A loft conversion in the UK costs between £20,000 and £145,000 in 2026, depending on the type, size, and location of your property. It remains one of the best-value home improvements you can make — adding up to 24% to your property’s value according to Nationwide research.
The Short Answer
Costs vary significantly based on the type of conversion you choose. Here is a plain-English summary before we get into the detail:
- Velux (rooflight) conversion — simplest, cheapest: from £20,000–£45,000
- Dormer conversion — most popular type: £35,000–£65,000
- Hip-to-gable conversion — best for semis: £40,000–£70,000
- Mansard conversion — most space, highest cost: £55,000–£90,000+
- London / South East — add 20–40% to any of the above
Always add a 10–15% contingency on top of any quoted figure for unforeseen works.
Costs by Conversion Type
The table below gives a consolidated view of what each type of loft conversion costs across the UK in 2026, based on multiple industry sources.
| Conversion Type | UK Cost Range | London / South East | Best For |
|---|---|---|---|
| Velux / Rooflight | £20,000–£45,000 | £35,000–£60,000 | Properties with good existing ridge height; no structural changes needed |
| Rear Dormer | £35,000–£65,000 | £50,000–£90,000 | Most terraced and semi-detached homes; most popular UK type |
| L-Shaped Dormer | £50,000–£80,000 | £65,000–£110,000 | Victorian / Edwardian properties with rear extension |
| Hip-to-Gable | £40,000–£70,000 | £55,000–£90,000 | 1930s–1950s semis and detached homes with hipped roofs |
| Mansard | £55,000–£90,000+ | £75,000–£130,000+ | Terraced London properties; maximum space gain |
What Each Conversion Type Means
Velux / Rooflight Conversion
A Velux conversion is the simplest and least disruptive type — it involves reinforcing the existing floor, insulating the roof, fitting Velux-style skylights, and adding a staircase. No structural changes are made to the roofline itself, which keeps costs low. It is only suitable if your existing loft already has sufficient height — generally at least 2.2 metres from floor joist to ridge — so always check this before assuming a Velux conversion is possible.
Rear Dormer Conversion
The rear dormer is the most popular loft conversion in the UK. It involves building a box-like structure that extends vertically from the rear slope of the existing roof, creating a vertical rear wall with standard-height windows. This dramatically increases usable head height and floor space and typically creates a full bedroom with en-suite. Most rear dormers in England fall under permitted development rights — meaning no planning permission required — making them an accessible choice for most homeowners.
L-Shaped Dormer Conversion
An L-shaped dormer combines a rear dormer with a second dormer over the top of a back addition — common on Victorian and Edwardian terraced houses. This creates significantly more floor space than a standard rear dormer and can often accommodate two rooms. Costs are higher due to the additional structural complexity.
Hip-to-Gable Conversion
This type is designed specifically for houses with a hipped roof — where the roof slopes down on all four sides. The conversion involves replacing the sloping hipped end with a vertical gable wall, which dramatically increases the usable loft volume. It is typically combined with a rear dormer. If you live in a 1930s or 1950s semi-detached house, this is likely the right option for your property.
Mansard Conversion
A mansard is the most expensive and most structurally complex type — and delivers the most space. It involves rebuilding one or both roof slopes at a much steeper angle (typically 72 degrees) to create near-vertical walls, maximising usable floor area across the entire loft. Mansard conversions almost always require planning permission. They are particularly common in London terraced properties where they can create what effectively becomes a full additional storey.
What’s Included in the Price?
Most professional loft conversion quotes include the following.
