Velux loft conversions: the cheapest way into your roof

A velux loft conversion sets roof windows into the existing slope and turns the loft into a room without changing the shape of the roof. At £30,000 to £48,000 including VAT in 2026, it is the cheapest way to convert a loft, but it only works where the loft already has the height. We cover the height test, the full budget, the planning and building regulations rules in each UK nation, and the build time.

What a velux loft conversion is

A velux loft conversion, also called a rooflight or roof window conversion, turns the loft into a room using windows set into the existing roof slope. Velux is the best-known roof window brand, so its name stuck to the whole type. The roof keeps its shape and its height, and the work happens inside it.

It is still structural work. A new floor structure goes in above the old ceiling, often on steel beams, each window opening is framed with new timbers, and a staircase is cut through the ceiling below. Unlike a dormer conversion, which builds a box out from the slope, it adds no volume, so the standing room is only as wide as the space under the ridge.

Can your loft take a velux conversion?

Height decides it. Measure from the top of a ceiling joist to the underside of the ridge: you need about 2.2 to 2.4 metres, because the new floor, insulation and plasterboard take 250 to 400 millimetres of it. Below that, no window adds height, and the routes left are a mansard or a piggyback that lifts the whole roof, from £66,000 including VAT.

The pitch matters as much as the ridge. Below about 30 degrees, the slope comes down so fast that little of the floor has headroom. The parts of the room under about 1.5 metres work as storage, not as floor you can use.

Houses built before about 1965 usually have a cut roof, assembled on site from individual timbers, which leaves an open space to work in. Almost every house from the mid-1970s on has trussed rafters, braced by W-shaped webs that cannot simply be cut out. Converting one means new steel at wall plate level and a new floor hung from it, which adds £5,000 to £15,000.

Velux loft conversion cost

A velux conversion costs £30,000 to £48,000 including VAT at 20% in 2026, the lowest of the loft conversion prices by type, because the roof is not rebuilt. No official body publishes these prices, so they are market rates rather than a measured average.

Those prices cover the conversion and the fit-out of the room. These lines usually come on top:

• VAT at 20%, unless the quote says it is included. A loft in a lived-in home gets no reduced rate.
• The staircase: £3,000 to £10,000, depending on where it lands and how much of the room below it takes.
• Steelwork and the new floor structure: £2,000 to £5,000 on a cut roof, and considerably more on trussed rafters.
• Electrics for the new room: £1,500 to £3,000 for the first fix and sockets.
• Contingency: 10 to 15% of the build, for what the roof reveals once it is opened.

Roof window prices

The windows are a small share of the bill. Velux lists its basic centre-pivot roof window from £305 before VAT, and budgets an average of £100 on top for flashing plus installation. A roof balcony window, which opens out to form a small balcony, starts at £2,559 before VAT.

Six of the basic model come to £1,830 before VAT. On a £30,000 to £48,000 job, the gap between two quotes for the same loft is rarely the glass. It is the floor, the stair and the labour.

Velux loft conversion cost in London

A velux conversion in London costs £35,000 to £56,000 including VAT, because building prices in inner London run about 17% above the UK average. Per square metre, a London loft with rooflights only starts at about £1,900 before VAT and fees.

Do you need planning permission for a velux loft conversion?

In England, usually not. Roof windows fall under the permitted development limits for rooflights, which set three conditions:

• No part stands more than 150 millimetres proud of the roof slope.
• No part is higher than the highest part of the original roof.
• Windows in a side roof slope are obscure-glazed, with any opening part more than 1.7 metres above the floor.

A velux conversion adds no volume, so it uses none of the 40 cubic metre allowance on a terrace or the 50 on other houses that a dormer draws on. The rooflight limits say nothing about which slope, so windows on the front of the house are allowed within them.

Flats have no permitted development rights for the roof, and an Article 4 direction or a condition on a newer estate's planning permission can remove them from a house. A listed building needs planning permission and listed building consent for a loft conversion.

Conservation areas are where a velux conversion earns its place. In England, a dormer loses its permitted development route in a conservation area, but the rooflight limits still apply there, so a velux conversion is the one loft type that can go ahead without an application, unless an Article 4 direction has taken the right away.

Anything outside the limits, such as a window standing more than 150 millimetres proud of the slope, needs planning permission for the loft conversion. The householder fee in England is £548, with a decision due about 8 weeks from validation. Where the plan fits the limits, a £274 Lawful Development Certificate confirms it before you build.

Velux conversion rules in Wales, Scotland and Northern Ireland

The limits above are England's. Each of the other nations writes its own roof rules, and the differences matter most in protected areas.

