Roof windows and skylights: costs, types and rules (2026 UK)
Adding daylight overhead is one of the highest-impact, lowest-disruption improvements you can make to a loft, landing or extension. But roof window, skylight, rooflight, lantern and sun tunnel are used loosely by suppliers and they are not the same product, the same job or the same price. This guide sets out what each one actually is, what it costs fitted in 2026, and when you can proceed under permitted development.
- Standard roof window fitted: £1,200–£2,200
- Sun tunnel fitted: £600–£1,100
- Most roof windows need no planning permission — within the 150mm rule
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Roof window, skylight or rooflight: what is the difference?
The trade uses these words interchangeably, which makes comparing quotes harder than it should be. It helps to think in terms of what the unit does rather than what it is called.
- Roof window (in-plane): an opening unit installed within the slope of a pitched roof, sitting flush with the tiles or slates and sealed with a purpose-made flashing kit. This is the Velux-style product most people picture. It opens, so it gives light and ventilation, and it can be specified to meet escape requirements.
- Rooflight / skylight: most often used for fixed or flat-roof glazing — a flat glass pane on an upstand, a pyramid, or a walk-on unit. Many do not open at all.
- Roof lantern: a raised, multi-pane glazed structure on a flat roof, typical over a kitchen extension. It is as much an architectural feature as a window.
- Sun tunnel: a small rigid or flexible reflective tube that carries daylight from the roof surface down through a void into a room below. Light only, no view, no ventilation.
Roof windows versus dormers
This is the decision that matters most in a loft, and the cost gap is enormous. An in-plane roof window is a one-day or two-day job that cuts through the existing roof structure. A dormer is a structural extension: it projects out from the roof slope, adds a flat or pitched roof of its own, and creates genuine standing headroom and floor area.
If you need usable floor space and full-height headroom — typically to make a loft bedroom work, or to fit a staircase landing — a dormer is the answer and there is no cheap substitute. If you need daylight, ventilation and a view in a space that already has adequate headroom, roof windows do the job for a fraction of the price. Many loft conversions use both: a dormer at the rear for space, roof windows at the front for light and symmetry.
A useful rule of thumb
Two good roof windows will usually cost less than a tenth of a dormer. If the only problem with your loft is that it is dark, do not let anyone sell you a dormer.
What roof windows and skylights cost in 2026
The figures below are typical UK installed prices including labour, flashing, internal finishing and making good. They exclude scaffolding, which is usually a separate line.
| Type | Typical 2026 installed cost | Notes |
|---|---|---|
| Centre-pivot roof window (standard size) | £1,200 – £2,200 | The default choice; good value per unit of light |
| Top-hung / large roof window | £1,800 – £3,000 | Better view, opens wider, heavier to handle |
| Electric or solar-powered upgrade | +£350 – £700 | Worth it for out-of-reach windows; rain sensor included |
| Sun tunnel | £600 – £1,100 | Rigid tubes outperform flexible over longer runs |
| Flat rooflight (fixed, on upstand) | £1,200 – £2,600 | Price rises steeply with pane size |
| Roof lantern (approx. 1.5m x 1.0m) | £1,800 – £3,500 | Kitchen extension favourite; check upstand detail |
| Walk-on rooflight | £2,500 – £5,000+ | Structural glass; specialist install |
| Scaffolding (if required) | £600 – £1,200 | Often shared across several windows |
Fitting several windows at once is markedly cheaper per unit — the scaffold, the set-up and the travel are all shared. If you think you will want a second window within a couple of years, it is nearly always cheaper to do both now.
Permitted development: when you do not need planning permission
For most houses in England, adding a roof window is permitted development and does not require a planning application, provided it meets the conditions:
- It projects no more than 150mm beyond the plane of the existing roof slope
- No part sits higher than the highest part of the existing roof
- Any window in a side-facing roof slope is obscure-glazed and non-opening below 1.7m from the floor of the room
Those conditions are why standard in-plane roof windows are so popular: they are designed to sit within the 150mm limit. Dormers are a different matter and are subject to volume allowances and other restrictions.
When permitted development does not apply
Permitted development rights do not extend to flats and maisonettes, and they are restricted or removed for listed buildings, conservation areas, National Parks, AONBs and properties covered by an Article 4 direction. Some newer estates also have rights removed by planning condition. A quick call to your local planning authority is free and settles it.
The Building Regulations that apply
Planning and Building Regulations are separate things — you can be exempt from one and still need the other. A roof window installation will normally engage:
- Structure: cutting a rafter to form the opening means trimming with new timbers to carry the load. For anything wider than a single rafter bay, this needs to be designed properly, not improvised.
- Thermal performance: new and replacement windows must meet current minimum U-value standards, and the insulation and vapour control layer around the opening must be made good.
- Means of escape: habitable loft rooms often need an escape window. The usual specification is a clear openable area of at least 0.33 square metres, with a minimum opening height and width of 450mm, and the bottom of the opening around 800mm to 1,100mm above floor level.
- Safety glazing and ventilation: glazing in critical locations must be safety glass, and the room still needs to meet ventilation requirements.
Your installer should confirm whether the work is being self-certified under a competent person scheme or notified to building control. Get that answer in writing before work starts — it matters when you come to sell.
Getting the installation right
- Use the matched flashing kit for your roof covering. The overwhelming majority of leaking roof windows are flashing failures, not window failures.
- Splay the internal reveal — vertical at the head, angled at the sill. It spreads light far better and helps prevent condensation.
- Think about orientation. South-facing glazing can overheat badly. Specify solar control glass or external blinds rather than fitting internal blinds afterwards and hoping.
- Check reachability before choosing a manual unit. A pole-operated window you never bother to open is wasted money.
For a wider view of roof costs and materials, see our costs guides, or browse more roofing insights.
FAQs: roof windows and skylights (UK, 2026)
How much does it cost to fit a roof window in 2026?
Expect roughly £1,200–£2,200 fitted for a standard centre-pivot roof window in an existing pitched roof, including the flashing kit, internal finishing and making good. Larger top-hung units run to about £3,000, and electric or solar-powered models add £350–£700.
Do I need planning permission for a roof window?
Usually no. On most houses in England a roof window is permitted development provided it projects no more than 150mm beyond the plane of the roof slope and sits no higher than the highest part of the roof. Side-facing windows must be obscure-glazed and non-opening below 1.7m from the floor. Flats, maisonettes, listed buildings and designated land are treated differently, so always check with your local planning authority.
What is the difference between a roof window and a skylight?
In practice the terms overlap, but a roof window is an opening unit installed in the plane of a pitched roof and is usually reachable and openable. Skylight and rooflight tend to describe fixed or flat-roof glazing such as lanterns and flat panes, which may not open at all.
Is a sun tunnel worth it?
A sun tunnel is a good option where a full window is not practical, such as a windowless bathroom, hallway or landing under a loft void. Installed cost is typically £600–£1,100. It delivers daylight but no ventilation and no view, so treat it as a supplement to a roof window rather than a replacement.
Do roof windows count as fire escape windows?
Only if they meet the escape specification. An escape roof window generally needs a clear openable area of at least 0.33m² with a minimum height and width of 450mm, and the bottom of the opening should sit roughly 800mm–1,100mm above floor level. Standard roof windows are not always compliant, so specify an escape model where one is required.
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