House extension cost
in Balham.
Balham — SW12 — between Clapham and Tooting. Solid Edwardian terraces dominate, with a strong family-housing market driving consistent loft-conversion demand.
What makes extension work in Balham distinct.
Housing: Edwardian three-bay terraces with bay windows and outriggers, plus pockets of inter-war housing.
Planning: Heaver Estate and Nightingale Triangle conservation areas cover the more architecturally consistent streets.
Applications go to LB Wandsworth & 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 — SW12 numbers.
All figures inclusive of design, planning, build, contingency and VAT. The Balham multiplier (0.94×) 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 Balham and beyond.
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What Balham homeowners ask us.
How much does a house extension cost in Balham in 2026?
Typical 2026 Balham ranges (inc. design, planning, build, contingency & VAT): side-return extensions £85k–£150k; single-storey rear £103k–£197k; wraparound £160k–£301k; double-storey rear £169k–£357k; basement £235k–£705k. The Balham multiplier (0.94×) reflects local labour rates, scaffold logistics and finish expectations.
Do I need planning permission for an extension in Balham?
Heaver Estate and Nightingale Triangle conservation areas cover the more architecturally consistent streets. 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 Wandsworth & LB Lambeth.
What extension type works best for Balham houses?
Edwardian three-bay terraces with bay windows and outriggers, plus pockets of inter-war housing. 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 Balham?
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 Wandsworth & LB Lambeth processes planning applications in approximately 8–13 weeks depending on backlog.
What hidden costs catch Balham homeowners out on extensions?
In SW12 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 Balham extensions?
Yes — Balham is within our core London catchment. Our studio is at 20 Dawes Road in Fulham, 5.5km from Balham. We've delivered extensions across the SW12 postcode and our subcontractor network covers Wandsworth / Lambeth. Free site visit, fixed-price quote, 10-year HomePro guarantee on the finished work.
Extension pricing for Balham’s neighbours.
Twenty minutes on site in Balham.
On us.
Nick Elias RIBA and Vladimir will visit your Balham 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 Balham extension using the same 2026 rate card we quote real clients with.
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