UK cost guide · September 2026

How much does a house extension cost in 2026?

A mid-range single-storey rear extension in the UK costs about £2,500 to £3,100 per m² including VAT, or £63,000 to £78,000 for 25 m². Double-storey extensions cost less per m² (£2,300 to £2,900), wraparounds more (£2,800 to £3,500). London is about 35% higher. Allow £5,800 to £11,800 for fees and approvals, and hold a 15% contingency.

By Estiquote · Prices reviewed 25 September 2026, next review December 2026 · How we calculate

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Builder or surveyor? Price this extension element by element with editable, sourced unit rates.

House extension prices in 2026

Ranges are for a typical home outside London, including VAT, before fees and contingency. Use the calculator for your size, region and finish.

House extension costs by type and finish, UK average outside London, including VAT (September 2026)
Type	Budget	Mid-range	Premium
Single-storey rear (25 m²)	£51,000 to £63,000	£63,000 to £78,000	£81,000 to £99,000
Double-storey (40 m²)	£72,000 to £91,000	£91,000 to £115,000	£120,000 to £149,000
Wraparound or side return (30 m²)	£68,500 to £83,000	£83,000 to £104,000	£108,000 to £133,000

Single-storey rear house extension by size, including VAT
Floor area	Budget	Mid-range	Premium
15 m²	£30,500 to £38,000	£38,000 to £47,000	£48,500 to £59,500
25 m²	£51,000 to £63,000	£63,000 to £78,000	£81,000 to £99,000
40 m²	£81,500 to £101,000	£101,000 to £125,000	£130,000 to £158,000

House extension costs by region

Labour costs vary across the UK far more than materials. London runs about 35% above the UK average and Northern Ireland about 18% below.

House extension costs by region: Single-storey rear, 25 m², including VAT
Region	Mid-range cost	Per m²
UK average (outside London)	£63,000 to £78,000	£2,500 to £3,100
London	£85,000 to £105,000	£3,400 to £4,200
South East	£72,500 to £89,500	£2,900 to £3,600
East of England	£67,500 to £83,500	£2,700 to £3,300
South West	£65,500 to £81,000	£2,600 to £3,200
West Midlands	£61,000 to £75,500	£2,400 to £3,000
East Midlands	£60,000 to £74,000	£2,400 to £3,000
Scotland	£60,000 to £74,000	£2,400 to £3,000
North West	£58,500 to £72,500	£2,300 to £2,900
Yorkshire and the Humber	£58,000 to £72,000	£2,300 to £2,900
Wales	£56,500 to £70,000	£2,300 to £2,800
North East	£55,500 to £68,500	£2,200 to £2,700
Northern Ireland	£51,500 to £64,000	£2,100 to £2,600

Want it for your area? See local prices and council building control fees for 92 council areas.

Fees and approvals

Design, engineering and approvals come on top of the building work. Building control figures are the middle half of fees charged by the councils we checked in September 2026.

Typical fees and approvals, including VAT where charged
Fee	Typical cost	Notes
Measured survey	£600 to £1,800
Design drawings (planning and building regulations)	£3,600 to £6,000
Structural engineer	£900 to £3,000
Building control (council, full plans)	£740 to £1,000	Middle half of 91 councils in England and Wales for a 10 to 40 m² extension
Householder planning application (England)	£550	Only if your project needs planning permission Optional.
Party wall surveyor (per neighbour)	£1,100 to £1,800	Only if you build on or near a shared wall Optional.

What's included in these prices

Included

Foundations, walls, roof, insulation and weatherproofing
Windows and external doors to a standard specification
First fix and second fix electrics, heating and plumbing to the new space
Plastering, flooring and decoration to a finished shell
Opening into the existing house (steel beam included in the rate)
Site setup, skips and removal of spoil

Not included

A fitted kitchen (add it in the calculator)
Design, engineering, building control and planning fees (shown separately)
Party wall surveyors, if your neighbour needs one
Large bifold or sliding doors and roof lanterns above a standard allowance
Landscaping, driveways and work elsewhere in the house
Your contingency

What drives the cost

Size and shape. Fixed costs such as design, site setup and the opening into the house do not shrink with floor area, so small extensions cost more per m². Simple rectangles cost less than L-shapes and wraparounds.
Glazing. Wide sliding doors, bifolds and roof lanterns are the single biggest upgrade. A run of premium glazing can add £10,000 or more.
Ground conditions and drains. Clay soil, nearby trees or a drain under the footprint can mean deeper foundations or a build-over agreement with your water company.
Access. Terraced houses with no side access mean materials come through the house, which adds labour and time.
Specification. The finish you choose moves the price by 25% to 40% either way: flooring, kitchen, lighting and heating all count.
Where you live. London prices run about 35% above the UK average and the South East about 15%. The North East, Wales and Northern Ireland are below average.

Planning, regulations and VAT

Many single-storey rear extensions in England are permitted development and need no planning application, within size limits set out by the Planning Portal. Larger rear extensions can use the prior approval route (fee £249). Every extension needs building regulations approval, and work on or near a shared wall needs a party wall notice to your neighbours. If you do need planning permission, a householder application in England costs £548 from 1 April 2026.

Checklist: what to ask builders to confirm

Print this or save it as a PDF. Mark each line included, separate or not confirmed as quotes come in. An empty amount means unknown, not free.

Use one column per quote if you are comparing builders
Item	What to confirm	Included? Amount?
Design and investigations	Drawings, measured survey, structural calculations and any trial holes.
Permissions	Planning (if needed), building control and party wall agreements.
Site setup	Access, protection of the existing house, demolition, skips and waste.
Groundworks and drains	Foundation design, ground conditions and any drain diversions.
Structure and envelope	Walls, steel beam, roof, insulation, windows and doors.
Services	Heating, electrics, plumbing, ventilation and changes to existing systems.
Fixtures and finishes	Kitchen, flooring, joinery, lighting and decoration.
External work	Steps, paving, drainage outside doors and garden reinstatement.

Questions people ask

How much does a 4 x 5 metre extension cost?

A 20 m² single-storey extension costs about £50,500 to £62,500 including VAT for a mid-range finish in an average UK area, before fees. Small extensions cost more per m² because fixed costs stay the same.

Is it cheaper to build a double-storey extension?

Per square metre, yes. A mid-range double-storey extension costs about £2,300 to £2,900 per m² including VAT against £2,500 to £3,100 for single-storey, because the foundations and roof serve twice the floor area.

Do extension prices include VAT?

Most builders charge VAT at 20% on extensions. Our figures include it by default; untick VAT in the calculator to see prices without it. Small builders below the VAT threshold may not charge it.

How much does an extension cost in London?

About £85,000 to £105,000 for a 25 m² mid-range single-storey extension, including VAT and before fees. That is roughly 35% above the UK average.

Does an extension add value?

Often, but not always by more than it costs. Check sold prices for extended houses on your street before you commit, and speak to a local estate agent.

Sources and method

Our ranges combine published 2026 UK cost guides, industry data and our own survey of council fees. We check them every quarter. They are planning figures, not quotes: always get at least three detailed written quotes. Read how Estiquote estimates work, or download the full cost data.