Barnet · London
Double-Storey Extension in Barnet
North London borough with large 1930s semis ideal for loft conversions and wraparound extensions.
Barnet
Double-Storey Extension specialists across Barnet.
We deliver double-storey extension projects across the full Barnet postcode set — N2, N3, N11, N12, N20, NW4, NW7, NW11, EN4, EN5. North London borough with large 1930s semis ideal for loft conversions and wraparound extensions.
A double-storey extension extends the rear of the house over two floors, adding a kitchen-diner or family room downstairs and a bedroom plus bathroom upstairs. It's the biggest single intervention you can make on a London house without changing the roofline, and the most efficient way to add a bedroom and bathroom alongside ground-floor open-plan living. Common on semis and detached homes in outer boroughs; harder but achievable on terraces with full planning.
Every Barnet project includes a free desk-based planning assessment before we quote. We know the local planning officers, party wall surveyors and approved inspectors by name.
Costs
Double-Storey Extension cost in Barnet 2026.
| Configuration | Cost range | Timeline |
|---|---|---|
| Standard double-storey (3m × full width) | £110,000–£150,000 | 16–20 wks |
| Larger double-storey (4m × full width) | £140,000–£180,000 | 18–22 wks |
| Premium double-storey + structural glass + bespoke kitchen | £175,000–£220,000 | 20–24 wks |
Local advantage
Eight years of double-storey extension work in Barnet.
Familiarity with Barnet's planning officers, party wall surveyors and approved inspectors cuts weeks off the approval timeline. We deliver consistent quality across all 10 postcodes the borough covers.
Recent Barnet work
Double-Storey Extension examples.
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 £33,000–£74,250 on a double-storey extension in Barnet.
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 £165,000.
FAQ
Double-Storey Extension in Barnet.
How much does a double-storey extension cost in Barnet?+
Double-Storey Extension projects in Barnet typically cost £110,000–£220,000. Barnet sits across postcodes N2, N3, N11, N12; local rates align with the wider London market.
Do double-storey extensions in Barnet need planning permission?+
North London borough with large 1930s semis ideal for loft conversions and wraparound extensions. We carry out a free desk-based planning assessment for your specific address before quoting, identifying whether permitted development, prior approval, or full planning applies.
Do you work across all Barnet postcodes?+
Yes — we deliver double-storey extension projects across all Barnet postcodes including N2, N3, N11, N12, N20, NW4, NW7, NW11, EN4, EN5.
How much does a double-storey extension cost in London?+
Typically £110,000–£220,000 depending on size and spec. A standard full-width double-storey on a Victorian terrace usually runs £130–170k.
Do I need planning permission for a double-storey?+
Almost always yes. PD limits make most useful double-storey extensions impossible without full planning.
Get a Barnet double-storey extension quote.
Senior consultant call within one business hour. Fixed-scope quote for your Barnet project — no provisional sums.
Other types in Barnet
Explore other build types in Barnet.
Double-Storey Extension across London