey extensions)
- Self-cleaning glass: +£200–£400
Flat skylights have almost no profile above the roof line — flush mounted into a flat roof’s existing membrane. Architectural choice when you don’t want a lantern’s structural look but you have flat-roof construction. Brands: Glazing Vision, EOS, Sunsquare.
Building Regs and planning
- Building Regs always apply — installation must comply with Part L (energy / U-value), Part B (fire safety, escape), Part F (ventilation), Part K (glass safety at low level). Self-certifying installers via FENSA / CertAss / Glass and Glazing Federation handle the notification.
- U-value: 1.4 W/m²K is the Building Regs ceiling for replacement; 1.2 for new-build. Most modern roof lanterns/skylights achieve 1.2–1.6.
- Planning permission isn’t usually required for a roof window, lantern or skylight that doesn’t extend more than 150mm above the existing roof slope. But: Conservation areas, listed buildings, Article 4 directions all override permitted development — always check with the local planning office.
- Loft conversion roof windows often qualify under permitted development — but the planning rules are nuanced (single side-facing rear-facing only in some cases). Check before ordering.
What affects the price most
- Size — surface area drives both glass cost and structural complexity. 4m × 2m is roughly 4× the cost of 1m × 1m.
- Material — aluminium frames cost 50–80% more than uPVC for the same opening.
- Brand — Korniche and Atlas premium-priced; mass-market uPVC alternatives much cheaper for similar performance.
- Glass spec — standard A-rated double glazing is included; solar control adds 15–25%; self-cleaning adds £150–£400; triple glazing adds 25–35%.
- Opening mechanism — fixed cheapest; manual openable adds £150–£400; electric openable with rain sensor adds £600–£1,200.
- Structural alterations — cutting through a flat roof and creating a new opening (with timber kerb upstand) is £300–£800 of fitter time. Not always quoted clearly upfront.
- Scaffolding — roof access for ground-floor extensions usually doesn’t need scaffold; first-floor and above does (£400–£1,200).
- Existing roof type — installing into an EPDM rubber flat roof is straightforward; into a felt roof or older built-up roof is messier and often costs more.
Common mistakes to avoid
- Going for the largest lantern that fits — bigger lantern means more solar gain and more glare in summer. Add solar-control glass or a powered blind unless your room is north-facing.
- Forgetting ventilation — a fixed lantern in a south-facing kitchen can push room temperatures to 35°C in summer. An electric opening vent is worth the £600–£1,200.
- Ignoring U-value — cheap lanterns with single-glazed dome plastic still exist. Always confirm Uw ≤1.4. See our U-values & WER guide.
- Cutting an opening yourself — DIY roof openings into a habitable room are a Building Regs nightmare. Always use a competent person scheme installer.
- Skipping the timber kerb upstand on a flat roof skylight — water pools at the base of the unit and leaks within 2 winters. Kerb is non-negotiable on flat-roof installs.
- Choosing a “lifetime” guarantee over a real insurance-backed guarantee — same risk as with windows.
Frequently asked questions
Do I need planning permission for a Velux roof window?
Usually no — most fall under permitted development if they don’t project more than 150mm above the existing roof slope and aren’t on the front of the property. Conservation areas and listed buildings are exceptions. Check with your council’s duty planning officer (free 5-minute call) before ordering.
Will a roof lantern leak?
Not if installed correctly. Modern aluminium lanterns sit on a timber kerb that’s flashed into the existing flat roof membrane — well-detailed installs can outlast the surrounding roof. Cheap installs that skip the kerb or use silicone-only seals start leaking within 2–5 winters.
How long do roof lanterns and skylights last?
Frames: 25–35 years for aluminium, 20–30 for uPVC. Sealed glass units: 10–25 years (same as windows — see our window lifespan guide). Velux roof windows are guaranteed for 10 years on the unit, separately on the glass.
Will a roof lantern overheat my room in summer?
South-facing yes, unless you specify solar-control glass or fit a powered blind. Solar-control glass blocks ~70% of heat gain while letting in most of the visible light — non-negotiable for a south-facing kitchen lantern.
Can I fit a roof lantern myself?
Technically possible if you’re competent in roofing and Building Regs notification, but very few homeowners are. Building Regs require either a FENSA / CertAss-certified installer (who self-certifies) or a Building Notice + inspection (£300–£600 + fitter cost). Almost always cheaper and easier to use a certified installer.
Sun tunnel vs roof window — which is better for a windowless bathroom?
Sun tunnel (£450–£800 fitted) is far cheaper and easier when there’s loft space between bathroom ceiling and roof. Delivers daylight equivalent to a 60W bulb on a sunny day. Roof window only makes sense if you also want the ventilation and the roof is directly above (no loft void).
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Related: Conservatory Roof Replacement Cost · Orangery vs Conservatory vs Extension · U-Values & WER
Sources: Korniche / Atlas / Ultraframe published price ranges 2026, Velux UK product datasheets, Glazing Vision flat skylight pricing, Checkatrade roof lantern installation cost guide (2026), MyJobQuote roof lantern price data, Building Regulations Approved Documents B, F, K, L. Last reviewed: April 2026.
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