House extension cost per square metre in 2026
Per-square-metre prices for single-storey, two-storey, side return and kitchen extensions, costs by size, the fees outside the build price, and planning limits by nation.
A single-storey house extension costs £1,900 to £3,300 per square metre before VAT in 2026, or £2,280 to £3,960 with VAT at 20%. A 4 by 5 metre rear extension at a standard finish comes to £48,000 to £66,000 with VAT, before fees and a kitchen. We give prices per m² by type and size, two-storey and kitchen extension costs, the fees outside the build, and the planning limits in each nation.
House extension cost per square metre
These are 2026 build rates: labour and materials for a finished, watertight extension. Professional fees, planning and building control, a kitchen and any bathroom fittings sit outside them.
| Type | Per m² before VAT | Per m² with VAT | What it is |
|---|---|---|---|
| Single-storey extension | £1,900 – £3,300 | £2,280 – £3,960 | One storey, usually across the back of the house |
| Two-storey extension | £2,000 – £3,200 | £2,400 – £3,840 | Two floors; the rate is per m² across both |
| Side extension | £1,900 – £3,000 | £2,280 – £3,600 | Built out to the side, including a side return |
| Wraparound extension | £2,200 – £3,400 | £2,640 – £4,080 | One L shape across the back and down one side |
| Shell only | £1,300 – £1,900 | £1,560 – £2,280 | The watertight structure with no internal finish |
The finish sets where a single storey lands in its range. A basic build runs £1,900 to £2,200 per m² before VAT, a standard one £2,200 to £2,700, and a premium finish £2,700 to £3,300. Per square foot, the single-storey range works out at about £177 to £307 before VAT.
New space costs more per square metre than refitting old space, because it needs foundations, walls and a roof. By comparison, the cost of renovating the existing house runs £800 to £1,500 per m² for a standard job.
Single-storey extension cost by size
These are standard-finish prices for the build alone, by footprint.
| Extension | Floor area | Before VAT | With VAT |
|---|---|---|---|
| 3 × 3 m | 9 m² | £18,000 – £25,000 | £21,600 – £30,000 |
| 3 × 4 m | 12 m² | £24,000 – £33,000 | £28,800 – £39,600 |
| 3 × 5 m | 15 m² | £30,000 – £42,000 | £36,000 – £50,400 |
| 4 × 4 m | 16 m² | £32,000 – £45,000 | £38,400 – £54,000 |
| 4 × 5 m | 20 m² | £40,000 – £55,000 | £48,000 – £66,000 |
| 4 × 6 m | 24 m² | £48,000 – £65,000 | £57,600 – £78,000 |
| 5 × 5 m | 25 m² | £50,000 – £68,000 | £60,000 – £81,600 |
| Medium | 30 m² | £57,000 – £81,000 | £68,400 – £97,200 |
| Large | 50 m² | £95,000 – £135,000 | £114,000 – £162,000 |
Small extensions cost more per square metre than large ones. Scaffolding, foundations, site setup and fees cost much the same for 9 m² as for 20 m², so they weigh far more on a small build.
A shell-only build gives you the watertight structure without the internal finish, at £1,300 to £1,900 per m² before VAT. A 20 m² shell costs £26,000 to £38,000 before VAT, and the finishing inside is then yours to arrange and pay for.
Two-storey extension cost
A two-storey extension costs £2,000 to £3,200 per m² of floor before VAT, about the same rate as a single storey, but it builds twice the floor area on one set of foundations and under one roof. A 60 m² build over two floors runs £120,000 to £195,000 before VAT, or £144,000 to £234,000 with it.
Against a single storey on the same footprint, the second floor adds 50 to 60% to the price. That makes the upstairs rooms the cheapest square metres in the project.
Planning is the harder part. In England, a second storey outside the permitted development limits needs a planning application at £548, and every two-storey side extension needs one.
