House extension cost
in Westminster.
Westminster — SW1 — the political and ceremonial heart of London. Residential stock is concentrated in pockets around Westminster Abbey, Victoria Street and St James's Park, with grand mansion flats and a small number of single-family terraces.
What makes extension work in Westminster distinct.
Housing: Mansion blocks, listed Georgian terraces, and a small number of mews properties.
Planning: Westminster Abbey and Parliament Square Conservation Area, plus overlapping Whitehall and St James's. Many properties are Grade I or Grade II* listed.
Applications go to City of Westminster. We submit on your behalf and handle party wall awards, build-over agreements and conservation officer correspondence end-to-end.
The five extension types — SW1 numbers.
All figures inclusive of design, planning, build, contingency and VAT. The Westminster multiplier (1.28×) 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 Westminster and beyond.
Send me the guide.
What Westminster homeowners ask us.
How much does a house extension cost in Westminster in 2026?
Typical 2026 Westminster ranges (inc. design, planning, build, contingency & VAT): side-return extensions £115k–£205k; single-storey rear £141k–£269k; wraparound £218k–£410k; double-storey rear £230k–£486k; basement £320k–£960k. The Westminster multiplier (1.28×) reflects local labour rates, scaffold logistics and finish expectations.
Do I need planning permission for an extension in Westminster?
Westminster Abbey and Parliament Square Conservation Area, plus overlapping Whitehall and St James's. Many properties are Grade I or Grade II* listed. 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 City of Westminster.
What extension type works best for Westminster houses?
Mansion blocks, listed Georgian terraces, and a small number of mews properties. 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 Westminster?
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. City of Westminster processes planning applications in approximately 8–13 weeks depending on backlog.
What hidden costs catch Westminster homeowners out on extensions?
In SW1 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 Westminster extensions?
Yes — Westminster is within our core London catchment. Our studio is at 20 Dawes Road in Fulham, 6.0km from Westminster. We've delivered extensions across the SW1 postcode and our subcontractor network covers Westminster. Free site visit, fixed-price quote, 10-year HomePro guarantee on the finished work.
Extension pricing for Westminster’s neighbours.
Twenty minutes on site in Westminster.
On us.
Nick Elias RIBA and Vladimir will visit your Westminster 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 Westminster extension using the same 2026 rate card we quote real clients with.
Price my Westminster extension →