Flat Conversions Southwark

Flat conversion work in Southwark starts from a small pool of houses. Only 19% of the borough's homes are houses, and the council protects them: a home with 130sqm or less of original net internal floorspace cannot be split into two or more homes under Policy P3 of the Southwark Plan 2022. The houses that can be converted are the larger ones above that line, and each new flat is built to the space standards and to fire and sound separation from its neighbours.

In Southwark, 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 Southwark: 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.

Policy P3 and the 130sqm test for splitting a Southwark house

Before any drawing, check the original internal floorspace of the house, because Southwark does not permit small family homes to be split. Policy P3 of the Southwark Plan 2022 rules out dividing a single home of 130sqm or less, measured as original net internal floorspace, into two or more homes. Dividing a house into flats also needs planning permission in its own right, and P3 is the first test the application meets.

For you, that measurement decides whether there is a project at all. A later rear extension does not count towards the original figure, and nor does a loft room added since, so the designer measures the house as first built and sets that against the threshold. The plan's stated aim is to keep family housing, so the planning officer may ask whether the scheme still offers a home a family could use, such as a larger ground floor flat with the garden.

Housing in Southwark

Count the homes in Southwark and you get about 149,990: 64% built since 1945, 7% between the wars and 25% before 1919, with flats at 81% and houses at 19%. Where most homes are flats, changing the number of flats in Southwark needs the freeholder and usually planning.

Space standards and ceiling heights in the new Southwark flats

Every flat made from a Southwark conversion has to meet the national minimum space standards. Southwark Plan Policy P15 applies them to conversions in the same way as new build, and it asks for a floor to ceiling height of 2.5 metres or more across at least 75 per cent of each flat's gross internal area. London Plan Policy D6 sets the same height rule across London and restates the bedroom minimums. These are planning standards, not building regulations, so they are settled at the application stage.

Under D6 a single bedroom needs at least 7.5 square metres and a width of 2.15m, and a double at least 11.5 square metres. In a Victorian house the ceiling rule often decides the layout more than the floor area: a top floor under the roof slope or a lower ground floor flat may fail on height. We check the heights on the survey so the designer can place bedrooms and living rooms where the building actually allows them.

Fire and sound separation between converted flats in Southwark

A large part of the work in a Southwark conversion goes into the floors and walls between the flats, because each flat must be protected from fire and noise from its neighbours. Approved Document E sets the sound insulation for flats formed by change of use at 43 dB airborne for walls, floors and stairs, and 64 dB maximum impact for floors and stairs. Old timber floors in a terrace do not reach that without work, and Part B sets the fire separation the same floors must give.

In practice we lift or ceiling over the existing joists, add mass and resilient layers, and fill the void with insulation, then form a protected stair with fire doors and an escape route that works for every flat. New services run in their own fire stopped risers. Pre-completion sound tests are carried out by a tester and the results go to building control, so the detailing is agreed with the designer before the first board is fixed, and the test date sits in the programme.

Meters, addresses, party walls and turning flats back into a house

Each new flat in a Southwark conversion needs its own electricity supply and meter, its own heating and hot water, and usually its own water supply, so the utility applications go in early because their lead times can hold up completion. The new flats also need addresses, which come through the council's street naming and numbering process. Where the work cuts into or builds on a party wall, the Householder SPD notes a Party Wall Agreement may be needed, separate from planning, and the building owner serves the notices.

Some owners go the other way and combine two flats back into one house. That reduces the number of homes, and Policy P3 of the Southwark Plan 2022 is titled Protection of existing homes, so your designer should take planning advice before anything is stripped out. The building work reverses a conversion: removing the second kitchen, opening the stair back into the house, and taking out separate meters and the second front door, under building regulations approval.

• Splitting a large flat in two, or joining two flats into one
• Flats converted back into a single family house
• Fire stopping round every pipe and cable through a separating floor

VOA Council Tax stock of properties, March 2025, for all 34 statistical areas in Southwark. Counts rounded by the VOA.

Plenty of Southwark projects start with one job and grow, so it helps to see structural alterations in Southwark, our Southwark area guide, building control sign-off for a conversion, party walls in a flat conversion, flat conversions across London and Central Heating Installation Cost.

Why Choose GS Renovation in Southwark

A conversion stacks structure, fire separation, acoustic floors and two or more sets of services into one building, and it has to be sequenced carefully. We build to the approved drawings and the planning consent the owner holds, keep building control inspections and the sound test in the programme, and bring in a registered electrician and a registered gas engineer for their parts. You get one site team from strip out to the handover of each flat.

• Every flat checked against the space standard before the layout is priced
• Separate meters, supplies and consumer units arranged for every flat
• One point of contact from first survey to handover

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.