First floor extension cost
Building a room on top of an existing single-storey part of the house, such as a garage, costs £50,000 to £82,000 before VAT for 20 to 25 m², or £60,000 to £98,400 with VAT. Whether the walls and foundations below can carry a new floor is the structural engineer's first question, and the answer moves the price.
Side return and wraparound extension cost
A side return extension fills the narrow strip beside the back addition of a terraced house, usually to widen the kitchen. Side extensions cost £1,900 to £3,000 per m² before VAT, close to a rear extension, but the site is tighter and a wall on the boundary brings the neighbours into the project.
A wraparound extension joins a side return and a rear extension in one L shape. It is the dearest single-storey layout at £2,200 to £3,400 per m² before VAT, because the corner needs more steel and more design. Structural calculations for a wraparound cost £1,200 to £1,500, against £550 to £900 for a straightforward rear extension.
Kitchen extension cost
A kitchen extension is two jobs priced together: the building work and the kitchen that goes into it. A new kitchen fitted into the extension adds £16,000 to £38,000 to the build, depending on the units, worktops and appliances.
Decide on the heating before the floor goes in. Wet underfloor heating kit for a new screed floor starts from about £20 per m² plus VAT, against £67 per m² plus VAT for a low-profile system retrofitted into an existing room.
A bathroom or shower room in the extension adds £6,000 to £10,000 for the plumbing, sanitaryware, tiling and waste connection.
What an extension quote leaves out
A builder's price per m² covers the build. Professional fees and compliance add around 15 to 20% on top, and some costs only appear once the drawings are done or the ground is dug.
| Item | Typical cost | When it applies |
|---|---|---|
| Drawings for planning and building regulations | £1,500 – £5,000 | Every extension; more for a complex design |
| Structural engineer's calculations | £550 – £1,500 | Every extension; building control asks for them |
| Building control | £600 – £1,200 | Plan approval and site inspections |
| Householder planning application, England | £548 | The extension is outside permitted development |
| Prior approval, larger rear extension, England | £249 | A single-storey rear extension of 6 or 8 m |
| Lawful development certificate, England | £274 | Proof that a permitted development extension is lawful |
| Party wall surveyor | £800 – £2,000 per neighbour | Work on or near a shared wall or boundary |
| Moving a drain run | £1,500 – £5,000 | The extension sits over a drain |
| Moving a manhole | £2,000 – £4,500 | A manhole sits inside the new footprint |
| VAT | 20% | Labour and materials on a lived-in home |
| Contingency | 10 – 15% | Held back for what the groundwork finds |
Groundwork is where a budget moves most. Footings for a single storey go at least 1 metre deep in normal ground and 1.5 metres or more in clay, and standard groundwork takes £3,000 to £8,000 of the build before anything unexpected turns up.
Steel is the other big variable. Wide openings for bifold doors or structural glazing need heavier beams, which raise both the engineer's fee and the price of the steel.
Extension costs in London and the regions
London and the South East are the dearest places to extend. In London a single-storey extension runs £3,000 to £5,000 per m² before VAT and fees, so a 20 m² extension in London costs £60,000 to £100,000 before VAT.
Across London and the South East, extensions can cost 30 to 50% more per m² than the UK average. The gap is mostly labour. Materials cost much the same everywhere, while labour rates change with the location.
Outside London and the South East, budget from the UK ranges in the tables above. A town-centre site with no parking or tight access can cost more than a suburban plot with a clear run to the garden.
