London Construction Cost Guides
Every London building cost we publish, in one place: extensions, lofts, basements, renovations, structural work and fees.
Planning a house extension, loft conversion or renovation in London? Our free cost guides give you real 2026 prices, typical project timelines, and honest guidance on what drives costs — so you can budget accurately before speaking to a builder.
Every guide is written by Alstruct, an active London construction company. The figures reflect what we actually quote and charge, not estimates pulled from national averages.
London building costs in 2026, at a glance: a house extension costs £2,500–£4,000 per m², a loft conversion £25,000–£100,000+, a basement £2,500–£6,500 per m² and a full house renovation £80,000–£250,000+. Every range below comes from our own guides, written from the projects we price and build across London.
All London cost guides
Thirteen guides, each with 2026 London prices taken from the work we price and build.
House Extension Cost London 2026
Single-storey, double-storey, side and wrap-around extensions: price per square metre, what is included and what drives the cost up.
£2,500–£4,000 per m²
Read guide
Single-Storey Rear Extension Cost London 2026
Ground floor rear extensions: totals and rates per m² at mid and high specification, what drives the price, permitted development, party wall and programme.
£80,000–£160,000
Read guide
Double-Storey Extension Cost London 2026
Two-storey extensions: totals and rate per m² at mid and high specification, single vs double storey, planning approval odds, structure, party wall and programme.
£170,000–£320,000
Read guide
Wrap-Around Extension Cost London 2026
Rear extension plus side return in one L-shaped build: mid and high specification totals, what moves the price, planning as one extension, party wall and the 16–22 week build.
£190,000–£380,000
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Loft Conversion Cost London 2026
Velux, dormer, hip-to-gable and Mansard conversions, with real London prices and planning requirements.
£25,000–£100,000+
Read guide
Dormer Loft Conversion Cost London 2026
Rear dormer £45,000–£75,000, L-shaped £55,000–£85,000 and hip-to-gable £55,000–£80,000, plus permitted development limits, the £274 lawful development certificate, fees and build times.
£45,000–£75,000
Read guideVelux Loft Conversion Cost
Rooflight loft conversions in London: £25,000–£45,000 inc. VAT, the headroom you need and the permitted development rules.
£45,000–£75,000
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Mansard Loft Conversion Cost London 2026
Mansard costs of £60,000–£100,000+ (£120,000–£150,000 in prime central London), the planning application, conservation areas, steel and party walls, fees and the 14–20 week build.
£60,000–£100,000+
Read guide
Victorian Side Return Extension Cost London 2026
Side return costs on Victorian terraces: cost per square metre, planning rules, party wall requirements and value added.
£65,000–£130,000 mid to high specification
Read guide
Kitchen Extension Cost London 2026
Rear, side-return, wraparound and double-storey kitchen extensions, with the kitchen itself budgeted separately.
£80,000–£160,000 mid to high specification
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Basement Conversion Cost London 2026
Cellar conversions, full excavations, lightwells and underpinning, plus the fees, party wall and planning costs to budget for.
£2,500–£6,500 per m² excluding VAT
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Victorian Terrace Renovation Cost London 2026
Per square metre costs for cosmetic, mid-range, high-specification and full structural renovations, including period repairs.
£100,000–£220,000 two-storey mid-terrace
Read guide
Removing a Load-Bearing Wall: Cost London 2026
What it costs to take out a load-bearing wall: the steel beam, the structural engineer, Building Regulations and when a party wall notice applies.
£2,500–£15,000+
Read guide
Party Wall Agreement Cost London 2026
Surveyor fees, the legal process, timescales and how to keep costs down when your project affects a shared wall.
£0–£3,500 per neighbour
Read guideLondon building costs in 2026
Every headline figure we publish, with the guide it comes from.
