Single Dwelling to Flats in Lewisham

In planning law, every building has a 'use class' that describes what it is used for. An ordinary house occupied by a single household — a family, a couple or a single person — sits in Use Class C3, the dwellinghouse class. A self-contained flat sits in exactly the same class: a flat is still a C3 dwelling. So on paper, converting a house into flats does not move the building from one use class to another. That surprises people, and it leads to a common and expensive misunderstanding: because the use class does not change, some owners assume no permission is needed.

That is wrong. The relevant test in planning law is not only whether the use class changes but whether there is a 'material change of use'. Subdividing a single dwelling into two or more separate dwellings is, in law, a material change of use — you are creating additional, independent units of accommodation where there was one. The Town and Country Planning Act treats the creation of new dwellings this way precisely because each new flat is a separate planning unit with its own occupiers, its own comings and goings, and its own impact on the street. That is why the conversion needs planning permission even though everything stays within Class C3.

The distinction matters because it decides whether you can proceed. There is a permitted development right that lets you extend or alter a house within limits, and there are permitted-development change-of-use routes for some commercial-to-residential conversions — but there is no permitted development right to subdivide a house into flats. It has never existed. Whether you are making two generous maisonettes or six compact flats, the creation of the additional dwellings is a full planning matter, assessed against Lewisham's local policies.

It is also worth being clear about what counts as 'self-contained'. A self-contained flat has its own front door, its own kitchen and its own bathroom, and does not rely on shared facilities. That is what distinguishes a house-to-flats conversion from a house in multiple occupation (an HMO), where occupiers rent rooms and share a kitchen or bathroom. The two are different planning matters with different policies and different licensing regimes. This page is about self-contained flats; if your scheme is really a shared house, the HMO rules apply instead, and we will tell you which route your project actually falls into at the outset.

Yes — always. Converting a single dwelling into two or more self-contained flats in Lewisham is a material change of use, and there is no permitted development route that allows it. You must apply for full planning permission for the change of use, and the council will assess the application against its Local Plan policies on housing, design, amenity and residential standards. This is true everywhere in the borough, from Deptford and New Cross in the north to Sydenham, Bellingham and Downham in the south.

That requirement is separate from, and additional to, Building Regulations approval, which every conversion also needs. Planning permission decides whether the building may be used as flats at all; the Building Regulations govern how the flats must be built — fire safety, sound insulation, means of escape, ventilation, drainage and energy. You need both, and they run on parallel tracks. A common and costly mistake is to treat the works as 'just building regs' and skip the planning application; doing so exposes you to enforcement and makes the flats very difficult to sell, let or mortgage.

There are a few situations where the position is more nuanced, and each is worth checking rather than assuming. If a property was already lawfully in use as flats before the current single-house use, an existing lawful use might subsist and can be confirmed through a Certificate of Lawfulness — a separate evidence-based application. Equally, taking in a lodger or two, or an ancillary annexe used as part of the same household, is generally not a separate dwelling and does not create flats. But the safe default for any genuine subdivision into independent units is that full planning permission is required, and that is the assumption we work from.

Because permission is always needed, the quality of the application is what determines the outcome. Lewisham does not refuse conversions on principle — the borough grants many every year — but it does refuse the ones that lose family housing it wants to keep, that provide sub-standard flats, or that harm neighbours and the street. The whole of the rest of this page is about designing and arguing a scheme that Lewisham can say yes to.

Lewisham has taken a consistent line on house-to-flats conversions for a very long time, and knowing that line lets us design and argue a scheme around it rather than hoping to satisfy it by accident. The council's core concern is the protection of family-sized housing, and its conversion policy is built to balance the borough's need for more homes against the risk of losing the larger houses that families depend on.

The most important single number in that policy is a minimum property size. Under the borough's established approach — set out in the old Unitary Development Plan (Policy HSG 9, Conversion of residential property) and carried into the Development Management Local Plan (Policy DM 3, Housing conversions) — the council will not normally permit the conversion of a dwelling into self-contained flats unless the original property has an internal floor area of at least around 130 square metres. Critically, that is measured on the original, pre-1948, unextended house: you cannot rely on a rear or loft extension to push a smaller house over the threshold. The logic is that a house below that size is genuinely family-suitable stock that the borough wants to keep whole.

The policy also protects family accommodation within the scheme itself. Lewisham has long looked for a family-sized unit to be provided in a conversion where the building can support one — typically a unit of three or more bedrooms, located on the ground floor with direct access to a usable garden — and it discourages schemes made up entirely of small flats or studios. Converted houses are expected to keep a usable rear garden (the borough's long-standing figure is in the order of 50 square metres) and to make sensible provision for parking, bins and cycles while retaining as much front garden as is practical.

