Velux Loft Conversion Cost 2026: Prices, Windows + Is It Enough Space?
A Velux loft conversion costs £25,000–£40,000 in the UK in 2026, making it the cheapest loft conversion type by a clear margin. The roof keeps its shape, so the budget goes on floor steels, insulation, a staircase and roof windows rather than structural alterations — and the whole job stays inside permitted development, with no planning application.
The trade is space: a Velux conversion adds light and floor strength but no headroom, so it only works where the existing ridge already stands 2.3m+ above the joists. This page — part of our loft conversion cost guide — sets out the price bands by floor area, what VELUX windows themselves cost, the planning and building-regulations position, and how to tell when a Velux conversion is not enough and a dormer is the answer.
What is a Velux loft conversion?
A Velux loft conversion turns the existing roofspace into a habitable room without altering the roof shape: new floor steels and joists, insulation between and under the rafters, a compliant staircase, and roof windows set flush into the existing slopes. VELUX is the dominant roof-window brand, and the type is also called a rooflight or skylight conversion; Fakro and Keylite units do the same job.
Because nothing projects from the roof, the conversion is invisible from the street and planning-free, and the build is the fastest of any loft type at 4–8 weeks on site. What it cannot do is create headroom: the usable floor is the strip where the sloping ceilings stand above 1.5m, which is why the existing ridge height decides everything.
How much does it cost to convert a Velux loft in the UK?
A Velux loft conversion costs £25,000–£40,000 in the UK in 2026, per Checkatrade and MyJobQuote's 2026 guides, with floor area setting the band and the number of rooflights and any en-suite moving the price within it. London adds 15–20%, so £30,000–£48,000.
| Floor area | UK cost (2026) | London cost (+15–20%) | What you get |
|---|---|---|---|
| 15–20m² | £25,000 – £30,000 | £30,000 – £36,000 | Single room or home office; 2 rooflights; basic spec |
| 20–30m² | £30,000 – £35,000 | £36,000 – £42,000 | Double bedroom; 3–4 rooflights; mid-range spec |
| 30–40m² | £35,000 – £40,000 | £42,000 – £48,000 | Large bedroom or two rooms; 5+ rooflights; room for an en-suite (+£4,000–£8,000) |
Post-1965 trussed-rafter roofs add £5,000–£10,000 of steel to any band, because the W-shaped trusses filling the loft are removed and the load carried on new beams. A structural engineer's calculations run £400–£1,200 and building control £500–£1,000, both excluded from most headline quotes.
How much do VELUX windows cost?
VELUX centre-pivot roof windows cost £400–£900 per unit supplied and £1,200–£2,000 per unit installed in 2026, per MyJobQuote and Checkatrade, depending on size, glazing spec and access. The windows are a small share of the conversion total — five units at the installed rate add £6,000–£10,000 to a £30,000 build — but the per-unit price moves sharply with spec.
| Window | Supplied (2026) | Installed (2026) | Notes |
|---|---|---|---|
| Centre-pivot, standard (MK04-ish) | £400 – £600 | £1,200 – £1,500 | The default bedroom window; pine or white-painted finish |
| Centre-pivot, large / triple-glazed | £600 – £900 | £1,500 – £2,000 | Better U-values for Part L; larger structural opening between rafters |
| Top-hung (escape-spec) | £500 – £800 | £1,400 – £1,900 | Opens fully for the Part B escape-window requirement |
| Cabrio / balcony unit | £2,500 – £4,000 | £3,500 – £5,500 | Folds out to a small balcony; check permitted development projection rules |
Velux Loft Conversion Cost Calculator
The calculator applies the floor-area bands from the cost table above, adjusts for rooflight count and region, and adds £4,000–£8,000 if you include an en-suite. Results round to the nearest £500 and exclude the items listed under the result.
Floor area, windows and region for a 2026 range.
Do you need planning permission for a Velux window in your loft?
No. Rooflights are permitted development under Class C of the Planning Portal's householder rules provided each window projects no more than 150mm beyond the plane of the roof slope and nothing sits higher than the existing ridge. Side-facing windows must be obscure-glazed and non-opening below 1.7m. No volume allowance is consumed, because Class C alterations are not roof enlargements — the 40m³/50m³ caps that govern dormers do not apply to windows.
The exceptions: listed buildings need listed building consent, flats and maisonettes have no permitted development rights, and Article 4 streets can remove them. A Lawful Development Certificate is not needed for rooflights alone, but Home Renovation Guides recommends keeping the installer's FENSA-style certificate and the building control completion certificate together for the sale file.
Which building regulations apply to a Velux conversion?
