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Cost guide

How much does a house extension cost in London?

Build cost per square metre and typical totals for side-return, wraparound, double-storey and kitchen extensions, compiled in September 2026 from published London cost guides, with the fees on top.

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Single-storey build cost, typical London range

£2,650–£4,500

per m²VAT varies by source; see the noteTypical London prices, September 2026

Typical London prices compiled in September 2026 from published cost guides (Build Team, My/Architect, Studio Mass, Rise Design Studio, MVV London, Hampstead Renovations, BVDS Architects and others), not a quotation from MO Team Construction. The sources are a mix of prices with and without VAT and assume different sizes, so treat each range as a planning bracket, add the fees listed further down, and confirm the VAT position and the size assumed on any quote you receive.

Published London guides put single-storey extension build cost at £2,650–£4,500 per square metre in 2026, before the kitchen, upgraded glazing and fees. As totals, a side-return extension runs about £40,000–£78,000, a wraparound £80,000–£165,000, a double-storey extension £120,000–£200,000, and a kitchen extension including the kitchen £70,000–£120,000. These are market ranges from the sources named below, not a quote from MO Team, and the sources are a mix of prices with and without VAT.

What each type of extension costs

Where these figures come from: the per-square-metre range is the median of ten London guides, principally Build Team, My/Architect, Studio Mass, Rise Design Studio, MVV London, Hampstead Renovations and BVDS Architects. The per-project rows add LCCL Construction, Mayfair Studio, NGC Build, BH Studio, TrustBuilt Projects and Apex Glazing. Per-project rows are rounded to the nearest thousand pounds. They are market figures, not our quotes: for a price on your own house, see house extensions in London and the rear extension with a skylight roof we built. The planning, party wall and VAT rules quoted on this page are from the Planning Portal, the Party Wall etc. Act 1996 and gov.uk's VAT for builders, checked September 2026; confirm the position for your address with your borough or a party wall surveyor.

ScenarioTypical rangeWhat that includes
Single-storey extension build cost per m²Standard £2,800–£3,200, mid £3,150–£4,000, high £3,750–£5,000 per m²£2,650–£4,500 per m²Foundations, structure, roof, standard glazing, first fix, plaster and basic decoration; before the kitchen, upgraded glazing and fees
Side return extensionHighs disagree widely between structure-only and all-in figures£40,000–£78,000Infill of the side passage beside the back addition, roughly 12–18 m², with the wall between opened up; before the kitchen
Wraparound extensionSize assumptions differ between sources, which drives the spread£80,000–£165,000Side return and rear extension together, roughly 25–40 m², before the kitchen
Double-storey extensionGood agreement on the low; the high depends on floor area£120,000–£200,000Two-storey rear or side extension of roughly 40–70 m², shell and first fix, before the kitchen and bathroom fit-out
Kitchen extension including the kitchenThe all-in figure most people are actually asking about£70,000–£120,000A 20–30 m² rear extension with a mid-range kitchen fitted; the sources agree unusually well
Steel beam or new structural openingA whole steel package on a side-return or wraparound is quoted at £4,000–£20,000£1,500–£5,000 per beamOne beam supplied and fitted; the engineer's design and building control are extra
Bi-fold or sliding door set, aluminium, 3–5 panelsWide spans and steel-look framed systems are quoted at £8,000–£15,000 a set£3,500–£8,000 per door setSupplied and fitted; a rooflight or lantern is £2,000–£5,000 each on top

VAT: an extension to an existing house is standard-rated at 20%. Six of the ten per-square-metre sources quote without VAT, one with it, and three do not say, so add 20% to any figure you are not sure about. The rules are on gov.uk under VAT for builders.

Build cost per square metre by specification

SpecificationPer m²Notes
Standard£2,800–£3,200Blockwork, a flat or simple pitched roof, standard doors and rooflights, plaster and paint
Mid£3,150–£4,000Better glazing, underfloor heating, engineered flooring, more steel for wider openings
High£3,750–£5,000Large structural openings, framed or frameless glazing, stone or polished concrete floors

What moves the price

  • Size, and the shape of the footprint

    bigger costs more, smaller costs more per m² — A larger extension costs more in total but less per square metre, because the expensive parts (foundations, steel, glazing, drainage) do not grow with the floor area. A wraparound needs two junctions with the house and more steel than a simple rear box, which is why its range starts at twice the side-return figure.

  • Steel and structural openings

    £1,500–£5,000 per beam — Opening the back of the house needs at least one beam, and a side return usually needs several plus a goalpost frame. Published London figures for the whole steel package on a side-return or wraparound extension run £4,000–£20,000, with the engineer's design on top.

  • Glazing

    £3,500–£8,000 per door set — A three-to-five panel aluminium bi-fold or sliding set, supplied and fitted, with rooflights or a lantern at £2,000–£5,000 each on top. One London guide quotes wide spans and steel-look framed systems at £8,000–£15,000 a set, and glazing is the quickest way to move a standard extension into the high band.

  • The kitchen

    £70,000–£120,000 all in — A kitchen extension is two projects: the shell and the kitchen inside it. London sources agree unusually well that a 20–30 m² rear extension with a mid-range kitchen lands at £70,000–£120,000 in total. Our kitchen renovation cost guide covers what the kitchen itself is likely to cost.