The council also controls the cumulative impact of conversions. Even a well-designed individual scheme can be resisted where a street or small area already has a high proportion of converted properties, because the concentration of flats — with more comings and goings, more pressure on kerbside parking and more waste — can change the character and amenity of a residential neighbourhood. Lewisham's own evidence work identified wards where the remaining unconverted family-house stock was at risk, which is exactly the kind of area where a further conversion faces the sharpest scrutiny.

All of this now sits within the Lewisham Local Plan 2020-2040, which the council adopted on 16 July 2025 and which replaces the older UDP and Development Management plans as the up-to-date development plan for the borough. The new plan raises Lewisham's housing ambitions but keeps the long-standing thread of protecting family housing and securing a proper standard of accommodation. Because plans and policy numbers change over time, we always check the current adopted policy and any supporting guidance against your specific property before we design — the principles above are durable, but the exact reference should always be confirmed for the day you apply.

Getting a conversion past Lewisham is not only about whether the house is big enough to divide — it is about whether each resulting flat is a proper home. The council assesses every new unit against national and London space standards, and a layout that squeezes in an extra flat at the cost of cramped, sub-standard units is one of the most reliable ways to earn a refusal.

The baseline is the Nationally Described Space Standard (NDSS). A one-person studio must be at least 37 square metres (with a shower room) or 39 square metres (with a bathroom); a one-bedroom, two-person flat must be at least 50 square metres on one level; and larger units step up from there — broadly 61 square metres for a two-bed three-person flat and around 70 square metres for a two-bed four-person flat, with defined minimums for bedrooms, storage and floor-to-ceiling height. Because Lewisham is in London, the London Plan overlays its own requirements: a floor-to-ceiling height of at least 2.5 metres over at least 75% of the internal area (higher than the national 2.3 metre minimum), and private or shared amenity space of at least 5 square metres for a one- to two-person flat, plus a further 1 square metre for each additional occupant.

Amenity and outlook matter as much as raw floor area. Each flat needs adequate daylight and natural ventilation, a sensible internal layout, and proper storage; the council will look hard at any bedroom that relies on a light well, any 'flat' that is really a habitable basement without proper light, and any unit whose only outlook is onto a narrow rear yard. Ground-floor and lower-ground flats attract particular attention on light, damp and flood risk near the borough's rivers. Refuse and recycling storage that is accessible but not an eyesore, and secure cycle parking, are expected and are drawn on the plans, not left as an afterthought.

We design to these standards from the first sketch. That means testing the real dimensions of the house against the NDSS and the London Plan before we decide how many flats it can sensibly yield, laying out each unit so that bedrooms, storage, ceiling height and amenity all comply, and annotating the areas on the drawings so the case officer can check them at a glance. It is far better to propose fewer, genuinely good flats that the council can approve than to propose one flat too many and have the whole scheme refused for sub-standard accommodation.

Lewisham is an old part of London with a surprisingly deep and often turbulent history for a borough now defined by railways, high streets and suburban terraces. The modern London Borough of Lewisham was created in 1965 by merging the former metropolitan boroughs of Lewisham and Deptford, and it stretches from the Thames at Deptford in the north down through New Cross, Brockley, Catford and Forest Hill to the green edges of Beckenham Place Park and the Downham and Bellingham estates in the south. That north-to-south spread — riverside industrial past, dense Victorian and Edwardian inner suburbs, and interwar council estates — is exactly why conversions here have to be judged street by street.

Deptford, on the borough's northern edge, was one of the most important places in maritime England. Henry VIII founded the Royal Dockyard at Deptford in 1513, and for centuries ships were built and provisioned there; Sir Francis Drake was knighted aboard the Golden Hind at Deptford by Elizabeth I. The playwright Christopher Marlowe, Shakespeare's great contemporary, was killed in Deptford in 1593 in a dispute whose circumstances are still debated. Deptford High Street and Deptford Town Hall are both protected conservation areas today, and the area's layered history sits directly beneath a modern, fast-changing neighbourhood.

Blackheath, straddling the boundary with Greenwich, is one of the borough's grandest landmarks and one of its most historically charged open spaces. It was on Blackheath that Wat Tyler mustered the rebels of the Peasants' Revolt in 1381, and Jack Cade's rebellion assembled there in 1450. The heath is overlooked by fine Georgian and Victorian houses, provides the traditional start of the London Marathon, and lies within the Blackheath Conservation Area — England's first conservation area, designated jointly with Greenwich in 1968. Nearby, Frederick Horniman, a Victorian tea merchant and obsessive collector, gave Forest Hill the Horniman Museum and Gardens, open to the public since 1901 and still one of south London's best-loved attractions.

The borough's more recent history is just as much a part of its identity. In 1977 thousands of local people confronted a National Front march in what became known as the Battle of Lewisham, a defining moment in the area's tradition of activism and its strong sense of a diverse, mixed community. The rivers Ravensbourne and Quaggy, and Deptford Creek, thread through the borough and shaped both its industry and its flood history — the 1968 floods hit Lewisham hard — which is why watercourses and flood risk remain a live planning consideration on lower-lying sites today.