| Project | Typical London cost | What that covers | Full guide |
|---|---|---|---|
| House extension, per square metre | £2,500–£4,000 per m² | Basic £2,000–£2,500, mid-range £2,500–£3,200, high-spec £3,200–£4,500, ultra-premium £4,500–£6,000+ per m² | House extension cost guide |
| Single-storey rear extension (20–40m²) | £50,000–£160,000 | Low spec £50,000–£70,000, mid £80,000–£110,000, high £120,000–£160,000 | Single-storey rear extension cost guide |
| Victorian side return extension (15–25m²) | £65,000–£130,000 | Mid to high specification, including VAT; the build itself runs at £2,800–£3,500 per m² at mid-specification | Side return cost guide |
| Double-storey rear extension (40–70m²) | £120,000–£320,000 | Low spec £120,000–£160,000, mid £170,000–£230,000, high £240,000–£320,000 | Double-storey extension cost guide |
| Wrap-around extension (40–80m²) | £130,000–£380,000 | Low spec £130,000–£180,000, mid £190,000–£260,000, high £270,000–£380,000 | Wrap-around extension cost guide |
| Kitchen extension, fully finished | £80,000–£160,000 | Mid to high specification: single-storey rear £80,000–£160,000, side return £65,000–£130,000, wraparound £190,000–£380,000, double-storey £170,000–£320,000. Kitchen units, worktops and appliances are separate: £15,000–£60,000+ | Kitchen extension costs |
| Loft conversion | £25,000–£100,000+ | Velux £25,000–£45,000, dormer £45,000–£75,000, L-shaped dormer £55,000–£85,000, hip-to-gable £55,000–£80,000, Mansard £60,000–£100,000+ | Loft conversion cost guide |
| Basement conversion | £2,500–£6,500 per m² | Cellar conversion £2,500–£4,000 per m² (£80,000–£150,000 for 30–40 sqm); full excavation £4,500–£6,500 per m² (£150,000–£300,000+); lightwells £15,000–£25,000 each. Figures exclude VAT | Basement conversion cost guide |
| Full house renovation | £80,000–£250,000+ | Victorian terrace per sqm: cosmetic £400–£700, mid-range £700–£1,100, high specification £1,100–£1,600, full structural £1,200–£2,000 | Victorian terrace renovation costs |
| Kitchen or bathroom renovation | £8,000–£40,000 | Kitchen renovations £15,000–£40,000; bathrooms £8,000–£25,000 | Home renovations |
| Removing a load-bearing wall | £2,500–£15,000+ | Single wall and steel beam £2,500–£5,000; through-lounge £4,000–£8,000; large open-plan £8,000–£15,000+; engineer's calculations £500–£1,000 | Load-bearing wall guide |
| Party wall agreement | £0–£3,500 | Neighbour consents £0–£300 (notices only); one agreed surveyor £800–£1,500; separate surveyors up to £3,500 per neighbour | Party wall cost guide |
| Groundworks and drainage | £3,000–£30,000 | Foundation work £10,000–£30,000; drainage installation £5,000–£20,000; site clearance £3,000–£10,000 | Groundworks and drainage |
| Hard landscaping | £5,000–£25,000 | Driveways £8,000–£25,000; patios £5,000–£15,000; garden walls £5,000–£20,000 | Hard landscaping |
| Professional fees on an extension | See notes | Architect and design £3,000–£8,000; structural engineer £800–£2,000; planning application £548; building regulations £1,000–£3,000; VAT 20% | House extension cost guide |
2026 London figures, each taken from the Alstruct guide linked in its row. Ranges run from basic to high specification; your own figure depends on size, structure, access and finishes, and is fixed after a site visit.
London building cost questions
How much does a house extension cost in London in 2026?
A house extension in London typically costs between £2,500 and £4,000 per square metre, depending on specification, type and location. For a standard 30m² single-storey rear extension, expect to pay £75,000–£120,000 including VAT and professional fees.
How much does a loft conversion cost in London?
A loft conversion in London costs between £25,000 and £100,000+ depending on the type and specification. A Velux (rooflight) conversion starts from £25,000–£45,000, a dormer from £45,000–£75,000 and a Mansard from £60,000–£100,000+.
How much does a basement conversion cost in London?
A cellar conversion in London typically costs £2,500–£4,000 per square metre, while a full basement excavation (dig-down) costs £4,500–£6,500 per square metre. For a typical 30–40 sqm basement, that is £80,000–£150,000 for a cellar conversion and £150,000–£300,000+ for a full excavation. These figures exclude VAT.
How much does a party wall agreement cost in London?
A party wall agreement in London costs £0–£3,500+ depending on whether neighbours consent and how many surveyors are involved. With one agreed surveyor expect £800–£1,500; if each side appoints their own, £800–£3,500 per neighbour is typical.