Flat Conversions Borough

Flat conversions in Borough start from a very small stock of houses. The VOA's count for the wider Borough & Southwark Street and Southwark St George's area puts 94% of homes as flats and 6% as houses, all terraced. So a house that could still be split is rare, and Southwark protects smaller family houses from subdivision. The work that does arise is a larger terrace divided into self-contained flats, the reworking of an older building already in flats, or flats combined back into one home. We build to the planning consent and building regulations.

In Borough, 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 Borough: 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.

The 130sqm test decides whether a Borough house can be split

Whether a Borough house can become two or more flats turns first on its size. Under Southwark Plan 2022 Policy P3, a home whose original net internal floorspace is 130sqm or less cannot be split into two or more homes. The Plan explains that the policy protects existing family housing from conversion into smaller homes unsuitable for families. With houses only 6% of homes in the VOA's wider count for the area, the few terraces here are exactly the homes the policy is written to keep.

So the first step is a measured survey of the house as originally built, before any design fee is spent. A terrace just over the threshold may be a candidate; one just under it is not, however cleverly the flats are drawn. Clearing the threshold only opens the door: a house into flats always needs planning permission, which the owner or their designer applies for. The London Plan counts residential conversions that add homes as small site intensification, which is the policy context for a borderline case.

Housing in Borough

For Borough the Council Tax list gives about 12,140 homes; by type 94% flats and 6% houses, by age 73% post-war, 3% interwar and 18% older than 1919. Since most homes here are flats, changing the number of flats in Borough needs the freeholder and usually planning.

Space and ceiling heights each new Borough flat must meet

Each flat created in Borough counts as a new dwelling, so it must meet the space standards in full. The London Plan's standards table says a new dwelling includes conversions and change of use, and Southwark Plan 2022 Policy P15 requires conversions to meet the national space standards. Under Policy D6, a single bedroom must be at least 7.5 square metres and 2.15m wide, and a double or twin bedroom at least 11.5 square metres. Your designer lays the flats out around those minimums and the storage the standard adds.

Height is often the tighter constraint in an older terrace. Policy P15 asks for a floor to ceiling height of at least 2.5 metres over at least 75 per cent of each flat's gross internal area. A low rear addition or top floor may fail, and the new separating floor build up takes height away. We check existing levels against the drawings before any ceiling is removed, so a shortfall is solved on paper. The standards sit in the planning system, not in building regulations.

Fire separation and sound testing between Borough flats

Turning a Borough terrace into flats is a material change of use, so building regulations apply to the whole house, not just the new kitchens. Part B requires fire separation between the flats and a protected escape route: the shared stair gets fire rated linings and self closing fire doors onto each flat, with fire stopping wherever services pass through. Part E requires sound insulation between the flats, and Approved Document E sets 43 dB airborne and a 64 dB impact maximum for flats formed by a change of use.

An original timber floor with a lath and plaster ceiling will not reach those figures unaided. The usual answer is an independent ceiling or resilient bars below, with acoustic insulation in the void and a new deck above. Pre-completion sound testing then proves the result, and a failed test means opening up again. We sequence the separating floors early, because every pipe and cable crossing them must be sleeved and sealed before they close, and Part L and Part M apply to the new work too.

Services, addresses, party walls and turning Borough flats back into a house

Each self-contained flat in a Borough conversion needs its own services: an electricity supply and meter, usually its own water supply, a gas meter where gas is used, and a separate heating system. The utilities need the new postal addresses first, so the owner applies to Southwark for street naming and numbering early. Southwark's Householder SPD notes that a Party Wall Agreement may be needed, separate from planning permission. Cutting into a party wall for steel bearings or fire separation needs a party wall notice, so you serve it and the work waits for written consent or an award.

The reverse also happens: combining two flats back into a single family home. Southwark's Plan values family housing, but a de-conversion still loses a home, and in most London boroughs the loss of a flat needs planning permission. Ask the owner's designer to confirm Southwark's position before any design is paid for. The building work is simpler, removing a kitchen, reopening the stair and taking out one set of meters.

• Full plans building control applications coordinated for you
• A consumer unit in every flat, with a registered electrician signing off each installation for Part P
• Separate gas, electricity and water supplies for each flat

VOA Council Tax stock of properties, March 2025, for Borough & Southwark Street and Southwark St George's. Counts rounded by the VOA.

If this is your first project in Borough, these are worth a look: structural alterations in Borough, flat conversions across Southwark, building control sign-off for a conversion, the Party Wall Act when a conversion cuts a shared wall, our London flat conversions page and Who Pays the Party Wall Surveyor.

The GS Renovation Difference in Borough

A conversion is a building control job full of hidden details: separating floors, fire stopping, new drainage stacks and a meter for each flat. After a site visit we set out a written quotation and a programme that your designer, the building control inspector and any lender can follow. One team builds the structural alterations to the engineer's design, the partitions, plastering, kitchens and bathrooms for each unit. Gas work is done by an engineer on the Gas Safe Register and a registered electrician certifies the electrics, both inside our programme.

• Itemised pricing, so you can see what every stage costs
• Mains-wired, interlinked smoke and heat alarms to the approved fire strategy
• Every flat checked against the space standard before the layout is priced

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.