For a house-to-flats project, this context is not just colour; it is planning-relevant. A conversion within or adjoining one of Lewisham's conservation areas — Blackheath, Brockley, Telegraph Hill, Ladywell, Lee Manor, Deptford High Street, Forest Hill and others — faces additional design and heritage tests, and the external changes a conversion often wants to make (extra front doors, meter boxes, bin stores, bike stores, rooflights or rear alterations) are exactly the things heritage policy scrutinises. Knowing where your property sits in Lewisham's map, and its history, is the starting point for a credible application.

The reason Lewisham controls conversions so carefully is written into the borough's own housing stock. From the 1850s onwards, the arrival of the railways transformed what had been villages and market gardens into dense inner suburbs. When the line reached Blackheath in 1849 and stations opened across the borough, developers threw up mile after mile of substantial Victorian and Edwardian terraces and semis in Brockley, Telegraph Hill, Forest Hill, Lee, Ladywell and Catford — many of them large, three- and four-storey family houses designed for prosperous commuting households with servants.

Those big houses are exactly the raw material that conversions feed on. As household sizes shrank through the twentieth century and demand for smaller, cheaper homes near central London grew, generations of owners divided these houses into flats and bedsits. By the later twentieth century whole streets in parts of the borough had been converted, and the council began to worry that its irreplaceable supply of larger family houses was quietly disappearing one property at a time.

That concern produced policy. Lewisham commissioned housing conversion studies that mapped where family-house stock survived and where it was most at risk, and it used that evidence to justify a minimum-size threshold and a family-housing test in its plans — the 130 square-metre rule and the requirement to protect family accommodation. The studies found, for example, that in some inner wards a large share of the remaining unconverted single-family houses could realistically be lost to conversion, while in the interwar-estate wards of the south almost no houses even reached the size threshold. That granular evidence is why the policy is applied so differently in different parts of the borough.

The picture has intensified again in recent years. High London rents have driven a wave of investor interest in splitting houses into flats and, separately, into HMOs — to the point that the council brought in Article 4 controls on small HMOs and, in its 2025 Local Plan, tightened the criteria for both types of conversion, refusing schemes that would strip out family homes. Local campaigns in areas such as Ladywell have pressed the council to hold the line on family housing. Understanding this history helps you understand the council's mindset: when it assesses your conversion, it is weighing your scheme against a long, deliberate effort to keep family houses in the borough.

The classic Lewisham conversion candidate is a large Victorian or Edwardian terrace or semi in the inner and central parts of the borough — Brockley, Telegraph Hill, Ladywell, Lee, Hither Green, Forest Hill and the older parts of Catford and Sydenham. These houses commonly run to three storeys plus a basement or half-basement, with generous room heights, a rear back-addition (the 'outrigger' that held the original kitchen and scullery), and a decent rear garden. Their scale is what lets them clear the 130 square-metre threshold comfortably and still yield well-proportioned flats.

A well-designed conversion of a house like this usually reads as a natural stack of homes. The lower ground and ground floors often form a family maisonette with direct access to the rear garden — precisely the family unit the council wants to see retained — while the upper floors become one- and two-bedroom flats, and the roof space is sometimes brought into use to give a top-floor flat proper head height. Each move has planning, structural, fire and sound implications that have to be designed in from the start, which is why we plan the whole vertical arrangement before committing to a unit count.

Larger detached and semi-detached houses, and the occasional former institutional or commercial building, can support more units and more ambitious layouts, though they bring their own complexity around means of escape, sound separation and external alterations. At the other end, smaller two-bedroom terraces and the interwar estate houses of the southern wards rarely make good conversions: many fall below the size threshold, and even where they scrape over it, once you provide compliant flats with proper amenity there is little to gain, and the council is likely to resist the loss of a genuinely family-sized small home.

Whatever the building, the design has to reconcile two things that pull in opposite directions: the owner's wish to maximise the number of flats, and Lewisham's insistence on retaining family housing and delivering each flat to a proper standard. The schemes that gain permission are the ones that treat the council's standards and its family-housing test as the design brief rather than as obstacles — and that is precisely how we approach every Lewisham conversion we draw.

If there is one test that decides Lewisham conversion applications more than any other, it is the loss of family-sized housing. The council's settled position is that larger houses are a scarce resource, and it will resist proposals that convert a family-suitable house into flats where doing so would erode the borough's housing choice. This is the concern behind the 130 square-metre threshold, behind the requirement to retain a family unit, and behind the cumulative-impact assessment — three angles on the same underlying policy.

