Roof Lantern vs Skylight: Which Is Best for Your Extension?
Flat roof extensions need overhead glazing to bring in natural light. The choice between a roof lantern and skylights affects the cost, character, and light quality of your new space. Here is what you need to know.
Quick Answer
Skylights cost £500-2,500 each installed and sit flush with the roof. Roof lanterns cost £2,500-8,000+ and create a dramatic raised glass feature. Skylights are practical and affordable; roof lanterns are an architectural statement that floods the room with light.
£500-£2.5k
Skylight Cost
£2.5k-£8k+
Roof Lantern
3x more (lantern)
Light Increase
Check your specific property constraints
Free Property CheckWhy Roof Glazing Matters for Flat Roof Extensions
The vast majority of single-storey rear extensions in London have flat roofs. While the rear wall typically features large bifold or sliding doors, the middle and front of the extension can feel dark without overhead glazing. This is especially true for deeper extensions (over 3 metres) where daylight from the rear doors does not reach the area closest to the original house.
Roof glazing solves this by bringing light directly down into the heart of the space. The type you choose determines how much light you get, what character it adds to the room, and how much it costs. Both skylights and roof lanterns are excellent options, but they serve different purposes and suit different budgets.
Skylights and Rooflights Explained
Skylights (also called rooflights) sit flush with or just above the flat roof surface. They are essentially glazed panels set into the roof structure, allowing light to pass directly into the room below. They come in a range of sizes, from compact 600mm x 600mm units to large walk-on panels spanning 1.5m or more.
Types of Skylights
- Fixed flat rooflights: Sealed units that do not open. Most affordable option, great for light but offer no ventilation. From £500 installed
- Opening rooflights (manual): Hinged units with a manual pole or handle. Provide ventilation and light. From £800 installed
- Electric opening rooflights: Motor-operated with remote control or rain sensor. Most convenient but priciest skylight option. From £1,500 installed
- Velux-style pitched rooflights: Designed for pitched roofs but can be used on flat roofs with a kerb adapter. Well-known brand with extensive accessory range. From £600 installed
Skylight Advantages
- Affordable: Multiple skylights cost less than a single roof lantern, giving you more flexibility with placement
- Easy to install: Standard rooflights fit into the roof structure without major modifications, keeping construction time and costs down
- Good thermal performance: Modern double-glazed flat rooflights achieve U-values of 1.0-1.4 W/m2K, meeting Part L easily
- Low profile: Minimal visual impact from outside, which is an advantage in conservation areas or where neighbours overlook the extension roof
Skylight Disadvantages
- Limited design impact: Skylights are functional but do not create the same wow factor as a roof lantern when you look up
- Smaller light spread: Each skylight illuminates a relatively contained area directly below. You may need 2-3 to light a large extension evenly
- Can feel flat: The ceiling remains at the same height throughout, missing the opportunity to create a sense of vertical space
Roof Lanterns Explained
A roof lantern is a raised glass structure that sits above the roofline, typically with a ridged or hipped design. It projects upwards from the flat roof, creating a miniature glass house on top of your extension. Light enters from the sides and top, spreading across the room below far more effectively than a flat skylight.
Inside, the lantern creates a vaulted ceiling effect with an exposed glass roof, adding genuine architectural drama to what might otherwise be a standard flat-ceiling extension. They range from compact 1m x 1.5m units to grand 3m x 4m structures that dominate the room.
