Flat Conversions London

Flat conversions in London divide one house into two or more self-contained flats, each with its own front door, kitchen, bathroom, services and postal address. This page is for a London owner or developer deciding whether a house will divide, what the council and building control will ask for, what the work costs and how it runs on site. It also covers the reverse job, putting flats back together as one house. We write it as the contractor who builds the conversion. Your architect or designer draws the flats and applies for planning permission. The structural engineer we appoint designs any new steel or openings, and we build to the approved drawings. We programme the work so building control can inspect the separation before it is covered. A conversion stands or falls on work nobody sees once the flats are finished, so that is where this page spends most of its time.

Across London, 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 ranges, Architectural Drawings and Mayfair Studio, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in London: 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 London houses convert well into self-contained flats?

The London houses that convert best into flats are the tall Victorian and Edwardian terraces and the larger semis, where each storey is big enough to be a home on its own. The stair usually runs up one side, so it can be enclosed as a protected route to every flat without moving it. A three or four storey terrace often gives a garden flat below and a flat or maisonette above. Georgian townhouses divide well too. Where one is listed, listed building consent is needed for works inside and out, and it limits what can change. Interwar and post-war houses are more compact. Splitting one into two flats is often tight against the minimum floor areas a council accepts, and some councils will not consider a house below a set original size.

The layout decides whether a house will divide at all. A plan that stacks like rooms over like rooms, bathroom over bathroom and bedroom over bedroom, is easier to defend on amenity grounds. A kitchen or living room over a bedroom in the flat below needs more sound work and may be refused. Many councils also want at least one family-sized flat kept, usually on the ground floor with the garden, so the split is rarely a free choice. The reverse job suits a different house. Where two cramped flats sit in a house that would work well as one family home, de-conversion is mostly subtraction: fire lobbies, a second kitchen and extra meters come out and the stair is opened up. Test the numbers both ways before anything is drawn.

How a London house to flats conversion runs on site

A London flat conversion runs in a fixed order: drawings and consents, strip-out, structure and separation, services, finishes, then testing and sign-off. Your designer's approved drawings go to building control with a fire strategy for the stair and each flat entrance, as full plans to the council or through a registered building control approver. The structural engineer we appoint designs any new openings or steel. On site we strip the house back to joists and brick, then enclose the stair as a protected route and rebuild each separating floor. That means an independent ceiling below, mineral wool in the void and a resilient layer above, so neither sound nor fire passes through the old boards. We programme the work so building control can inspect each separating floor before it is closed up.

First fix is heavy on a conversion, because every flat needs a full set of services of its own. Each gets its own consumer unit, heating and hot water, and new supplies are brought in so each flat can be metered separately. Soil stacks are run for each new bathroom, and every pipe and cable through a separating floor or wall is fire stopped. Only then do plaster, kitchens, bathrooms, flooring laid on resilient underlay and decoration follow. Before completion an acoustic tester measures the separating floors and walls, early enough that a failed result can be put right before handover. A registered electrician certifies each flat, a Gas Safe registered engineer commissions any gas appliances, and building control issues the completion certificate once the test results are in.

Planning permission, space standards and building regulations for London flat conversions

Converting a house into flats in London always needs full planning permission, because using one dwelling as two or more is a material change of use with no permitted development route. The council judges each flat against the nationally described space standard, which London Plan policy D6 adopts along with a minimum ceiling height and storage. It also applies its own conversion policy, which may set a minimum original house size, ask for a family-sized flat to be kept, and resist the loss of family homes. Bins, cycle storage and daylight to each habitable room are checked too. You need a designer, and sometimes a planning consultant, before you need us. The reverse, turning flats back into one house, reduces the number of homes, so it often needs permission as well, judged against the council's housing policies.

Building regulations apply to the whole result, since a change of use is a material change under them. Part B covers fire separation between flats, the protected stair, fire doors to each flat entrance and detection. Part E covers sound between flats, and flats formed by a change of use are sound tested before completion. Part L applies too: a roof or external wall worse than the Approved Document L threshold is normally upgraded. Part K covers any new or altered stair. Part F covers ventilation to each new kitchen and bathroom, and Part G covers each flat's sanitary provision and hot water safety, including any unvented cylinder. Steel or joists bearing into a party wall need a party wall notice, which you as building owner serve.

A developer converting a house is a commercial client under CDM 2015, and a homeowner converting to sell or let the new flats may be one too. A commercial client keeps its own client duties, appoints a principal designer and a principal contractor where more than one contractor will work on the job, and notifies the HSE where the job is large enough. A homeowner converting for their own occupation is normally a domestic client, and those duties pass to the contractor, or to the principal contractor where there is more than one. Since October 2023 the building regulations have their own principal designer and principal contractor roles, on the same trigger. A commercial client that does not appoint carries those duties itself; for a domestic client they fall to the designer and contractor in control of the work. Settle each role in writing before the strip-out.

