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Greater London

Rear extension cost in London

Single-storey rear extensions opening kitchens, dining and living space onto the garden — usually 30–50 m².

Local context — London

Council
Varies by borough (32 boroughs + City of London)
Open planning portal →
Cost premium
+18-25% vs UK average (inner London) / +8-15% (outer boroughs)
Typical extension price
A 25 m² rear extension in London typically runs £78,000-£125,000 (standard to luxury, 2026). Side-return extensions in Victorian terraces (Clapham, Islington, Hackney) cluster at £85-110k for a standard spec.
Building Control
Every London borough has its own Building Control; most homeowners use private Approved Inspectors (LABC, BBS, Stroma) for faster turnaround. Inspection lead time is 1-3 working days across most boroughs.
Conservation & Article 4
London has 1,000+ conservation areas. Article 4 directions are extensive across Camden, Hackney, Islington, Kensington & Chelsea and Westminster — assume PD rights are removed in any pre-1940 street until the borough confirms otherwise.
Local quirks that move the price
Parking suspensions (£40-110/day depending on borough) and CPZ dispensations are mandatory on most builds. Party-wall agreements typically needed on both sides for terraces. London Plan policy now requires sustainable urban drainage (SUDS) on most extensions over 5 m² of new hard surface.
High-demand areas in London
ClaphamIslingtonHackneyWandsworthLewishamEaling
Typical 40 m² project in London
£66,029
to
£106,632
Mid-range (premium spec): £86,340
standard
£66,029
premium
£86,340
luxury
£106,632
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What's typically included

Rear extension costs in London — FAQs

How much does a rear extension cost in London?

Rear extensions in London typically cost between £66,029 and £106,632 depending on size, specification and site conditions. A mid-range 40 m² project averages around £86,340. London pricing reflects higher labour rates, parking permits and tighter site access.

How long will it take?

Most rear extensions take between 6 and 16 weeks on site, depending on scope, structural complexity and planning requirements in Greater London.

Do I need planning permission?

Many rear extensions fall under permitted development, but conservation areas, listed buildings and larger projects in London can require a full planning application. Use the cost checker to see what applies to your address.

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Disclaimer: This is an industry-informed estimate for guidance only — not a fixed quote, valuation, survey or legal advice. Figures are based on regional averages and the details you provided. Site-specific factors (access, ground conditions, structural surprises, planning constraints) can materially change the cost. Always confirm with a site inspection, written quotes from qualified tradespeople, and supplier pricing before committing to work. Build Price IQ (trading under Services R Us Ltd) accepts no liability for any decisions, costs, losses or damages arising from the use of these estimates.