Types of Roof Lanterns
- Traditional lanterns: Feature decorative cresting, finials, and ornate frame details. Suit period properties and conservation areas. From £3,500 installed
- Contemporary lanterns: Ultra-slim aluminium frames with minimal visual interruption. Clean, modern aesthetic that suits most extension styles. From £2,500 installed
Roof Lantern Advantages
- Dramatic focal point: A roof lantern becomes the centrepiece of your extension, drawing the eye upward and creating a sense of grandeur
- Superior light spread: Light enters from the sides as well as the top, illuminating a much wider area than an equivalent flat skylight
- Sense of height: The raised ceiling within the lantern area adds vertical space, making the room feel taller and more spacious
- Architectural feature: Adds visual interest both internally and externally, enhancing the overall design quality of the extension
- Property value: Estate agents report that a well-designed roof lantern over a kitchen island or dining table is a genuine selling point
Roof Lantern Disadvantages
- Expensive: A single roof lantern costs as much as 3-5 skylights, which may not be justified for smaller or budget-focused projects
- Heat gain and loss: The larger glazed area and raised profile can cause overheating in summer and heat loss in winter without proper specification
- Cleaning access: The raised glass surfaces are harder to clean than flush skylights, especially the exterior. Budget for periodic professional cleaning
- Conservation area restrictions: The raised profile is visible from neighbouring properties, which may trigger planning concerns in sensitive areas
Side-by-Side Comparison
| Factor | Skylight | Roof Lantern |
|---|---|---|
| Cost (installed) | £500-£2,500 each | £2,500-£8,000+ |
| Light spread | Focused pool directly below | Wide, diffused across room |
| Design impact | Subtle, functional | Dramatic focal point |
| Ceiling height | Remains flat | Raised within lantern area |
| U-value (typical) | 1.0-1.4 W/m2K | 1.2-1.6 W/m2K |
| Ventilation | Opening models available | Usually fixed (some open) |
| Maintenance | Easy to clean, low upkeep | Harder to clean, more seals |
| Installation | Half day per unit | 1-2 days |
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Which Suits Your Extension?
The right choice depends on your extension type, budget, and the atmosphere you want to create. Here are the most common scenarios.
Kitchen-Diners: Roof Lantern as Centrepiece
For open-plan kitchen-diners, a roof lantern positioned over the dining table or kitchen island creates a spectacular focal point. The light falls naturally onto the area where you spend the most time, and the raised ceiling gives the dining zone a distinct sense of occasion. This is the single most popular use of roof lanterns in London extensions.
Utility Rooms and Bathrooms: Skylights
For practical spaces like utility rooms, bathrooms, or home offices within extensions, a skylight delivers all the natural light you need at a fraction of the cost. An opening skylight in a bathroom satisfies Part F ventilation requirements while bringing in daylight. There is no need for the design drama of a roof lantern in these spaces.
Budget Builds: Multiple Skylights
If budget is the primary concern, two or three well-placed skylights (total cost £1,500-£4,000) will light a 20m2 extension effectively. Position them at third-points along the length of the room to avoid dark spots. This approach costs 40-60% less than a single roof lantern while providing excellent light coverage.
Architect tip: Many London architects recommend a combination approach for larger extensions. A roof lantern over the main living or dining area for visual impact, plus one or two smaller skylights over the kitchen worktop or corridor areas for practical task lighting. This gives you the best of both worlds.
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Get instant advice on the best roof glazing for your projectBuilding Regulations for Roof Glazing
Both skylights and roof lanterns must comply with Building Regulations. The two key areas are thermal performance (Part L) and ventilation (Part F).
Part L: Glazing Area Limits
Part L limits the total area of roof glazing to 25% of the extension floor area. For a typical 20m2 extension, that means a maximum of 5m2 of roof glazing. This is generous enough for most designs but can become a constraint if you want both a large roof lantern and multiple skylights.
Important: The 25% limit applies to rooflights specifically. Wall glazing (bifold doors, windows) is calculated separately. Your architect or building control officer will check compliance. If you exceed the limit, you may need to compensate with higher-performance insulation elsewhere.
Part F: Ventilation
If the extension includes a kitchen or bathroom, Part F requires purge ventilation. An opening skylight can satisfy this requirement, provided it has sufficient free area (typically 1/20th of the floor area). Roof lanterns are usually fixed and do not contribute to ventilation, so you may need a separate opening skylight or mechanical extract fan.
