Loft Conversion Cost UK – 2025 Price Guide

Average Loft Conversion Cost in the UK

Loft conversion costs in the UK typically start around £25,000 for a basic rooflight conversion and can exceed £70,000 for large dormer or mansard projects in high-cost areas such as London and the South East. The final price depends on the loft type, size, structural work, finishes, and whether you add bathrooms or multiple rooms.

As a rule of thumb, most homeowners should budget £1,500 – £2,500 per m² of new floor space for a fully finished loft conversion, including design, structural work, windows, insulation, electrics, plumbing, and decorating.

These are guide prices only. Build costs can vary significantly between regions and even between neighbouring streets. For an accurate figure tailored to your loft and specification, compare itemised quotes from multiple trusted loft conversion companies.

Loft Conversion Cost by Type

Different styles of loft conversion require different levels of structural work and materials. Below is a breakdown of typical UK costs for each main loft type, along with what is usually included.

Rooflight / Velux Loft Conversion Cost

A rooflight conversion (sometimes called a Velux loft conversion) is the most cost-effective way to convert your loft space. It uses the existing roof shape, adding roof windows for light, plus insulation, floor joists, electrics, and access.

• Typical cost: £25,000 – £35,000
• What you get: 1 new bedroom or home office, basic storage, no major change to roofline
• Best for: Lofts that already have decent head height in the centre

This option is popular when budgets are tight or planning constraints make dormers difficult. However, it adds less usable floor area than a dormer or mansard conversion.

Rear Dormer Loft Conversion Cost

A rear dormer is the most common UK loft conversion. A box-shaped structure is added to the back of the roof, providing full-height ceilings across much of the new room.

• Typical cost: £35,000 – £55,000
• What you get: 1 large bedroom plus an en-suite, or 2 smaller rooms (depending on size)
• Best for: Terraced and semi-detached houses

Dormer lofts give an excellent balance of cost, extra space and return on investment. Many rear dormers can be built under permitted development rights, reducing planning time and fees.

Hip to Gable Loft Conversion Cost

Hip to gable loft conversions are common on semi-detached and detached houses with sloping side roofs (hipped roofs). The sloping side is built up into a vertical gable wall to create more internal volume, often combined with a rear dormer.

• Typical cost: £40,000 – £60,000
• What you get: 1–2 bedrooms and a bathroom, with improved head height across the loft
• Best for: Homes with small existing loft footprints

This type of conversion usually involves more structural work and roof tiling, which is why it tends to cost slightly more than a simple rear dormer.

Mansard Loft Conversion Cost

Mansard loft conversions are popular in dense urban areas and on period terraces. The rear pitch of the roof is replaced with a near-vertical wall and a flat roof, maximising usable space.

• Typical cost: £55,000 – £75,000+
• What you get: Large bedroom(s), bathroom and flexible layout, often similar to a full extra storey
• Best for: Victorian / Edwardian terraces, properties in conservation areas (subject to planning)

Mansard conversions almost always require full planning permission, structural steels and extensive roofing work, which increases both cost and build time. However they often provide the largest increase in property value.

Bungalow Loft Conversion Cost

Converting a bungalow loft can essentially turn a single-storey home into a two-storey property. The cost depends heavily on whether you simply convert part of the roof space or restructure and raise the roof.

• Typical cost: £45,000 – £80,000+
• What you get: 2–3 bedrooms and one or more bathrooms, plus new staircase and landings
• Best for: Bungalows with unused roof space and good plot size

Because bungalow lofts often involve more extensive structural work, it is vital to obtain detailed drawings and a fixed-price quotation before committing.

Key Factors Affecting Loft Conversion Cost

Two similar-looking loft conversions can vary in price by tens of thousands of pounds. Below are the main factors that influence what your project will cost.

1. Size and complexity

• Floor area: Larger footprints require more materials, labour and time.
• Number of rooms: Adding multiple bedrooms or a separate office and bathroom increases plumbing, electrics and partitioning.
• Structural steel: RSJs, beams and joists are required to support new loads, especially in older properties.

2. Existing roof structure and head height

Trussed roofs and low ridge heights are more complex to convert than traditional cut roofs with generous headroom. In some cases, raising the ridge or lowering ceilings below is required – both significantly increase the cost.

3. Specification and finishes

• Windows: Standard rooflights vs. large dormer windows, Juliet balconies or aluminium glazing.
• Bathrooms: The choice of sanitaryware, tiling, underfloor heating and ventilation can add £3,000 – £8,000+.
• Staircase: Bespoke timber, glass balustrades and feature designs cost more than standard softwood stairs.
• Built-in storage: Wardrobes and eaves cupboards are worth budgeting for to maximise awkward spaces.