What does converting a house into flats cost in London?

Converting a London house into two or three flats is put at £50,000 to £120,000 in total, including professional fees, council fees and build works (Architectural Drawings, 2026, London). The same London guide prices the build at £1,000 to £2,000 per square metre and separate utility connections for three flats at £3,000 to £6,000. Those two figures do not agree on a big house. Multiply the per square metre rate by the floor area of a larger terrace and the build alone passes the headline, so treat the headline as a smaller-house figure. An England-wide guide (Mayfair Studio, 2026) puts construction alone for a straightforward conversion of a three-bedroom terrace into two flats at £40,000 to £80,000, with sound insulation and fire safety work adding £5,000 to £15,000. These are published ranges, not a quotation.

The number of flats moves the price most, then how the separating floors are built, then the stair and what the strip-out finds. Each flat carries its own kitchen, bathroom, consumer unit, heating and meters, so three flats cost more than two. A separating floor costs less where the old ceiling can come down than where it is built up from above. A stair already at one side costs less to protect than one that must move, and rot or failed joists only show at strip-out. The networks price and date supply connections, not us. Check Community Infrastructure Levy, where the council charges it, with your designer early. A reduced VAT rate can apply where the number of dwellings changes, so ask how a quotation treats it. De-conversion has no published range. You get a firm figure once we have surveyed the house and seen the approved drawings.

Access, neighbours, meters and addresses during a London conversion

A conversion is best built with the house empty, because the strip-out opens every floor and there is nowhere safe to live while it is open. On a terrace with no side access, every joist, sheet of board and length of steel is carried in through the hall, and all the rubble leaves the same way in bags. Skips on the road are licensed by the council, and where parking is controlled a bay has to be suspended as well. Noisy work stays inside the council's permitted hours, since noisy work outside them needs prior consent under section 61 of the Control of Pollution Act 1974. We tell the neighbours on both sides the programme before the strip-out. Work that cuts into a shared wall starts only on the neighbour's written consent or a party wall award.

The paperwork that makes each flat a separate home runs alongside the build, and it sets the finish date as often as the building work does. Separate gas, electricity and water supplies are applied for through the networks and the water company, and the applications go in early. Each flat needs a postal address from the council's street naming and numbering team. A supplier may not register a meter without one, so we ask you to apply once permission is granted. Council tax bands come from the Valuation Office Agency. Your solicitor drafts the new leases or titles. None of that is ours to do, but we plan the handover around it, so meters, doorbells and letter boxes match the addresses the council issues.

What goes wrong with London flat conversions, and how to choose a contractor

The separating floor is where a conversion is most likely to fail. Plasterboard screwed straight to the old joists, an empty void and laminate on top is unlikely to pass the pre-completion sound test, and the only cure is to take the ceiling down again. A well built floor can still fail through flanking, where sound runs round it through a chimney breast, a partition that carries on past the floor or joists that run on under a separating wall. An unlagged soil stack boxed into a bedroom below carries every flush. Services cause the rest: one electricity supply shared through sub-meters instead of a supply per flat, or meters fitted before the council has issued addresses, so no supplier will register them. A layout drawn without checking the space standard is likely to be refused.

Choose a contractor for a flat conversion on separation and services, not on the kitchen brochure. Ask for the build-up of each separating floor in writing, layer by layer, and check it against the drawings. Ask who books the pre-completion sound test, how early, and what happens and who pays if a result fails. Ask when each supply application goes in and how meter positions, doorbells and letter boxes will follow the council's addresses. Check that the quotation lists the separating floors, acoustic lagging to the soil stacks, the sound test with a retest allowance, each supply connection and the making good as separate lines, because a low price leaves those out. Ask who will be on site each day, who you call, and how the programme allows for each building control inspection.

• Steel beams and new openings built to the engineer's design
• New soil stacks, wastes and bathrooms stacked floor over floor
• Separating floors with independent ceilings and acoustic insulation

When comparing flat conversions in London with other work, it helps to read structural alterations in London, a building contractor for the whole conversion, party walls in a flat conversion and Building Regulations Explained.

Trusted Flat Conversions in London

A house to flats conversion needs a builder who treats the separating floors, the protected stair and the services as the main job, and that is how GS Renovation Ltd (company number 14611254) prices and runs one. The company is led by its founder, Abdelaaziz Saaid, who has over 30 years of hands-on experience, and you deal with one named point of contact from survey to completion. Our own team does the building work, a registered electrician certifies the electrics, an independent tester runs the sound test, and we coordinate building control. After the survey we send a written quotation that lists the separation work line by line, and our MyBuilder rating stands at 4.9 from 31 reviews.

• Each flat numbered and supplied before the keys are handed over
• A written scope and programme agreed before work starts
• Wet rooms stacked floor over floor to keep the drainage simple

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.