House Extension Cost London (2026): Prices by Type

London house extension prices by type

These are typical 2026 London ranges. The UK averages show how far London sits above the rest of the country. Neither is a quotation for your house.

Extension type	London range (2026)	UK average	Typical build time
Single-storey rear	£45,000–£90,000	£52,000 (20–30 m²: £44,000–£60,000)	10–18 weeks for most extensions
Side return	£35,000–£65,000	£20,000	9–12 weeks
Wraparound	£65,000–£120,000	£70,000	10–14 weeks
Double-storey	£80,000–£160,000	£82,500 (40–60 m²: £80,000–£120,000)	16–19 weeks
Kitchen extension	£45,000–£70,000	£62,500	10–14 weeks

The London ranges include labour, materials, structural steelwork, structural engineer coordination and Building Regulations; kitchens, second-fix finishes, planning fees and party wall fees are excluded, and VAT is not stated. London labour costs typically run about 10–25% above the national average.

Single-storey flat-roof rear extension with a roof lantern and sliding doors on a 1930s semi-detached house — Illustration: single-storey rear extension. Typical London range: £45,000–£90,000.

Kitchen in a side-return extension with a glass roof along an exposed brick party wall — Illustration: side-return extension. Typical London range: £35,000–£65,000.

L-shaped wraparound extension with a glazed side-return roof and black glazed doors on a Victorian house — Illustration: wraparound extension. Typical London range: £65,000–£120,000.

Two-storey rear extension in matching brick with a hipped tiled roof on a 1930s semi-detached house — Illustration: double-storey rear extension. Typical London range: £80,000–£160,000.

Per square metre: why the rates disagree

Figure	Rate	What the rate covers
Typical London and UK range	London single-storey: £2,300–£3,400 per m². UK: £1,800–£3,000.	VAT is not stated for these ranges. Architect fees and the kitchen are listed separately.
UK range with London uplift	UK single-storey: £1,800–£3,000 per m². London and the South East: 30–50% more.	Extensions carry 20% VAT on labour and materials; check whether a quote includes it.
Construction-only range	London: £3,000–£5,000 per m². Elsewhere in the UK: £2,000–£3,500.	Excludes VAT and professional fees, typically 15–20% on top.

Read each rate against what it covers. A rate that excludes VAT and fees and a rate that may include them can describe the same build.

Turn a rate per m² into a total budget

A worked example for a hypothetical 25 m² single-storey rear extension, using the typical London range above. It shows the arithmetic, not a price for your project.

Budget line	Lower figure	Higher figure
Construction: 25 m² at £2,300–£3,400 per m²	£57,500	£85,000
VAT at 20%, if the rate excludes it	£11,500	£17,000
Design and engineering at 15–20% of construction	£8,625	£17,000
New kitchen, if the kitchen moves into the extension	£15,000	£35,000
Householder planning application (England)	£548	£548
Party wall surveyor, per neighbour	£600	£2,000
Worked total	£93,773	£156,548

The £548 householder planning fee applies in England from 1 April 2026. Building control fees vary by council and are not included. A Lawful Development Certificate for a permitted-development scheme is normally half the householder planning fee.

In this example the total comes to about 1.6 to 1.8 times the construction figure, before any contingency. Ask every builder to price the same drawings and to say what their figure includes.

What pushes a London extension price up

Two extensions with the same floor area can need very different work. These are the points that most often change the price.

Foundations, drains and ground

London clay, nearby trees and shared drains can deepen or change the foundation design. A drain survey before the design is fixed can prevent a redesign once the ground is open. Read our drain survey guide.

Opening up the back of the house

Removing a rear or side-return wall needs specified steelwork and temporary support. A wider opening usually means a larger beam and more making good inside the existing rooms. See structural alterations.

Glazing and roof

Large sliding doors, roof lanterns and frameless glass roofs are often among the largest single items. A glazed side-return roof along a party wall also needs careful detailing at the boundary.

