How Much Does a Loft Conversion Cost in 2026? UK Pricing Guide

A loft conversion is one of the most popular home improvement projects in the UK, and for good reason. It adds valuable living space without reducing your garden, typically adds 15 to 20 percent to your property value, and in most cases does not require planning permission. But the costs vary enormously depending on the type of conversion, where you live, and the specification you choose.

This guide breaks down the real costs of every type of loft conversion in the UK in 2026, including materials, labour, professional fees, and the hidden costs that catch homeowners off guard. Whether you are a homeowner planning a project or a builder quoting for loft conversion work, these figures reflect current market rates across the UK.

Loft Conversion Cost Summary

Here is a quick overview of what each type of loft conversion costs in 2026. These prices include materials, labour, structural work, plastering, electrics, insulation, and a basic staircase. They do not include bathrooms, decoration, or fixtures and fittings.

Conversion Type	Typical Cost	Duration
Velux / Rooflight	£15,000 – £30,000	6 – 8 weeks
Rear Dormer	£35,000 – £55,000	8 – 10 weeks
Hip-to-Gable	£40,000 – £65,000	10 – 12 weeks
Mansard	£50,000 – £75,000	10 – 14 weeks
L-Shaped Dormer	£45,000 – £70,000	10 – 14 weeks

London and the South East are typically 15 to 25 percent more expensive than these national averages. Scotland and the North of England tend to be 10 to 15 percent below the national average.

Velux / Rooflight Conversion: £15,000 – £30,000

A Velux or rooflight conversion is the simplest and cheapest option because it does not alter the roof structure. Instead, it works within the existing roof shape and adds Velux windows (or similar roof windows) for light and ventilation. The existing floor is strengthened, insulation is upgraded, and a staircase is installed.

This type of conversion works best when the existing loft has sufficient head height — you need at least 2.2 metres from the top of the ceiling joists to the underside of the ridge. If the head height is borderline, a Velux conversion may not provide enough usable floor space to justify the expense.

Typical cost breakdown:

• Structural floor strengthening: £1,500 – £3,000
• Staircase: £2,000 – £4,000
• Velux windows (2 to 3): £1,500 – £3,500
• Insulation: £1,000 – £2,000
• Electrics (first and second fix): £1,500 – £2,500
• Plastering: £1,500 – £2,500
• Fire door and fire alarm: £500 – £1,000
• Labour: £5,000 – £10,000

Rear Dormer Conversion: £35,000 – £55,000

A rear dormer is the most common type of loft conversion in the UK. It extends from the rear roof slope to create a flat-roofed box structure, which dramatically increases the usable floor space and provides full standing head height across most of the new room. Rear dormers typically fall under permitted development, meaning no planning permission is required.

The dormer structure itself is usually built from a timber frame with a flat or slightly pitched GRP (fibreglass) or felt roof. The rear wall of the dormer is typically finished in hanging tiles, cladding, or render to match the existing property.

What affects the price:

• Width of the dormer (full-width dormers cost more but maximise space)
• Roof construction (new steel beams, ridge board modifications)
• Whether the existing roof structure is cut or purlin-based
• En-suite bathroom (adds £3,000 to £6,000)
• Access and scaffolding requirements

Hip-to-Gable Conversion: £40,000 – £65,000

A hip-to-gable conversion is typically carried out on semi-detached or detached properties that have a hipped roof (where the side of the roof slopes inward rather than ending at a flat gable wall). The hipped section is removed and replaced with a vertical gable wall, which extends the loft floor area significantly.

A hip-to-gable conversion is often combined with a rear dormer to maximise the usable space. This combination is particularly popular on 1930s semi-detached houses, which have hipped roofs as standard. The combined hip-to-gable plus rear dormer conversion typically costs £45,000 to £65,000.

Key cost factors:

• Steel beam installation to support the new gable wall: £2,000 – £4,000
• New gable wall construction (blockwork or timber frame): £3,000 – £5,000
• Scaffolding (typically more extensive due to side access): £1,500 – £3,000
• Party wall agreement (if semi-detached): £700 – £1,500 per neighbour

Mansard Conversion: £50,000 – £75,000

A mansard conversion is the most extensive type of loft conversion. It alters the entire roof structure, replacing the existing roof slope with an almost vertical wall (typically at a 72-degree angle) topped by a flat or near-flat roof. This creates the maximum possible floor space and head height.

Mansard conversions almost always require planning permission because they significantly alter the external appearance of the property. They are most common in London, where property values are high enough to justify the additional cost, and in terraced properties where a dormer or hip-to-gable is not an option.

Why mansard conversions cost more:

• Complete roof structure rebuild
• Planning permission application fee (currently £258 in England)
• Architect or designer fees for planning drawings: £2,000 – £4,000
• More extensive scaffolding due to the structural work involved
• Longer project timeline — typically 10 to 14 weeks
• Party wall agreements with both neighbours (terraced properties)

Additional Costs to Factor In

The headline cost of a loft conversion covers the core structural work. But there are several additional costs that homeowners and builders alike need to account for.