In practice, the test bites in two ways. First, at the level of the individual house: if the property is a genuine family home and there is no good planning reason to lose it, the council may refuse the conversion outright, regardless of how well the flats are designed. Second, at the level of the scheme's internal mix: even where conversion is acceptable in principle, Lewisham looks for a family-sized unit — three or more bedrooms, ideally on the ground floor with garden access — to be provided within the conversion, so that the family accommodation is re-provided rather than simply replaced by a stack of one-beds.

There are recognised ways to satisfy the test. The strongest schemes provide a proper family maisonette across the lower floors with real garden access, so the council can see that family accommodation survives in the building. Where the house's location or character genuinely makes it unsuitable for family occupation — for example, a large house fronting directly onto a very busy road with no usable garden — that can be part of the argument that a family unit is not required, but it has to be evidenced, not asserted, and the council decides.

This is where honest feasibility earns its keep. We assess at the outset whether your house is one the council will allow to be converted at all, and if so what unit mix will satisfy the family-housing test, before you spend money on a full application. There is no value in submitting a scheme that is designed to fail this test — far better to design a mix Lewisham can accept, or to know early that a given house is not a realistic candidate.

Even a well-designed conversion of a suitable house can run into difficulty if the surrounding area is already saturated with flats. Lewisham assesses the cumulative impact of conversions: the concern is that once a large proportion of houses in a street or small area have been divided, the neighbourhood tips in character — more households, more comings and goings, more pressure on already-scarce kerbside parking, more waste and bin storage on the street, and a gradual loss of the settled, family-occupied feel that residential policy is there to protect.

The council's own conversion studies mapped exactly this, identifying wards and smaller areas where the remaining unconverted family-house stock was under real pressure. In those locations a further conversion faces the sharpest scrutiny, because each additional loss matters more. In areas with little existing conversion, and where the house is clearly suitable, the cumulative concern is weaker and the principle of conversion is easier to establish.

There is no single national percentage that automatically triggers a refusal, and Lewisham assesses concentration as a matter of planning judgement rather than by a rigid mathematical rule. But a high existing proportion of flats and conversions in the immediate streets is a genuine and common reason for resistance, and it is a factor we check as part of feasibility — because the surrounding context can matter as much as the merits of your own property.

Where concentration is a concern, the planning case has to work harder: demonstrating that the scheme retains family accommodation, provides proper amenity and parking/cycle/refuse provision, and does not add materially to the problems the policy is guarding against. We assess the local picture honestly at the outset and advise accordingly, rather than submitting an application blind into a saturated street.

A large share of Lewisham's convertible housing sits within, or close to, one of the borough's conservation areas — Blackheath, Brockley, Telegraph Hill, Ladywell, Lee Manor, Sydenham Hill, Forest Hill, Deptford High Street and Deptford Town Hall among them. Blackheath, designated jointly with Greenwich in 1968, was the first conservation area in the country, and these areas contain many listed and locally listed buildings. Where a conversion affects a designated heritage asset, additional design and heritage tests apply, and a heritage statement is usually needed.

The friction point in most conversions is not the internal subdivision, which the street never sees, but the external changes the scheme wants to make. Additional front doors, extra letterboxes and bell panels, external meter cupboards, bin and cycle stores in the front garden, new or enlarged rooflights, altered fenestration, satellite and services runs, and any rear or side extension all have a visual impact, and in a conservation area they are exactly what the council scrutinises. A conversion can succeed internally and still be refused on the harm its external clutter would do to a protected street scene.

The design answer is to keep external change to a minimum and to handle what is unavoidable with care: retaining a single dignified entrance where possible, concealing meters and bins tastefully, using conservation rooflights and matching materials, and preserving the rhythm and detailing of the terrace. On listed buildings, listed building consent is a separate consent needed in addition to planning permission for internal and external alterations, and the internal subdivision of a listed house is itself a heritage-sensitive operation.

We survey the property's heritage context at the outset, design the external elements to sit comfortably in the street, and prepare the heritage justification the council needs. Getting the heritage response right is often the difference between an approvable conversion and one that founders on its impact on Lewisham's protected townscapes.

Dividing a house into flats is rarely just a matter of adding front doors. To create self-contained units that meet space and Building Regulations standards, most conversions involve real construction — and that means real structural design. Crown handles the architecture, the structure and the building services together, so the drawings you submit are not just a planning layout but a buildable, coordinated scheme.

The most common structural elements are new or altered openings and, crucially, new means of access. Giving upper-floor flats their own front door often means forming a new entrance and a compliant common stair or hallway, which can require new openings, altered floor structure and correctly sized steel beams or lintels with supporting calculations. Removing chimney breasts to free up floor space, widening openings, or forming a lower-ground family maisonette can all need structural support, and where a party wall is affected the correct party wall notices must be served on neighbours.

