Costs & Materials
House extension and building costs in London 2026: an indicative guide
London building work typically costs £1,750 to £4,500+ per square metre, depending on where you are and what you build. Here are indicative 2026 ranges, the extras to budget for, and where the figures come from.
Figures are indicative; get a fixed quote. The ranges below are typical 2026 market ranges for standard above-ground residential work. They are not a quotation and your project may cost more or less. Where a published source states a figure, we link it; ranges marked "Indicative industry range, 2026" are compiled from industry guidance and could not be matched exactly to a single published source. The only reliable number for your project is a fixed, written quote against drawings.
The headline: London versus the rest of the UK
For standard above-ground work, London typically runs from about £1,750 to £4,500+ per m² (indicative industry range, 2026). London labour rates are 25–45% above the national average, according to RapidQS UK, The Real Cost of Building in the UK: 2026, and the same firm puts the London premium over regional UK averages at typically 25–45% depending on building type (RapidQS UK, Construction Cost Per m² UK 2026).
| Location | Typical range | Source |
|---|---|---|
| Central London (e.g. Westminster, Camden, Kensington) | £3,500 to £4,500+ (a 25–40% premium over outer areas) | Indicative industry range, 2026 |
| Outer London (e.g. Ealing, Croydon, Enfield) | £2,500 to £3,500 | Indicative industry range, 2026 |
| Rest of the UK | £1,750 to £2,800 | Indicative industry range, 2026 (RapidQS gives £2,000–£2,800 as a benchmark for most regions outside London) |
Inner boroughs such as Hammersmith & Fulham, Wandsworth and Lambeth usually sit between the outer and central ranges, depending on the street, access and specification.
Costs by type of project
| Project | Typical range | Source |
|---|---|---|
| Single-storey extension | £1,900 to £2,800 | Indicative industry range, 2026 (RapidQS: £1,800–£2,800 for a single-storey rear extension) |
| Two-storey extension (shared foundations and roof make it cheaper per m²) | £1,600 to £2,200 | Indicative industry range, 2026 (RapidQS: £1,600–£2,500) |
| Side-return extension (London terraces) | £2,200 to £3,500 | RapidQS UK, The Real Cost of Building in the UK: 2026 |
| Basement | £3,000 to £6,000+ | Indicative industry range, 2026 (RapidQS: £3,000–£5,000 for a basement conversion) |
| Standard new-build house, London | £2,800 to £4,000 | RapidQS UK, Construction Cost Per m² UK 2026 (London residential, depending on specification) |
These are UK-wide project ranges; in central London expect the upper end or above, in line with the location table.
Extras to budget for
| Item | Typical allowance | Source |
|---|---|---|
| Professional fees (architect, structural engineer, surveyors) | About 15% of build cost | Indicative industry range, 2026 |
| Consents (planning, building control, party wall) and contingency | 8 to 15% | Indicative industry range, 2026 |
| VAT on extensions and renovations | 20% (standard rate) | GOV.UK VAT Notice 708 |
| VAT on qualifying new-build homes | Zero-rated (0%) | GOV.UK VAT Notice 708 |
What pushes the price up in London
- Access: terraces with no side access mean materials and spoil move through the house, and skips or scaffolding on the road may need a council licence.
- Structure: opening rear walls usually needs steel beams designed by an engineer; London clay and nearby trees affect foundation depth.
- Glazing and specification: large sliding doors, rooflights and underfloor heating are often the biggest variables.
- Kitchens and finishes: often priced separately from the shell, so check what each quote includes.
How to compare builders' quotes
Ask every builder to price the same drawings and specification, itemised by stage, with provisional sums clearly marked. A low quote that leaves out drainage, steel or finishes is not cheaper. Our guide to choosing a builder in London covers what to check, and our quote form gets you a fixed, written price.
Sources: RapidQS UK, Construction Cost Per m² UK 2026 (London premium, London residential and commercial benchmarks); RapidQS UK, The Real Cost of Building in the UK: 2026 (London labour premium, side-return range); GOV.UK VAT Notice 708 (VAT). Ranges labelled "Indicative industry range, 2026" are compiled from industry guidance, including summaries of RapidQS UK, Ideal Home, Architecture for London and Checkatrade, but are not stated in that exact form by any one source we could confirm. Planning fees: see the Planning Portal.
Frequently asked questions
How much does building work cost per m² in London in 2026?
As an indicative 2026 guide, standard above-ground residential work in London typically costs about £1,750 to £4,500+ per m²: roughly £2,500–£3,500 in outer London and £3,500–£4,500+ in central London, before VAT, fees and contingency. Always get a fixed quote.
How much does a house extension cost per m² in London?
Indicatively, around £1,900–£2,800 per m² for a single-storey extension, £1,600–£2,200 for two-storey, £2,200–£3,500 for a side return and £3,000–£6,000+ for a basement, with central London at the upper end or above.
Is VAT charged on house extensions?
Extensions and renovations are standard-rated at 20%. Qualifying new-build homes are zero-rated. See GOV.UK VAT Notice 708.