What £30,000, £50,000 or £100,000 buys
These are with-VAT build prices for a standard single-storey finish, before fees, a kitchen or a contingency.
| Budget with VAT | What it covers | What it leaves out |
|---|---|---|
| £30,000 | A 3 × 3 m (9 m²) extension, or a 15 m² shell you finish yourself | Fees of £2,650 – £7,700 and a new kitchen |
| £50,000 | A 3 × 5 m (15 m²) extension, or a 4 × 4 m (16 m²) one at the lower end | A new kitchen |
| £75,000 | A 4 × 6 m (24 m²) or 5 × 5 m (25 m²) extension, or a 20 m² kitchen extension at the lower end | A premium finish |
| £100,000 | A 30 m² extension, or a 20 m² kitchen extension with a mid-range kitchen | A second storey |
| £150,000 | A 50 m² single storey at the lower end, or a 60 m² two-storey build from £144,000 | A premium two-storey build |
Below £30,000 an extension is hard to make work once the fees are paid. Converting the garage instead costs £9,000 to £22,000 before VAT, because the walls, roof and foundations are already there.
Planning permission for an extension
Many single-storey rear extensions need no planning application, because they fall within permitted development limits. Each nation sets its own limits, and England, Wales and Scotland differ.
In England, a single-storey rear extension can go 3 metres beyond the rear wall of a terraced or semi-detached house and 4 metres on a detached house, up to 4 metres high. Under the Planning Portal's permitted development rules, it also cannot sit higher than the existing roof or come forward of the front of the house.
A deeper single storey, up to 6 metres on a terraced or semi-detached house and 8 metres on a detached one, goes through prior approval instead of a full application. The council has to be told about the proposed work first, and the fee is £249 from 1 April 2026.
Outside those limits, or on a flat or maisonette, you need householder planning permission, and the application costs £548 in England. In a conservation area, National Park, Area of Outstanding Natural Beauty or World Heritage Site, every side extension and every rear extension of more than one storey needs it.
An extension built under permitted development needs no application, but a lawful development certificate at £274 proves it met the rules. A buyer's solicitor regularly asks for proof that an extension was lawful when you come to sell.
| Rule | England | Wales | Scotland |
|---|---|---|---|
| Single-storey rear depth | 3 m, or 4 m on a detached house; 6 m or 8 m with prior approval | 4 m | 3 m on a terraced house, 4 m on others, where within 1 m of a boundary |
| Single-storey height | 4 m; eaves 3 m within 2 m of a boundary | 4 m; eaves 3 m within 2 m of a boundary | 4 m; eaves 3 m |
| Ground covered | Half the land around the original house | Half the land around the original house | Half the front or rear garden |
| More than one storey | 3 m deep, 7 m from the boundary opposite | Upper floor 3 m deep, 10.5 m from the rear boundary | No part within 10 m of any boundary |
Wales, Scotland and Northern Ireland
Wales runs its own planning system, and the Welsh Government's rules for extensions allow a single-storey rear extension 4 metres deep on any house, with no lower limit for a terrace.
Scotland caps the depth only where the extension comes within 1 metre of a boundary, under the Scottish Government's 2024 householder rules. There are no permitted development rights for extensions in conservation areas, and a building warrant from the council is usually needed as well.
Northern Ireland has separate planning and building control, so the English, Welsh and Scottish limits above do not apply there.
Building regulations and party walls
Planning and building regulations are separate. An extension that needs no planning application still goes through building control, which checks the foundations, structure, drainage and insulation, and it will not approve an extension without a structural engineer's calculations.
Council building control fees are based on the council's own costs and depend on the type of work, the number of inspections and the floor area, so there is no national price. £600 to £1,200 is typical for an extension, and a registered building control approver agrees its fee with you directly. As the owner, you stay responsible for meeting the regulations even when a builder does the work.
Digging foundations within 3 metres of a neighbour's, or building on a shared wall, can bring the Party Wall etc. Act 1996 into play. In England and Wales you must tell your neighbours before the work starts, and party wall costs run £800 to £2,000 per neighbour where a surveyor is appointed. Scotland has different rules.
