House extension cost
in Mayfair.
Mayfair — W1 — the Georgian and early Victorian district between Hyde Park and Regent Street. Most properties are commercial or converted to flats; remaining single-family homes are among the most valuable in London.
What makes extension work in Mayfair distinct.
Housing: Georgian and early Victorian terraces, plus mews properties; many Grade II or Grade II* listed.
Planning: Mayfair Conservation Area, with overlapping Hanover Square, Conduit Street and Berkeley Square conservation areas. A high listed-building density.
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 — W1 numbers.
All figures inclusive of design, planning, build, contingency and VAT. The Mayfair multiplier (1.30×) 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 Mayfair and beyond.
Send me the guide.
What Mayfair homeowners ask us.
How much does a house extension cost in Mayfair in 2026?
Typical 2026 Mayfair ranges (inc. design, planning, build, contingency & VAT): side-return extensions £117k–£208k; single-storey rear £143k–£273k; wraparound £221k–£416k; double-storey rear £234k–£494k; basement £325k–£975k. The Mayfair multiplier (1.30×) reflects local labour rates, scaffold logistics and finish expectations.
Do I need planning permission for an extension in Mayfair?
Mayfair Conservation Area, with overlapping Hanover Square, Conduit Street and Berkeley Square conservation areas. A high listed-building density. 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 Mayfair houses?
Georgian and early Victorian terraces, plus mews properties; many Grade II or Grade II* listed. 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 Mayfair?
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 Mayfair homeowners out on extensions?
In W1 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 Mayfair extensions?
Yes — Mayfair is within our core London catchment. Our studio is at 20 Dawes Road in Fulham, 5.5km from Mayfair. We've delivered extensions across the W1 postcode and our subcontractor network covers Westminster. Free site visit, fixed-price quote, 10-year HomePro guarantee on the finished work.
Extension pricing for Mayfair’s neighbours.
Twenty minutes on site in Mayfair.
On us.
Nick Elias RIBA and Vladimir will visit your Mayfair 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 Mayfair extension using the same 2026 rate card we quote real clients with.
Price my Mayfair extension →