Kensington and Chelsea · London
Double-Storey Extension in Kensington and Chelsea
Premium borough with listed and conservation stock — basement and interior work dominates.
Kensington and Chelsea
Double-Storey Extension specialists across Kensington and Chelsea.
We deliver double-storey extension projects across the full Kensington and Chelsea postcode set — SW3, SW5, SW7, SW10, W2, W8, W10, W11. Premium borough with listed and conservation stock — basement and interior work dominates.
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 Kensington and Chelsea 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 Kensington and Chelsea 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 Kensington and Chelsea.
Familiarity with Kensington and Chelsea's planning officers, party wall surveyors and approved inspectors cuts weeks off the approval timeline. We deliver consistent quality across all 8 postcodes the borough covers.
Recent Kensington and Chelsea 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 Kensington and Chelsea.
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 Kensington and Chelsea.
How much does a double-storey extension cost in Kensington and Chelsea?+
Double-Storey Extension projects in Kensington and Chelsea typically cost £110,000–£220,000. Kensington and Chelsea sits across postcodes SW3, SW5, SW7, SW10; local rates align with the wider London market.
Do double-storey extensions in Kensington and Chelsea need planning permission?+
Premium borough with listed and conservation stock — basement and interior work dominates. 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 Kensington and Chelsea postcodes?+
Yes — we deliver double-storey extension projects across all Kensington and Chelsea postcodes including SW3, SW5, SW7, SW10, W2, W8, W10, W11.
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 Kensington and Chelsea double-storey extension quote.
Senior consultant call within one business hour. Fixed-scope quote for your Kensington and Chelsea project — no provisional sums.
Other types in Kensington and Chelsea
Explore other build types in Kensington and Chelsea.
Double-Storey Extension across London