Loft Conversion Cost Guide 2026 — Full Breakdown for UK Homeowners

A loft conversion is one of the smartest ways to add space and value to a UK home without the disruption of a full extension. For builders and tradespeople, loft conversions represent high-value projects with strong margins — but only when they are quoted accurately. Get the price wrong and you will either lose money or lose the job to someone who priced it better.

This guide covers what loft conversions cost in 2026 across the UK, the differences between conversion types, what drives prices up or down, and how to build a quote that wins work while protecting your profit. Whether you are a homeowner planning a conversion or a builder looking to sharpen your estimating, this is the complete breakdown.

Types of Loft Conversion

Not all loft conversions are created equal. The type you choose — or recommend to a customer — depends on the existing roof structure, the property type, the available budget, and how much usable space is needed. Here are the four main types.

Velux (Rooflight) Conversion

A Velux conversion is the simplest and most affordable option. It involves adding roof windows to the existing roof slope without changing the roof structure. The existing rafters are strengthened, the floor is upgraded, insulation is added, and a staircase is installed. Because the roof shape stays the same, the headroom is limited to whatever the existing roof pitch provides.

Velux conversions work best on properties with a steep roof pitch and plenty of existing headroom. They are ideal for a home office, playroom, or spare bedroom where maximum standing space is not critical. They are rarely suitable as a primary bedroom or bathroom because of the restricted headroom at the eaves.

• Cost range: twenty thousand to thirty thousand pounds
• Build time: four to six weeks
• Planning permission: usually not required under permitted development

Dormer Conversion

A dormer conversion is the most popular type of loft conversion in the UK. It involves building a box-shaped extension that projects vertically from the rear roof slope, creating a flat roof section with full standing headroom. A rear dormer can run the full width of the house or cover just part of the roof.

Dormers dramatically increase the usable floor area compared to a Velux conversion. A full-width rear dormer on a typical three-bedroom semi can create enough space for a double bedroom with en-suite bathroom and still leave room for built-in storage. This is the conversion type that delivers the best balance of cost, space, and return on investment.

• Cost range: thirty-five thousand to fifty-five thousand pounds
• Build time: eight to ten weeks
• Planning permission: often permitted development for rear dormers, but check local rules

Hip-to-Gable Conversion

A hip-to-gable conversion is designed for properties with a hipped roof — where the roof slopes inward on the side as well as the front and back. The hipped end is replaced with a vertical gable wall, extending the ridge line to the full width of the house. This is often combined with a rear dormer to maximise the loft space.

Hip-to-gable conversions are common on nineteen-thirties semi-detached houses, which almost always have hipped roofs. By squaring off the hip, you gain significant extra floor area that would otherwise be lost to the sloping roof. The structural work is more involved than a standard dormer because you are rebuilding part of the roof structure.

• Cost range: forty thousand to sixty-five thousand pounds
• Build time: ten to twelve weeks
• Planning permission: usually permitted development on semi-detached, check for detached properties

Mansard Conversion

A mansard conversion is the most extensive and expensive type. It involves rebuilding one or both roof slopes to a near-vertical angle (typically seventy-two degrees), with a small flat roof section at the top. This creates the maximum possible internal space and is essentially a new storey added to the house.

Mansard conversions are most common in London and other urban areas where property values are high enough to justify the cost. They are particularly popular on Victorian and Edwardian terraces. Because they significantly alter the roof profile, mansard conversions almost always require full planning permission.

• Cost range: fifty thousand to seventy-five thousand pounds
• Build time: ten to fourteen weeks
• Planning permission: almost always required

Full Cost Breakdown

Understanding where the money goes in a loft conversion helps both homeowners and builders. Here is a detailed breakdown for a typical rear dormer conversion — the most common type — on a standard three-bedroom semi-detached house.

Structural Work

The structural work includes new steel beams to support the floor, reinforcing existing joists or installing new ones, and building the dormer frame. This typically costs four thousand to eight thousand pounds depending on the span and load requirements. The structural engineer's design and calculations add four hundred to eight hundred pounds. If the existing floor joists need to be completely replaced rather than supplemented, costs increase by one thousand to two thousand pounds.

Roof and Dormer Construction

Building the dormer structure — framing, cladding, lead work or GRP to the cheeks and flat roof, and tiling — costs six thousand to twelve thousand pounds. If the project also requires external scaffolding, use our scaffolding cost calculator to estimate that element separately. The cladding material affects cost significantly. Hanging tiles are the most common choice and cost less than zinc or lead cladding. A full-width dormer costs more than a partial dormer because of the additional structural support and weatherproofing required.

Windows and Doors

Dormer windows (typically uPVC double-glazed casement or sash windows) cost five hundred to one thousand two hundred pounds per window supplied and fitted. Most dormers have two or three windows. Velux rooflights to the front slope cost four hundred to nine hundred pounds each depending on size. A Juliet balcony — a popular feature — adds five hundred to one thousand pounds per opening.

