Roof Lantern Installation and Replacement Cost Calculator

How this calculator works

This calculator estimates a realistic price range rather than a single figure, because real-world quotes genuinely vary that much. It starts from typical UK supplied-and-fitted price ranges drawn from published 2026 industry cost guides, then multiplies them by the number of units you enter and by adjustment factors for each choice you make below. The result is a low-to-high band that a fair quote is likely to fall within, not a promise of the exact price you will pay.

A roof lantern typically costs around to supplied and fitted in 2026, which makes it roughly three to six times the cost of covering the same roof area with flat skylights. Slim aluminium systems dominate the market, with double or triple glazed panels, U-values around 1.0 to 1.4 and ten year warranties as standard on the leading brands.

Number of roof lanterns

Enter how many roof lanterns you are pricing. Almost all projects involve a single lantern as the centrepiece of an extension roof, though very large extensions occasionally pair two.

Lantern size

Lantern pricing scales strongly with footprint, since a bigger lantern means more aluminium framework, more glass panels and a bigger structural opening. The most common installation in current guides is around the 3 x 2 metre size fitted as the central feature of a kitchen extension, typically at to , while a roughly 3 x 3 metre lantern lands around including installation.

Glazing

Double glazing with a U-value of roughly 1.0 to 1.4 is standard on quality lantern systems. Solar control glass adds around 15 percent and is strongly recommended on south-facing roofs, where an untreated lantern can overheat the room below in summer. Triple glazing improves thermal performance further but adds weight and cost, and is usually only specified on very low energy builds.

Specification level

Two windows that look similar from the street can sit at very different price points. Budget products use simpler profiles, standard hardware and basic glass. Mid-range covers the typical A-rated units most UK installers quote by default. Premium covers high-end systems with upgraded security hardware, better thermal performance, special finishes or designer profiles, and typically adds around 30 percent to the price.

Where you live

Labour rates are not uniform across the UK. Published cost guides consistently show installation prices in London and the South East running roughly 20 to 30 percent above the national average, driven by higher labour costs, travel, parking and congestion charges. The calculator applies an uplift of around 20 percent if you select London and the South East. Product prices themselves are broadly similar nationwide, so the difference mostly reflects fitting costs.

What else affects the price

A lantern is a structural feature as much as a window: the flat roof must be designed or checked to carry it, the kerb upstand must be built accurately, and the junction with the roof membrane is critical to keeping water out. Lantern prices rise with size, glazing specification and frame colour, and internal finishing around the opening adds plastering and decorating costs. The honest question in most projects is lantern versus skylights, since two or three well placed flat rooflights usually deliver more even light for much less money, so a lantern earns its cost as an architectural feature rather than purely as a light source.

Planning permission, building regulations and certification

Most roof glazing falls under permitted development rights, provided the units do not project more than 150 millimetres above the roof plane and sit no higher than the highest part of the roof, but conservation areas, listed buildings and flats have tighter rules, so check with your local planning authority before ordering. Building regulations apply regardless of planning status, covering structural alterations, thermal performance, safety glazing and, in loft conversions, escape and ventilation requirements. Installers registered with a competent person scheme can self-certify that replacement glazing complies with the regulations and issue a certificate you will need when selling the property; for structural roof work, building control involvement is normally required.