A loft conversion is one of the smartest ways to add space and value to your home without the upheaval of moving. It is also one of the most variable home improvement projects in terms of cost, because the type of conversion, your property structure, and your location all have a massive impact on the final bill.
This guide covers every type of loft conversion available in the UK, with real pricing for 2026 so you can plan your budget before you speak to a single builder.
A basic Velux loft conversion costs £15,000 to £30,000. A rear dormer runs £35,000 to £60,000. Hip to gable conversions cost around £55,000 to £70,000. A mansard conversion typically starts at £60,000 and can reach £80,000+. London prices are 30% to 60% higher across the board.
Loft Conversion Costs by Type
| Conversion Type | UK Average | London |
|---|---|---|
| Velux (rooflight only) | £15,000 to £30,000 | £25,000 to £45,000 |
| Rear dormer | £35,000 to £60,000 | £50,000 to £80,000 |
| Hip to gable | £55,000 to £70,000 | £70,000 to £95,000 |
| Mansard | £60,000 to £80,000 | £80,000 to £130,000 |
| L shaped dormer | £50,000 to £75,000 | £65,000 to £100,000 |
Budget vs Mid Range vs Premium Loft Conversions
| Feature | Budget (£15,000 to £30,000) | Mid Range (£35,000 to £60,000) | Premium (£60,000+) |
|---|---|---|---|
| Type | Velux only | Rear dormer | Mansard or hip to gable + dormer |
| Floor space | Limited by roof angle | Good usable space | Maximum floor area |
| En suite | Unlikely (adds too much cost) | Standard en suite | Full bathroom with premium fittings |
| Staircase | Basic, space efficient | Standard with balustrade | Bespoke design, oak or glass |
| Finish | Ready for decorating | Plastered and painted | Fully fitted, wardrobes, flooring |
| Planning | Permitted development | Usually permitted development | Full planning application |
What Each Type Involves
Velux (Rooflight) Conversion
The simplest and cheapest option. The existing roof structure stays as it is, and Velux windows are fitted into the slope. Works well if your loft already has enough headroom (minimum 2.2 metres at the highest point). No changes to the external appearance of the house, which usually means no planning permission required.
Rear Dormer
The most popular type of loft conversion in the UK. A flat roofed or pitched roof box is built out from the rear roof slope, creating full height space across most of the room. Usually falls under permitted development (no planning permission needed) provided it meets the size limits.
Hip to Gable
Common on semi detached and detached houses with hipped roofs. The sloping side wall is extended vertically to create a gable end, dramatically increasing the usable floor space. Usually combined with a rear dormer for maximum room size.
Mansard
The most expensive but most spacious option. The rear roof slope is replaced with an almost vertical wall and a flat roof on top. Creates the maximum possible living space. Almost always requires planning permission because it significantly changes the roof profile.
Cost Breakdown: Where the Money Goes
| Cost Element | Typical Percentage | Approximate Cost (Dormer) |
|---|---|---|
| Structural steelwork | 10% to 15% | £4,000 to £8,000 |
| Dormer construction | 25% to 30% | £10,000 to £18,000 |
| Staircase | 8% to 12% | £3,000 to £6,000 |
| Electrics | 5% to 8% | £2,000 to £4,000 |
| Plumbing (if en suite) | 8% to 12% | £3,000 to £6,000 |
| Plastering and finishing | 10% to 15% | £4,000 to £8,000 |
| Windows (Velux or dormer) | 5% to 8% | £2,000 to £4,000 |
| Insulation | 3% to 5% | £1,500 to £3,000 |
| Flooring | 3% to 5% | £1,000 to £2,500 |
Choosing the Right Loft Conversion Company
Loft conversions are specialist work. A general builder can do it, but a company that specialises in loft conversions will do it faster, more efficiently, and often at a lower total cost because they have done hundreds of them. They know the regulations, they have established relationships with structural engineers and building control inspectors, and they can anticipate problems before they become expensive.
When comparing quotes, make sure every quote covers the same scope of work. A cheaper quote may exclude the staircase, electrics, or plastering, which are significant additional costs. Ask each company to provide a line by line breakdown so you can compare fairly. Visit at least two completed conversions from each company to assess the quality of their work in person.
Planning Permission and Building Regs
Most rear dormer conversions fall under permitted development, meaning no planning permission is needed. However, you will always need building regulations approval, regardless of the type. A building regulations application costs £200 to £500. Structural calculations from a structural engineer cost an additional £300 to £800.
You will need planning permission for mansard conversions, any work on listed buildings, conversions in conservation areas, and any conversion that exceeds the permitted development volume limits.
Does a Loft Conversion Add Value?
According to most estate agents, a well done loft conversion adds 15% to 20% to the value of your home. On a £300,000 house, that is £45,000 to £60,000 of added value. Given that a dormer conversion costs £35,000 to £60,000, the maths usually works out in your favour, particularly if the conversion adds a bedroom and en suite bathroom.
Hidden Costs to Budget For
- Party wall agreement: If your conversion involves work on or near a shared wall with a neighbour, you will need a party wall agreement. Surveyor fees run £700 to £1,500 per neighbour.
- Architect or designer fees: Drawings and design typically cost £1,000 to £3,000.
- Building control inspection fees: £200 to £500.
