A loft conversion in the UK typically costs between £27,500 and £75,000 in 2026, with most homeowners spending around £50,000. A simple Velux (rooflight) conversion is the cheapest option, starting from around £22,500, while a dormer usually costs £40,000–£60,000. Hip-to-gable and mansard conversions cost more, from around £50,000 up to £80,000 or more, and London prices can be 15–30% higher.
This guide explains what each type of loft conversion costs, what is included, the extra fees to plan for, and how to get an accurate price for your own project.
Loft Conversion Cost UK 2026: Quick Summary
| Type of loft conversion | Typical cost (around 30m²) | Cost per m² | Typical build time |
|---|---|---|---|
| Velux / rooflight | £22,500 – £30,000 | around £920 | 4–6 weeks |
| Dormer | £40,000 – £60,000 | around £1,670 | 10–12 weeks |
| Hip-to-gable | £50,000 – £70,000 | around £2,000 | 10–12 weeks |
| Mansard | £50,000 – £80,000+ | around £2,170 | 8–10 weeks |
| Modular | £30,000 – £60,000 | around £1,500 | 2–3 weeks on site |
Figures are based on 2026 UK cost guides from Checkatrade, Homebuilding & Renovating and the Federation of Master Builders (sources listed at the end). Prices vary by location, house type, size and specification. Use them as a guide, not a quote.
How Much Does a Velux Loft Conversion Cost?
A Velux or rooflight loft conversion usually costs £22,500 to £30,000. It is the cheapest type because the shape of the roof does not change. Windows are fitted into the existing roof slope, the floor is strengthened, and a staircase, insulation and finishes are added.
A Velux conversion works best where the loft already has enough headroom. Each roof window typically costs around £1,000–£1,200 to supply. Many rooflight conversions fall under permitted development, so planning permission is often not needed.
How Much Does a Dormer Loft Conversion Cost?
A dormer loft conversion typically costs £40,000 to £60,000, with an average of around £50,000. A dormer is a box-shaped extension built out from the roof slope, usually at the rear. It adds headroom and usable floor space, which makes it the most popular type of loft conversion in the UK.
The main costs in a dormer conversion are the dormer structure itself, steel beams (often around £6,000), the staircase (often £1,200–£3,000 or more), windows, insulation, plastering and electrics. A larger full-width dormer, or a double dormer, will cost more than a small single dormer.
How Much Does a Hip-to-Gable Loft Conversion Cost?
A hip-to-gable loft conversion usually costs £50,000 to £70,000. It is common on semi-detached and detached houses with a hipped roof, where one side of the roof slopes inwards. The sloping side is built up into a vertical gable wall, which creates much more space inside. Many homeowners combine a hip-to-gable with a rear dormer for even more room, which adds to the cost.
How Much Does a Mansard Loft Conversion Cost?
A mansard loft conversion typically costs £50,000 to £80,000, and can exceed £100,000 on larger or complex projects. A mansard replaces most of the roof slope with a near-vertical wall and a flatter top, creating the largest amount of new space. Because it changes the shape of the roof, it usually needs planning permission and takes the most structural work.
Loft Conversion Cost per m²
Loft conversions are often priced per square metre of new floor space. As a rough guide in 2026:
- Velux / rooflight: around £900–£1,000 per m²
- Dormer: around £1,600–£1,800 per m²
- Hip-to-gable: around £2,000 per m²
- Mansard: around £2,100–£2,300 per m²
- Higher-specification finishes: £2,200–£3,000+ per m²
Smaller lofts often cost more per m², because fixed costs such as the staircase, steelwork and scaffolding are spread over fewer square metres.
What Affects the Cost of a Loft Conversion?
- Type of conversion: changing the roof shape (dormer, hip-to-gable, mansard) costs more than rooflights alone.
- Size: larger lofts cost more overall, but less per m².
- Headroom: if the loft is too low, the roof may need raising or the ceiling below lowering, which adds cost.
- Structure: steel beams, new floor joists and changes to the existing roof timbers.
- Staircase: a simple straight stair costs much less than a bespoke design.
- Bathroom or en-suite: adding one usually adds £3,000–£7,000 or more.
- Location: London and the South East are typically 15–30% more expensive.
- Finishes: windows, flooring, built-in storage and lighting all affect the final price.