Sound insulation is one of the defining challenges of a conversion, because unrelated households will now live directly above and beside one another. The Building Regulations (the Part E family of requirements) set demanding standards for airborne and impact sound between separate flats, and meeting them in an old timber-floored Victorian house usually means significant upgrades to floor build-ups and separating walls — independent ceilings, resilient layers, and careful detailing at junctions. This is not a cosmetic add-on; it shapes floor thicknesses, ceiling heights and therefore the whole section of the building, which is why it has to be designed alongside the plan, not after it.

Fire safety is equally structural. Each flat must be a protected compartment, with a protected common escape route, fire doors, and compartmentation between units and floors that actually achieves its fire resistance (Building Regulations Part B). Bringing a roof space into use, upgrading floors for residential loading and sound, providing fire-rated separation, and upsizing heating, hot water, electrics and drainage for multiple independent households are all part of the package. By designing the layout, the structure, the fire strategy and the services as one coordinated set of information, we avoid the classic conversion failure: a planning drawing that looks fine but cannot be built as drawn once the beams, escape routes, sound build-ups and services are worked out.

Every house-to-flats conversion needs Building Regulations approval as well as planning permission, and on a conversion the building-control side is genuinely demanding — far more so than for a simple extension. The conversion is a 'material change of use' under the Building Regulations too, which triggers a series of requirements that the whole building must be brought up to meet, not just the parts being altered.

Fire safety (Part B) is central. Each flat has to be a fire-resisting compartment, with fire doors, protected escape routes and, in most conversions, interlinked mains-powered smoke and heat detection. The common parts — the shared hallway and stair that give access to the upper flats — must provide a safe route out for everyone in a fire, which frequently dictates where partitions, doors and even flat entrances can go. Taller or more complex conversions bring further requirements, and it is far cheaper to resolve the escape strategy on paper than to rebuild it after a failed inspection.

Sound insulation (Part E) is the requirement most often underestimated. Separating floors and walls between flats must achieve set levels of resistance to airborne and impact sound, tested where required, and achieving this in a period house means real construction — not a token layer of insulation. Alongside fire and sound sit ventilation (Part F), moisture and damp (Part C, important for lower-ground flats near the borough's rivers), drainage (Part H, since each flat needs proper waste and soil connections), and energy efficiency (Part L) for the upgraded building.

We prepare the conversion so that the planning layout and the building-regulations design are consistent from the outset — the flat that works on the planning drawing is the same flat that can be built, compartmented, sound-insulated and signed off. Coordinating planning and building control from the start is the single most effective way to avoid the expensive surprises that derail conversions on site.

Many Lewisham conversions want to bring a basement or lower-ground floor into use as a self-contained flat, because it can provide the family unit with garden access that the council likes to see. That is often a good move, but it comes with its own set of technical and policy issues that have to be handled properly, and it is a frequent source of refusals when it is not.

The first issue is habitable-room quality. A lower-ground flat must have adequate natural light and ventilation, proper ceiling height, and protection against damp — a dark, low, damp basement 'flat' with a light well as its only outlook will fail both the space standards and the council's amenity expectations. Excavating or lowering a floor to gain height is itself structural work, and works to basements are subject to particular scrutiny for their effect on the building's stability and on neighbouring properties.

The second issue is flood risk. The rivers Ravensbourne and Quaggy and Deptford Creek run through the borough, and Lewisham suffered serious flooding within living memory, most notably in 1968. On lower-lying sites, and anywhere within a mapped flood zone, the council will expect flood risk to be addressed, and creating new habitable accommodation at or below ground level in a flood-risk area raises real questions that a flood risk assessment must answer. Sleeping accommodation in a basement in a flood-risk area is treated especially cautiously.

We check flood mapping and ground conditions as part of feasibility, design lower-ground and basement flats to provide genuine light, height and dryness, and prepare the flood and structural information the council needs. Where a basement flat is not realistic, we say so early and reconfigure the scheme, rather than pushing a unit that will be refused.

Some conversions fail not on the principle but on the practical details, so it is worth understanding the tests that most often catch schemes out. The first is neighbour and occupier amenity: the council looks at whether the intensified use will materially harm neighbours through noise, overlooking or loss of privacy — particularly from new rear windows, roof terraces or altered openings — and whether the future occupiers of each flat will have adequate light, outlook, privacy and amenity space of their own.

The second is refuse and recycling. Several flats generate far more waste than a single household, and Lewisham expects properly sized, accessible, screened bin and recycling storage that does not end up as bags dumped in the front garden or on the pavement. This sounds minor but is a recurring reason for objections and refusals; it is entirely avoidable with a designed bin store shown clearly on the plans, positioned so it does not blight the street or, in a conservation area, harm the setting.

The third is parking, cycles and gardens. Lewisham is generally well served by rail, DLR and Overground, and the council does not expect every flat to have a car space; but it does look at the transport impact of the intensified use, expects secure cycle parking for residents, and wants to retain as much front garden as is practical rather than see it hardstanding over for cars. The rear garden matters too — the council's long-standing expectation is that a converted house keeps a usable garden (in the order of 50 square metres), ideally serving the family unit.

