House extension cost
in Mortlake.
Mortlake — SW14 — west of Barnes, on the south bank of the Thames. A quieter neighbourhood with Edwardian terraces and a strong river-village character.
What makes extension work in Mortlake distinct.
Housing: Edwardian terraces with outriggers, plus older cottages near the riverside and 1920s semis on the southern edges.
Planning: Mortlake Conservation Area covers the historic core; outside it, PD rights are usually intact.
Applications go to LB Richmond upon Thames. We submit on your behalf and handle party wall awards, build-over agreements and conservation officer correspondence end-to-end.
The five extension types — SW14 numbers.
All figures inclusive of design, planning, build, contingency and VAT. The Mortlake 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 Mortlake and beyond.
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What Mortlake homeowners ask us.
How much does a house extension cost in Mortlake in 2026?
Typical 2026 Mortlake 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 Mortlake multiplier (0.96×) reflects local labour rates, scaffold logistics and finish expectations.
Do I need planning permission for an extension in Mortlake?
Mortlake Conservation Area covers the historic core; outside it, PD rights are usually intact. 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 Richmond upon Thames.
What extension type works best for Mortlake houses?
Edwardian terraces with outriggers, plus older cottages near the riverside and 1920s semis 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 Mortlake?
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 Richmond upon Thames processes planning applications in approximately 8–13 weeks depending on backlog.
What hidden costs catch Mortlake homeowners out on extensions?
In SW14 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 Mortlake extensions?
Yes — Mortlake is within our core London catchment. Our studio is at 20 Dawes Road in Fulham, 5.0km from Mortlake. We've delivered extensions across the SW14 postcode and our subcontractor network covers Richmond upon Thames. Free site visit, fixed-price quote, 10-year HomePro guarantee on the finished work.
Extension pricing for Mortlake’s neighbours.
Twenty minutes on site in Mortlake.
On us.
Nick Elias RIBA and Vladimir will visit your Mortlake 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 Mortlake extension using the same 2026 rate card we quote real clients with.
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