House extension cost
in Clapham.
Clapham — SW4 — south-east of Battersea, centred on the common. A mix of Victorian terraces, Georgian houses around the common, and pockets of inter-war housing.
What makes extension work in Clapham distinct.
Housing: Two- and three-storey Victorian terraces, Georgian houses on the common itself, and 1920s/30s housing on the southern edges.
Planning: Clapham Common conservation areas (multiple) cover the common itself and adjoining streets. Most of central Clapham retains PD rights.
Applications go to LB Lambeth. We submit on your behalf and handle party wall awards, build-over agreements and conservation officer correspondence end-to-end.
The five extension types — SW4 numbers.
All figures inclusive of design, planning, build, contingency and VAT. The Clapham multiplier (0.96×) reflects local labour, scaffolding logistics, conservation requirements and finish expectations.
The 2026 London Extension Cost Guide.
Borough-by-borough pricing, a full £200k cost breakdown, PD vs full planning explained, and the seven hidden costs to watch for in Clapham and beyond.
Send me the guide.
What Clapham homeowners ask us.
How much does a house extension cost in Clapham in 2026?
Typical 2026 Clapham ranges (inc. design, planning, build, contingency & VAT): side-return extensions £86k–£154k; single-storey rear £106k–£202k; wraparound £163k–£307k; double-storey rear £173k–£365k; basement £240k–£720k. The Clapham multiplier (0.96×) reflects local labour rates, scaffold logistics and finish expectations.
Do I need planning permission for an extension in Clapham?
Clapham Common conservation areas (multiple) cover the common itself and adjoining streets. Most of central Clapham retains PD rights. Outside conservation areas, single-storey rear extensions up to 3m (terrace/semi) or 4m (detached) usually qualify for permitted development. Side-returns, wraparounds, double-storey extensions and anything in a conservation area need full planning. Applications go to LB Lambeth.
What extension type works best for Clapham houses?
Two- and three-storey Victorian terraces, Georgian houses on the common itself, and 1920s/30s housing on the southern edges. On this housing stock, the most common 2VP extension is a single-storey rear or wraparound — adding 20–35 m² of open-plan kitchen-diner. Double-storey extensions become viable on properties with rear gardens deep enough to absorb the additional volume without overshadowing.
How long does an extension take in Clapham?
Allow 8–12 weeks for design and planning (longer in conservation areas), then 16–22 weeks on site for a single-storey, 22–30 weeks for a wraparound or double-storey, and 28–40 weeks for a basement. LB Lambeth processes planning applications in approximately 8–13 weeks depending on backlog.
What hidden costs catch Clapham homeowners out on extensions?
In SW4 the top items are: party wall awards (£1,000–£3,000 per neighbour — common on terraced streets), build-over agreements with Thames Water (£300–£1,500 where drains run beneath the proposed extension), conservation officer consultations, structural engineer fees, drainage and asbestos surveys, and VAT at 20% on top of the base build cost. All of these are itemised in our fixed-price quote.
Does 2VP work on Clapham extensions?
Yes — Clapham is within our core London catchment. Our studio is at 20 Dawes Road in Fulham, 5.0km from Clapham. We've delivered extensions across the SW4 postcode and our subcontractor network covers Lambeth. Free site visit, fixed-price quote, 10-year HomePro guarantee on the finished work.
Extension pricing for Clapham’s neighbours.
Twenty minutes on site in Clapham.
On us.
Nick Elias RIBA and Vladimir will visit your Clapham home, walk the site, check planning constraints, advise on PD vs full planning, and give you a realistic budget and programme — even if an extension isn’t the right move.
One number. Sixty seconds. No callback.
Price your Clapham extension using the same 2026 rate card we quote real clients with.
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