Rear & side extensions in Mayfair
Mayfair is City of Westminster's georgian and victorian terraces (1720-1890) interspersed with early-20th-century mansion blocks on the grosvenor estate submarket. The Grosvenor Estate owns the freehold on roughly 300 acres of Mayfair and Belgravia, and the Estate's Licence to Alter process requires detailed condition specifications that typically exceed what Westminster Council alone would demand — for a kitchen remodel that means Estate-approved joinery suppliers, Estate-approved stone suppliers, and a Grosvenor-standard dilapidations schedule at handover.
What a rear & side extensions project looks like here
The Grosvenor Estate owns the freehold on roughly 300 acres of Mayfair and Belgravia, and the Estate's Licence to Alter process requires detailed condition specifications that typically exceed what Westminster Council alone would demand — for a kitchen remodel that means Estate-approved joinery suppliers, Estate-approved stone suppliers, and a Grosvenor-standard dilapidations schedule at handover.
Mayfair's mews houses (originally servant-and-horse accommodation behind the main Georgian terraces) are often curtilage-listed to the principal terrace, meaning an apparently standalone mews cottage can still require Listed Building Consent for internal works — a frequent surprise for first-time mews buyers.
Because Mayfair sits within Westminster's Mayfair Special Policy Area, changes of use from retail/office to residential face additional tests on preserving the area's commercial character — even a basement flat in a predominantly commercial terrace can be refused on those grounds.
Rear extensions, side-return infills, wraparound extensions — Permitted Development Class A rights or planning consent under the Article 4 borough overlay; Party Wall etc. Act 1996 notice on any party-wall touch. In Mayfair specifically, georgian and victorian terraces (1720-1890) interspersed with early-20th-century mansion blocks on the grosvenor estate stock means rear & side extensions scope is shaped by the neighborhood's dominant construction typology. Baily's London scoping flow factors mayfair conservation area (ca 14) and grosvenor estate leasehold consents on ~70% of freeholds into the estimate before a contractor is involved.
Start your Mayfair scope — Baily asks the right questions.
Pre-seeded for rear & side extensions in Mayfair. Mention your 150-600 m² (1,615-6,460 sqft), your timeline, and any known constraints — Baily factors the city of westminster planning + grosvenor estate consent review queue into the scope.
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Who is Baily?
Baily is named after Francis Baily — an English stockbroker who retired at 51, became an astronomer, and in 1836 described something on the edge of a solar eclipse that nobody had properly articulated before: a string of bright beads of sunlight breaking through the valleys along the moon’s rim.
He wasn’t the first to see them. Edmond Halley saw them in 1715 and barely noticed. Baily’s contribution was clarity — describing exactly what was happening, in plain language, so vividly that the whole field of astronomy paid attention. The phenomenon is still called Baily’s beads.
That’s what we wanted our AI to do. Every inbound call and text has signal in it — a homeowner’s real question, a timeline, a budget, a hesitation that means “yes but.” Baily listens to every one, 24/7, and finds the beads of light.
Baily was a businessman before he was a scientist. That’s our vibe too.
Questions LA homeowners actually ask
Mayfair rear & side extensions projects typically run $75K–$385K. Mayfair's georgian and victorian terraces (1720-1890) interspersed with early-20th-century mansion blocks on the grosvenor estate stock, combined with mayfair conservation area (ca 14), puts most mid-complexity projects in the $230K range. Baily scopes the exact band once you describe the work.
Nearest neighborhoods
Same service, adjacent London submarkets.