Loft Conversion Costs: A Complete Guide

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Introduction

A loft conversion remains one of the most popular and cost-effective ways to add living space to a UK home. Rather than extending outwards and sacrificing garden space, or going through the upheaval of moving house, converting your loft allows you to unlock valuable square footage that is already sitting above your head. It is no surprise that loft conversions consistently rank among the top home improvement projects for adding both space and value to a property.

However, the cost of a loft conversion can vary enormously depending on the type of conversion you choose, the size and condition of your existing roof structure, your location within the UK, and the specification of the finished space. At the lower end, a simple Velux rooflight conversion might start at around 20,000 pounds, while a full mansard conversion in London or the South East can easily exceed 70,000 pounds once all the finishing touches are in place.

Understanding where these costs come from, and what factors will push your project towards the higher or lower end of the range, is essential for setting a realistic budget. This guide will walk you through the main types of loft conversion, provide indicative cost ranges for each, explain the planning and regulatory requirements you need to be aware of, and highlight the hidden costs that catch many homeowners out.

Whether you are at the early daydreaming stage or ready to commission drawings and obtain quotes, this article will give you the knowledge you need to plan your loft conversion budget with confidence.

Types of Loft Conversion

Before you can understand the costs involved, it is important to know the main types of loft conversion available. Each type involves a different level of structural work, offers different amounts of usable space, and sits at a different point on the cost spectrum. The right choice for your home will depend on the shape of your existing roof, the amount of headroom available, your budget and what you want to achieve with the finished space.

The Velux or rooflight conversion is the simplest and most affordable option. It involves no changes to the external structure of the roof. Instead, Velux-style roof windows are installed into the existing roof slope to bring in natural light, and the internal space is fitted out with flooring, insulation, a staircase, electrics and decoration. This type of conversion works best where there is already good headroom in the loft, typically in properties with a steep roof pitch. Because no structural alterations are made to the roof, it is usually the quickest and least disruptive option.

The dormer conversion is the most common type in the UK. A dormer is a box-shaped structure that projects out from the existing roof slope, creating additional headroom and floor space. Rear dormers are the most popular, as they are often achievable under permitted development rights without the need for a formal planning application. Dormers can be built as a single small feature or extended across the full width of the property, known as a full-width dormer, which maximises the usable space.

A hip-to-gable conversion is used on properties where the side roof slopes inward, such as semi-detached and detached houses with hipped roofs. The sloping hip end is rebuilt as a vertical gable wall, creating a much larger internal floor area. This type of conversion is often combined with a rear dormer to maximise the overall space gained. It involves more structural work than a standard dormer but can transform the usable area significantly.

The mansard conversion is the most extensive and expensive type. It involves altering the entire roof structure, typically raising the party wall and creating a near-vertical rear wall with a flat or very shallow-pitched roof above. Mansard conversions create the most usable space of any loft conversion type and are particularly popular in terraced properties in urban areas where every square metre of floor space counts. Due to the extent of the structural changes, a mansard conversion almost always requires planning permission.

Cost Breakdown by Type

The cost of a loft conversion depends heavily on which type you choose, and the ranges below reflect typical prices across England and Wales in 2026. It is important to remember that these are indicative figures. Your actual costs will depend on your location, the size and complexity of your specific project, the specification of finishes, and the current state of the construction market in your area.

A Velux or rooflight conversion typically costs between 20,000 and 35,000 pounds. This covers the structural floor strengthening, insulation, Velux windows, staircase, electrics, plastering and basic decoration. It is the most affordable option because it does not require any changes to the external roof structure. The lower end of this range would be a modest conversion in a lower-cost region, while the upper end would cover a more generous specification or a property in London and the South East.

A dormer loft conversion generally falls between 35,000 and 55,000 pounds. The exact cost depends on whether you are building a small single dormer or a full-width rear dormer that spans the entire back of the property. A full-width dormer creates substantially more usable space and is worth the additional investment in most cases. The dormer structure itself involves steelwork, roofing, cladding and weatherproofing, all of which add to the cost compared with a Velux conversion.

A hip-to-gable conversion typically costs between 40,000 and 60,000 pounds. The additional cost compared with a standard dormer reflects the structural work required to remove the hipped roof section and rebuild it as a vertical gable wall. When combined with a rear dormer, which is the most common approach, this type of conversion offers an excellent balance of space and value.

A mansard conversion is the most expensive option, typically ranging from 50,000 to 70,000 pounds or more. The higher cost reflects the extent of the structural work involved, the requirement for planning permission and potentially a party wall agreement, and the additional scaffolding and temporary weatherproofing needed while the roof is open. For properties where headroom is limited or where maximising every square metre is the priority, a mansard conversion can be well worth the investment, particularly given the value it adds to the property.

Structural & Planning Considerations

Understanding the planning and regulatory landscape before you begin is crucial, as it can have a significant impact on both your budget and your timeline. The good news is that many loft conversions fall within permitted development rights, which means you may not need a formal planning application. However, this is not always the case, and getting it wrong can be costly.

Velux conversions and most rear dormers on houses that have not already been extended under permitted development are typically allowed without planning permission, provided they meet certain conditions. These include limits on the overall volume added, requirements to use materials that match the existing property, and restrictions on the dormer not extending beyond the plane of the existing roof slope at the front of the property. Side-facing windows must be obscure glazed and non-opening if they are within 1.7 metres of the floor.

However, planning permission is usually required in the following circumstances: if your property is in a conservation area or is a listed building, if you are building a mansard conversion that alters the entire roofline, if you want to add a dormer to the front of the property, or if the property is a flat or maisonette. If you are in any doubt, it is always advisable to check with your local planning authority or engage a planning consultant before proceeding with detailed design.

