Introduction
A loft conversion is widely regarded as one of the most cost-effective ways to add living space and value to a UK home. Unlike a ground-floor extension, which eats into garden space and requires expensive foundation work, a loft conversion uses the volume that already exists above your head. The structural envelope is largely in place, the footprint of the house does not change and, in many cases, planning permission is not even required.
Whether you need an extra bedroom, a dedicated home office, a playroom for the children or a self-contained guest suite, converting your loft can deliver the space you need at a fraction of the cost of moving house. Average house prices in the UK have risen sharply in recent years, and stamp duty, legal fees and removal costs make the financial case for staying put and improving even stronger.
In this comprehensive guide, we break down the costs of every major type of loft conversion in 2026, explain what is included in the price, outline the additional costs you should budget for and help you navigate planning permission and building regulations. For a shorter overview of loft conversion pricing, see our concise guide to loft conversion costs.
Types of Loft Conversion
The type of loft conversion that is right for your property depends on the existing roof structure, the available head height, local planning constraints and your budget. Below, we explain the five most common types, along with their typical costs in 2026.
Velux (Rooflight) Conversion
A Velux conversion is the simplest and most affordable type of loft conversion. It involves installing roof windows (commonly Velux-branded, though other manufacturers are available) into the existing roof slope without altering the external shape of the roof. The interior is then fitted out with insulation, plasterboard, flooring, electrics and a new staircase.
Because there are no structural changes to the roof profile, a Velux conversion is quicker to complete, causes less disruption and almost always falls within permitted development rights. The main limitation is head height: the existing ridge height and roof pitch must provide enough standing room across a usable floor area. Properties with a steep roof pitch and a ridge height of at least 2.4 metres are the best candidates.
A Velux conversion typically costs between £20,000 and £35,000 depending on the size of the loft, the number of roof windows, the specification of finishes and whether a bathroom is included.
Dormer Conversion
The dormer is the most popular type of loft conversion in the UK and for good reason. A dormer is a structural extension that projects vertically from the sloping roof, creating additional floor space and full-height headroom where the roof previously sloped down to the eaves. The most common configuration is a flat-roof rear dormer, which extends across all or part of the rear roof slope.
A well-designed rear dormer can transform an awkward, low-ceilinged loft into a spacious bedroom with an en-suite bathroom and built-in storage along the eaves. Most rear dormers fall within permitted development rights, provided they do not exceed certain volume limits and are set back from the eaves and ridge lines.
A standard rear dormer loft conversion typically costs between £40,000 and £65,000. The price depends on the width of the dormer, the internal specification, the complexity of the steelwork and whether the project includes an en-suite. In London and the South East, expect to pay 20 to 35 per cent more.
Hip-to-Gable Conversion
A hip-to-gable conversion is specifically designed for properties with a hipped roof, where the side of the roof slopes inward rather than terminating at a vertical gable wall. The conversion involves removing the hipped section and building a new vertical gable wall in its place, which extends the internal floor area of the loft significantly.
Hip-to-gable conversions are particularly common on 1930s semi-detached and detached houses, many of which have hipped roofs as a standard feature. The conversion is often combined with a rear dormer to maximise the usable space.
A hip-to-gable loft conversion typically costs between £45,000 and £65,000. When combined with a rear dormer, the total cost can reach £70,000 to £80,000 depending on specification. Planning permission is sometimes required for the gable wall alteration, particularly on semi-detached properties where the new gable changes the visual symmetry of the pair.
Mansard Conversion
A mansard conversion is the most extensive and expensive type of loft conversion. It involves replacing one or both roof slopes with a near-vertical wall (typically set at 72 degrees) topped by a flat roof. This creates the maximum possible internal volume and effectively adds a full new storey to the property.
Mansard conversions are most commonly seen on Victorian and Edwardian terraced houses, particularly in London, where property values are high enough to justify the investment. Because a mansard significantly alters the external appearance of the roof, it always requires planning permission.
