Flat Conversions Marylebone

In Marylebone there are few houses left to divide: the VOA figures for the wider Marylebone & Park Lane and Bryanston & Dorset Square statistical areas show 92% of homes are already flats and 8% are houses. Flat conversion work here means splitting one of the remaining terraced townhouses into self-contained flats, re-planning an older conversion into fewer, larger flats, or joining flats back into a single house. Each route changes the number of homes, so each needs planning permission from Westminster, and the new layout needs building control approval.

In Marylebone, converting a house into two or three flats is published at £50,000 to £120,000 including professional and council fees, and an England-wide guide puts a straightforward two-flat split at £40,000 to £80,000 in construction alone, which is the part a builder prices (indicative London ranges, Architectural Drawings and Mayfair Studio, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Marylebone: we build the conversion to the approved drawings, building control inspects the fire and sound separation, and a registered electrician certifies each flat's electrics.

Which Marylebone houses get divided, and which get joined back

In Marylebone the stock to convert is small. In the VOA figures for the wider Marylebone & Park Lane and Bryanston & Dorset Square areas, houses are 8% of homes, almost all terraced, and 54% of homes were built before 1919. The candidates are tall Georgian townhouses, where each storey can form a flat with the original stair kept as the shared route. Such a house brings solid party walls, timber floors and a single stair that shapes every layout choice, from where the bathrooms stack to how each front door opens onto the landing.

The reverse also happens. A townhouse split into small flats decades ago may suit an owner better as one house again, and joining flats means reopening the stair to the whole house and taking out duplicate kitchens and meters. That generally needs planning permission too, because it reduces the number of homes, and your designer or agent confirms the position with Westminster. We price either route from the same survey, so you can compare them before an application is prepared.

Housing in Marylebone

Around 12,620 homes make up Marylebone on the valuation list; 92% are flats and 8% houses, and 54% date from before 1919, 16% from between the wars and 29% from after 1945. Since most homes here are flats, a flat in Marylebone can be split or combined only with the freeholder's consent, and changing the number of homes usually needs planning permission as well.

The planning case for converting a Marylebone townhouse

Turning a Marylebone house into flats always needs planning permission, and the application is judged against Westminster's City Plan, whose current version was adopted by full council on 21 January 2026 after a Partial Review. The London Plan small sites text lists residential conversions among the forms of incremental intensification that count where they result in net additional housing. Your designer or agent makes the case, including how the scheme treats family-sized homes, and we build to the permission that comes back.

The consent also brings charges and conditions. Westminster charges CIL per square metre on new dwellings of any size and on development where the internal area of a new building, extension or change of use exceeds 100 square metres. Its charging schedule first took effect on 1 May 2016. Your agent confirms whether a Marylebone scheme is liable and how existing floorspace is treated. Pre-commencement conditions are cleared before we start, so the site programme begins with those, not the strip out.

Space standards that fix a Marylebone flat layout

A new flat in a Marylebone conversion must meet the London Plan space standards. Policy D6 applies them to all tenures and all self-contained homes, and the London Plan counts conversions and changes of use as new dwellings. A single bedroom must be at least 7.5 square metres and 2.15m wide, a double at least 11.5 square metres, and at least 75 per cent of each flat needs a floor to ceiling height of 2.5m. Policy D6 also asks developments to maximise dual aspect homes.

The height rule matters in a Marylebone townhouse, where the attic storey is often lower than the grand first floor. A flat running front to back on one storey gets its dual aspect naturally, while a flat squeezed into the back half of a floor does not. The space standard sits within planning, not the building regulations, so it is settled at design stage. Where the numbers do not fit, the answer is usually fewer, larger flats, and we check room sizes on site before partitions are boarded.

Fire, sound and services between flats in a Marylebone conversion

Sound is the hardest standard to reach in a period townhouse conversion. Approved Document E sets the level for flats formed by material change of use at 43 dB airborne for walls, floors and stairs and 64 dB maximum impact for floors and stairs, and pre-completion sound testing proves it. In a Marylebone townhouse that means resilient ceilings, insulation between joists and a floating floor build-up, detailed around surviving cornices. Part B needs each flat separated from its neighbours and from the shared stair, with fire doors and detection to the approved specification.

Each flat also needs its own services. That means a separate electricity meter and consumer unit for each flat, a gas supply or electric heating, water and drainage routed through the shared structure, and a postal address through Westminster's street naming and numbering process. Where the works cut into or build on a party wall, the building owner serves notice under the Party Wall Act, and that work goes ahead once the neighbour consents in writing or an award is made. We sequence the job so services run up the house once and each flat is tested and certified in turn.

• Heating and hot water for each flat, gas by a Gas Safe registered engineer
• Pre-completion sound testing arranged before sign-off
• Insulation to the walls, roof and floors the conversion touches

VOA Council Tax stock of properties, March 2025, for Marylebone & Park Lane and Bryanston & Dorset Square. Counts rounded by the VOA.

Next steps that tend to follow flat conversions in Marylebone: structural alterations in Marylebone, flat conversions across Westminster, builders in London who take on conversions, the Party Wall Act when a conversion cuts a shared wall, how we handle flat conversions across London and Renovation Budget & Contingency.

Why Choose GS Renovation in Marylebone

A conversion succeeds or fails on its tests and paperwork as much as its build. We work from your approved plans, coordinate with the structural engineer we appoint and your designer, and check every room against the consented sizes before boarding. Sound testing is booked well ahead of completion, and each flat's meters, address and certificates are lined up in turn, so the completion file is ready when you come to sell or let the flats.

• Neighbours given notice before the noisy stages
• Mains-wired, interlinked smoke and heat alarms to the approved fire strategy
• Each flat numbered and supplied before the keys are handed over

Checked by Abdelaaziz Saaid, founder and director of GS Renovation Ltd (Companies House no. 14611254). Structural design is by the consulting engineer appointed to your project.