Building regulations approval is mandatory for every loft conversion, Velux included — permitted development only waives planning, never the regs. Four parts do the work:
| Regulation | What it requires in a Velux conversion |
|---|---|
| Part A — Structure | Floor steels and new joists sized by an engineer (£400–£1,200 of calculations); the old ceiling joists cannot carry a room |
| Part B — Fire safety | Protected staircase enclosure, interlinked alarms on every floor, and an escape window in the new room — a top-hung rooflight at the right size and sill height satisfies it |
| Part L — Insulation | Roof U-value 0.16; in a rooflight conversion that means insulation between and under the rafters, which eats 100–150mm of headroom |
| Part K — Staircase | Max 42° pitch and 2m headroom at the centre of the tread; the stair usually stacks over the existing one |
The Part L line is the hidden cost of the Velux route: the insulation that makes the room legal takes the headroom the design depends on. On a 2.3m ridge, floor build-up above and insulation below leave 2.0–2.1m of finished ceiling — usable, but tight. That arithmetic is why 2.3m, not the 2.2m dormer minimum, is the Velux gate.
How much head height does a Velux conversion need?
A Velux conversion needs 2.3m or more from the top of the ceiling joists to the underside of the ridge, measured before any work. The new floor build-up (joists, deck, underlay) takes 150–200mm and the Part L insulation and plasterboard take 100–150mm off the slope below, so a 2.3m ridge finishes at 2.0–2.1m of headroom across the usable strip.
Between 2.2m and 2.3m, a rear dormer at £30,000–£65,000 is the fix: it adds a full-height box where the room actually stands. Under 2.2m, the roof itself has to change — a mansard rebuilds the rear slope higher, and a hip to gable recovers the width a hip steals. On a hipped roof even a 2.4m ridge disappoints with rooflights alone, because the sloping hip cuts one side of the room to nothing. The test is cheap: a surveyor or loft company measures the ridge height in ten minutes, and it decides the whole design.
What is the cheapest way to convert a loft?
A Velux conversion at £25,000–£40,000 is the cheapest way to convert a loft, full stop — no roof alteration, no planning application, the shortest build. Every other type costs more because it changes the roof: a dormer £30,000–£65,000, a hip to gable £33,000–£70,000, a mansard £38,000–£90,000. Where the head height exists, the Velux conversion is also the best value per pound, because none of the budget goes on structure the room does not need.
Is £20,000 enough? Only just, and only as a Velux conversion outside London on a small loft at basic spec: £20,000 covers the floor, stair, insulation and two rooflights with nothing left for an en-suite, fees or contingency. In London the same project starts at £30,000. Any quote under £25,000 for a full conversion has excluded the staircase, the steels or building control — ask for the exclusion list in writing.
How long does a Velux loft conversion take?
A Velux loft conversion takes 4–8 weeks on site, the shortest of any loft type, and 2–4 months end to end including structural design and building control approval. Floor steels and joists go in during weeks 1–3, the staircase lands in weeks 3–5, and insulation, first fix, plasterboard and second fix follow in weeks 4–8. Most of the work enters through the roof or the stairwell, so the house stays liveable throughout — the reason Velux conversions are the standard choice for a fast home office or spare room.
What is the average cost of converting a loft in 2026?
The average UK loft conversion in 2026 costs around £45,000 — the figure for the mid-spec dormer that makes up most of the market. By type, 2026 bands from Checkatrade and MyJobQuote run: Velux £25,000–£40,000, dormer £30,000–£65,000, hip to gable £33,000–£70,000, mansard £38,000–£90,000 and L-shaped dormer £55,000–£100,000+, with London 15–20% above each. The Velux band sits at the bottom because it buys the least alteration, and the value uplift for a bedroom plus en-suite — around 20% of property value per Nationwide — applies to it exactly as it does to a dormer where the finished room is genuinely full height.
Related loft conversion guides
- Dormer loft conversion cost — the £30,000–£65,000 upgrade where head height falls short
- Terraced house loft conversion — why terraces suit Velux conversions on the rear slope
- Bungalow loft conversion cost — big footprints where rooflights often suffice
- Detached house loft conversion — the 50m³ allowance and zero party walls
- Cottage loft conversion — low ridges, listed buildings and the head-height gate
- 1930s house loft conversion — steep pitches with the head height Velux needs
Frequently asked questions
How much does it cost to convert a Velux loft in the UK?
£25,000–£40,000 in 2026: 15–20m² £25k–£30k, 20–30m² £30k–£35k, 30–40m² £35k–£40k. En-suite +£4k–£8k; London +15–20%.
Do you need planning permission for a Velux window in your loft?
No — permitted development under Class C when windows project under 150mm and stay below the ridge. Listed buildings and flats need consent; building regs always apply.
What is the cheapest way to convert a loft?
A Velux conversion at £25,000–£40,000 — but only where 2.3m+ head height already exists. Below that, the cheapest usable option is a rear dormer.
What is the average cost of converting a loft in 2026?
Around £45,000 — the mid-spec dormer average. Velux £25k–£40k, dormer £30k–£65k, hip-to-gable £33k–£70k, mansard £38k–£90k. London +15–20%.
Can you do a loft conversion for 20k?
Only just: a basic Velux conversion outside London on a small loft, with nothing left for an en-suite or fees. Every other type starts at £30,000+.
Which lofts cannot be converted?
For Velux: under 2.3m joist-to-ridge, no staircase landing space, or a flat without freeholder consent. Low head height is fixable with a dormer or mansard.
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