None of these tests is insurmountable, but each has sunk applications that ignored it. We design the scheme so that amenity, refuse, cycle parking, garden retention and parking are answered on the drawings and in the planning statement from the outset, rather than left for the case officer to raise as objections halfway through.

A Lewisham house-to-flats application has to tell the council two stories clearly: what the building is now, and what it will become. We prepare a full, measured set of drawings and the supporting documents that carry the planning argument, so the application is complete, consistent and easy to assess.

The drawing package normally includes an accurate measured survey of the existing house, existing plans, sections and elevations, and then the proposed plans, sections and elevations showing the flat layout — each unit's floor area annotated, bedrooms and their sizes noted, ceiling heights where relevant, the common access and escape route, private and shared amenity space, and the refuse and cycle storage. Floor areas are labelled so the council can check them against the space standards without having to scale off the drawing, and the family unit and its garden access are shown clearly. A location plan and site/block plan complete the set.

Alongside the drawings we prepare the supporting documents the application needs: a planning statement (and, where useful, a design and access statement) setting out how the scheme meets Lewisham's Local Plan policies and answers the family-housing, size-threshold, amenity, concentration and design tests; a heritage statement where a conservation area or listed building is involved; and a flood risk assessment where the site requires one. Where structural work is involved, the building-regulations and structural design follow so the scheme can move smoothly to construction.

Everything is prepared to be internally consistent — the floor areas on the plans match the figures quoted in the statement, the family unit shown on the drawings is the one argued in the text, the fire and sound strategy matches the layout, and the bins and cycles appear on both the plans and the words. A coordinated, self-consistent application is materially more likely to be approved than a set of drawings and a statement that contradict each other.

The process starts with feasibility. We survey the property, confirm its planning history and lawful use, measure the original floor area against the 130 square-metre threshold, and test the building against Lewisham's space and amenity standards to see what scheme it can realistically support and whether it can satisfy the family-housing test. This is where we give you an honest view of whether the project is likely to succeed, and at what unit mix, before you spend money on a full application.

Lewisham offers pre-application advice, and on conversions it is often worth using: a written steer from the council on your proposal reduces the risk of a refusal, can flag family-housing or concentration concerns early while there is still time to adjust the scheme, and shows the eventual case officer that the proposal has been developed thoughtfully. We prepare and manage the pre-application submission where it adds value.

We then prepare the full drawing package and supporting statements, submit the application to Lewisham through the Planning Portal, and manage it through validation and determination — responding to the case officer's queries, providing additional information, and negotiating amendments where that will secure approval. Most householder-scale change-of-use applications run against an eight-week target from validation, though conversions can take longer if they are complex, affect a heritage asset, or attract neighbour objections.

Once permission is granted, we can take the scheme forward into the building-regulations and construction drawings, so the same coordinated team that won the permission also delivers the information your builder needs on site. Because we design the fire, sound and structural strategy in from the start, the project moves from a planning permission to a compliant, sign-off-ready building without the layout having to be reinvented.

Understanding why applications fail is the best way to make sure yours does not. The most fundamental reason for refusal in Lewisham is the loss of a family-sized home where the council judges that harm to the borough's housing choice outweighs the benefit of the extra flats — the very concern behind the size threshold and the family-housing test. This is most acute where the property is a genuinely family-suitable house and where the scheme provides no re-provided family unit.

Below-threshold size is a related and clear-cut reason: if the original, unextended house falls short of around 130 square metres, the council will normally refuse the conversion, and a scheme cannot rely on proposed extensions to get over the line. Sub-standard flats are another common ground — units that fall below the national space standards, bedrooms without adequate light, cramped or windowless rooms, insufficient ceiling height, or a lack of amenity space.

Concentration and cumulative impact account for many refusals in the more heavily converted streets, where a further loss of a family house or a further intensification of use is judged to harm the character and amenity of the area. And then there are the practical grounds already discussed: inadequate or unsightly refuse and cycle storage, harm to a conservation area or listed building through external alterations, unacceptable amenity impacts on neighbours, and unresolved flood risk on lower-lying sites.

Our approach is to anticipate every one of these reasons and answer it in the application itself. We are honest with you at feasibility if a property is likely to hit the size threshold, the family-housing test or a concentration objection, because there is no value in submitting an application designed to fail — better to know early and, where possible, adjust the scheme or reconsider the property.

The cost of a Lewisham house-to-flats conversion depends on the size and complexity of the property and how much of the full package you need — from a straightforward split of a large terrace into two generous flats, through to a multi-unit conversion of a substantial house with a basement flat, significant structural work, a full fire and sound strategy and services upgrades. We scope the work to your specific project and give you a clear, fixed fee for our part before any drawing work begins.