Extra Costs and Fees to Budget For
| Item | Typical cost |
|---|---|
| Architectural drawings | £1,500 – £4,000 |
| Planning application (householder, England) | £528 |
| Lawful development certificate (England) | around £240 |
| Building Control fees | around £600 – £1,500 |
| Structural engineer | £750 – £2,500 |
| Party wall surveyor (semi-detached and terraced homes) | £1,000 – £2,500+ |
| Skip hire | £300 – £600 per skip |
| Contingency | 10–15% of the build cost |
A contingency is important. Older roofs often hide problems, such as rotten timbers or poor wiring, that only appear once work starts.
Do You Need Planning Permission for a Loft Conversion?
Many loft conversions in England fall under permitted development, so a full planning application is not always needed. Limits apply, including the amount of extra roof space (typically 40m³ for terraced houses and 50m³ for detached and semi-detached houses) and rules about the front roof slope. Mansard conversions, conversions in conservation areas, and flats usually need planning permission. Always check with your local planning authority before you start.
Almost every loft conversion needs Building Regulations approval, whether or not planning is needed. This covers structure, fire safety and escape, insulation, stairs and ventilation. You will need building regulations drawings for this.
How Long Does a Loft Conversion Take?
Most loft conversions take 6 to 12 weeks on site. A Velux conversion can take as little as 4–6 weeks, while a dormer or hip-to-gable usually takes 10–12 weeks. Design, drawings and approvals should be added before work starts, which often takes several weeks.
Loft Conversion Cost Breakdown: Where the Money Goes
For a typical dormer loft conversion, the budget is usually split across:
- Structural work: steel beams, padstones, new floor joists and the dormer structure
- Roof work: roof coverings, felt, battens, flashings and dormer cheeks
- Windows and rooflights
- Staircase and fire safety work
- Insulation, plasterboard and plastering
- First fix and second fix electrics and plumbing
- Doors, skirting, flooring and decoration
- Scaffolding, skips and site costs
A line-by-line loft conversion estimate shows each of these separately, so you can see exactly where the cost sits and compare builders' quotes fairly.
How to Keep Loft Conversion Costs Down
- Choose a rooflight or simple dormer where the headroom allows.
- Keep the layout simple, and place a bathroom above an existing one to shorten pipe runs.
- Get clear drawings before you ask for quotes, so builders price the same scope.
- Ask for itemised quotes, not a single lump sum.
- Agree a contingency and a clear process for changes before work starts.
How to Get an Accurate Loft Conversion Price
Online averages are a useful starting point, but the only way to know what your loft will cost is to price it from drawings. At Nextron Estimating, we prepare detailed loft conversion estimates for UK builders and loft conversion specialists, with quantities, materials and labour priced line by line.
- Loft conversion estimating: an itemised price from your drawings
- Loft conversion design drawings: layouts, planning and technical drawings
- Building regulations drawings: for your Building Control application
- House extension cost guide: compare the cost of extending your home
Frequently Asked Questions
How much does a loft conversion cost in the UK?
Most UK loft conversions cost between £27,500 and £75,000 in 2026, with an average of around £50,000. The final price depends on the type, size, location and finish.
What is the cheapest type of loft conversion?
A Velux or rooflight conversion is the cheapest, usually £22,500–£30,000, because the roof shape stays the same.
How much does a dormer loft conversion cost?
A dormer loft conversion typically costs £40,000–£60,000, with an average of around £50,000.
How much does a loft conversion cost per m²?
As a guide, from around £900 per m² for a Velux conversion to around £2,000–£2,300 per m² for hip-to-gable and mansard conversions.
Is a loft conversion cheaper than an extension?
Often, yes, per square metre, because a loft conversion uses existing space and does not need new foundations. However, prices depend on the project, so compare itemised quotes for both.
How long does a loft conversion take?
Usually 6–12 weeks on site, depending on the type. Allow extra time for design and approvals.
Do I need planning permission for a loft conversion?
Not always. Many fall under permitted development, but mansards, conservation areas and flats usually need planning permission. Building Regulations approval is almost always required.
Sources
- Checkatrade: Loft Conversion Cost 2026 UK Price Guide
- Homebuilding & Renovating: Loft conversion costs
- Federation of Master Builders: Loft conversion cost breakdown
Get a Loft Conversion Estimate
Send us your drawings and we will prepare a clear, itemised loft conversion estimate. If you want to see our format first, ask for a free sample estimate.
Call us on +44 7576 532125, or email info@nextronestimating.co.uk