How long an extension takes
Much of the time passes before the builder arrives. The design, the engineer's calculations, planning and building control all run ahead of the first dig.
| Stage | Typical time |
|---|---|
| Structural calculations | 5 – 7 working days |
| Householder planning application | About 8 weeks from validation |
| Building control decision on full plans | 5 weeks, or 2 months with your consent |
| Build on site, single storey | 8 – 14 weeks |
| Build on site, one or two storeys | 8 – 16 weeks |
| Completion certificate | Usually within 8 weeks of completion |
If the extension opens into the kitchen, expect to be without it for much of the build, which is when a temporary kitchen earns its cost.
Common questions
How much does a house extension cost in the UK?
A single-storey house extension costs £1,900 to £3,300 per square metre before VAT in 2026, or £2,280 to £3,960 with VAT. A 20 m² rear extension at a standard finish costs £48,000 to £66,000 with VAT for the build. Drawings, structural calculations and building control add £2,650 to £7,700, and a kitchen is extra.
How much does a single storey extension cost?
A single-storey extension costs £2,280 to £3,960 per m² with VAT in 2026, depending on the finish. A basic build runs £1,900 to £2,200 per m² before VAT and a premium one £2,700 to £3,300. A 15 m² extension costs £36,000 to £50,400 with VAT and a 30 m² one £68,400 to £97,200.
How much is a 3 metre extension?
A 3 metre deep single-storey extension costs £21,600 to £50,400 with VAT in 2026, depending on its width. At 3 metres wide it costs £21,600 to £30,000, at 4 metres £28,800 to £39,600, and at 5 metres £36,000 to £50,400. In England, 3 metres is also the permitted development depth for a terraced or semi-detached house.
Is £30,000 enough for an extension?
£30,000 with VAT covers the build of a 3 by 3 metre single-storey extension at a standard finish, and little more. That leaves nothing for the £2,650 to £7,700 of drawings, structural calculations and building control. The same money buys a 15 m² shell you finish yourself, or a garage conversion at £9,000 to £22,000 before VAT.
Can you build an extension for £50,000?
£50,000 with VAT builds a single-storey extension of about 15 to 16 m² at a standard finish. A 3 by 5 metre extension costs £36,000 to £50,400 with VAT and a 4 by 4 metre one £38,400 to £54,000. Before VAT, £50,000 reaches the lower end for a 4 by 5 metre build, and fees and a new kitchen come on top.
Is a 2 metre extension worth it?
A 2 metre extension is worth it when those 2 metres change how a room works, such as turning a narrow kitchen into a kitchen-diner. It costs the most per m² of any size, because scaffolding, foundations, site setup and fees cost much the same as for a 3 metre build. In England a 3 metre single-storey rear extension on a terraced or semi-detached house needs no planning application, so price the extra metre before settling on 2.
How much does a two storey extension cost?
A two-storey extension costs £2,000 to £3,200 per m² of floor before VAT in 2026. A 60 m² build over two floors runs £120,000 to £195,000 before VAT, or £144,000 to £234,000 with it. The second floor adds about 50 to 60% to the price of a single storey on the same footprint.
How much does a kitchen extension cost?
A 20 m² kitchen extension costs about £67,000 to £114,000 in 2026, with VAT on the build and the fees included. That covers the build at £48,000 to £66,000, a kitchen at £16,000 to £38,000, and the drawings, engineer, building control and planning fees. A contingency of 10 to 15% sits on top.
How much does a 25m2 extension cost?
A 25 m² single-storey extension costs £50,000 to £68,000 before VAT in 2026, or £60,000 to £81,600 with VAT, at a standard finish. Fees of £2,650 to £7,700 and any kitchen are extra, and in London the build runs £75,000 to £125,000 before VAT.
Do I need planning permission for a single storey extension?
A single-storey rear extension in England needs no planning application if it stays within 3 metres of the rear wall on a terraced or semi-detached house, or 4 metres on a detached house, and meets the height and garden limits. Up to 6 or 8 metres is possible through prior approval, at £249. Flats, maisonettes and extensions outside the limits need a householder application at £548.