Loft Conversion Prices in 2026 at a Glance

For most UK homes, the total build budget for a loft conversion in 2026 sits between £20000 and £70000. The range is wide because not all loft conversions are structurally similar. A simple rooflight conversion can use most of the existing roof, while a mansard often rebuilds a large part of it. The type you choose has the biggest influence on cost, followed by size, roof shape, access, and finish level.

If you want the fastest cost snapshot, use these base ranges: Velux or rooflight £20000-£30000, dormer £35000-£55000, hip-to-gable £45000-£65000, and mansard £45000-£70000. Those figures are common for mainstream contractors in 2026 for a standard bedroom conversion, before luxury upgrades. They can rise where scaffold access is difficult, engineering is complex, or high-end interior specs are selected.

These figures should be treated as planning numbers, not fixed quotes. Your final contract price depends on site survey findings, specification detail, insulation strategy, fireproofing scope, staircase complexity, electrical layout, and whether you are adding a full bathroom. If you are collecting builder quotes, request a written inclusion schedule so you can compare like-for-like. A lower headline figure is often missing key items such as plaster finish level, sanitaryware allowance, or waste removal.

All cost figures in this guide are UK estimates for 2026 and intended for budgeting and comparison.

Loft Conversion Cost Calculator (2026)

Use this quick calculator to estimate a likely budget range from loft type and floor area. It scales standard UK 2026 base prices by size and gives a realistic estimate range. For financial decisions, always confirm with a measured survey and detailed contractor quote.

Calculator estimate includes core conversion assumptions and does not automatically include premium finishes, major steel redesign, or complex planning-related redesign work.

Detailed Cost by Loft Conversion Type

1) Velux / Rooflight Loft Conversion: £20000-£30000

A Velux or rooflight conversion is usually the most affordable route because it keeps the existing roof form and avoids major rear or side roof extensions. In most cases, this means less structural alteration, faster labour time, and lower scaffold complexity. It is often the first option homeowners consider when they already have enough ridge height and can fit a compliant staircase without major layout disruption on the floor below.

This option is commonly suitable where you want a straightforward extra bedroom, home office, or guest room. A typical budget in 2026 includes strengthening floor joists, roof insulation, roof windows, first-fix plumbing and electrics where relevant, plasterboard, plaster finish, second-fix joinery, and decoration-ready walls. Where possible, this approach keeps costs predictable because the roof shell itself is largely retained.

Planning permission is not typically required when the external roof shape is not substantially changed and permitted development limits are followed, so many households can proceed faster. Even so, it is sensible to secure a Lawful Development Certificate for proof during future sale. Velux conversions can become more expensive when steel beams are required due to unusual spans, or when chimney positions, water tanks, or awkward structural bracing force design changes.

If your objective is practical extra space at the lowest possible cost, this is usually the strongest value option. The trade-off is that usable floor area and standing head height may be less than a dormer or mansard.

2) Dormer Loft Conversion: £35000-£55000

A dormer conversion extends out from the existing roof slope to create additional floor area and headroom. It is popular because it offers a strong balance between cost and usable space. Rear dormers are common in UK terraced and semi-detached housing stock where the goal is to create a full main bedroom with en-suite and practical circulation space.

The build cost in 2026 normally covers structural framing, dormer roof and cladding, insulation upgrades, windows, internal partitions, and full internal finishing. Because a dormer changes roof geometry, scaffold, weatherproofing, and structural design complexity are higher than rooflight-only projects. That is why the range is typically £35000-£55000 rather than entry-level rooflight prices.

In many cases, rear dormers are still possible under permitted development, but design limits and location factors matter. Front dormers are often more planning-sensitive, especially where the property faces a highway. If you are in a conservation area or your home has specific restrictions, planning requirements can tighten significantly. Always check before commissioning final drawings.

A dormer is often the best middle-ground option where you need a meaningful increase in usable space but want to avoid the cost and planning burden of a full mansard reconstruction.

3) Hip-to-Gable Loft Conversion: £45000-£65000

Hip-to-gable conversions are common on semi-detached or end-terrace properties with a hipped roof. The sloping side roof is rebuilt as a vertical gable wall, which creates significant additional internal volume. This can transform lofts that previously felt too narrow for practical room layout and allows better staircase alignment.

Because this method involves major structural and roofing changes, costs sit higher than standard dormers. In 2026, the realistic planning range is usually £45000-£65000, with upper values seen where roof geometry is awkward, neighbours are very close, or the project includes premium finishes and a full en-suite specification. Some homes combine a hip-to-gable with a rear dormer, which can further increase costs but delivers substantial usable space.

Planning permission may not always be required if works remain within permitted development and design limits, but the legal position depends on property type, prior roof extensions, and local constraints. A professional design package and formal planning check are essential before construction commitment.

When done well, hip-to-gable conversions deliver one of the best outcomes for floor area gained relative to footprint, especially in suburbs where moving to a larger house would be significantly more expensive.