4. Location in the UK

Build costs in London and the South East are generally 15–30% higher than in many other parts of the UK due to labour and access costs. Rural areas can be cheaper, but long travel times or limited access may offset savings.

5. Planning, design and regulations

• Planning permission: Application fees, drawings and potential redesigns.
• Architects / designers: Expect to pay 5–10% of build cost for design, drawings and technical details.
• Building Control: Inspection and sign-off fees from your local authority or an approved inspector.
• Party Wall Awards: If your property is terraced or semi-detached, you may need Party Wall agreements with neighbours.

Typical Loft Conversion Cost Breakdown

Every project is unique, but most loft conversion quotes will include similar categories of work. Below is an example of how a £45,000 dormer loft conversion might be broken down:

Ask each builder to provide an itemised quotation so you can see exactly where your money is going and compare like for like.

Planning Permission, Building Regulations & Party Wall

Most loft conversions in the UK fall under either permitted development or require full planning permission. Regardless of the route, all conversions must comply with Building Regulations.

Permitted development vs planning permission

• Permitted development: Many rear dormers and rooflight conversions can be built without full planning permission, provided they meet strict volume and design criteria.
• Planning permission: Required for mansard conversions, front dormers, major changes in appearance, properties in conservation areas, or where volume limits are exceeded.

A professional designer or loft specialist can confirm which rules apply to your property and include application costs within their fee.

Building Regulations

Compliance with Building Regulations ensures your new loft is safe, structurally sound and energy efficient. Key areas include:

• Structural integrity (joists, steels, load-bearing walls)
• Fire safety (escape routes, fire doors, alarms)
• Stair design, handrails and balustrades
• Insulation, ventilation and condensation control
• Electrics, plumbing and drainage

Party Wall Agreements

If you live in a terraced or semi-detached property, you may need to serve Party Wall notices on your neighbours before work starts. Party Wall surveyor fees are often shared and typically range between £700 – £1,500 per neighbour, depending on complexity.

How Long Does a Loft Conversion Take?

The timescale varies by size and complexity, but a typical programme for a standard loft conversion in the UK is:

• Design & approvals: 4 – 10 weeks (including planning where required)
• Construction:
  • Rooflight / Velux loft: 4 – 6 weeks
  • Rear dormer loft: 6 – 10 weeks
  • Mansard / large conversion: 10 – 14+ weeks

Most reputable loft specialists will provide a detailed programme and phase the work to minimise disruption, often constructing the majority of the shell from scaffolding before breaking through into the existing house.

Will a Loft Conversion Add Value to My Property?

In many parts of the UK, a well-designed loft conversion is one of the highest-return home improvements you can undertake. Estate agents often estimate an uplift of 15–25% of current property value, especially when adding an extra double bedroom and a bathroom.

The exact return on investment depends on your local property market, the quality of the work and whether the new space matches what buyers are looking for. For example, taking a 3-bed house to a 4-bed with a master suite often commands a significant price premium.

How to Save Money on Your Loft Conversion

Keeping to budget doesn’t have to mean cutting corners. Consider the following cost-saving tips when planning your loft:

• Keep the design simple: Fewer structural changes, straightforward roofs and standard-sized windows are all more economical.
• Limit bathroom numbers: One well-designed bathroom is cheaper than multiple smaller shower rooms.
• Choose mid-range finishes: Good quality, durable fittings without the designer price tag can make a big difference.
• Reuse existing plumbing runs: Position new bathrooms above existing ones to reduce pipework and labour.
• Plan everything upfront: Late changes to layout, windows or stair position are expensive once work has started.
• Get multiple quotes: Comparing like-for-like quotations helps you avoid overpaying and spot unrealistic low bids.

Choosing the Right Loft Conversion Company

The builder or loft specialist you choose will have a major impact on cost, quality and overall experience. When comparing companies:

• Check they have recent loft conversion experience on properties similar to yours.
• Ask to see previous projects and speak to recent customers.
• Ensure they provide a fixed-price, itemised quote and clear payment schedule.
• Confirm insurance cover, guarantees and how snagging is handled.
• Understand what is and isn’t included – design, approvals, decorating, flooring and fixtures can vary between quotes.

Best Builders works across the UK with vetted, reviewed professionals who specialise in loft conversions. Tell us about your project and we’ll connect you with suitable companies in your area.