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Cost Comparison for a Typical 20m2 Extension
Here is what you would typically spend on roof glazing for a standard 20m2 single-storey rear extension in London, including supply and installation.
| Option | Specification | Cost (Installed) |
|---|---|---|
| 2x fixed skylights | 900mm x 1200mm flat rooflights | £1,200-£2,000 |
| 3x fixed skylights | 900mm x 1200mm flat rooflights | £1,800-£3,000 |
| 2x electric opening skylights | 900mm x 1200mm with rain sensor | £3,000-£5,000 |
| 1x contemporary roof lantern | 1500mm x 2000mm aluminium | £3,500-£5,500 |
| 1x large roof lantern | 2000mm x 3000mm aluminium | £5,500-£8,000 |
| Combination (lantern + 1 skylight) | 1500mm x 2000mm lantern + 900mm x 1200mm rooflight | £4,200-£6,500 |
Frequently Asked Questions
Do roof lanterns make extensions too hot in summer?
This is a common concern, but modern roof lanterns with solar control glass and thermally broken aluminium frames manage heat gain effectively. Specify glass with a solar control coating (g-value of 0.3-0.4) to reject 60-70% of solar heat while still allowing plenty of light through. Blinds can also be fitted internally or within the glass cavity for additional control on the hottest days.
Do I need planning permission for a roof lantern?
In most cases, no. Roof lanterns on single-storey rear extensions fall within Permitted Development as long as the extension itself complies with PD rules. However, in conservation areas, the raised profile of a roof lantern may be considered a material alteration that requires planning permission. Check with your local planning authority before committing. Flush-fitting skylights are less likely to trigger planning issues in sensitive areas.
How often do skylights and roof lanterns need cleaning?
Skylights benefit from cleaning twice a year, which you can do yourself with an extendable window cleaner from inside if you have opening models, or from the flat roof during dry weather. Roof lanterns are harder to reach, especially the external ridge and side panels. Budget for professional cleaning 1-2 times per year at £80-150 per visit. Self-cleaning glass coatings add 10-15% to the cost but significantly reduce cleaning frequency.
Can I retrofit a roof lantern to an existing flat roof extension?
Yes, but it requires structural modification. The existing roof joists around the lantern opening need to be doubled up or replaced with a trimmed opening, and the new lantern needs a properly formed upstand. Budget £1,500-3,000 for the structural work on top of the lantern cost itself. It is significantly cheaper to include a roof lantern in the original extension build rather than retrofitting later.
Which is better for energy efficiency?
Skylights generally achieve better U-values (1.0-1.4 W/m2K) compared to roof lanterns (1.2-1.6 W/m2K) because they have a simpler profile with fewer joints. However, the difference in real-world energy costs is modest, typically £30-60 per year for a typical London extension. Both comfortably meet Part L Building Regulations requirements when properly specified.
What size roof lantern do I need for my extension?
As a rule of thumb, the lantern should be roughly one-third to one-half the width of the room and positioned centrally over the key living area (dining table, kitchen island). For a 4m-wide extension, a lantern 1.5-2m wide works well. Anything wider can feel out of proportion. Your architect will calculate the optimal size based on Part L glazing limits (max 25% of floor area for all rooflights combined).
Summary: Roof Lantern vs Skylight
Choose skylights if you want affordable, practical overhead lighting. Multiple skylights at £500-2,500 each provide effective light coverage for utility rooms, bathrooms, and budget-conscious kitchen extensions. Easy to install, simple to maintain, and rarely cause planning issues.
Choose a roof lantern if you want an architectural centrepiece that transforms the character of your extension. Positioned over a dining table or kitchen island, a lantern at £2,500-8,000 creates dramatic light and a sense of height that skylights cannot match. Best for kitchen-diners and living spaces where you want the wow factor.
Consider both for larger extensions. A roof lantern over the main living area combined with skylights for secondary zones gives you design drama where it matters most and practical lighting everywhere else.
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