Separate from our fee, you should budget for the council's planning application fee, which is set nationally and charged per additional dwelling created, so a conversion into several flats carries a higher fee than a two-flat split; there is also a fee for pre-application advice if you choose to use that service. If structural work is involved there will be structural design and building-control costs, and the construction itself — new stairs, sound-rated floors, fire compartmentation, separate services and drainage — is the largest single cost on most conversions. We set all of this out at the start so there are no surprises.

On timescales, feasibility and drawings typically take a couple of weeks once we have access to survey the property, pre-application advice (if used) adds a few weeks, and the planning application itself runs against an eight-week target from validation, sometimes longer for complex, heritage or contested cases. We give you a realistic programme for your specific scheme at the outset, and we flag any Community Infrastructure Levy liability, which can apply to schemes that create additional floorspace.

It is worth remembering that good design and a well-argued application are not where money is lost on conversion projects — money is lost on refusals, on abortive schemes that ignore the size threshold or family-housing test, and on buildings that have to be re-worked on site because fire, sound and structure were not designed in. Getting the change of use right first time, to a standard that also satisfies Building Regulations, is the most cost-effective way to bring a Lewisham conversion into use.

To make the process concrete, consider a common Lewisham scenario: a three-storey-plus-basement Victorian semi in Brockley, a few minutes from Brockley station on the Overground, that an owner wants to convert into three self-contained flats. It is exactly the kind of property the borough's conversion market is built on — large, well-built, generously proportioned — and exactly the kind of change of use Lewisham scrutinises through its family-housing lens.

At feasibility, we survey the house and measure its original, unextended floor area: comfortably over 130 square metres, so it clears the size threshold. We then test what mix the council will accept. The lower-ground and ground floors become a three-bedroom family maisonette with direct access to the retained rear garden — the family unit Lewisham wants to see kept — while the first floor becomes a two-bedroom flat and the top floor a one-bedroom flat, the roof space brought into use to give it proper head height. Every unit is checked against the national space standards and the London Plan ceiling-height and amenity requirements before the layout is fixed, and if the numbers only worked at the cost of a sub-standard unit, we would propose two flats rather than three.

The construction and structural design follow from that layout. A new common entrance and a compliant protected stair serve the upper flats, needing new openings and steel support with calculations; the floors between flats are rebuilt to meet the Part E sound standards and upgraded for residential loading; each flat is formed as a fire compartment with fire doors, protected escape and interlinked detection to Part B; and the heating, hot water, electrics and drainage are separated and upsized so each flat is genuinely independent. The basement family unit is designed with proper light, ceiling height and damp protection, and we check the flood mapping given the borough's rivers. All of this is designed as one coordinated package so the planning layout is genuinely buildable.

On the planning side, we prepare existing and proposed drawings with every flat's area annotated, plus a planning statement that meets Lewisham's Local Plan policies head-on: it confirms the size threshold, shows the retained family maisonette and its garden, demonstrates each flat against the space standards, addresses neighbour amenity and the sustainable location by the station, shows the designed refuse and cycle storage, keeps external alterations sympathetic to the Brockley streetscape, and makes an honest case on conversion concentration in the immediate streets. Where the surrounding area is already heavily converted, we say so at feasibility and advise accordingly rather than submitting blind.

Submitted through the Planning Portal and managed through Lewisham's validation and determination, a scheme like this runs against the eight-week target and — because it is designed to the council's standards, retains family accommodation and is argued against its policies — it goes in as a proposal the case officer can recommend for approval. Once permission and any conditions are dealt with, the same coordinated drawings carry the project into construction. That is the difference between a conversion designed to succeed and one that is simply hoped through.

It helps to understand who actually lives in Lewisham conversion flats, because the housing need they meet is part of the planning story the council recognises. The borough's excellent and improving transport — National Rail to London Bridge, Cannon Street and Charing Cross, the DLR at Deptford Bridge and Lewisham, and the Overground through New Cross, Brockley and Forest Hill — makes it a natural home for first-time buyers, young professionals and small households priced out of the boroughs closer to the centre. A one- or two-bedroom flat in a converted Victorian house near a station is, for many, the affordable route into home ownership or a settled rented home in inner south-east London.

That demand is structural, not a fad. Lewisham combines fast central-London access, a strong and diverse local economy, ongoing regeneration around Lewisham, Catford and Deptford, and prices that undercut Greenwich and the inner boroughs. As long as those conditions hold there will be strong demand for well-designed flats — which is exactly why the borough has such an active conversion market, and also why the council is careful to manage it so that the supply of larger family houses is not quietly eroded in the process.

For your application, the point is that a good conversion meets a genuine housing need the council's own policies acknowledge: additional homes in a sustainable, well-connected location. A scheme that adds those homes at a proper standard, while retaining a family unit and respecting the street, is contributing to the borough's housing supply — and framing the proposal in those terms, honestly and with evidence, is part of building a persuasive planning case rather than presenting the conversion simply as a loss of a family house.

