Flat Conversions Lewisham

Flat conversion in Lewisham means turning a house into self-contained flats, or occasionally flats back into a house. Houses are 40% of Lewisham's homes and terraces 31%, and it is these houses, not the existing flats, that a conversion starts from. Planning permission comes first: under Policy HO2 a family house can be split only when set criteria are met, one being that a home of 3 or more bedrooms is re-provided unless the house is shown to be unsuitable for families. Once your designer has the consent, we build the layout to it, with the fire separation and sound insulation each flat needs.

In Lewisham, 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 Lewisham: 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.

Splitting a Lewisham house into flats under Policy HO2

Policy HO2 allows a family house, or any home of 3+ bedrooms, to be divided into smaller self contained homes only when its criteria are satisfied. The criterion with the biggest effect on a Lewisham layout is keeping one family home: the scheme has to include a unit of 3 or more bedrooms, unless the building is shown to be unsuited to families. In a terrace that often means a three bedroom garden flat with a smaller flat or two above it.

Each new flat has size rules to satisfy as well. Lewisham's Local Plan Policy QD8 asks every housing scheme, changes of use included, to reach the London Plan minimum space standards and to beat them where it can. The owner or their designer applies for planning permission, since a house split into flats is a material change of use. Your designer checks each floor against those areas before the application goes in, and we set out walls on site to the approved dimensions, since a room built short of its consented size is hard to put right later.

Housing in Lewisham

Lewisham counts roughly 133,910 homes for Council Tax; 34% are older than 1919, 18% interwar and 45% post-war, with 60% flats and 40% houses. Since most homes here are flats, a flat in Lewisham can be split or combined only with the freeholder's consent, and changing the number of homes usually needs planning permission as well.

Room sizes and ceiling heights for Lewisham conversions

The London Plan figures under Policy D6 decide whether a Lewisham layout works at all. A single bedroom for one person needs 7.5 square metres of floor and a width of 2.15m or more. A double or twin for two people needs 11.5 square metres. In a narrow Victorian terrace the back addition bedrooms are where those numbers pinch. A partition moved by a few hundred millimetres can decide whether a room counts as a double.

Height is the other constraint. Policy D6 asks for 2.5m or more between floor and ceiling across 75 per cent or more of each home's Gross Internal Area. In the top flat of a Lewisham conversion, sloping ceilings under the roof can eat into that share quickly, and in the lower flat new acoustic ceilings lower the room. We check finished heights against the drawings before the ceilings are boarded.

Fire separation and sound tests between Lewisham flats

Once a Lewisham house becomes two or three flats, each floor has to hold back fire and smoke from the one below. Part B asks for fire resisting separating floors and walls, a protected stair or escape route shared by the upper flats, fire doors to each flat and linked smoke detection. In a house with a timber floor and lath ceilings, that usually means a new fire rated ceiling below every separating floor, sealed around each pipe and cable that passes through.

For flats made by a change of use, Approved Document E asks for 43 dB of airborne sound insulation through separating walls and floors. Impact sound through floors must not exceed 64 dB. The floors between Lewisham flats therefore usually need a new ceiling, insulation and a resilient layer. Sound is tested before completion and fire separation is inspected before it is covered, so we build the floors and linings in the order the inspector needs to see them.

Services, party walls and reversing a Lewisham conversion

Each flat needs its own services: a separate electricity supply and consumer unit certified by a registered electrician, its own heating, water and meters, and its own postal address from the council's street naming and numbering team. Where steel or new walls bear on a party wall, the Party Wall Act applies. Lewisham Building Control says the Act is a civil matter and it is not involved in its administration, so the building owner serves notices separately from building control. That part of the work then starts on the neighbour's written consent or a surveyor's award.

The reverse happens too. A period terrace that was split in the past can sometimes be put back together as a family house, which suits houses where the original plan is still readable. The work takes out the extra kitchens and bathrooms, reopens the stair and merges the meters. Losing homes this way can need planning permission in London boroughs, so the owner or their designer checks that with the council before any work starts.

• Full plans building control applications coordinated for you
• Steel beams and new openings built to the engineer's design
• Fire detection in every flat and the common hall, laid out to the fire strategy

VOA Council Tax stock of properties, March 2025, for all 37 statistical areas in Lewisham. Counts rounded by the VOA.

Two or three things usually come up alongside flat conversions on a Lewisham job: structural alterations in Lewisham, our Lewisham area guide, builders in London who take on conversions, refurbishing a flat that has already been converted, our London flat conversions page and House Rewire Cost.

Why Choose GS Renovation in Lewisham

A conversion goes wrong in the gaps between planning, building control and the trades. We come in once your designer has the layout and consent, check the Lewisham house's floors, stair and party walls on a visit, and give a written quotation with a programme. Abdelaaziz Saaid, our founder, has more than three decades on site. A structural engineer designs any steel, and we sequence the separating floors, fire doors and sound test so each flat is ready to be signed off and lived in.

• Neighbours given notice before the noisy stages
• Wet rooms stacked floor over floor to keep the drainage simple
• Every flat checked against the space standard before the layout is priced

Reviewed jobs near Lewisham

1 MyBuilder review from Crofton Park, with each customer's own job title:

• Replace small section of wooden worktop, sink, tap and gas hob, Crofton Park, 17 Apr 2024 (5 out of 5)

Read all 31 on our reviews page.

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.