4) Mansard Loft Conversion: £45000-£70000

A mansard conversion is usually the most comprehensive loft strategy. It creates a near-flat roof with a steep rear slope and substantially alters the existing roof profile, generating large and practical internal space. Because of the scope of structural alteration, planning, and roofing work, mansards generally sit at the upper end of loft pricing.

Typical UK budgets in 2026 run from £45000 to £70000, and complex city projects can exceed this where party wall coordination, crane access, acoustic treatment, and high-end architectural finishes are required. The upper range often reflects not only build complexity but also additional professional coordination and approval timelines.

Unlike many rooflight or rear dormer projects, a mansard usually needs planning permission. Councils evaluate visual impact, streetscape character, overlooking, and design detail more closely. If the planning route is accepted, the conversion can create near full-height accommodation and strong long-term value, often with layout flexibility similar to a conventional upper floor.

This option suits homeowners planning to remain in the property for years and wanting a substantial quality-of-space upgrade rather than minimal extra room.

Essential Additional Costs Beyond the Main Build Quote

Many budgeting errors happen because homeowners compare contractor quotes without adding professional and statutory costs. A builder may provide an attractive headline price, but you still need engineering, design, approvals, and compliance work. These are not optional extras; they are core elements of a safe and legal loft conversion.

Fireproofing is frequently underestimated at quotation stage. Building control can require upgrades to doors, ceilings, and stair enclosures to maintain a compliant means of escape from the new loft level to final exit. If existing lower floors need door replacements or upgraded detectors, costs rise quickly. It is better to budget this clearly from the beginning than discover it late during inspections.

The staircase is another major variable. A compliant staircase must meet headroom, pitch, rise, and going requirements, and it has to fit into your existing floor plan with minimal disruption. Where the best route cuts through a key room or requires major reconfiguration, structural and finishing costs can rise. Early design coordination between architect, engineer, and builder can avoid expensive redesign during build.

Planning Permission and Permitted Development Rules

One of the biggest questions is whether planning permission is needed. The short answer is that many loft conversions can proceed under permitted development, but this is never automatic. Rules vary by nation and local authority, and specific property constraints can override general rights. Mansard conversions generally need planning permission because they significantly alter roof form. Velux and some rear dormer projects are often possible without full planning when conditions are met.

For homes in England, common permitted development checks include:

• Additional roof volume allowance is typically up to 40m³ for terraced homes and up to 50m³ for detached or semi-detached homes, including previous roof additions.
• No extension should project beyond the plane of the existing roof slope facing the highway.
• Materials should be similar in appearance to the existing house.
• No part of the extension should be higher than the highest part of the existing roof.
• Side-facing windows should be obscure glazed and non-opening below specified heights.
• Raised platforms, balconies, and verandas are generally not permitted under standard loft PD rights.

Even when a project appears to meet permitted development criteria, homeowners should strongly consider applying for a Lawful Development Certificate. It provides written legal confirmation from the council, which can prevent disputes later and is valuable at sale or remortgage stage. Mortgage lenders and buyers often ask for formal evidence that works were lawful.

If your home is listed, in a conservation area, or subject to prior restrictions, your planning route can be more complex. In these cases, early planning advice and strong design documentation can save months. Delays usually occur when applications are submitted without a complete set of drawings or without enough detail on materials and neighbour impact.

A practical approach is to decide loft type first, then verify planning position with a specialist designer before committing to structural calculations and contractor appointments. This sequence limits redesign costs and keeps project momentum realistic.

Building Regulations, Fireproofing, and Compliance Requirements

Building regulations are mandatory for loft conversions, regardless of whether planning permission is needed. They govern structural safety, fire safety, thermal performance, stair design, and ventilation. A project can look complete and still fail approval if these standards are not met. That is why the most reliable builders coordinate closely with building control from early stages.

Key compliance areas that affect your budget and design include:

• Structural integrity of new floor joists and roof supports, often requiring steel beams.
• Fire safety strategy, including protected escape routes and interconnected smoke alarms.
• Fire-resisting doors and upgraded ceiling/floor protection where required.
• Staircase dimensions, pitch, and safe headroom.
• Thermal insulation standards for roof, walls, and floor junctions.
• Ventilation and condensation control to protect long-term building health.
• Electrical and plumbing compliance certification where services are installed.

Fireproofing can include multiple layers of work: upgrading existing doors on lower levels, adding fire-rated plasterboard assemblies, improving alarm coverage, and ensuring stair routes are protected to the final exit. These upgrades are often essential to pass inspection and should be priced openly in your tender package.

The most common compliance mistake is treating the loft as a simple room fit-out. In reality, once you create a new storey, the safety approach for the house can change. Build quality and regulatory clarity matter as much as visual finish. If the goal is long-term value and smooth resale, documented compliance is non-negotiable.

Party Wall Agreement: When It Applies and What It Costs

If your loft conversion involves work on or near a shared wall, you may need to follow the Party Wall etc. Act 1996 (England and Wales). This often applies when steel beams are inserted into a party wall, when wall cutting is required, or where excavation near neighbouring foundations is involved. It is common in terraced and semi-detached housing.