The flip side is that a poorly conceived conversion — cramped flats, no retained family unit, no thought for waste, bikes or the conservation street scene, in an area already saturated with flats — meets that need badly and hands the council every reason to refuse. The market rewards quality too: well-designed, well-built Lewisham flats sell and let quickly and hold their value, so designing to a proper standard serves the investment as well as the planning case.

A grant of planning permission for a house-to-flats conversion rarely comes without conditions, and it is worth knowing what to expect so they can be discharged smoothly rather than becoming a stumbling block later. Conditions are requirements attached to the permission that must be met, either before work starts, before the flats are occupied, or on an ongoing basis, and failing to comply with them can put the lawful use of the flats at risk.

On Lewisham conversion permissions, common conditions include the provision and permanent retention of the refuse and cycle storage shown on the approved plans, details of external materials and finishes (especially in conservation areas), retention of the rear garden and any amenity space, and sometimes obscure glazing or restrictions on new windows to protect neighbours' privacy. There may be conditions securing the sound-insulation or other measures that formed part of the approved scheme, and conditions fixing the approved unit mix so that the family unit is actually delivered.

Some conditions require details to be submitted and approved before work starts or before occupation — for example, precise details of the bin store, cycle store, materials, or a construction management plan. These 'pre-commencement' or 'pre-occupation' conditions are each discharged by a short further application to the council providing the required information. We flag any onerous conditions when the decision arrives and can prepare the discharge submissions so the flats can be brought into use without delay.

The practical message is that the permission is the beginning of a compliant conversion, not the whole of it: the conditions, the Building Regulations sign-off and the completion of the works all have to line up. Because we design the scheme with all of this in mind, the conditions Lewisham attaches are generally ones the scheme already meets — which makes discharging them straightforward.

Not every application is approved first time, and a refusal is not necessarily the end of the road. When Lewisham refuses a conversion, it must give its reasons, and those reasons are the roadmap for what happens next. Sometimes the sensible response is to revise the scheme to overcome the objections and resubmit; sometimes, where the refusal turns on a point of planning judgement we consider wrong, the right route is an appeal to the Planning Inspectorate.

A revised application is often the faster and cheaper route where the reasons for refusal are about design and detail — flat sizes, amenity, refuse or cycle storage, external alterations, or a specific amenity impact — because those can be addressed by amending the scheme. Many authorities, Lewisham included, allow a 'free go' resubmission of a similar application within a set period after a refusal, which we can use to submit an improved scheme without a further application fee.

An appeal is the route where the refusal turns on a matter of principle — for example, a disputed conclusion about loss of family housing or an over-concentration of conversions — that a revised scheme cannot resolve. Appeals take longer and require a properly argued case drawing on national policy, the development plan and appeal precedent, but a well-founded appeal against an unreasonable refusal can and does succeed, and appeal decisions on conversion cases help clarify how the borough's policies are applied in practice.

The best defence against a refusal is, of course, an application designed not to be refused — which is why we invest in feasibility and in answering the council's tests up front. But if a refusal does come, we will give you a straight assessment of whether to revise and resubmit or to appeal, and prepare whichever route gives the scheme its best prospects.

Crown Architecture prepares house-to-flats conversion schemes across Lewisham and the surrounding boroughs, and we do it as a single coordinated service: the planning design, the structural design and the building services under one roof. That matters on conversions more than almost any other project type, because the planning layout, the common escape stair, the sound-rated floors and the structural work are completely interdependent — design them separately and they clash.

We know the Lewisham regime: the borough's long-standing protection of family housing, the 130 square-metre size threshold, the requirement to retain a family unit, the space and amenity standards each flat must meet, the cumulative-impact and conservation tests, and the way the Lewisham Local Plan 2020-2040 (adopted July 2025) now frames all of it. We use that knowledge to give you honest advice at feasibility and to build applications designed to pass.

Just as importantly, we are straightforward to work with. We tell you early whether a house will make a good conversion and at what unit mix, we quote a clear fixed fee, and we prepare a coordinated, self-consistent application that a case officer can approve without having to fill in the gaps. Then, once permission is granted, we can carry the scheme through to the structural and building-regulations information your builder needs.

We also stay with the project after the drawings are done. We manage the application through Lewisham's validation and determination, respond to the case officer, negotiate amendments where that will secure approval, and — once permission is granted — help discharge the conditions and prepare the construction information. The aim is a single, accountable point of contact from the first survey to a buildable, sign-off-ready set of flats, rather than a set of drawings handed over and a client left to navigate the council alone.

If you are considering converting a house into flats in Lewisham — whether it is a single project or part of a wider plan — send us the address and what you have in mind, and we will tell you honestly what is achievable and how to get there.