HMO Conversions Mayfair

HMO conversion in Mayfair is a narrow field: the VOA's count for the wider Strand, St James & Mayfair area records 96% of homes as flats and 4% as houses. The work that arises is turning a flat or a house into a shared let, or upgrading an existing HMO or an older converted building to meet Westminster's standards. The renewed Additional HMO Licensing Scheme covers the whole city from 31 August 2026, so a share of three or more people from two or more households sharing basic amenities needs a licence. Westminster's HMO standards for fire, rooms and kitchens then decide the build.

In Mayfair, a light HMO conversion for four to six tenants typically costs £40,000 to £75,000 in construction, or £90,000 to £150,000 with an en-suite to every bedroom (indicative London ranges, Mayfair Studio and LetCompliance, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Mayfair: we build the fire doors, detection, bathrooms and kitchens to the council's HMO standards, the landlord applies for the licence, and a registered electrician certifies the electrics.

Planning for a Mayfair HMO: C4, sui generis and Article 4

Under Class L of the 2015 permitted development order, a family home in use class C3 can become a C4 HMO for three to six sharers with no planning application, unless an Article 4 direction removes that right. The London Plan asks boroughs to weigh the strategic as well as local importance of HMOs when considering such directions, so your planning agent checks the position for the Mayfair address before anything else. Class L also does not let a single house become two or more separate C4 HMOs.

Above six occupants the use is sui generis, as the London Plan glossary defines it, and planning permission is needed. London Plan Policy H9 says HMOs of a reasonable standard should generally be protected, which matters if you later want to take an existing Mayfair HMO back to a single home. A flat in a block brings the lease into it too: leases can restrict sharing or subletting, so check the lease and the freeholder's position before paying for a design.

Housing in Mayfair

Around 7,560 homes make up the Strand, St James & Mayfair statistical area on the valuation list; 96% are flats and 4% houses, and 52% date from before 1919, 5% from between the wars and 41% from after 1945.

Licensing a Mayfair HMO: mandatory and additional schemes

Two HMO licences can apply. A large HMO, rented to 5 or more people who form more than 1 household, needs a mandatory licence, unless it is a flat in a purpose-built block of three or more flats. Westminster's renewed borough-wide Additional HMO Licensing Scheme was designated on 21 April 2026, came into effect on 31 August 2026 and runs until 30 August 2031, following the first scheme introduced on 30 August 2021. It covers shared houses or flats where three or more people from two or more households share basic amenities, across the whole city including Mayfair.

That exception matters in a flat-dominated area like Mayfair. A shared flat of five or more people in a purpose-built block of three or more flats is outside mandatory licensing, and Westminster's additional scheme covers it instead, as it covers flat shares, bedsits and some converted flats outside mandatory licensing. A home licensed as an HMO does not also need a selective licence. The landlord or their agent applies for the licence, and we build the works its conditions and standards call for.

Room sizes, kitchens and HMO standards in Mayfair

Four sets of Westminster HMO standards, each for a different type of shared building and updated in April 2021, set the benchmark, and the council may put works conditions on a licence to reach them. On top of those, national licence conditions set minimum bedroom sizes: 6.51 square metres for one person over 10, 10.22 for two people over 10, and no room under 4.64 used for sleeping. Where a let bedroom falls below the statutory size, Westminster must act, though it gives the landlord 18 months to put it right. In a Mayfair flat or townhouse with small attic or half-landing rooms, those minimums decide which rooms can be let as bedrooms.

Amenities follow the occupant count. In a Westminster shared house or flat, the kitchen needs a floor area of 5.5 square metres or more and a layout that is safe to work in. No bedroom may sleep more than two, and a child counts as one of them. We plan the kitchen, bathrooms and WCs against the number of occupants the licence will name, build worktops, sinks and cooking points to the standard, and fit the extract and drainage those rooms need in an older Mayfair building.

Fire safety, sound and energy in a Mayfair HMO

In a Mayfair HMO every letting gets a self-closing fire door, interlinked detection and alarms to the grade the risk assessment requires, and a protected escape route through the building. The design follows Part B, Westminster's HMO standards and the LACORS housing fire safety guidance. For an older converted Mayfair building of self-contained flats, Westminster's standard names 60 minutes fire resistance as the benchmark, but accepts 30 minutes in most existing conversions with appropriate automatic fire detection. In a listed Mayfair building, new fire doors, partitions and bathrooms usually need listed building consent, which the owner or their designer obtains before work starts.

Those standards can also catch a Mayfair block of self-contained flats. If its conversion falls short of the 1991 Building Regulations and fewer than two thirds of the flats are owner-occupied, the Housing Act makes it an HMO. Westminster's self-contained flat standard then applies. Sound between lettings matters as well, and resilient ceilings and sealed partitions cut complaints between rooms. Where the HMO as a whole needs an EPC, MEES applies, with no letting below E since 1 April 2020 without a valid exemption, so insulation and heating controls go in while the Mayfair rooms are stripped.

• Large HMO conversions for seven or more, once planning is granted
• Extra shared bathrooms and shower rooms
• En-suite shower rooms added to bedrooms

VOA Council Tax stock of properties, March 2025, for the Strand, St James & Mayfair statistical area, which also covers St James's and the Strand. Counts rounded by the VOA.

If this is your first project in Mayfair, these are worth a look: bathroom renovation in Mayfair, hmo conversions across Westminster, what a main building contractor does, how snagging works at handover, hmo conversions across London and Kitchen Renovation Cost.

The GS Renovation Difference in Mayfair

An HMO is built to a licence as much as to drawings, so we price from the licensing standards, the fire strategy and your designer's layout together. We check each room against the minimum sizes, plan kitchens and bathrooms for the occupant count, and build the fire doors, detection and escape route first. The founder, Abdelaaziz Saaid, oversees the programme, the landlord or their agent applies for the licence, and at handover you receive the electrical, gas and alarm certificates the licence file needs.

• Sound lining between bedrooms so one sharer does not keep another awake
• Dust screens and floor protection in occupied homes
• EPC upgrades done while the walls and floors are still open

Checked by Abdelaaziz Saaid, founder and director of GS Renovation Ltd (Companies House no. 14611254).