Case studies · London · September 2026
Build Team case studies: real London extensions, with the real numbers
16 completed projects, each documented with its floor area, build cost and time on site. Across them the median build cost is £86,000 excluding VAT, the median build time is 14 weeks, and the median build rate is £1,993 per square metre for the year each was built. Every project below links to the full write-up, and most to the lookbook PDF with the drawings and photography.
Compare the numbers
| Project | Borough | What we built | Size | Build cost | Per m² | On site | Year |
|---|---|---|---|---|---|---|---|
| Mayfield Road, N8 | Haringey | Wraparound Ground Floor Extension | 50 m² | £87,000 | £1,740 | 14 weeks | 2025 |
| Cricklade Avenue, SW2 | Lambeth | Ground Floor Rear Extension | 42 m² | £91,000 | £2,167 | 14 weeks | 2025 |
| Bonham Road, SW2 | Lambeth | Ground Floor Rear Extension | 50 m² | £91,000 | £1,820 | 14 weeks | 2025 |
| Milton Road | Lambeth | Side and Rear Extension | 50 m² | £74,000 | £1,480 | 16 weeks | 2024 |
| Nightingale Mansions, SW128TN | Wandsworth | Rear Extension | 50 m² | £85,000 | £1,700 | 16 weeks | 2024 |
| Heber Ro, SE229JZ | Southwark | Wraparound Extension | 50 m² | £60,000 | £1,200 | 12 weeks | 2024 |
| Adelaide Ro, W139EB | Ealing | Ground Floor Extension | 50 m² | — | — | — | 2023 |
| Lidfieldr, N169NA | Hackney | Ground Floor Extension | 50 m² | — | — | — | 2023 |
| Scholars Ro, SW120PG | Wandsworth | Ground Floor Extension | 15 m² | £70,000 | £4,667 | 16 weeks | 2023 |
| Antillrd, N154BA | Haringey | Ground Floor Extension | 32 m² | — | — | — | 2022 |
| Therapi | Southwark | Rear Extension | 50 m² | £150,000 | £3,000 | 16 weeks | 2022 |
| Thorpedale, N43DP | Islington | Wraparound Extension | 22 m² | £90,000 | £4,091 | 14 weeks | 2021 |
| Dulwich Road, SE228PW | Southwark | Wraparound Extension | 27 m² | £60,000 | £2,222 | 12 weeks | 2021 |
| Littlewood | Lewisham | Loft Conversion | 28 m² | — | — | — | 2021 |
| Plato Road, SW25UP | Lambeth | Ground Floor Extension | 18 m² | — | — | — | 2021 |
| Exeter Road, NW24SE | Brent | Ground Floor Extension | 32 m² | — | — | — | 2021 |
Build cost excludes VAT and professional fees, and reflects prices at the time each project was built, which is why older projects show a lower rate per square metre. For current pricing see our extension cost calculator.
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