Wales's rules for roof alterations match England on the 150 millimetres and the ridge height, but rule out roof lights under permitted development in conservation areas, national parks, areas of outstanding natural beauty and World Heritage Sites. A roof light that creates a roof terrace needs permission, and side windows within 10.5 metres of a side boundary are obscure-glazed and fixed. Welsh building regulations guidance for roof lights asks for the same trimmers, insulation and ventilation checks as England's.

Scotland's permitted development for alterations that add no volume, which covers rooflights, allows a projection of up to 1 metre but nothing in a conservation area, according to the Scottish Government's householder circular. The conversion is checked against Scottish building standards, and a building warrant from the council may be needed before work starts.

Northern Ireland's 2015 order puts any addition or alteration to a roof in one class, with no volume limit. Nothing may rise above the ridge, and none of it applies in a conservation area or, without listed building consent, within the grounds of a listed building. Northern Ireland also runs its own building control, and the Party Wall etc. Act 1996 does not apply there or in Scotland.

Building regulations for a velux loft conversion

Every loft conversion needs building regulations approval, including one built under permitted development. A full plans application to the council or a registered building control approver gets a decision within 5 weeks, or 2 months if you agree. Building control checks the structure (Part A), fire safety and escape (Part B), the stair (Part K) and insulation (Part L).

The windows bring their own checks. The building regulations guidance for rooflights expects the cut rafters to be carried by trimmers, two timbers joined across the opening, with the rafters either side strengthened where needed. Each window has to meet the U-value limits in Approved Document L, one close to a boundary needs its fire performance checked, and both the room and the remaining roof void need ventilation.

On a two-storey house, the loft becomes a third storey, and escaping from a window that high is too dangerous. So the stairway is protected instead, with fire-resisting doors and sometimes new partitions, and mains-powered interlinked smoke alarms go in the stairway at each level.

Building control issues a completion certificate, usually within 8 weeks of finishing. A buyer's solicitor will ask for it when you sell.

The stair and its headroom

A velux loft needs a permanent stair, and a retractable ladder is not normally acceptable. The stair regulations ask for 2 metres of headroom, relaxed for a loft conversion to 1.9 metres at the centre of the stair and 1.8 metres at the side. Under a sloping roof, that usually means the top of the stair has to arrive under the ridge.

Where a full stair will not fit, an alternating tread stair is allowed for a loft conversion that serves one habitable room, plus a bathroom or WC, as long as it is not the home's only WC.

Roof windows: how many and where

Velux's own daylight guidance is glazing of at least 20% of the room's floor area. It is a maker's recommendation rather than a rule, and a quick check on any drawing.

A centre-pivot window turns on a hinge across its middle, and a top-hung window swings out from a hinge at its head. Placement follows the headroom: a window you walk up to belongs where the ceiling is high enough to stand, and one over a bed or a desk can sit lower on the slope.

Adding an en suite

An en suite adds £5,000 to £12,000, and more where the soil stack has to be extended up to the loft. Put the shower and the basin under the ridge, where you stand, and a bath under the lower slope, where you sit or lie. The drain run to the stack fixes where the bathroom can go, so place it before the windows.

How long a velux loft conversion takes

A velux conversion takes 4 to 6 weeks on site, the shortest of the loft types, after 2 to 3 months of drawings, calculations and approvals. The windows themselves go in quickly: Velux puts a single roof window installation at as little as four hours.

On a terrace or semi in England and Wales, a new floor beam cut into the shared wall means a party wall notice at least 2 months before work, and the neighbour has 14 days to reply. Written consent costs nothing, and a dispute means a surveyor's award at £1,200 to £3,000.

In a wider renovation, book the loft early. Structural work and roofing come before services, insulation and finishes, and the new stair cuts through the landing below.

Velux, dormer or mansard: which to choose

Against the other types of loft conversion, a velux conversion gives up floor space at full height in return for a lower price, a shorter build and, in England, no planning application.

The deciding question is whether one room along the ridge is enough. If you need the full floor at standing height, such as a double bedroom with an en suite, a dormer earns its extra £12,000 to £24,000.

Is a velux conversion right for your house?

A velux conversion suits:

• Tall, steep lofts: 2.2 to 2.4 metres or more under the ridge and a pitch of about 30 degrees or steeper.
• Conservation areas in England: the rooflight limits still apply there, while a dormer needs an application.
• A study, playroom or guest room: a room used sitting or lying down makes the most of the low edges.
• A tighter budget: at £30,000 to £48,000 including VAT, it costs £12,000 to £24,000 less than a dormer.

It is the wrong choice when:

• The loft is under about 2.2 metres to the ridge, because no window adds height.
• The roof pitch is shallow, which leaves only a narrow strip of standing room.
• The home is a flat, which has no permitted development rights for the roof.
• The house is in a Welsh conservation area, where roof lights need an application.