Skylight 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 fixed flat-roof skylight typically costs around to supplied and fitted in 2026, with small fixed units starting from roughly all-in in published guides and opening or electric versions running from to or more. In UK usage, a skylight or rooflight generally means a glazed panel in a flat roof, as distinct from a roof window fitted into a pitched slope.

Number of skylights

Enter how many skylights or flat rooflights you are pricing. Kitchen extensions commonly use one to three units, and spreading two or three smaller units across a room usually distributes light better than one large one.

Window size

Size is one of the biggest cost drivers for any glazed unit. A larger opening needs more frame material and a bigger, heavier sealed glass unit, and it usually takes longer to fit. The calculator uses three broad size bands based on common UK window dimensions: choosing the small band reduces the typical range by around 20 percent, while the large band increases it by around 40 percent. If your windows vary in size, run the calculator once per size band and add the results together.

Operation type

Fixed skylights are the most affordable and most common choice for flat roofs. Opening versions add ventilation, which is valuable over kitchens, but the mechanism carries a real premium: manual opening adds roughly 30 percent and electric or solar operation, often with rain sensors, can add 60 percent or more. Bespoke walk-on or oversized units are priced individually and can run to several thousand pounds each.

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

The upstand and the waterproofing are as important as the glass with flat roof skylights: the unit sits on a kerb that must be built, insulated and integrated with the roof membrane, and poor detailing here is the main cause of leaks. If your flat roof covering is nearing the end of its life, combining the skylight with recovering the roof is often better value than two separate jobs. Structural openings in joisted roofs need trimming, and larger openings may need engineered support. Glazing choices matter for comfort, since a flat rooflight takes the full force of summer sun, so solar control glass is usually worth the extra on south-facing roofs.

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.