If your property is a semi-detached or terraced house, you may also need to serve a Party Wall Notice on your adjoining neighbours under the Party Wall etc. Act 1996. This applies where the conversion involves work to a shared wall or within specified distances of the boundary. Party wall agreements can add both cost and time to the project, so it is worth factoring this in early. Surveyor fees for a straightforward party wall agreement typically range from 800 to 1,500 pounds per neighbour, though costs can increase significantly if disputes arise.

Hidden Costs to Budget For

One of the biggest mistakes homeowners make when budgeting for a loft conversion is focusing only on the headline construction cost and overlooking the many additional expenses that come with the project. These hidden costs can easily add 10-20% to your total budget if they are not properly accounted for from the start.

The following items are commonly forgotten or underestimated when planning a loft conversion budget:

• Staircase: A new staircase to access the loft is a significant item. Depending on the layout and whether you need to reconfigure an existing bedroom to accommodate it, this can cost between 2,000 and 5,000 pounds including all associated builder's work.
• Electrics: A full electrical installation for the new floor, including lighting, sockets, smoke detectors and any underfloor heating, typically costs between 2,500 and 4,500 pounds.
• Plumbing: If your conversion includes a bathroom or en-suite, plumbing costs will include hot and cold water supply, waste connections, soil pipe routing and sanitaryware installation. Budget 3,000 to 6,000 pounds depending on specification.
• Fire doors: Building Regulations require fire doors to be fitted throughout the escape route from the new loft room to the final exit at ground floor level. This often means replacing existing internal doors on every floor, which can cost 1,500 to 3,000 pounds.
• Insulation upgrades: The new loft space must meet current thermal performance standards, which means high-performance insulation in the roof, walls and floor. This is included in most estimates but can be more costly than expected if the roof structure limits the space available for insulation.
• Scaffolding: External scaffolding is essential for dormer, hip-to-gable and mansard conversions. Scaffold hire typically costs between 1,500 and 3,500 pounds depending on the size of the property and the duration of the hire.
• Building control fees: Fees for building control inspections and the completion certificate vary by local authority but typically range from 500 to 1,000 pounds.
• Structural engineer fees: A structural engineer will need to design the steel beams and floor strengthening for your conversion. Fees typically range from 500 to 1,500 pounds.
• Architectural drawings: If you need planning permission or want detailed construction drawings, architectural fees can range from 1,500 to 4,000 pounds depending on the complexity of the project.

When you add all of these items together, the additional costs beyond the core construction work can easily total 15,000 to 25,000 pounds. This is why it is so important to get a comprehensive, fully detailed estimate before you set your budget, rather than relying on a simple quotation that may not include everything.

How to Keep Costs Under Control

A loft conversion is a significant financial investment, and keeping costs under control requires careful planning, clear decision-making and a disciplined approach to managing changes during the build. The good news is that the most effective cost control measures are also the simplest, and they all start before a single brick is laid or a single nail is driven.

The single most important step you can take is to get a detailed estimate upfront. A professional estimate from a qualified Quantity Surveyor will break down every element of the project, from structural steelwork to door handles, giving you a clear and complete picture of the total cost before you commit. This is not the same as a builder's quotation, which may cover only the main construction works and leave significant items unpriced or excluded.

Before construction begins, make sure your specification is fixed. Choose your sanitaryware, tiles, flooring, windows, doors and electrical fittings before the build starts, and resist the temptation to upgrade mid-project. Changes made during construction are far more expensive than decisions made on paper, because they often involve abortive work, delays, and re-ordering materials. If you have not yet decided on a particular item, include a realistic provisional sum in your budget and make the final decision as early as possible.

Finally, always allow a contingency in your budget. Even with the most thorough planning, unexpected issues can and do arise. A contingency of 5-10% of the total project cost gives you a financial buffer to deal with surprises without derailing the project. For loft conversions, common unexpected costs include additional structural work once the existing roof structure is opened up, remedial work to existing timbers, and upgrades to existing services to meet current Building Regulations. Having a contingency in place means these issues can be dealt with quickly and calmly, rather than becoming a source of stress and delay.

Getting a Professional Estimate

If you are planning a loft conversion, one of the best investments you can make at the outset is a professional estimate. An independent, detailed estimate gives you a comprehensive understanding of what your project is likely to cost, broken down by every trade and every element. It allows you to set a realistic budget, compare contractor quotations on a like-for-like basis, and identify potential cost savings before work begins.

At First4Estimating, we prepare detailed loft conversion estimates for homeowners, builders and architects across the UK. Our qualified Quantity Surveyors will measure your drawings, price every element of the works, and provide you with a clear, itemised breakdown that you can use to manage your project with confidence. Whether you are converting a simple Velux loft or planning a full mansard with en-suite bathroom, we can help you understand the true cost of your project.

Our estimates cover all of the items discussed in this article, including structural works, roofing, insulation, staircase, electrics, plumbing, plastering, decoration, preliminaries, provisional sums and contingencies. Everything is presented in a clear, easy-to-read format that makes it simple to see where the money is going and to compare our figures with any quotations you receive from contractors.

If you are a homeowner or self-builder, visit our Home Owners and Self Builders page to learn more about how we can help. If you would like to see the full range of services we offer, head to our Estimating Services page. For more guidance on managing construction costs, you may also find our article on house extension costs helpful. When you are ready to get started, simply send us your plans and we will provide a detailed estimate for your loft conversion project.