Roof Lantern Costs UK — What to Charge for Roof Lantern Supply and Fit in 2026
Roof lanterns are one of the most profitable add-ons a builder or glazier can offer on flat-roof extensions, kitchen rear additions, and orangeries. The market has grown steadily as homeowners push for more natural light without committing to a full conservatory — and the margins available, especially on thermally broken aluminium units, are significantly better than standard window or door replacements.
This guide covers the full cost picture for roof lantern supply and fit in 2026: material by material, size by size, and every variable from glazing upgrades to structural prep work that changes what you need to charge.
Roof Lantern Types — Supply and Fit Price Ranges
The four main categories of roof lantern differ on frame material, thermal performance, and fabrication complexity. The table below gives supply-only and installation-labour breakdowns alongside total fitted costs.
Prices are for standard sizes on an existing structural opening with a formed kerb/upstand. Excludes structural opening works, plastering make-good, and VAT.
uPVC Roof Lanterns
uPVC lanterns are the entry-level option and suit budget-conscious customers or properties where the roof lantern is secondary to the main extension works. Supply costs run £800–£2,000 depending on size, with installation labour adding £700–£1,500, giving a typical fitted range of £1,500–£3,500.
The practical limitations of uPVC at this scale are worth flagging to customers: the profiles are visually bulkier than aluminium, colour options are restricted (white is standard; coloured foils add cost), and the long-term performance on a roof-mounted unit exposed to UV and temperature cycling is inferior to thermally broken aluminium. For most builders, uPVC lanterns make sense on extension jobs where the overall budget is tight and the customer has been quoted a higher-spec unit elsewhere.
On a standard 1m×1.5m uPVC lantern, supply cost is typically around £900–£1,200. A 2m×1.5m unit moves to £1,300–£1,800. Fit time is usually half a day for a prepared opening with a formed kerb — factor one operative plus a second for handling and flashing.
Aluminium Roof Lanterns
Powder-coated aluminium is the mid-market standard and the most common specification on new flat-roof extensions and kitchen additions. Supply runs £1,500–£4,000, installation £1,000–£2,000, total fitted £2,500–£6,000.
The main commercial advantage of aluminium is colour flexibility — powder coating is available in any RAL with no colour uplift from most fabricators, and dual-colour (white internal, anthracite external, for example) is standard on better-specified units. Slim sightlines give a more architecturally refined finish than uPVC, and customers increasingly expect this on an extension that's costing £30,000–£60,000 overall.
Standard aluminium lanterns are not thermally broken — the inner and outer aluminium profiles are connected directly, creating a thermal bridge. This matters for Part L compliance (see below). Check your specification before quoting; some fabricators market "aluminium" lanterns that are in fact thermally broken, while others that appear similar in marketing are not.
Thermally Broken Aluminium (Premium)
Thermally broken aluminium units incorporate a polyamide thermal break between the inner and outer profiles, dramatically reducing heat loss and eliminating cold bridging. Supply cost is £2,500–£6,000, fit £1,500–£2,500, total £4,000–£8,500.
The thermal performance difference is significant: a standard aluminium lantern might achieve a U-value of 2.0–2.5 W/m²K for the frame element, while a thermally broken unit can reach 1.4–1.8 W/m²K or better. Combined with high-performance glazing, this makes it far easier to demonstrate Part L compliance — which is why specifying thermally broken aluminium upfront saves you complications at the building control stage.
For customers investing in a high-specification extension, the thermally broken premium is usually easy to justify: lower heating bills, no condensation on the frame in winter, and a better U-value figure in any energy performance assessment. It's also the correct specification for any glazed rooflight on a new extension where building regulations apply.
Timber and Hardwood Bespoke Lanterns
Bespoke timber lanterns — typically hardwood such as oak or accoya — are the premium end of the market and usually commissioned for heritage properties, listed buildings, or high-specification new builds where the customer wants a material that ages naturally rather than requiring repainting. Supply runs £3,000–£8,000+ and fit £1,500–£3,500, total £4,000–£12,000+.
The installation complexity is higher than aluminium: bespoke timber units are heavier, require more careful handling on-site, and the joinery detailing at the kerb junction needs more time to execute properly. Lead times from specialist fabricators are typically 8–12 weeks versus 3–6 for aluminium. Factor this into your programme and your quote.
Maintenance is a genuine ongoing commitment — a hardwood lantern needs periodic oiling or painting every 3–5 years depending on specification and exposure. Make this clear to customers; it's not a reason not to buy, but it's information they need and an opportunity to offer an annual maintenance contract.
Size Impact on Pricing
Roof lantern pricing scales with size — larger units require more glazed area, heavier structural sections, and more installation time. The table below gives fitted price ranges across standard sizes for uPVC and aluminium (thermally broken aluminium runs approximately 50–80% above standard aluminium at equivalent sizes).
Fitted prices include standard double-glazed toughened safety glass, supply, delivery, and installation on a prepared kerb. Excludes structural works, flashing, and VAT.