A mansard loft conversion typically costs between £55,000 and £80,000+. In London and prime South East locations, costs regularly exceed £90,000, particularly where the specification includes high-end finishes, structural glazing or a large en-suite bathroom. Despite the higher cost, the return on investment can be substantial in areas with high property values.
L-Shaped Dormer
An L-shaped dormer consists of two dormers that meet at a right angle, typically on the rear and side of a roof. This configuration is most often used on end-of-terrace and semi-detached properties where the roof geometry allows dormers on two elevations. The result is a significantly larger floor area than a single rear dormer alone.
L-shaped dormers are structurally more complex than a standard single dormer, requiring careful design of the steelwork at the junction of the two dormers. They also require more extensive scaffolding and may have additional planning considerations depending on the visibility of the side dormer from the street.
An L-shaped dormer loft conversion typically costs between £50,000 and £75,000, reflecting the additional structural and construction complexity compared to a standard rear dormer.
Cost Comparison Table
The table below provides a side-by-side comparison of the five main types of loft conversion, covering typical costs, construction duration and whether planning permission is usually required.
| Conversion Type | Typical Cost Range | Typical Duration | Planning Required? |
|---|---|---|---|
| Velux (Rooflight) | £20,000 – £35,000 | 4–6 weeks | Usually not (PD) |
| Rear Dormer | £40,000 – £65,000 | 8–12 weeks | Usually not (PD) |
| Hip-to-Gable | £45,000 – £65,000 | 10–14 weeks | Sometimes |
| Mansard | £55,000 – £80,000+ | 10–14 weeks | Always |
| L-Shaped Dormer | £50,000 – £75,000 | 10–14 weeks | Sometimes |
Important: These are guide prices based on a mid-range specification outside London in 2026. Actual costs will depend on your specific drawings, site conditions and chosen finishes. A professional budget estimate is the most reliable way to understand what your loft conversion will cost.
What’s Included in the Price
When a loft conversion company or builder quotes you a price, it is essential to understand exactly what is and is not included. A comprehensive loft conversion price should cover the following elements:
Structural steelwork: Steel beams (typically universal beams or RSJs) are needed to support the new floor, transfer loads to the existing walls and, in the case of dormers, support the new roof structure. Steelwork is one of the most significant cost items, often accounting for £3,000 to £8,000 of the total price.
Staircase: Building regulations require a permanent, fixed staircase to the loft. The staircase must comply with regulations regarding pitch, head height, width and handrail design. A standard softwood staircase typically costs £2,000 to £4,000 installed, while a bespoke hardwood or space-saving design can cost significantly more.
Insulation: The loft must be insulated to meet current building regulations, which require a U-value of 0.18 W/m²K or better for a roof conversion. This is typically achieved using rigid insulation boards between and below the rafters, combined with a vapour control layer. Insulation costs are usually in the range of £1,500 to £3,000.
Electrics: First and second fix electrical work, including lighting, sockets, switches and smoke detection. Loft conversions also require compliance with Part B (fire safety) of the building regulations, which may include mains-wired, interlinked smoke and heat detectors throughout the property.
Plumbing: If the conversion includes a bathroom or en-suite, plumbing for hot and cold water supply and waste drainage will be included. Plumbing costs depend on the distance from existing services and whether a new soil stack or waste run is required.
Plastering and decoration: Plasterboard dry-lining to walls and ceilings, skim coat plastering and final decoration. The angled ceiling sections in a loft are more time-consuming to plasterboard than standard vertical walls, which is reflected in the price.
Windows: Velux roof windows for rooflight conversions or windows within dormer cheeks and faces for dormer conversions. Window costs vary considerably depending on size, specification and whether you choose standard, triple-glazed or conservation-style units.
Fire safety compliance: Part B of the building regulations requires a protected escape route from the loft to the final exit of the property. This typically involves upgrading existing doors to FD30 fire doors, installing intumescent strips, fitting mains-wired interlinked smoke detectors and, in some cases, enclosing open-plan areas at lower levels.
Additional Costs to Budget For
Beyond the core conversion price, there are a number of additional costs that homeowners often overlook when setting their budget. Being aware of these from the outset will help you avoid unwelcome surprises during the project.
