Cost guide · 2026
HouseExtensionCostNorthLondon2026
2026 house extension pricing for North London — Camden, Islington, Haringey, Barnet, Enfield, Waltham Forest. Edwardian and Victorian terrace cluster, plus the suburban 1930s semis of outer Barnet and Enfield.
Quick answer
A house extension in North London costs £55,000–£230,000 in 2026. Side returns run £55,000–£95,000; single-storey rears £65,000–£150,000; wraparounds £100,000–£180,000; double-storeys £115,000–£230,000. Conservation areas in Camden (Hampstead, Highgate) and Islington (Canonbury, Barnsbury) push pricing 10–18% higher. Cost per m² is £2,900–£4,400. All Builderr North London quotes are fixed-price.
What moves the price
The seven cost factors that matter most.
Camden's Hampstead, Belsize, Highgate, Primrose Hill; Islington's Canonbury, Barnsbury, Highbury — full planning standard, planning fees +£6,500.
Crouch End, Muswell Hill, Stroud Green, Highbury — strong cluster suits side returns + 4-6m rear, typically £90–150k.
Barnet, Enfield — generous gardens, easier permitted development routes, single-storey rears £75–115k with kitchen.
Removes PD on parts of NW1, NW3, NW5, N1, N4, N8 — full planning even for standard rears.
Mid-terrace runs in Islington, Stoke Newington, Tufnell Park trigger PWA on both neighbours — £2,400–£4,800 surveyor budget.
Inner North postcodes default to steel Crittall or premium sliders at £14–22k; outer borough projects often bifold at £8–12k.
Camden, Islington — narrow streets, CPZ, skip permit costs +£1,500–£3,500 vs outer Barnet/Enfield.
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 | 11% | £15,675 |
| Superstructure & roof | 15% | £21,375 |
| Glazing | 14% | £19,950 |
| First fix MEP | 9% | £12,825 |
| Plaster & decoration | 7% | £9,975 |
| Kitchen fit-out | 9% | £12,825 |
| Flooring | 6% | £8,550 |
| Second fix & lighting | 4% | £5,700 |
| External works | 3% | £4,275 |
| Fees | 11% | £15,675 |
| Site management | 6% | £8,550 |
| Margin & contingency | 5% | £7,125 |
Real projects
Worked examples from completed builds.
London zones
Where your borough sits in the price band.
| Zone | Multiplier | Notes |
|---|---|---|
| Prime (NW1, NW3, NW5, N1) | 1.15–1.28× | Camden, Islington — listed common, prime spec |
| Inner (N4, N5, N6, N7, N8, N10, N16, N19) | 1.05–1.15× | Edwardian/Victorian terraces and villas |
| Outer mid (N11, N12, N13, N14, N17, N20, N21, N22) | 0.95–1.05× | Mostly 1930s semis |
| Outer (EN1-EN5, parts of Barnet) | 0.88–0.95× | Detached and large semi stock |
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 £28,500–£64,125 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 £142,500.
Related
See the full house extensions service page.
FAQ
House Extension Cost North London:
common questions.
How much does a house extension cost in North London?
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A North London house extension costs £55,000–£230,000. Side returns in Islington, Stoke Newington and Crouch End run £65,000–£95,000. 4m rear extensions with open-plan kitchen £95,000–£140,000. Double-storey rears on Edwardian semis £150,000–£200,000. Prime Camden conservation projects with steel Crittall and bespoke kitchen reach £200,000–£230,000.
Do I need planning permission for an extension in Camden or Islington?
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Often yes. Both boroughs have extensive Article 4 directions removing permitted development rights — Camden across Hampstead, Belsize, Highgate, Primrose Hill, Bloomsbury and most of NW1-NW5; Islington across Canonbury, Barnsbury, Highbury and most of N1. Conservation areas across both add further restrictions. Full planning is typically required; budget £6,500 in fees and 10–14 weeks to decision.
Which North London borough is cheapest for an extension?
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Barnet and Enfield. Lower trade rates, easier access, larger gardens that enable bigger PD extensions without planning, and no Article 4 coverage on most postcodes. A 4m rear extension on a 1930s semi in Barnet typically runs £85,000–£115,000 vs £110,000–£150,000 for the same project in Camden or Islington.
How long does a North London extension take?
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10–22 weeks on site depending on type. Side returns 12–14 weeks; 4m rears 14–17 weeks; wraparounds 18–20 weeks; double-storeys 20–22 weeks. Pre-construction adds 4–6 weeks for PD projects in outer Barnet/Enfield, 12–16 weeks for full planning in Camden/Islington conservation areas.
What's the cost per m² for a North London extension?
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£2,900–£4,400 per m² for the building work. Inner Camden, Islington and prime Hampstead/Highgate sit at the upper end (£3,800–£4,400). Outer Barnet, Enfield and mid-Haringey sit at £2,900–£3,400. Kitchen units, bespoke joinery and high-spec glazing are itemised separately and not in the per-m² figure.
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