Velux Loft Conversion: Costs, Suitability, and What to Expect

What a Velux Loft Conversion Actually Involves

A Velux loft conversion fits windows flush into your existing roof slope without changing the roof structure, pitch, or roofline. The name is just shorthand — Velux is a window brand — but a roof light conversion can use windows from any manufacturer. What defines it is what stays the same: the shape of your roof never alters.

This is exactly why both cost and planning stay so simple. Nearly all the work happens inside the loft. First, a structural engineer specifies new or reinforced floor joists so the loft floor is safe to live on. Next, we install insulation between and below the rafters to meet building regulations.

The roof windows are then cut into the existing felt and tiles and sealed with factory-made flashings. After that, we fit a new staircase to the floor below, run the electrics, and plaster and finish the space. From the outside, the only visible change is the windows themselves — and that is precisely why planning permission is rarely needed.

Costs: What You Should Expect to Pay

A Velux loft conversion typically costs £15,000–£28,000 in London. That makes it the cheapest type by a wide margin. The table below breaks the figure down for a standard two-bedroom terraced or semi-detached house.

These prices reflect London rates in 2026. Outside the capital, costs are generally 10–20% lower. For a full breakdown of every conversion type, see our London loft conversion costs guide.

The Advantages of a Velux Conversion

For a suitable loft, a Velux conversion is one of the cheapest and quickest ways to add real living space. Crucially, it sidesteps the cost, delay, and uncertainty of a planning application. Here is what you gain:

• Most affordable conversion type. At £15,000–£28,000, it costs roughly half the price of a rear dormer and a third of a full mansard.
• Fastest build programme. The typical site duration is 4–6 weeks — significantly shorter than the 6–10 weeks for a dormer, or 10–14 weeks for a mansard. Disruption to the household is minimal.
• No planning permission needed in most cases. Because the roofline is unchanged, most Velux conversions sit comfortably within Permitted Development rights. There are exceptions — listed buildings, conservation areas with Article 4 directions, and flats — but for the vast majority of London houses, no application is required.
• Roof stays watertight. Because the structure is not opened up as it would be for a dormer, the existing weatherproofing is maintained throughout most of the build. There is no period where your roof is exposed to the elements.
• Building regulations only. While building regulations approval is always required (for any loft conversion), the absence of a planning application removes one layer of process, cost, and waiting time.

The Limitations You Need to Know

A Velux conversion is not right for every loft. Because the roof structure stays exactly as it is, you are limited to the space already inside the void. In practice, that means three real constraints:

• Headroom is fixed. The available height at the ridge is what you have — you cannot gain more without altering the roof. If headroom is marginal, a Velux conversion may produce a room that feels awkward to use. See our guide to loft conversion ceiling height requirements for how to assess your own roof.
• Floor area is limited. You gain only the floor area that already exists within the roof void. A dormer conversion, by extending outward from the slope, can meaningfully increase the usable floor area.
• Pitched walls reduce usable space. Rooms with sloping ceilings on both sides are narrower at standing height than the total floor footprint suggests. Furniture placement and practical usability are constrained by the geometry of the roof.

Is Your Loft Suitable? The Headroom Test

The single biggest factor is headroom. A Velux conversion needs at least 2.2m from the finished floor to the highest point at the ridge. Below that, the room feels cramped and impractical — especially away from the central ridge, where the sloping ceiling drops sharply.

To check your own loft, take a tape measure up through the hatch and measure straight up from the existing floor to the underside of the ridge beam. Remember that the finished floor sits slightly higher than the existing one, because of new joists and floorboards. As a result, you should subtract roughly 150–200mm from your raw figure.

Roof pitch matters too. A steeper pitch above 35° gives a more usable room, because the ridge sits higher and the slopes encroach less on standing-height space. By contrast, a shallow pitch below 25° can leave a decent ridge height but very little usable width where you actually stand.

If your numbers are marginal — say 2.0–2.2m at the ridge — speak to a structural engineer or loft specialist before you commit. In some cases, lowering the floor by reducing the depth of the floor structure recovers the 100–150mm needed to make the room work.

Velux vs Dormer: Choosing the Right Type

The choice between a Velux and a dormer comes down to headroom. If your loft already measures 2.2m or more at the ridge and the room suits your needs, a Velux conversion is the better value — lower cost, shorter build, and no planning application.

However, if headroom falls below 2.2m, or you want more floor space and a conventional room shape with vertical walls, a rear dormer conversion usually wins. A dormer pushes the roof outward to form a vertical wall section. As a result, it adds both headroom and usable floor area beyond the existing void. The trade-off is a higher cost, typically £28,000–£45,000 for a rear dormer in London, and a longer build.

For hipped-roof homes, a hip-to-gable conversion is often paired with a rear dormer to unlock the most space. That said, it is a bigger structural job and usually does need planning permission.

So if cost is your main driver and your headroom passes the 2.2m test, start with a Velux conversion. You can always add a dormer later if your needs change. Even so, combining both in one project is generally cheaper than doing them separately.

Planning and Building Regulations

A Velux conversion almost always qualifies as Permitted Development, so no planning application is needed. The reason is simple: the roofline never changes. There is no projection from the roof slope, no increase in ridge height, and no change to the front elevation. The few things that would force a planning application — a conservation area, a listed building, or a flat — are uncommon for this type of work.

Building regulations approval, however, is always required. Inspectors visit at key stages to check the structural floor, insulation, staircase, fire escape windows, fire doors on the floors below, and the electrics. We submit the building regulations application and manage every inspection for you. On sign-off you receive a Completion Certificate — an important document when you sell or remortgage. For a full walkthrough of what inspectors check, see our building regulations guide.

Which Rooms Work Best in a Velux Conversion?

A Velux loft works best as a home office, child's bedroom, hobby room, or guest bedroom — rooms where most of life happens at or below seated height. The shape of the space drives this: sloping ceilings, a high central ridge, and lower zones at the eaves. As a result, some uses fit far better than others.

• Home office. A desk is placed near the ridge where full standing height is available; the lower zones under the slope house shelving and storage. Roof lights also deliver excellent natural light for daytime working.
• Children's bedroom. Children are typically shorter, and play areas often take place at floor level — the lower eave zones become cosy dens rather than wasted space.
• Hobby room or studio. Painting, crafting, reading — activities centred on a work surface rather than full-height movement suit the loft geometry well.
• Guest bedroom. Occasional use means the spatial constraints are less of a day-to-day issue than in a primary bedroom.

A Velux conversion is less suited to a primary master bedroom, where you expect to move freely across the full floor. If that is your goal, a dormer or mansard conversion will serve you better.