Loft Conversion Cost UK 2026: £20,000 to £95,000 by Type

A loft conversion is still one of the highest-return home improvements in the UK, but the price varies widely by type, size, property and location. This 2026 guide breaks down realistic costs by conversion type, per square metre, by property and by region, plus professional fees and what a premium design-and-build loft conversion in London actually costs. All figures are updated for 2026 and drawn from live UK projects.

How much does a loft conversion cost?

A loft conversion in the UK typically costs £20,000 to £75,000 in 2026, or about £2,400 to £4,100 per square metre (build only). A simple rooflight conversion starts around £20,000 to £40,000, a dormer runs £40,000 to £70,000, and a mansard, the most expensive type, costs £55,000 to £95,000. London projects cost roughly 20 to 40 percent more, and professional fees add a further £6,000 to £15,000.

Loft conversion type	Typical UK cost (2026)	London (approx.)
Rooflight / Velux	£20,000 -£40,000	£28,000 -£50,000
Dormer (standard rear)	£40,000 -£70,000	£50,000 -£90,000
L-shaped dormer	£55,000 -£90,000	£70,000 -£120,000
Hip-to-gable (with dormer)	£50,000 -£85,000	£65,000 -£110,000
Mansard	£55,000 -£95,000	£75,000 -£140,000

Loft conversion cost by type (2026)

Rooflight (Velux) loft conversion cost: £20,000 to £40,000

The cheapest option. Rooflight windows are set into the existing roofline, with floor strengthening, insulation, plasterboarding and a new staircase. There is no change to the roof shape, it is usually permitted development, and it is the fastest type to build. It works best where you already have enough head height, around 2.2 metres at the ridge.

Read the full guide to Velux and rooflight loft conversions

Dormer loft conversion cost: £40,000 to £70,000

The most popular UK choice. A box-shaped structure replaces one roof slope to create full headroom and full-height windows. The cost rises with size, a full-width dormer, or an added bathroom. An L-shaped dormer, which adds a second dormer over a rear addition, typically costs £55,000 to £90,000 and creates the most usable space on a terraced house.

Planning a dormer in the capital? See our full dormer loft conversion London guide for dormer types, borough-by-borough planning rules and real project costs.

Hip-to-gable loft conversion cost: £50,000 to £85,000

For end-of-terrace, semi-detached and detached homes. The sloping hip end of the roof is rebuilt as a vertical gable wall, almost always combined with a rear dormer to maximise space. It involves more structural work than a dormer, which is why it costs more.

Read the full guide to hip to gable loft conversions

Mansard loft conversion cost: £55,000 to £95,000

The most expensive and most space-creating type. The rear roof slope is rebuilt at roughly 72 degrees to form a near-vertical wall and a flat roof. A mansard always needs planning permission and a structural engineer, and is common on period London terraces.

Read the full guide to mansard loft conversions

Loft conversion cost per square metre

Excluding finishes such as windows, flooring and sanitaryware, a UK loft conversion costs £2,400 to £4,100 per square metre. The variation comes from the conversion type, the scale of the roof alterations, access, finish level and location. Use the per-square-metre figure as a sanity check: a typical 25 to 30 square metre dormer at around £2,500 per square metre lands at roughly £62,000 to £75,000 before premium finishes.

Estimate your loft conversion cost: a quick calculation

To estimate your loft conversion cost, measure the loft's usable floor area and multiply it by £2,400 to £4,100 per square metre (excluding finishes). A typical 20 m² loft works out at £48,000 to £82,000 before finishes, then use the type bands above to sanity-check the result.

Three steps: first, measure the floor area you could realistically convert. Second, multiply by £2,400 per m² for a budget specification or £4,100 per m² for a premium one. Third, add professional fees (see the professional fees section below) and £8,000 to £15,000 if you want an en-suite. Treat the result, and any online loft conversion cost calculator, as a ballpark: the only accurate number is a fixed quote based on a survey of your actual roof, because head height, roof structure and access change the price more than floor area alone.

Loft conversion cost by property type

• Terraced house: a dormer or L-shaped dormer is most common, at £45,000 to £90,000.
• Semi-detached: a hip-to-gable plus dormer is typical, at £50,000 to £90,000.
• Detached: most options are open and footprints are larger, at £45,000 to £110,000.
• Bungalow: often needs structural reinforcement and a new staircase footprint, at £45,000 to £80,000.
• Flat or maisonette: depends on the lease, freeholder consent and party wall, from £40,000 plus legal and licence costs.

Small loft conversion cost

A small loft conversion costs £20,000 to £40,000 in 2026. That budget covers a rooflight (Velux) conversion within the existing roofline, typically a single bedroom or home office. You need roughly 2.2 m of head height at the ridge; if yours is tighter, a small rear dormer from £40,000 creates the missing headroom.