Bespoke and non-standard openings — odd aspect ratios, irregular polygonal shapes, or openings specified to match an existing architectural feature — add 20–40% to standard pricing. The additional cost reflects higher fabrication complexity and the fact that non-standard units cannot be batch-produced alongside standard sizes. Always clarify the opening dimensions and whether the customer's preferred size falls within a fabricator's standard range before quoting.
Glazing Options and Upgrades
Standard roof lanterns are supplied with 4mm toughened safety glass in a double-glazed unit — this is the baseline specification required under Part N (safety glazing) and is included in the supply prices above. The main upgrades to offer and price are:
A third glass pane in the sealed unit improves the centre-pane U-value from around 1.1 W/m²K (double) to 0.6–0.8 W/m²K. Most worthwhile on larger lanterns where the glazed area is the dominant heat loss route. Adds meaningful weight — check the kerb structure can carry the additional load before specifying.
A photocatalytic coating on the outer pane breaks down organic matter in UV light; rain then sheets off rather than beading, carrying debris with it. On a pitched roof lantern that is difficult to access safely for cleaning, self-cleaning glass is a straightforward upsell. Typically specified on Pilkington Activ or equivalent.
Reduces solar heat gain (g-value) to mitigate overheating in south-facing rooms. Typically a blue-grey or bronze tint at 30–40% light transmission reduction. More relevant on lanterns that receive direct sun for much of the day — the customer's aspect and the room use should drive whether you recommend this.
An interlayer (typically PVB) bonded between two glass panes means the unit holds together if broken rather than shattering. Relevant on accessible roof areas or on jobs where the customer has security concerns. Note that toughened glass already satisfies Part N safety glazing requirements — laminated is an additional upgrade rather than a compliance requirement in most cases.
Installation Process
A roof lantern installation on an existing flat roof with a prepared kerb is a relatively contained job. The sequence is:
- Site survey — check the existing flat roof or extension structure, confirm the opening dimensions are square and level, assess ceiling height and whether there is any service routing above (pipes, cables), and establish access for delivery and working at height.
- Structural opening check — if the lantern is going into an existing opening with a formed kerb, confirm the kerb is the right height (typically 150mm minimum above the roof surface) and that the surrounding structure is adequate for the lantern's weight. If you are cutting a new opening through an existing flat roof, a lintel or structural beam may be required — add £500–£2,000 for this work depending on span and structural complexity.
- Weathering and flashing — the junction between the lantern kerb and the existing roof finish must be watertight. On EPDM or GRP flat roofs, the kerb upstand is typically dressed with lead flashing or bonded with EPDM tape into the existing membrane. Allow £200–£500 for flashing and weathering works depending on the roof finish and the complexity of the junction.
- Lantern installation — the unit is lifted onto the kerb, squared and levelled, and fixed through the kerb plate. Glazing bars are assembled if the unit arrives in components. External sealing is applied to all joints.
- Internal make-good — the reveal around the new opening typically requires plastering or dry-lining to finish neatly. Allow £200–£600 for internal plastering make-good depending on the depth of the reveal and the finish required.
- Drainage check — confirm that the fall direction on the surrounding roof drains away from the kerb, not toward it, and that existing outlets are clear before handing over.
Total installation time on a prepared opening is typically half a day to a full day for a standard-sized aluminium lantern with two operatives. Larger or more complex units — heavy timber lanterns, bespoke non-standard shapes, or any job requiring structural opening works — should be priced at 1.5–2 days.
Flat Roof Compatibility and Kerb Details
Roof lanterns are most commonly fitted to flat roofs finished in EPDM rubber, GRP (glass-reinforced plastic), or traditional felt. The compatibility and detailing approach differs slightly for each.
The most common modern flat roof finish. EPDM bonds reliably to the kerb upstand using EPDM primer and bonding adhesive, creating a seamless and durable weathering detail. Most roof lantern manufacturers provide a proprietary kerb with a pre-formed upstand that the EPDM membrane is lapped and bonded into. This is the simplest and most reliable detailing option.
GRP is harder than EPDM and requires a GRP-compatible upstand detail. Proprietary GRP kerb trims are available from most flat roofing manufacturers, and the junction is finished with GRP laminate and gel coat. It's a more skilled and time-consuming detail than EPDM — factor this into your labour rate if the existing roof is GRP.
Older felt roofs require careful assessment before installing a roof lantern. If the felt is in poor condition or near the end of its service life, the disruption of fitting a kerb may be the trigger point to recommend a full roof replacement before the lantern goes in — far better to do this as part of the same package than to have the customer back in 18 months for a leak investigation. Lead flashing dressed into the felt is the traditional weathering method.
Regardless of roof finish, the kerb upstand must be a minimum of 150mm above the finished roof surface to provide adequate clearance from standing water. Self-draining frames — where the glazing bars incorporate internal drainage channels that route water to the outside of the kerb — are standard on better-specified aluminium units and eliminate the risk of condensation pooling inside the frame.
