How to Price Velux and Roof Light Installation: Supply, Fit and Structural Upstands

Quick Answer: A standard Velux roof window installation in a UK pitched tile or slate roof costs £900–£1,800 supply-and-fit per unit in 2026, with the window itself £350–£900, flashings £100–£250, and labour £350–£600 for a 1–1.5 day install per unit. Flat-roof rooflights cost more (£1,800–£3,500) due to upstand and waterproofing complexity. Building Regulations Approved Document L applies to U-value (1.4 W/m²K target for replacements, 1.2 W/m²K for new openings) and Approved Document F for ventilation. New openings require structural calculations for cut rafters.

Summary

Roof windows have moved from "occasional luxury" to "standard expectation" on most UK loft conversions and many bathroom/kitchen refurbs. Velux is the dominant brand (50%+ market share) but Fakro, Roto and Keylite are credible alternatives at 10–25% lower price. The product range is wide: pivot, top-hung, electric, solar-powered, balcony rooflights, sun tunnels and dormer windows.

For a builder pricing a job, the variables are the roof type (existing pitched, existing flat, new opening), structural intervention required, and finish to internal lining. A like-for-like replacement (existing Velux, same size) is a 4–6 hour job for a competent fitter; a new opening cut into a tile roof, with new rafter cuts, structural lintels and internal box lining, is 1.5–2 days.

The compliance side is straightforward but consistently underquoted: U-value 1.4 W/m²K minimum for the window itself (replacement) or 1.2 W/m²K for new openings, BS 5288 ventilation provision when habitable rooms are converted, and Part B fire escape where the roof window is the means of escape from a habitable loft. Get the specification right at the quote stage — substituting a non-compliant window late in the job costs 2–3× the original price difference.

Key Facts

Quick Reference Table

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Window type Supply cost Fit cost Total typical Programme
Velux replacement (like for like) £350–£900 £200–£400 £550–£1,300 4–6 hours
New Velux into tile/slate (single) £350–£900 £400–£900 £900–£1,800 1–1.5 days
New Velux into flat roof £700–£1,400 £600–£1,000 £1,800–£3,500 1.5–2 days
Walk-on rooflight (flat roof) £1,200–£2,500 £800–£1,200 £2,500–£4,500 2 days
Sun tunnel £400–£800 £350–£550 £750–£1,400 1 day
Twin Velux combination £900–£1,800 £700–£1,200 £1,800–£3,500 1.5 days
Velux balcony / cabrio £2,500–£5,500 £1,200–£2,000 £4,000–£7,500 2–3 days

Detailed Guidance

Sizing: The Velux Code System

Velux uses a two-letter + two-number code that defines size:

Common UK sizes:

Fakro, Roto and Keylite use similar sizing with their own codes; flashings are sometimes interchangeable but always check.

Pitch and Roof Type

Velux windows have a stated pitch range — typically 15° to 90° for standard models. Outside that range, special flashings or alternatives are required:

Roof type also matters for the flashing:

New Opening: Structural Considerations

Cutting a new opening in a pitched roof affects rafters. The required process:

  1. Survey rafter spacing — typical 400 or 600 mm centres
  2. Window width — usually wider than rafter centre, requiring cut and trimmer
  3. Trimmer — a beam between adjacent uncut rafters to support the cut rafter ends
  4. Engineer's calculations — required for any opening over 1 m wide or where structural rafters cut

Typical new opening rafter detail:

For larger openings (wider than 2 rafter spaces), a steel beam or LVL beam is often needed. Engineer's calc £150–£350.

Flashing: The Critical Detail

Velux supplies flashing kits matched to roof type:

Flashings are essential — without them, the window will leak. Most Veluxes are sold with flashing as a separate £80–£250 line item. Quote always includes the matched flashing — never substitute.

Lead flashing is the alternative for heritage and bespoke work — see leadwork specifications.

Internal Lining

The internal box (lining around the window from rafters to plasterboard) is often missed in quotes. Required:

Cost £150–£350 per window in materials and labour. Customers expecting "just install the window" are surprised by the additional finishing cost.

Insulation Around the Window

Critical for U-value compliance. The detail:

Cold bridges around poorly insulated Veluxes cause condensation, which customers blame on the window. The fix is in the install detail.

Flat Roof Rooflights

Different game from Velux. Flat-roof rooflights have:

Installation cost is higher because of the upstand and the waterproofing detail. Typical flat-roof rooflight install is £1,800–£3,500 fully fitted.

See flat roof skylights and rooflights for the specialist flat-roof side.

Loft Conversion Means of Escape

Where a Velux is the means of escape from a converted habitable loft, Building Regulations Part B requires:

Velux MK06 size or larger is the typical compliant choice. If the only Velux is on the wrong side of the room (e.g. high cill), an additional escape window may be needed.

Triple Glazing and Acoustic

Triple-glazed Velux — U-value 1.0 W/m²K vs 1.4 standard. Adds £250–£500 per window. Worth it for:

Acoustic glazing (laminated outer pane) — reduces transmission by 5–8 dB(A). Worth it under flight paths and in cities.

Frequently Asked Questions

Can I install a Velux without planning permission?

In most cases yes — roof windows are permitted development on rear and side roof slopes. Front-facing roof slopes (the main public elevation) require planning unless they don't extend more than 150 mm beyond the roof plane. Conservation areas, listed buildings and Article 4 directions strip permitted development; check first.

Solar or electric — which to spec?

Solar-powered (Velux Integra Solar) — no wiring required, suitable for bathrooms and locations far from the consumer unit. Premium of £200–£400 over manual.

Electric mains-powered (Velux Integra) — needs wiring to a fused spur. Cheaper than solar where wiring is feasible.

Manual — cheapest, requires a long pole for ceiling-height openings. Customers retrofitting electric kits later usually find the wiring cost adds 50%+ of the original window cost.

How long does a Velux replacement take?

A like-for-like (same size, same flashing kit) replacement is 4–6 hours: scaffold up, old window out, new in, new flashings, internal lining touch-up, scaffold down. Typically a half-day on site plus scaffold setup time.

What about condensation on Veluxes?

Most condensation on Veluxes is due to:

  1. Bathroom or kitchen high humidity hitting cold glass
  2. Trickle vent closed
  3. Cold bridge in the install (poor insulation around window)

Triple glazing helps; trickle vent open helps; mechanical extract in wet rooms helps most. Always advise customers to leave trickle vents open in winter.

Is Velux always the right brand?

For known-quality, decade-of-use, easy availability of replacement parts and flashings, yes. Fakro and Keylite offer similar quality at 10–25% lower price; specifying these is a legitimate cost-saving move on tight budgets. Avoid unbranded or own-brand DIY-store roof windows — flashing failures and gasket degradation are common.

Regulations & Standards