En-suite bathroom: Adding an en-suite shower room or bathroom to your loft conversion is one of the most popular upgrades. Depending on the size and specification, an en-suite typically adds £5,000 to £12,000 to the total cost. A compact shower room with standard fittings sits at the lower end, while a larger bathroom with high-end sanitaryware, tiling and underfloor heating will be towards the upper end.
Upgraded electrics: Older properties may require upgrades to the existing consumer unit (fuse board) and wiring to accommodate the additional circuits in the loft. A consumer unit upgrade typically costs £500 to £1,000, and additional rewiring work can add further costs depending on the age and condition of the existing installation.
Scaffolding: Most loft conversions require scaffolding for safe access to the roof. Scaffolding hire for a typical dormer conversion lasts 8 to 12 weeks and typically costs £1,500 to £3,500 depending on the size of the property and the configuration required.
Skip hire and waste removal: Loft conversions generate significant quantities of waste, including old roof tiles, timbers, plasterboard and general building debris. Budget £500 to £1,500 for skip hire and waste disposal over the course of the project.
Building control fees: All loft conversions require building regulations approval. Building control fees typically range from £500 to £1,000 depending on the local authority or approved inspector you choose.
Structural engineer fees: A structural engineer will design the steelwork, floor strengthening and any other structural elements. Engineering fees for a domestic loft conversion typically range from £500 to £1,500, depending on complexity.
Party wall costs: If your loft conversion involves work on or near a party wall (common in terraced and semi-detached properties), you may need to serve notice under the Party Wall etc. Act 1996. If your neighbour dissents, party wall surveyor fees typically range from £700 to £1,500 per neighbour.
Tip: When comparing quotes, make sure each builder has included the same scope of work. A headline price that excludes scaffolding, building control fees or fire door upgrades may look attractive initially but will end up costing more once these items are added. Contact us for an independent, itemised estimate that covers every element of your project.
Planning Permission and Building Regulations
Understanding the planning and regulatory framework for loft conversions is essential before you commit to a project. The rules determine what you can build, how much it will cost in fees and how long the approval process takes.
Permitted Development Rights
Many loft conversions in England fall within permitted development (PD) rights, which means you do not need to submit a formal planning application. Under PD rules, you are generally allowed to add up to 40 cubic metres of additional roof space to a terraced house, or up to 50 cubic metres to a semi-detached or detached house. The conversion must not extend beyond the plane of the existing roof slope facing a highway, must not increase the height of the existing roof, and dormer windows (other than hip-to-gable elements) must be set back at least 20cm from the original eaves.
However, permitted development rights can be removed or restricted in certain situations. Properties in conservation areas, Areas of Outstanding Natural Beauty, national parks, the Broads and World Heritage Sites face stricter rules, and side-facing dormers are not permitted under PD in these designated areas. If your property has had a previous loft extension or the original PD rights have been removed by a planning condition (known as an Article 4 direction), you will need to apply for planning permission regardless of size.
When Planning Permission Is Required
Planning permission is always required for mansard conversions because they fundamentally change the roof profile. Hip-to-gable conversions and L-shaped dormers may or may not require permission depending on the specific circumstances. If your project exceeds the PD volume limits, involves work on a listed building or falls within a designated area, you will need to submit a householder planning application. The application fee in England is currently £258, and you should allow 8 to 12 weeks for a decision.
Building Regulations
Building regulations approval is required for all loft conversions, regardless of whether planning permission is needed. The regulations cover structural stability, fire safety, thermal insulation, sound insulation, ventilation, staircase design and electrical safety. A building control inspector (either from your local authority or a private approved inspector) will visit at key stages during the conversion to check compliance. For more detail on what building regulation compliance involves and how we can help with your estimates, see our building regulation estimates page.
Structural Considerations
Every loft conversion involves structural work, and the extent of that work is one of the main factors that determines cost. Understanding the key structural considerations will help you anticipate what your project requires.