Three things keep a small conversion at the bottom of the range: staying within the existing roofline (no structural change to the roof), a simple staircase layout (see the stairs section further down), and skipping the en-suite, adding one typically adds £8,000 to £15,000. Even a compact loft room raises your bedroom count, which is where most of the value uplift comes from. If you are not sure your roof has the height, start with our guide to whether your loft is suitable for a conversion.

Is an attic conversion the same as a loft conversion?

Yes. An attic conversion and a loft conversion are the same thing in the UK and cost the same, £20,000 to £75,000 depending on type. "Attic" is used more in Scotland, Ireland and the US, and "loft" in England and Wales. The costs, planning rules and build times are identical. What changes the price is the conversion type and your location, not the word used.

Loft conversion cost in London and by region

Building costs are highest where property prices, labour rates and access constraints are highest. London adds roughly 20 to 40 percent over the UK average, driven by parking and skip restrictions, the congestion and ULEZ zones, higher labour and delivery costs, and tighter planning. Scotland and the South East are next, while Northern Ireland and the North of England are the cheapest. A dormer that costs £55,000 in the Midlands can be £80,000 or more in inner London.

Professional fees (2026)

On top of the build, budget £6,000 to £15,000 for the following.

• Certificate of Lawful Development (when permitted development applies): around £274 in England. A householder planning application (when permission is needed) is £548. Check current fees on the Planning Portal.
• Architectural and design drawings: £3,000 to £6,000.
• Structural engineer's calculations: £1,800 to £3,600.
• Party wall agreement: £1,000 to £2,000 per neighbour if a surveyor is appointed, and often free if your neighbour consents in writing. See our guide to the party wall agreement for a loft conversion.
• Building Control certificate: around £1,000.

A design-and-build company usually rolls design, structural and sometimes planning fees into a single quote.

What makes a loft conversion cost more?

Costs rise above average when there are multiple party-wall neighbours or a dispute, complex structural design needing extra steels or columns, difficult site access, an older building with surprises on strip-out, height (flats need more scaffolding and hoisting), bespoke or high-end finishes, or a compressed timeline that needs more trades on site at once.

Loft conversion stairs: rules, position and cost

Every loft conversion needs a fixed staircase to meet Building Regulations, a loft ladder does not make the room a legal bedroom. A new staircase is already included in the £20,000 to £75,000 build costs in this guide; as a standalone item in London, expect £2,000 to £3,600 for a standard flight supplied and fitted, and £6,000 to £14,000 or more for a bespoke joinery design in prime London.

The staircase decides how much space you lose on the floor below, so its position is one of the first things we resolve at design stage. Stacking the new flight directly above the existing staircase is the most efficient layout; turning it into a landing or borrowing space from a bedroom costs more and eats floor area. Building Regulations also govern the pitch and the headroom over the stairs, and the new flight must connect to a protected escape route, usually the existing hallway with fire doors. Space-saver (alternating-tread) stairs are only accepted in limited single-room cases, so treat them as a last resort rather than a budget fix.

DIY loft conversion: what you can legally do yourself

A true DIY loft conversion is rarely legal or safe. Structural work must follow a structural engineer's calculations, every conversion needs Building Regulations approval, and most electrical work must be carried out or certified by a registered electrician. Realistically, DIY is limited to decorating, flooring and finishing, which typically saves £1,500 to £2,500 in London.

The risk of skipping the rules is bigger than the saving. Without a Building Control completion certificate the space cannot be marketed as a bedroom when you sell, your buyer's solicitor will flag it, and your home insurance may be invalidated. Boarding out a loft and adding a ladder is fine for storage, but it does not create habitable space, and if it involves structural alterations or new wiring it still needs approval. Where DIY genuinely helps: painting and decorating, laying finished flooring, fitting wardrobes, and sourcing your own sanitaryware. For everything structural, use a design-and-build firm that handles design, planning permission, Building Regulations and the build under one contract.

Budget vs premium: what you get at each price

Tier	Typical specification	Indicative cost (standard dormer)
Budget	Smaller contractor, standard finishes, minimal structural work	£40,000 -£55,000
Mid-range	Established builder, better insulation and glazing, en-suite	£55,000 -£75,000
Premium (design and build)	Architect-led, in-house engineers, bespoke joinery, prime finishes, full project management	£80,000+

Premium and prime-London pricing: what houseUP delivers

houseUP is a high-end design-and-build contractor working across prime London boroughs including Chelsea, Kensington, Hampstead and Chiswick. Our loft conversions are architect-led, structurally engineered in-house and finished to a bespoke specification, with full project management and a fixed, transparent quote. At that level, a high-specification dormer in prime London typically runs £90,000 to £160,000, and a bespoke mansard £130,000 to £210,000 or more, depending on size, planning constraints and finish. Get a free, fixed quote.