The process usually starts with serving formal notice to affected neighbours before works begin. If neighbours consent in writing, the process can stay simple. If they dissent or do not respond, surveyors are typically appointed and a party wall award is prepared. This document sets out how works proceed and how property condition is managed.

Costs vary depending on complexity and whether one agreed surveyor or two separate surveyors are appointed. For budgeting, allow contingency because party wall administration can affect both timeline and pre-start costs. Even where relations are good, a clear documented process reduces disputes and protects both sides.

The practical point is to check party wall implications during design stage, not after contractor mobilisation. Early notices and realistic programming prevent delays that can otherwise push labour and scaffold costs higher.

How Much Value Does a Loft Conversion Add?

In many UK markets, a well-executed loft conversion typically adds around 20-25% to property value, especially where it creates a genuine extra bedroom and, ideally, an additional bathroom. Value uplift depends on local buyer demand, comparable sale evidence, and whether the new level feels like natural house accommodation rather than a compromised add-on.

For example, if a home is valued at £320000 before conversion, a 20-25% uplift suggests a potential increase of roughly £64000-£80000, subject to market conditions. That does not guarantee profit in every case, but it explains why loft projects remain popular where moving costs are high. Stamp duty, legal fees, removals, and higher mortgage costs often make relocation materially more expensive than extension of existing space.

Design quality has a major effect on realised value. Buyers respond strongly to good natural light, practical ceiling heights, sensible stair placement, and useful storage integration. Poor layout, weak fire safety documentation, or unfinished detailing can reduce return even when spend is high.

If your objective includes future resale, focus on creating market-recognised functional space: a true bedroom, compliant access, quality bathroom where possible, and complete paperwork for planning and building control. This is the difference between nominal floor area and genuine marketable value.

Regional Cost and Value Variability

Build costs and uplift potential vary significantly by location. Labour rates, scaffold access, local demand, and planning complexity all differ across the UK. London and parts of the South East often carry higher contractor pricing and consultant fees, while some regions may offer lower build rates but different resale uplift dynamics.

Typical Loft Conversion Timeline and Project Stages

Understanding programme duration helps with financing, accommodation planning, and contractor selection. A typical loft conversion can run anywhere from 6 to 16 weeks on site, depending on type and complexity, with pre-construction design and approvals adding several weeks.

1. Feasibility and survey: initial measurements, options review, head height checks, and budget outline.
2. Design and engineering: architectural plans, structural calculations, and staircase coordination.
3. Planning and lawful development checks: submit required applications where needed.
4. Party wall process: issue notices and secure agreements when applicable.
5. Tender and contract: compare quotes, clarify inclusion schedule, and confirm programme.
6. Construction: scaffold, structural works, weatherproofing, first-fix, insulation, plastering, and second-fix.
7. Inspection and sign-off: building control approval and completion documentation.

Budget reliability improves when each stage is clearly documented before work starts. Most cost overruns come from late scope additions, unclear finish allowances, or underestimating compliance upgrades. If time certainty matters, choose contractors who provide weekly progress logs and milestone payment structure rather than open-ended billing.

A careful front-end process can feel slower, but it usually saves money and reduces stress during build. Good documentation is cheaper than rework.

How to Keep Loft Conversion Costs Under Control in 2026

Price pressure in 2026 means cost control should be proactive. The objective is not to chase the cheapest quote, but to reduce avoidable risk. A lower quote with weak detail can become the most expensive route once variations begin.

• Lock your design before appointing a builder, including staircase position and bathroom layout.
• Use itemised quotes with explicit allowances for sanitaryware, electrics, and finishes.
• Confirm what fireproofing work is included to avoid inspection-stage surprises.
• Include structural engineer details in the tender pack so all builders price the same scope.
• Set aside a contingency fund for hidden defects or scope adjustments.
• Prioritise buildability and durable materials over purely cosmetic upgrades at first fix stage.
• Keep communication centralised so client, designer, engineer, and builder work from one current drawing set.

A practical target is to define must-have items first, then rank optional upgrades. This lets you protect core structural and compliance quality while controlling finish spend. If budget tightens mid-project, reducing optional specification is far safer than cutting safety or compliance work.

Loft Conversion Cost FAQ (7 Questions)

Final Budgeting Summary

If you want a clear 2026 budgeting framework, start with the core ranges: Velux £20000-£30000, dormer £35000-£55000, hip-to-gable £45000-£65000, mansard £45000-£70000. Then add professional fees, building regulations costs, staircase allowance, fireproofing requirements, and any party wall administration. This gives a realistic project total rather than a partial build-only number.

The highest-return loft conversions are usually those that combine sensible design, full compliance, and practical everyday usability. A conversion that works well for living will also perform better at valuation and resale stage. Use the calculator above for first-pass planning, then move to measured survey and itemised quotes for decision-ready figures.