Staircase

The staircase is one of the most critical elements of a loft conversion, both practically and in terms of Building Regulations compliance. A standard softwood staircase costs one thousand five hundred to three thousand pounds supplied and fitted. A space-saving design or a more complex configuration to work around existing room layouts can cost three thousand to five thousand pounds. The staircase location often dictates the layout of both the new loft room and the landing below, so getting this right early is essential.

Insulation

Loft conversions must meet current Building Regulations for thermal performance, which are significantly more demanding than when most houses were built. Insulating between and over the rafters with rigid insulation board and plasterboard costs two thousand to four thousand pounds. This includes the walls of the dormer and the remaining roof slopes. The floor also needs sound insulation if the rooms below are habitable.

Plumbing

If the conversion includes an en-suite bathroom or shower room — and most do — plumbing costs run to two thousand five hundred to five thousand pounds. This covers hot and cold water supply, waste pipes, soil pipe connection, toilet, basin, shower or bath, and any associated tiling. The soil pipe routing can be a significant cost factor if it needs to run externally down the back of the house.

Electrics

First and second fix electrics for a loft conversion typically cost one thousand five hundred to three thousand pounds. This covers new circuits for lighting, sockets, extractor fans, and smoke alarms (required by Building Regulations). If the existing consumer unit does not have space for additional circuits, upgrading or replacing it adds five hundred to one thousand pounds.

Plastering and Finishing

Dry-lining and plastering the new space costs one thousand five hundred to three thousand pounds. Flooring (carpet, engineered wood, or vinyl in the en-suite) adds eight hundred to two thousand pounds. Skirting boards, architraves, and internal doors add five hundred to one thousand two hundred pounds. Decorating the completed space adds five hundred to one thousand five hundred pounds.

Fire Safety

Building Regulations require a protected escape route from the new loft room to the front door. This typically means upgrading existing doors on the landing and stairs to FD30 fire doors, installing interlinked smoke alarms on every level, and ensuring the staircase has adequate width and headroom. Fire safety upgrades cost one thousand to two thousand five hundred pounds, often more in older properties where existing doors are non-standard sizes.

Planning Permission and Building Regulations

Understanding the regulatory requirements is essential for both pricing and advising customers correctly. Getting this wrong can cause expensive delays and even require work to be undone.

Permitted Development Rights

Many loft conversions fall under permitted development rights, which means you do not need to apply for planning permission. However, there are strict conditions that must be met.

• The volume added must not exceed forty cubic metres for terraced houses or fifty cubic metres for detached and semi-detached houses
• The conversion must not extend beyond the plane of the existing roof slope facing the highway
• No part of the extension can be higher than the highest part of the existing roof
• Materials used on the exterior must be similar in appearance to the existing house
• Side-facing windows must be obscure-glazed and non-opening (unless the opening part is more than one point seven metres above the floor)
• The property must not be in a conservation area, Area of Outstanding Natural Beauty, or National Park unless specific conditions are met

Even if the conversion qualifies as permitted development, it is worth applying for a Lawful Development Certificate from the local planning authority. This costs around eighty-five pounds and provides formal confirmation that the work is lawful — useful when the homeowner comes to sell the property.

Building Regulations

All loft conversions require Building Regulations approval, regardless of planning permission status. The key areas covered include structural stability, fire safety and escape routes, thermal insulation, sound insulation, staircase design, electrical safety, and drainage. Building Regulations fees vary by local authority but typically range from five hundred to one thousand two hundred pounds. A building control inspector will visit at key stages — typically foundations or steel installation, pre-plaster, and final inspection.

Regional Cost Variations

Loft conversion costs vary across the UK, primarily driven by differences in labour rates. Here are approximate ranges for a standard rear dormer conversion in 2026.

• London: fifty thousand to seventy thousand pounds
• South East England: forty-five thousand to sixty thousand pounds
• South West England: thirty-eight thousand to fifty-two thousand pounds
• Midlands: thirty-five thousand to forty-eight thousand pounds
• North West England: thirty-two thousand to forty-five thousand pounds
• North East England: twenty-eight thousand to forty-two thousand pounds
• Wales: twenty-eight thousand to forty-two thousand pounds
• Scotland: thirty thousand to forty-five thousand pounds

These figures assume a standard specification with en-suite. High-end finishes, complex structural work, or mansard conversions will exceed these ranges in any region.

How to Quote a Loft Conversion Accurately

Quoting a loft conversion correctly requires thoroughness and experience. Here is a practical approach that works.

Carry out a proper survey. You need to get into the loft and assess the existing structure. Check the roof type, rafter size and spacing, purlin positions, chimney breast location, ridge height, and available headroom. Measure the footprint carefully — our square metre calculator can help you work out the usable floor area quickly. Look for water tanks, boilers, or other services that will need relocating. Check the condition of existing timbers for rot or woodworm. If you are not confident assessing the structural requirements, bring a structural engineer to the survey — their fee is a worthwhile investment.