Is a loft conversion worth it? Value added to your home

A loft conversion typically adds 15 to 25 percent to a property's value, usually the strongest return of any extension when it adds a double bedroom with an en-suite, because it moves the home into a higher bedroom bracket on Rightmove and Zoopla. On a £600,000 home, a £70,000 dormer that adds a bedroom with en-suite can add £90,000 to £150,000 of value. See our comparison of loft versus basement conversion value.

How long does a loft conversion take?

On site, a rooflight takes 4 to 6 weeks, a dormer 6 to 8 weeks, and a mansard 10 to 12 weeks or more. Add 4 to 8 weeks beforehand for design, structural calculations, building-regulations sign-off and, if needed, planning.

Loft conversion ideas: what to use the space for

The most popular loft conversion ideas are a master bedroom with en-suite, a home office and a guest bedroom. A rooflight conversion (£20,000 to £40,000) suits a single bedroom or office; a dormer (£40,000 to £70,000) fits a bedroom with en-suite; a mansard (£55,000 to £95,000) can take a full master suite.

Match the idea to the budget rather than the other way round. An en-suite adds £8,000 to £15,000, so a bedroom-only loft is the cheapest way to add a room, and because most of the value uplift comes from raising your bedroom count, it is also the best-returning one. A home office needs the least plumbing and works well in a compact rooflight conversion. Other popular uses: a children's bedroom, a dressing room off the main bedroom, and a snug or TV room. The finished houseUP projects in the next section show what these look like in practice.

Real houseUP loft conversions

• Luxury loft with roof terrace, Hammersmith: a premium mansard with roof-terrace access and bespoke finishes in West London, in the £130,000 to £210,000 range typical of our prime-London projects.
• Loft and side extension with full renovation, Willesden: a dormer loft combined with a side-return extension and a whole-house refurbishment in North West London.

How to budget for your loft conversion

Start from the value uplift by asking two local estate agents, choose the type that suits your roof and budget, then get a fixed design-and-build quote so the design, structural and management fees are clear up front. See our design-and-build loft conversions in London or get a free quote from houseUP.

Frequently asked questions

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

Between £20,000 and £75,000 for most types, or about £2,400 to £4,100 per square metre. A rooflight costs £20,000 to £40,000, a dormer £40,000 to £70,000, and a mansard £55,000 to £95,000. London adds roughly 20 to 40 percent.

How much does a dormer loft conversion cost?

A standard rear dormer costs £40,000 to £70,000 in the UK in 2026, or £50,000 to £90,000 in London. An L-shaped dormer runs £55,000 to £90,000. Adding an en-suite typically adds £8,000 to £15,000.

What is the cheapest type of loft conversion?

A rooflight or Velux conversion is the cheapest at £20,000 to £40,000, because it keeps the existing roofline and needs no major structural change. You do need enough existing head height, about 2.2 metres at the ridge.

Do I need planning permission for a loft conversion?

Most loft conversions are permitted development and do not need planning permission, provided you stay under 40 cubic metres for a terraced house or 50 cubic metres for a semi or detached home, and match the existing materials. Mansards, conservation areas and Article 4 zones usually do need permission. You always need Building Regulations approval.

Does a loft conversion add value to your home?

Yes, typically 15 to 25 percent, the best return of any extension when it adds a double bedroom with an en-suite, because it raises the property's bedroom count.

How long does a loft conversion take?

Between 6 and 12 weeks on site for most types: a rooflight 4 to 6 weeks, a dormer 6 to 8 weeks, and a mansard 10 to 12 weeks or more, plus 4 to 8 weeks beforehand for design, structural sign-off and any planning. 

Do I need a party wall agreement for a loft conversion?

Yes, if the new steel beams bear on a shared wall. You must serve notice under the Party Wall etc. Act 1996 before work starts. Consenting neighbours cost nothing; if surveyors are appointed, budget £1,000 to £2,000 per neighbour.

What is the minimum height for a loft conversion?

You need around 2.2 metres of head height at the ridge. Below that, a rooflight conversion will not work, but a dormer or mansard can create the headroom at extra cost. An architect can confirm feasibility on a first visit.

How much does a small loft conversion cost?

A small loft conversion costs £20,000 to £40,000 as a rooflight conversion that keeps the existing roofline. It suits a single bedroom or home office with around 2.2 m of ridge height. Adding an en-suite typically adds £8,000 to £15,000.

Can I do a loft conversion myself?

Not fully. Structural alterations, Building Regulations approval, fire safety and most electrics must be handled by professionals, and an unapproved conversion cannot be sold as a bedroom. You can legally do the decorating and finishing yourself, which typically saves £1,500 to £2,500 in London.