Velux Window Installation Cost UK (2026 Guide)
A Velux window (or equivalent branded roof window) transforms a dark loft or bedroom roof slope into a usable, light-filled space. Total installed cost for a standard unit runs from £900 to £2,500 per window depending on size, glass specification, roof material and whether internal finishing is included. Ignore any quote that gives you a window price without discussing flashing, structural checks and internal make-good — those costs are real and frequently omitted from initial estimates.
This guide covers the full cost picture, the structural question most competitors skip (trussed rafters), and the specific product options that change both performance and price.
Velux Window Installation Costs: Full Breakdown
A realistic installed price has four components. All four are required for a working, weatherproof installation.
| Cost component | Typical range | Notes |
|---|---|---|
| Window supply | £300 to £1,200 | Depends on size, type and glazing specification |
| Flashing kit | £80 to £180 | Must match your tile/slate profile exactly |
| Installation labour | £300 to £600 | One day for a standard unit, more for difficult access |
| Internal finishing | £150 to £400 | Plasterboard reveals, skimming, painting — frequently excluded from initial quotes |
| Scaffolding (if needed) | £400 to £1,200 | Required on most two-storey properties |
For a standard single centre-pivot window on a two-storey house: budget £1,200 to £1,800 all-in including internal finishing and scaffolding amortised across the project. Multiple windows on the same scaffold reduce the per-unit cost significantly.
Window Types and Their Costs
Velux produces several product families. The differences matter beyond aesthetics.
Centre pivot (GGL/GGU) — the standard roof window. Opens inward from a pivot point at the midpoint of the frame. Suitable for pitched roofs between 15 and 88 degrees. Supply cost: £300 to £700 depending on size. This is the most common installation by volume and what most quotes default to.
Top-hung (GHL/VFE) — the frame opens outward from a hinge at the top, creating more headroom clearance below when open. Requires a roof pitch between 15 and 55 degrees. Supply cost: £350 to £800. Better for rooms where the window is at low head height and you want to stand directly below it.
Balcony (GDL/GEL) — the lower section folds outward to create a small balcony. Dramatically increases light and creates a walkout. Requires 35-degree minimum pitch. Supply cost: £1,500 to £3,000. Installation takes one and a half to two days. Permit to determine full compliance is essential.
Sun tunnel (TWF/TWR) — a tubular daylight system that carries light down a reflective shaft rather than through a window opening. No structural modification required in most cases. Good for dark bathrooms and landings without roof slope access. Supply and install: £500 to £1,200. Not a substitute for a window where ventilation is needed.
Flat roof window (CFP/CVP) — for flat or low-pitch roofs (0 to 15 degrees). A kerb-mounted unit with specialist flashing. Supply and install: £1,000 to £3,000 depending on size.
The Trussed Rafter Problem: What Most Guides Skip
The single most important structural question before ordering any roof window: does your roof have trussed rafters or cut rafters?
Cut (traditional) rafters — each rafter is an individual structural member. Cutting one to create an opening for a window is a manageable job: a structural header is fitted above the opening and the load is redistributed to adjacent rafters. Standard practice, no specialist sign-off required for small openings.
Trussed rafters — the engineered triangulated trusses used in most UK houses built after about 1965. Each member of the truss plays a specific structural role. You cannot cut a truss member without a structural engineer calculating the required modification. Ignoring this is not a planning issue — it is a structural safety issue.
If your house was built after 1965, there is a high probability it has trussed rafters. Checking is simple: go into the loft. Traditional cut rafters look like individual diagonal beams. Trussed rafters are an engineered web of diagonal and vertical members forming triangles across the full roof width.
If you have trussed rafters and want a roof window:
- You need a structural engineer to specify the modification (typically £300 to £600 fee)
- A new structural header and hangers are fitted before any truss member is cut
- Building regulations approval is almost certainly required
- Budget an additional £500 to £1,200 over a standard installation for this work
Any installer who quotes a roof window for a post-1965 house without checking the roof structure first is cutting corners. This check should happen before any contract is signed.
Flashing: Where Roof Windows Leak
Incorrect or mismatched flashing is the primary cause of leaks around roof windows, not the window itself. Velux produces flashing kits specifically matched to each roof material — plain tiles, profiled concrete tiles, fibre cement slates, natural slates, flat roofs. Using the wrong kit, or a generic flashing, is a common installation shortcut that causes problems within a few years.