Structural work:
- Steel beams (RSJs) and structural engineer calculations
- New floor joists and decking
- Dormer construction / roof restructuring (where applicable)
- Scaffolding
Interior first fix:
- Loft staircase (typically a space-saving staircase design)
- Stud wall framing
- First-fix electrics and plumbing
Interior second fix and finishing:
- Insulation (walls, roof, floor)
- Plastering
- Skirting boards, doors, and window finishes
- Decoration (often excluded — check your quote)
What is typically NOT included:
- Flooring (add £800–£1,800 for carpet or LVT)
- Furniture and storage
- Planning permission application fees (~£258 in England if required)
- Architect / structural engineer fees (~£2,000–£5,000)
Cost Per m² in 2026
Understanding cost per square metre helps you reality-check quotes. In 2026, loft conversions in the UK typically cost between £1,600 and £2,500 per m² for a standard spec — though London and the South East will push this higher.
| Size | Estimated Total Cost (UK average) |
|---|---|
| 20m² (small) | £32,000–£50,000 |
| 30m² (typical) | £48,000–£75,000 |
| 40m² (large) | £64,000–£100,000 |
| 50m² (very large) | £80,000–£125,000 |
These are broad estimates. Always get at least three quotes from vetted builders — costs vary substantially between contractors, regions, and specifications.
What Affects the Final Cost?
Several factors can push your quote up or down significantly.
Factors that increase cost:
- Conversion type — a mansard costs roughly twice a Velux conversion
- Structural complexity — older properties, unusual roof configurations, and load-bearing issues add cost
- Specification — high-end materials, underfloor heating, bespoke joinery
- Access — restricted access to site increases scaffolding and labour costs
- Existing loft condition — discovering asbestos, rot, or inadequate joists mid-project adds unforeseen costs (hence the 10–15% contingency rule)
Factors that reduce cost:
- Simple roof structure with good existing ridge height
- Property in the Midlands, North of England, Wales, or Scotland
- Standard specification finishes
- Planning permission not required (permitted development)
Do You Need Planning Permission?
Most loft conversions in England do not require planning permission and fall under Permitted Development rights — provided they meet specific conditions.
You are likely covered by permitted development if:
- Your property is a standard house (not a flat, maisonette, or listed building)
- The volume added does not exceed 40 cubic metres for a terraced house or 50 cubic metres for a semi-detached or detached house
- The conversion does not exceed the height of the existing roof
- The conversion does not front the main highway (principal elevation)
- Your property is not in a Conservation Area or Area of Outstanding Natural Beauty
You will need planning permission if:
You are building a mansard (almost always requires permission)
You live in a Conservation Area or on Article 2(3) designated land
Permitted development rights have been removed from your area (check with your local council)
ℹ️ Always apply for a Lawful Development Certificate even when planning permission is not required — it costs ~£110 and provides legal proof that your conversion was lawful, which you will need when you sell the property.
Building regulations approval is always required, regardless of whether planning permission is needed. This is separate from planning permission and covers fire safety, structural integrity, insulation, and means of escape.
How Long Does a Loft Conversion Take?
A typical loft conversion in the UK takes between 4 and 10 weeks from start to completion, depending on type and complexity.
| Conversion Type | Typical Build Time |
|---|---|
| Velux / Rooflight | 4–6 weeks |
| Rear Dormer | 5–8 weeks |
| L-Shaped Dormer | 7–10 weeks |
| Hip-to-Gable | 6–9 weeks |
| Mansard | 8–12 weeks |
Note that this is build time only — the planning, design, and tendering process typically adds 2–4 months before work even begins on site. Factor in a realistic total project timeline of 4–6 months from the decision to proceed to completion.
How Much Value Does a Loft Conversion Add?
A loft conversion is one of the highest-return home improvements available in the UK. According to Nationwide Building Society research, adding a bedroom and bathroom via a loft conversion can increase a three-bedroom property’s value by up to 24% — equivalent to approximately £65,700 on an average UK home.