Confirm the regulatory position. Determine whether the conversion falls under permitted development or needs planning permission. Check if the property is in a conservation area. Understand the Building Regulations requirements that apply. Factor the costs and timeline for these approvals into your quote.

Break the job into elements. Price each trade and material cost separately — structural steel, carpentry, roofing, plumbing, electrics, plastering, joinery, flooring, decorating, and fire safety. Our material cost estimator can help you benchmark material spend for each element. This ensures nothing gets missed and makes it easy to adjust the quote if the customer changes the specification.

Get subcontractor prices. If you are not doing the plumbing, electrics, or plastering yourself, get firm prices from your subcontractors before quoting the customer. Guessing subcontractor prices is one of the most common causes of margin erosion on loft conversions. For more on this, see our guide on how to calculate labour costs.

Allow for the unknowns. Loft conversions regularly throw up surprises — undersized existing joists, hidden rot, services in unexpected locations, chimney breast removal complications. Add ten to fifteen per cent contingency. This is not profit padding — it is a realistic allowance for the work you cannot see until you open things up.

Present a professional proposal. A loft conversion is a major investment for the homeowner — typically thirty thousand to sixty thousand pounds. They expect a professional proposal, not a text message with a number. Break down the scope clearly, include a realistic timeline, specify what is and is not included, and set out your payment terms. QuoteSmith generates these proposals automatically, producing a branded PDF that sets you apart from competitors sending rough estimates. Read more about why professional proposals win more work.

Common Mistakes When Quoting Loft Conversions

These are the errors that catch builders out most often on loft conversion projects.

Underestimating the staircase. The staircase is more complex than most builders expect. It affects the room layout below, requires careful compliance with Building Regulations for headroom and width, and often involves relocating radiators, doors, or built-in furniture on the landing. Budget more time and money for this element than you think you need.

Ignoring Party Wall requirements. If the loft conversion involves work on or near a party wall — which it does on most terraced and semi-detached properties — the Party Wall Act applies. The homeowner must serve notice on adjoining neighbours, and if a surveyor is appointed, fees can run to one thousand to three thousand pounds. While this is the homeowner's cost, it affects the project timeline and you need to factor it into your programme.

Forgetting fire safety upgrades. Building Regulations require a protected escape route, which typically means upgrading existing doors throughout the house to FD30 fire doors and installing interlinked smoke alarms. This is not a small cost, and overlooking it will either eat into your margin or create an awkward conversation with the customer mid-project.

Not checking the existing structure properly. A quick look through the loft hatch is not enough. You need to physically get into the loft, check every timber, identify every service, and understand the roof structure. Problems found after the contract is signed are your problems.

Frequently Asked Questions

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

A loft conversion in the UK typically costs between twenty thousand and sixty-five thousand pounds in 2026. A basic Velux conversion starts from around twenty thousand pounds, a dormer conversion ranges from thirty-five thousand to fifty-five thousand pounds, a hip-to-gable conversion costs forty thousand to sixty-five thousand pounds, and a mansard conversion ranges from fifty thousand to seventy-five thousand pounds. Prices vary significantly by region, with London and the South East typically twenty to thirty per cent more expensive than the national average.

Do I need planning permission for a loft conversion?

Many loft conversions fall under permitted development rights and do not require planning permission, provided conditions are met. The volume added must not exceed forty cubic metres for terraced houses or fifty cubic metres for detached and semi-detached properties. Mansard conversions, conversions in conservation areas, and conversions on listed buildings will almost always require full planning permission. Building Regulations approval is required for all loft conversions regardless of planning permission status.

How long does a loft conversion take?

A typical loft conversion takes between six and twelve weeks. A Velux conversion is the quickest at four to six weeks. A dormer conversion takes eight to ten weeks. Hip-to-gable and mansard conversions are more complex and typically take ten to fourteen weeks. Allow additional time for planning permission if required and for any unforeseen structural issues discovered during the build.

What type of loft conversion is best?

The best type depends on your property, budget, and space requirements. A Velux conversion is cheapest but adds minimal headroom. A dormer conversion offers the best balance of cost and space for most properties. A hip-to-gable conversion is ideal for hipped-roof properties. A mansard conversion provides the most space but costs the most and requires planning permission. Most homeowners opt for a rear dormer as it delivers the best value for money.

Does a loft conversion add value to a house?

A well-executed loft conversion typically adds ten to twenty per cent to the value of a property. Adding a bedroom with en-suite is one of the most cost-effective ways to increase property value. The return depends on the quality of the conversion, the local property market, and how well the space integrates with the rest of the house. In high-value areas, the increase in property value often significantly exceeds the cost of the conversion itself.

What building regulations apply to loft conversions?

All loft conversions require Building Regulations approval. Key requirements include structural stability of the new floor and any alterations to the roof structure, fire safety measures including a protected escape route with FD30 fire doors and interlinked smoke alarms, thermal insulation to current standards, sound insulation if converting above a party wall, safe staircase design with adequate headroom, and compliance with electrical safety requirements. A building control inspector will visit at key stages to approve the work.