Standard flashing kits (EDN, BDX) cost £80 to £120 and suit most plain and plain-profiled tiles. Low pitch flashing (from 15 degrees) requires a specialist kit designed for shallow drainage angles. Conservation window flashing (used in conservation areas and on listed buildings where standard white frames are not approved) costs £150 to £250 and is designed to sit more flush with the roof surface.
Ask your installer which specific flashing kit is being used and confirm it is matched to your tile profile. Request the product code so you can verify it.
Glass Options and Their Impact on Cost and Performance
The glazing specification changes both the price and the performance significantly.
Standard double glazing — centre of glass U-value around 1.1 W/m2K. The default on most installer quotes. Fine for typical applications.
Triple glazing — U-value around 0.5 to 0.7 W/m2K. Reduces heat loss and condensation risk. Adds £80 to £200 per window. Worth considering for north-facing windows or bedrooms where condensation is a concern in winter.
Noise reduction glazing (Velux INTEGRA with acoustic laminate) — useful for properties near flight paths, roads or railways. Reduces exterior noise by an additional 5 to 8 dB compared to standard glazing. Adds £100 to £250 per window.
Privacy/diffuse glass — for bathrooms or windows visible from neighbours. Translucent without being clear. Adds £50 to £100.
Solar-controlled glass — reduces summer solar heat gain without significantly affecting winter light. Useful for south-facing windows in loft rooms that overheat. Standard on some Velux ranges, optional on others.
The operative vs decorative question also affects cost: manual-opening windows cost less than electric or solar-powered models (Velux INTEGRA). Electric models add £150 to £350 per window but can be operated remotely and include rain sensors that close the window automatically.
Planning Permission and Building Regulations
Planning permission is generally not required for roof windows on the back or sides of a house that: do not project more than 150mm from the existing roof plane, do not sit higher than the highest part of the roof, and are not on a roof slope facing a highway. Standard Velux windows meet these criteria on most installations.
Exceptions: listed buildings (almost always need Listed Building Consent), conservation areas (some have Article 4 Directions restricting roof alterations visible from public areas), and any property where permitted development rights have been removed by planning conditions.
Building regulations are required when cutting into rafters creates a structural opening. The approval covers the structural modification, any new floor loading, ventilation and fire safety requirements. If a structural engineer is involved (trussed rafter modification), building regulations approval is almost certain to be required. Your installer or structural engineer can advise.
A Lawful Development Certificate (LDC) can confirm no planning permission is needed. At £100 to £200 from the local planning authority, it is worth obtaining if you have any doubt, particularly before selling a property where the installation might be queried.
Frequently asked questions
How much does a Velux window cost to install in the UK?
Total installed cost for a standard centre-pivot Velux window runs from £900 to £2,500 per unit, including the window, flashing kit, installation labour and internal finishing. Scaffolding adds £400 to £1,200 if required. Multiple windows on the same scaffold reduce the per-unit cost. Balcony models and flat roof windows cost more: £2,000 to £4,500 installed.
Do I need planning permission for a Velux window?
Usually not. Velux windows on the rear or side slopes of a house are permitted development provided they do not project more than 150mm from the roof plane and do not exceed the highest part of the roof. Listed buildings and some conservation areas are exceptions and require consent. Front roof slopes facing a highway always require planning permission for new windows.
How long does Velux window installation take?
One day for a standard centre-pivot window on an accessible roof with cut rafters. Add half a day to a full day for scaffold erection and dismantling. Trussed rafter modifications, complex internal finishing or balcony models take two to three days. Multiple windows are more efficient — three windows rarely take three times as long as one.
What roof pitch is needed for a Velux window?
Centre-pivot windows (GGL/GGU) suit pitches from 15 to 88 degrees — virtually all pitched roofs. Top-hung models require 15 to 55 degrees. Balcony models need a minimum of 35 degrees. Below 15 degrees, you need a flat roof window (kerb-mounted). Your roofer can measure the pitch if you are unsure.
How long does a Velux window last?
Velux windows are typically guaranteed for 10 years, and well-maintained units last 20 to 30 years in practice. The most common issues after 15 to 20 years are seal failure (condensation between panes, indicating a failed unit) and hardware wear (closing mechanism, hinges). Replacement of the glazing unit or hardware is usually possible without replacing the entire window.