Floor Strengthening
The existing ceiling joists in most properties were designed to support the weight of a plasterboard ceiling and light loft storage, not habitable rooms with furniture, people and potentially a bathroom. In almost all cases, the existing joists will need to be supplemented with new, deeper floor joists or engineered timber joists to meet the load requirements of a habitable floor. This is one of the first items a structural engineer will assess.
Ridge Beam and Purlins
Traditional cut timber roofs are supported by a ridge board, purlins and struts. When you convert a loft, some or all of these supporting elements may need to be repositioned or replaced to create usable space. A structural ridge beam (typically a steel universal beam) can replace the ridge board and internal supports, transferring the roof loads to the party walls or gable walls and freeing up the internal space.
Steel Beams
Structural steel is used extensively in loft conversions. Common applications include ridge beams, dormer support beams, floor trimming beams (around the staircase opening) and beams to support new walls or redistribute loads. The size, number and position of steel beams are determined by the structural engineer based on calculated loads. Steelwork is one of the heavier cost items in any loft conversion and must be designed before construction begins.
Head Height Requirements
Building regulations do not prescribe a minimum ceiling height for loft conversions in the same way as for new-build rooms, but practical usability requires a minimum of around 2.2 metres at the highest point. Most designers aim for at least 2.3 to 2.4 metres at the ridge to ensure the room feels comfortable. If your existing ridge height is below 2.2 metres, a loft conversion may not be feasible without raising the ridge, which significantly increases cost and almost always requires planning permission.
Chimney Breast Support
Many older properties have chimney breasts that pass through the loft space. If a chimney breast is removed at loft level to gain space, the remaining stack above must be supported with a structural gallows bracket or steel beam. Alternatively, if the chimney breast is retained, the floor around it must be strengthened to carry the additional load. Chimney breast alterations add £1,000 to £3,000 to the structural costs depending on complexity.
Adding Value to Your Property
A well-executed loft conversion is consistently ranked as one of the best home improvements for return on investment. Industry estimates suggest that a loft conversion can add 15 to 20 per cent to the value of a property, and in some cases even more if it creates a much-needed additional bedroom in an area where larger homes command a significant premium.
To put this in context, a property worth £350,000 could see its value increase by £52,500 to £70,000 after a well-planned loft conversion. Even at the top end of the cost range, the conversion pays for itself in added value, and you gain the benefit of additional living space in the meantime.
Compare this to the cost of moving. Stamp duty on a £420,000 purchase would be approximately £11,000, with legal fees, estate agent commissions, survey costs and removal expenses easily adding another £10,000 to £15,000. A loft conversion avoids all of these costs while keeping you in the home and neighbourhood you already know.
The key to maximising value is ensuring the conversion is designed and built to a high standard, with proper building regulations sign-off (a completion certificate), a well-designed staircase and finishes that are in keeping with the rest of the property. Poorly executed conversions with steep ladders, low headroom or substandard finishes will not add the same value and may even deter buyers.
Getting an Accurate Estimate
Before you commit to a loft conversion, it is essential to understand the full cost of the project. Relying on rough online calculators or verbal quotes from builders is not sufficient for a project of this scale. A detailed, itemised estimate prepared by a qualified Quantity Surveyor gives you the confidence to set a realistic budget, compare builder quotations on a like-for-like basis and avoid costly surprises during construction.
At First4Estimating, we prepare comprehensive loft conversion estimates from your architectural drawings. Our estimates cover every element of the project, from structural steelwork and staircase installation through to plastering, electrics, plumbing and decoration. We itemise each trade and material so you can see exactly where your money is going.
Whether you need a budget estimate from initial design drawings to help you decide whether to proceed, or a full detailed estimate from building regulation drawings to use for tendering to builders, we can help. Our team of qualified Quantity Surveyors has extensive experience with loft conversions of all types, from simple Velux conversions to complex mansard projects.
Ready to find out what your loft conversion will cost? Send us your plans for a fixed-price quotation with no obligation, or browse our full range of estimating services. We typically turn around domestic loft conversion estimates within five working days of receiving your drawings.