Cost guide · 2026
HouseExtensionCostSouthLondon2026
2026 house extension pricing for South London — Lambeth, Lewisham, Southwark, Croydon, Bromley, Merton, Wandsworth, Greenwich. Victorian terrace density inner, suburban semi stock outer.
Quick answer
A house extension in South London costs £52,000–£215,000 in 2026. Side returns £52,000–£90,000; single-storey rears £62,000–£145,000; wraparounds £95,000–£175,000; double-storeys £110,000–£215,000. Inner conservation areas (Clapham, Brixton, Telegraph Hill, Greenwich) push pricing up 8–15%. Cost per m² is £2,800–£4,300. All Builderr South London quotes are fixed-price.
What moves the price
The seven cost factors that matter most.
Brixton, Clapham, Battersea, Camberwell, Peckham, East Dulwich — side returns are the dominant extension type, £58–95k including kitchen.
End-of-terrace stock in Tooting, Streatham, Honor Oak — wraparounds give significant footprint gain at £105–165k.
Croydon, Bromley, Sutton — generous gardens, easier PD routes, single-storey rears £72–120k with open-plan kitchen.
Lambeth 30+ CAs, Southwark 45+, Lewisham 30+. Brixton, Clapham Old Town, Herne Hill, Telegraph Hill, Forest Hill all designated.
World Heritage Site fringe — listed buildings common in SE10, SE3, SE9; extensions often need full planning with heritage statement.
Bromley, Sutton, Croydon — easier access, lower trade rates, 8–15% below inner South.
Mid-terrace runs in Tooting, Streatham, Brockley trigger PWA on both neighbours — £2,400–£4,800 surveyor budget.
Cost breakdown
Where the money actually goes.
Percentage breakdown of a typical mid-spec project. Add or subtract per your finish tier.
| Line item | % of total | £ on avg project |
|---|---|---|
| Groundworks & foundations | 12% | £16,020 |
| Superstructure & roof | 15% | £20,025 |
| Glazing | 13% | £17,355 |
| First fix MEP | 9% | £12,015 |
| Plaster & decoration | 7% | £9,345 |
| Kitchen fit-out | 9% | £12,015 |
| Flooring | 6% | £8,010 |
| Second fix & lighting | 4% | £5,340 |
| External works | 3% | £4,005 |
| Fees | 10% | £13,350 |
| Site management | 6% | £8,010 |
| Margin & contingency | 6% | £8,010 |
Real projects
Worked examples from completed builds.
London zones
Where your borough sits in the price band.
| Zone | Multiplier | Notes |
|---|---|---|
| Inner (SW3, SW10, SW11, SE1) | 1.15–1.25× | Battersea, Vauxhall, Bermondsey |
| Mid (SW2, SW4, SW8, SW9, SE5, SE15, SE22) | 1.05–1.12× | Brixton, Clapham, Camberwell, Peckham, East Dulwich |
| Outer mid (SW12, SW16, SW17, SE13, SE23, SE10) | 0.98–1.05× | Balham, Streatham, Tooting, Lewisham, Forest Hill, Greenwich |
| Outer (CR0-CR9, BR1-BR8, SM1-SM7, KT1-KT9) | 0.88–0.96× | Croydon, Bromley, Sutton, Kingston |
Builderr vs other London builders.
The construction industry has a wide distribution of operators. Here's what changes between a directly-employed, fixed-scope outfit and the alternatives.
| Criterion | Builderr | Typical London builder | Cowboy outfit |
|---|---|---|---|
| Labour model | Directly employed team (PAYE) | Mixed subcontract gangs | Day-rate cash labour |
| Pricing | Fixed-scope itemised quote | Estimate + provisional sums | Verbal price + variations |
| Design & engineering | In-house architect + SE | Outsourced, separate billing | Builder draws on the back of an envelope |
| Planning + LDC handled | Yes — included in price | Often charged extra | Builder asks you to apply |
| Party wall surveyors | Instructed by us | Your responsibility | Skipped (illegal) |
| Building control | Plans + site inspections booked by us | Building Notice route | Not registered |
| Project management | Dedicated PM, weekly photo updates | Foreman doubles up | Owner-manager juggles 5 jobs |
| Payment schedule | Stage payments against signed-off milestones | Weekly invoices | Cash up front |
| Insurance | £10M PL + 10yr structural warranty | £2–5M PL only | No documented cover |
| Snags at handover | <3 typical | 20–30 typical | Walk-off mid-job common |
| Variation creep | 0% — fixed scope | +15–25% over original quote | +40%+ regularly |
Save £26,700–£60,075 on a house extensions.
Industry data (FMB, RICS, Which? Trusted Trader 2024) shows the average London construction project overruns by 18–22% on cost and 25–35% on time. Fixed-scope contracts with a single accountable team eliminate that variance. The savings above assume a typical project at £133,500.
Related
See the full house extensions service page.
FAQ
House Extension Cost South London:
common questions.
How much does a house extension cost in South London?
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A South London house extension costs £52,000–£215,000. Side returns in Tooting, Clapham, Brixton and Peckham £62,000–£90,000. 4m rears with open-plan kitchen £90,000–£140,000. Wraparounds on end-of-terrace stock £105,000–£165,000. Outer South (Bromley, Sutton, Croydon) typically 8–15% below inner pricing.
What's the most common extension type in South London?
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Side returns on Victorian terraces. South London's terrace density — particularly in Lambeth, Wandsworth and Southwark — makes the side return alley the most natural extension space. A typical side return + kitchen extension runs £62,000–£95,000 with kitchen, takes 12–14 weeks, and is usually permitted development outside conservation areas.
Do South London conservation areas affect extension cost?
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Yes. Lambeth has 30+ conservation areas, Southwark 45+, Lewisham 30+. Conservation typically requires full planning even for permitted development sizes, restricts glazing to traditional profiles, and prohibits some materials. Cost uplift is £5,000–£12,000 plus 10–14 weeks for planning. We confirm conservation status before quoting.
Which South London borough is cheapest for an extension?
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Bromley, Sutton and Croydon. Lower trade rates, larger gardens that enable bigger PD extensions, easier access, no Article 4 coverage on most postcodes, and a 1930s and post-war semi stock that suits straightforward single-storey rears. A 4m rear in Bromley typically £80,000–£115,000 vs £105,000–£145,000 for the same project inner South.
How long does a South London extension take?
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12–22 weeks on site depending on type. Side returns 12–14 weeks; 4m rears 15–17 weeks; wraparounds 17–20 weeks; double-storeys 20–22 weeks. Pre-construction is 4–6 weeks for PD projects in outer South, 10–14 weeks for full planning in inner conservation areas.
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