- Decorating: Most quotes include plastering but not painting. Budget £500 to £1,500 for decorating the new room and the stairway area.
- Fire safety: Building regs require fire doors on all habitable rooms off the new staircase, plus a mains wired smoke alarm system. This can add £500 to £1,500.
What Affects the Price?
- Conversion type. A Velux conversion costs a third of a mansard. The type of conversion has the biggest single impact on the final bill.
- Location. London prices are 30% to 60% higher than the rest of the UK. Labour, scaffolding, and skip hire all cost more in the capital.
- Roof structure. Traditional cut timber roofs are easier (and cheaper) to convert than modern trussed roofs, which require more extensive structural work.
- Head height. If your loft already has 2.2m+ head height, a Velux conversion is feasible. If not, you need a dormer or mansard to create usable space, which costs significantly more.
- En suite bathroom. Adding a bathroom in the loft adds £5,000 to £10,000. The plumbing, waterproofing, and tiling all add up quickly.
- Staircase position. The staircase needs to fit within the existing footprint without making the landing below unusable. Complex staircase solutions cost more than straightforward ones.
- Access for scaffolding. Terraced houses with rear access issues or properties on busy roads may face higher scaffolding costs.
- Party wall agreements. If you share a wall with a neighbour (terraced or semi detached), you will likely need a party wall agreement, adding £700 to £1,500 per neighbour.
Red Flags to Watch For
- No structural engineer. Every loft conversion requires structural calculations. If the builder says they do not need an engineer, find a different builder.
- No building regulations application. Building regulations approval is required for every loft conversion, regardless of whether planning permission is needed. A builder who does not mention building regs is either inexperienced or planning to cut corners.
- Vague specification. The quote should detail exactly what is included: structural work, insulation, plasterboarding, electrics, plumbing, staircase, windows, and fire safety. A lump sum with no breakdown is impossible to compare with other quotes.
- No previous examples. A loft conversion specialist should have a portfolio of completed projects. Ask to see photos and, ideally, visit a completed conversion to check the quality of work.
- Unrealistically low price. If one quote is 30% below the others, something is being left out. Ask what is included and compare the scope of work line by line.
- No mention of fire safety. Building regulations require fire doors, mains wired smoke detectors, and a protected escape route from the loft. If the builder does not mention fire safety, they may not be familiar with the regulations.
How to Save Money
- Choose a Velux conversion if headroom allows. No structural changes to the roof means dramatically lower costs.
- Skip the en suite. A bathroom in the loft adds £5,000 to £10,000 to the project. If there is a bathroom on the floor below, you may not need one.
- Get quotes from loft conversion specialists, not general builders. Specialists do these conversions every week. They are faster, more efficient, and often cheaper than a general builder learning as they go.
- Be flexible on timing. Winter months (November to February) are quieter for builders, and you may get better rates.
A loft conversion in the UK costs £15,000 to £80,000+ depending on the type and location. A rear dormer at £35,000 to £60,000 is the most popular option and usually offers the best return on investment. Get at least three quotes from specialist loft conversion companies, check their previous work, and budget an extra 10% to 15% for hidden costs. See also our guides on electrician costs and bathroom renovation costs for related work.
Frequently Asked Questions
How much does a loft conversion cost in the UK in 2026?
A basic Velux loft conversion costs £15,000 to £30,000 in the UK in 2026. A rear dormer runs £35,000 to £60,000. Hip to gable conversions cost £55,000 to £70,000. A mansard conversion starts at £60,000 and can reach £80,000 or more. London prices are 30% to 60% higher across all types.
How much does a dormer loft conversion cost?
A rear dormer loft conversion costs £35,000 to £60,000 in the UK, or £50,000 to £80,000 in London. It is the most popular type of loft conversion and usually falls under permitted development, meaning no planning permission is needed.
Does a loft conversion add value to a house?
A well done loft conversion adds 15% to 20% to the value of a home according to most estate agents. On a £300,000 house, that is £45,000 to £60,000 in added value. A dormer conversion costing £35,000 to £60,000 usually offers a positive return.
Do I need planning permission for a loft conversion?
Most rear dormer conversions fall under permitted development and do not need planning permission. However, mansard conversions, work on listed buildings, conversions in conservation areas, and those exceeding volume limits do require planning permission. Building regulations approval is always required regardless.
How long does a loft conversion take?
A Velux loft conversion takes 4 to 6 weeks. A dormer conversion takes 6 to 10 weeks. A mansard or hip to gable conversion can take 8 to 12 weeks. These timelines exclude decorating and snagging.
Can I convert my loft if the ceiling height is low?
If your loft has less than 2.2 metres of head height at the ridge, a Velux conversion is unlikely to work. A dormer or mansard conversion can create sufficient head height by extending the roof structure. A specialist can assess your loft and advise which options are viable.
Do I need a party wall agreement for a loft conversion?
If your conversion involves work on or near a shared wall with a neighbour, you will likely need a party wall agreement under the Party Wall Act 1996. Surveyor fees run £700 to £1,500 per neighbour. Discuss this with your builder before work begins.
Is a loft conversion cheaper than an extension?
Generally yes. A loft conversion costs £15,000 to £80,000 while a ground floor extension costs £30,000 to £100,000+. Loft conversions also avoid the cost of foundations, which can be £5,000 to £10,000 alone. The space already exists; you are simply making it habitable.