Structural Engineer

You will need a structural engineer to design the steel beams, calculate loadings, and produce structural calculations for building control. This typically costs £500 to £1,500 depending on the complexity of the conversion.

Building Regulations

All loft conversions require building regulations approval, regardless of whether planning permission is needed. Building control fees are typically £400 to £800. Key requirements include fire safety (fire doors, smoke alarms, escape windows), insulation standards, structural adequacy, and staircase regulations.

Planning Permission

If your conversion requires planning permission, the application fee is currently £258 in England (2026). You will also need architectural drawings, which cost £1,500 to £3,000 for a full planning application package. The application process takes approximately 8 weeks.

Party Wall Agreement

If your property is semi-detached or terraced, you will likely need a party wall agreement with your neighbours before structural work can begin. If your neighbour agrees without dispute, the cost is minimal (a few hundred pounds for a surveyor to prepare the paperwork). If they dissent, you will need to appoint a party wall surveyor at a cost of £700 to £1,500 per neighbour.

En-Suite Bathroom

Adding an en-suite bathroom to a loft conversion is extremely popular and typically adds £3,000 to £6,000 to the project cost. This includes the plumbing, waste pipe routing, sanitaryware, tiling, and waterproofing. A small shower room with a toilet and basin is at the lower end; a larger bathroom with a bath is at the higher end. See our bathroom cost guide for more detail.

Staircase

The staircase is included in the headline costs above, but the type of staircase makes a significant difference. A standard softwood staircase costs £2,000 to £4,000 installed. A space-saving or spiral staircase costs £3,000 to £6,000. A bespoke hardwood staircase can cost £5,000 or more.

What Affects the Cost of a Loft Conversion?

Location. London and the South East are consistently 15 to 25 percent more expensive than the rest of the UK. A dormer conversion that costs £40,000 in Manchester might cost £50,000 in London.

Property type. Terraced houses are often more complex due to party wall requirements and restricted access. Detached properties are usually more straightforward but have larger roof areas, which increases material and labour costs.

Existing roof structure. Modern trussed roofs are more expensive to convert than traditional purlin-and-rafter roofs because the trusses need to be removed and replaced with a new structural frame. This can add £3,000 to £8,000 to the cost.

Specification level. A basic loft conversion with standard materials and minimal fittings will be at the lower end of the price range. Add underfloor heating, bespoke joinery, premium flooring, a high-spec en-suite, and designer lighting, and you can easily push the cost to the upper end or beyond. Our quote calculator can help you estimate costs based on your specific requirements.

Typical Timeline for a Loft Conversion

Most loft conversions follow a similar timeline, though the exact duration depends on the type and complexity of the conversion.

Weeks 1 to 2: Scaffolding erected, materials delivered, structural steels installed, roof alterations begin.
Weeks 3 to 4: Dormer or structural modifications completed, roof weatherproofed, floor strengthened.
Weeks 5 to 6: First fix electrics and plumbing, insulation installed, stud walls built.
Weeks 7 to 8: Plastering, staircase installed, fire doors fitted.
Weeks 9 to 10: Second fix electrics, bathroom installation (if applicable), flooring.
Weeks 11 to 12: Decoration, snagging, building control sign-off.

If you are a builder or tradesperson quoting for loft conversion work, including a clear timeline in your proposal helps the customer plan around the disruption and demonstrates your professionalism. Our scope of work guide covers how to structure this effectively.

Frequently Asked Questions

How much does a loft conversion cost in the UK in 2026?

Loft conversion costs in the UK in 2026 range from £15,000 to £75,000 depending on the type. A Velux or rooflight conversion costs £15,000 to £30,000, a rear dormer costs £35,000 to £55,000, a hip-to-gable conversion costs £40,000 to £65,000, and a mansard conversion costs £50,000 to £75,000. London and the South East are typically 15 to 25 percent more expensive than the national average.

Do I need planning permission for a loft conversion?

Most loft conversions fall under permitted development and do not require planning permission, provided the volume added does not exceed 40 cubic metres for terraced houses or 50 cubic metres for detached and semi-detached houses. However, mansard conversions, conversions in conservation areas, and any conversion that alters the roof line at the front of the property will typically require a full planning application. Building regulations approval is always required regardless of planning permission status.

How long does a loft conversion take?

A typical loft conversion takes 8 to 12 weeks from start to finish. A simple Velux conversion can be completed in 6 to 8 weeks, while a more complex mansard or hip-to-gable conversion may take 10 to 14 weeks. This timeline includes the structural work, first fix electrics and plumbing, insulation, plastering, second fix, and final decoration.

Does a loft conversion add value to a house?

A well-executed loft conversion typically adds 15 to 20 percent to the value of a property. For a property worth £300,000, that equates to an increase of £45,000 to £60,000, which often exceeds the cost of the conversion itself. Adding an en-suite bathroom to the loft conversion maximises the value increase.