In London, a well-executed loft conversion typically adds between 15% and 25% to property value — on a £500,000 London home, that represents an increase of £75,000 to £125,000.
| Property Type | Avg. Value Added | Approx. Conversion Cost | Estimated ROI |
|---|---|---|---|
| 3-bed terrace → 4-bed | 10–13% | £45,000–£65,000 | Strong — often cost-neutral or profitable |
| 3-bed semi → 4-bed | 13–18% | £50,000–£70,000 | Strong, especially in commuter belt |
| 3-bed detached → 4-bed | 15–24% | £55,000–£80,000 | Excellent if adding bedroom + en-suite |
| 2-bed semi → 3-bed | 17–24% | £40,000–£65,000 | Highest ROI category |
The key principle: converting an additional bedroom and bathroom consistently delivers a higher return than it costs in most UK regions — which cannot be said for many other types of home improvement.
Is a Loft Conversion Worth It in 2026?
BestBuilders’ 2026 ROI guide confirms that a loft conversion remains one of the few home improvements where the added value typically exceeds the cost of the work — particularly when adding a bedroom with en-suite bathroom. Compare that to a kitchen or bathroom renovation, where you rarely recoup more than 50–70% of the cost in added value.
The case is especially strong if:
- You are adding a bedroom (increases value by ~13%) and a bathroom (adds a further ~4%)
- You would otherwise need to move house to get extra space
- Your property is in London, the South East, or a high-demand commuter town
- You are on a popular street where comparable 4-bed properties command significantly higher prices than 3-beds
The case is weaker if:
- Your area already has abundant 4-bed supply and limited price premium between 3- and 4-bed properties
- Your loft is structurally complex and quotes are coming in above £90,000
- You are planning to sell in under two years (insufficient time to recoup costs)
How to Get the Best Price
Follow these steps to avoid overpaying and protect yourself from poor-quality work.
- Get at least three quotes — from LABC Warranty-registered or Federation of Master Builders-accredited contractors
- Check their previous loft conversion projects — ask to see photos and speak to previous clients
- Get a detailed written specification — ensure quotes cover the same scope before comparing prices
- Never pay more than 30% upfront — stage payments tied to project milestones protect you if there are problems
- Check building regulations approval is included in the quote — do not assume it is
- Get a Lawful Development Certificate from your local council even if planning permission is not required
- Add 10–15% contingency to your budget before you start — unforeseen works are common in older properties
Frequently Asked Questions
How much does a loft conversion cost in the UK in 2026?
A Velux loft conversion starts from around £20,000–£45,000. A rear dormer — the most popular type — typically costs £35,000–£65,000. A mansard conversion, which delivers the most space, costs £55,000–£90,000 or more. London and the South East add 20–40% to these figures.
Does a loft conversion add value to your home?
Yes — Nationwide research shows a loft conversion adding a bedroom and bathroom can increase a typical three-bedroom home’s value by up to 24%, equivalent to approximately £65,700. It is one of the highest-return home improvements available.
Do I need planning permission for a loft conversion?
Most loft conversions in England fall under permitted development rights and do not require planning permission — provided they meet volume, height, and materials conditions. Flats, listed buildings, conservation areas, and mansard conversions are the main exceptions. Building regulations approval is always required.
How long does a loft conversion take?
A typical loft conversion takes 4 to 10 weeks to build, depending on type and complexity. Add 2–4 months for planning, design, and contractor tendering before work starts. Total project time: realistically 4–6 months.
What is the cheapest type of loft conversion?
A Velux (rooflight) conversion is the cheapest — starting from around £20,000 — because it makes no structural changes to the roofline and simply reinforces the floor, insulates the roof space, and adds skylights and a staircase.
What is the most expensive type of loft conversion?
A mansard conversion is the most expensive, typically costing £55,000–£90,000+ across the UK and up to £130,000+ in London. It delivers the most usable floor space but almost always requires planning permission and involves rebuilding the entire rear roof slope.
How much does a loft conversion cost in London?
London loft conversion costs are typically 20–40% higher than the national average. A rear dormer in London costs approximately £50,000–£90,000; a mansard can reach £130,000 or more.