Always confirm the fall direction is directed away from the kerb before signing off. A roof that drains toward the lantern kerb will eventually test the weathering detail beyond its design limits.
Building Regulations
Roof lanterns on existing flat roofs are typically permitted development — they do not require a planning application in most residential cases, provided the existing structure is also permitted development. However, Building Regulations apply in all cases:
The glazed area of the lantern must achieve a minimum U-value of 1.6 W/m²K (whole unit, including frame). Standard double-glazed uPVC and aluminium units typically achieve 1.6–2.0 W/m²K — check the manufacturer's certified U-value. Thermally broken aluminium with a good centre-pane U-value can achieve 1.4–1.6 W/m²K, making compliance straightforward. There is also a limit on the proportion of the roof that can be glazed without triggering a compensatory calculation, though for a single lantern on a standard extension this is rarely an issue.
The existing structural opening must be adequate to carry the lantern's dead load plus wind and snow loads. For a standard-sized lantern in an existing extension, the surrounding structure is usually adequate. If you are forming a new opening, a structural engineer's specification for the lintel or beam is required — budget £300–£600 for the structural engineer's fee if needed.
All glass in a roof lantern must be toughened (thermally toughened to BS EN 12150) or laminated (to BS EN ISO 12543). Standard 4mm toughened safety glass in a double-glazed unit satisfies this requirement. Polycarbonate is not acceptable as a roof lantern glazing material under Part N. Make sure this is explicit with any supplier quoting a non-glass option.
Building regulations compliance for a roof lantern is typically handled through a Building Notice or full plans application to the local authority building control, or via an Approved Inspector. The inspection is usually a single visit to sign off the installation. Most builders include the BCO fee (£150–£350 typically) in the overall package price — it simplifies the customer experience and avoids a situation where the certificate is outstanding.
The Quoting Process
A site survey is essential before quoting any roof lantern job. The variables that change your price — opening size, roof finish, structural condition, ceiling height, access — cannot be reliably assessed from a photo or a phone call. A brief paid survey (or included in a quoted survey visit) also qualifies the customer and filters out tyre-kickers.
Key questions to answer at survey:
- Is the opening already formed, or does a new opening need to be cut?
- What is the flat roof finish, and what is its condition?
- Is a kerb/upstand already in place, or does one need to be formed?
- What is the ceiling height in the room below — does internal soffit depth matter to the customer?
- Are there services (pipes, cables, joists) above the proposed opening?
- What access is available for delivery and working — is scaffolding or a MEWP needed?
- What is the customer's preferred size — does it fall within standard sizes or will it be bespoke?
Manufacturing lead time for standard-sized aluminium lanterns is typically 3–6 weeks from order. Custom sizes, non-standard colours, or bespoke timber units can be 8–12 weeks. Make lead time explicit in your quote and agree a programme that accounts for it — customers consistently underestimate how long a custom unit takes.
Upsells Worth Including in Every Quote
A roof lantern installation is a natural anchor for related upsells that are genuinely useful to the customer and add meaningful margin to the job.
Bi-fold or patio doors alongside a roof lantern is the most lucrative combination — a customer spending £5,000–£8,000 on a premium aluminium lantern is typically in the process of creating a kitchen-diner or garden room that opens onto the garden. Positioning the door and lantern as a package — same aluminium spec, same colour, same manufacturer's warranty — gives you a stronger commercial proposition than treating them as separate line items.
Roof blinds are particularly easy to sell at the survey stage: ask whether the room gets warm in summer and offer solar control glass or blinds as the solution. Customers who can see the problem in front of them (a south-facing room that already gets hot) are far more receptive than those who need to be convinced of a hypothetical future problem.
LED strip lighting recessed into the kerb or internal reveal is a relatively low-cost addition that delivers a high perceived value — the before-and-after effect in an evening photograph is striking. It's also a straightforward first-fix electrical item that most builders can price and install without a specialist subcontractor if they have a Part P-registered electrician on the team.
Tracking Which Leads Turn Into Paid Jobs
Roof lantern and glazing enquiries come from multiple sources — Google searches, Checkatrade, Instagram photos of finished rooms, architect referrals, and word of mouth from previous extension customers. The problem most builders have is that they have no reliable way of knowing which source is producing the jobs that actually complete and pay, versus the enquiries that price-shop and go elsewhere.
Without that data, your marketing budget defaults to gut feel — you keep paying for the channel that feels busiest rather than the one that delivers margin. Trade2Base tracks every lead from first contact through to job completion and invoice, so you can see your actual cost per completed job by source. For glazing and lantern work specifically, that often means cutting spend on low-quality directories and reallocating to the channels that are sending customers who are ready to buy.
Track your best roof lantern leads
Trade2Base tracks which marketing brings in paid roof lantern and glazing jobs — so you know where to focus your advertising spend.
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