Access and party walls

Many London terraces have no side access, so materials and spoil move through the house or are loaded from the street. Work on or near a shared wall usually needs party wall notices, which GOV.UK says must be given between 2 months and a year before work starts.

Kitchen, services and finishes

An extension often becomes the new kitchen. Moving the sink, adding underfloor heating or relocating the boiler adds plumbing and electrical work beyond the shell.

Permission routes and what they cost

Planning, building regulations and party wall procedures are separate. Your designer should confirm the route for the particular address before the programme is fixed.

Route	When it may apply	Cost to budget
Permitted development	Single-storey rear extensions up to 3 m beyond the original rear wall of an attached house, or 4 m for a detached house, and no more than 4 m high	A Lawful Development Certificate is optional but useful; its fee is normally half the householder planning fee
Prior approval	Single-storey rear extensions up to 6 m (attached) or 8 m (detached), outside conservation areas and other designated land	An application to the council before work starts
Householder planning permission	Side, wraparound and double-storey extensions outside permitted development, and all side extensions on designated land such as conservation areas	£548 application fee in England from 1 April 2026
Building regulations	Almost every extension	Set by the council or approved inspector; varies with size and authority

Permitted development rules apply to houses, not to flats or maisonettes, and an Article 4 direction can remove them. Limits summarised from the Planning Portal’s extension guidance, checked 29 October 2026.

How long an extension takes

The build is often the shorter part. Design, approvals and notices come first, and the programme for your house depends on its design, access and specification.

Stage	Typical time	Basis
Householder planning decision	8 weeks from a valid application	Statutory period for householder applications
Party wall notices	Given between 2 months and a year before work starts	Party Wall etc. Act guidance
Side-return build	9–12 weeks	Typical build time
Wraparound or kitchen extension build	10–14 weeks	Typical build time
Double-storey build	16–19 weeks	Typical build time

Compare quotations on the same basis

Two quotations for the same drawings can still differ because they stop at different points. Ask each builder to answer the same questions.

Question	What to check
VAT	Is every figure shown with or without 20% VAT?
Design and engineering	Are drawings, structural calculations and building control fees included or separate?
Groundworks	What foundation depth and drainage work is allowed for, and how is extra depth priced?
Steel and opening up	Are the beam, temporary support and making good inside the house included?
Glazing and roof	Who supplies the doors, rooflights or lantern, and are their lead times in the programme?
Kitchen and finishes	Does the price stop at plaster, or include flooring, kitchen fitting and decoration?
Party walls	Are notices and surveyor fees with you or with the builder?
Payment stages	Are payments tied to completed stages? See our payment stages guide.

For two dated quotation examples from the director’s earlier business, see what small-extension quotation examples cover on our extensions page. They are not Vayton prices or current offers.

House extension cost questions

How much does a single-storey extension cost in London?

Typical London rates run from about £2,300–£3,400 per m² to £3,000–£5,000 per m² for construction alone, before VAT and fees. A single-storey rear extension typically costs £45,000–£90,000, excluding the kitchen and planning fees.

How much does a side return extension cost in London?

One London builder’s 2026 guide gives £35,000–£65,000. A national quote platform puts the UK average at about £20,000, a sign of how much higher London prices run.

Is a double-storey extension cheaper per m²?

Usually. As a rule of thumb, add 50–60% to a single-storey price for a two-storey extension on the same footprint, which doubles the floor area. It is more likely to need planning permission.

Do extension prices include VAT?

Not always. Home extensions carry 20% VAT on labour and materials, and some quoted rates exclude it. Ask whether each quotation is shown with or without VAT.

Can you price my extension from photographs?

Photographs help the first conversation. A price you can rely on needs drawings, structural information, an assessment of the ground and drains, and a finish schedule.

Plan the rest of the extension

House extensions in London · Structural alterations · Drain survey before an extension · Kitchen fitting · Loft conversion cost

Planning and party wall guidance: Planning Portal ↗ · GOV.UK party walls ↗

House extension cost in London

Price the extension you want.