  • Ground conditions and drainage

    the usual reason a price moves after the dig — London clay, nearby trees and shared sewers are the three things that change a foundation design once the ground is open. Building over or within three metres of a public sewer needs a build-over agreement with the water company, and deeper or piled foundations near mature trees are common in the outer boroughs.

  • The planning route

    fees and time, sometimes materials — Most single-storey rear extensions on a house use permitted development: 3 metres deep on a terrace or semi, 4 metres on a detached house, or 6 and 8 metres under the larger home extension scheme with prior approval from the borough. Flats, conservation areas, listed buildings and Article 4 streets change that and add a planning application.

  • Access and neighbours

    party wall notices and a one- or two-month clock — A rear extension on a terrace is built through the house or across a neighbour's garden by agreement, so protection, carrying distance and a skip on the street all show up in the labour. Party wall notices are almost guaranteed: one month for excavation within three or six metres of a neighbour's foundations or a new wall on the boundary, two months where steels bear into the party wall (Party Wall etc. Act 1996, ss.1, 3 and 6, checked September 2026). The notice period is the most common reason a start date moves, so serve early and ask a party wall surveyor which notices apply.

What is and is not in these figures

Usually included

  • Foundations, slab, walls and roof
  • Structural steel and the new openings into the house
  • Standard doors, windows and rooflights
  • First fix plumbing and electrics, plastering and basic decoration
  • Drainage connections and making good the garden immediately around the work
  • Building control inspections through to the completion certificate

Usually extra

  • The kitchen, appliances and worktops, unless a row says otherwise
  • Planning, building control and party wall fees, paid to the authority or the surveyor
  • Architect's and structural engineer's fees
  • Upgraded glazing, framed systems and large lanterns
  • Landscaping, paving and reinstating the rest of the garden
  • VAT, where the source quoted without it

The costs people forget to budget for

  • Planning application or lawful development certificate

    £274–£548

    A householder planning application in England costs £548, rising to £575 from 8 December 2026 if the draft regulations pass. Where the extension is permitted development, a lawful development certificate costs £274 for proposed work and £548 for work already built, and buyers' solicitors ask for it. The Planning Portal adds £99 or £149 including VAT as a service charge for online submissions.

  • Building control charge

    £859–£1,288

    The local-authority charge for a single-storey extension up to 60 m² across the four London boroughs whose schedules we read (Havering, Redbridge, Hillingdon and Bromley), including VAT. Other boroughs publish their own, and approved inspectors price separately.

  • Party wall surveyor

    £700–£1,800 per neighbour

    Excavating near a neighbour's foundations or building on the line of junction triggers the Act, so a terrace usually means notices to both sides. If a neighbour appoints their own surveyor you pay for both, and London surveyors quote two-surveyor cases at £1,400–£4,500 per neighbour.

  • Structural engineer

    £800–£4,200 for an extension

    A single beam calculation is quoted at £450–£800 in London. A full extension package, with foundations, steels and the openings into the house designed together, is quoted by the same practices at £800–£4,200 depending on complexity.

  • Skips, permits and bay suspensions

    £300–£425 per skip

    An 8-yard builder's skip in London, before the borough's road permit of £30–£120. An extension fills several. Where the skip needs a suspended parking bay the borough adds an administration fee and a daily charge.

  • A build-over agreement and water company charges

    priced by the water company

    If the extension sits over or within three metres of a public sewer, Thames Water or the relevant company has to approve the design. The application fee and any conditions on the foundation design are set by them, not the builder, and are worth checking before the drawings are finished.

How the fees vary across London

Build prices are not published borough by borough, but the local-authority building control charges for an extension are. One London builder, LCCL Construction, states an uplift of 10–15% for inner London and 20–25% for central London over outer London; we report it and have not applied it to the ranges.

BoroughTypical upliftNotes
Havering£859–£1,183 feeExtension up to 30 m² £859; 30–60 m² £1,183, including VAT (2026/27)
Redbridge£979–£1,288 feeExtension up to 20 m² £979; 20–60 m² £1,288, including VAT (from April 2025)
Hillingdon£1,020–£1,260 feeExtension under 40 m² £1,020; 40–60 m² £1,260, including VAT (2025/26)
Bromley£1,008–£1,224 feeExtension 10–40 m² £1,008; 40–60 m² £1,224, including VAT

Related

Common questions

Straight answers.

Not answered here?

Tell us what you are planning. We read every enquiry ourselves and reply within one working day.

Ask us directly07424 445105

For a small single-storey extension, sometimes. At the published London build cost of £2,650–£4,500 per square metre, £50,000 buys roughly 11–19 square metres of shell before fees, upgraded glazing and a kitchen, and the side-return ranges we compiled start at £40,000. For most kitchen extensions the honest answer is no, because the all-in totals cluster at £70,000–£120,000 once the kitchen and the wider openings are counted.

Want a figure for your extension, not a market range?

Send the address, the rough size you have in mind and any drawings you already have. We will tell you what the ground, the drainage and the planning position are likely to mean for the budget, before anyone visits.

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