Converting flats into a single house: A comprehensive guide to amalgamation and deconversion

Merging two or more flats into a single home can appear deceptively simple.

On paper, it may look like a matter of internal alterations and better use of space. In practice, however, amalgamation and deconversion are rarely that straightforward, particularly in London, where planning outcomes are often shaped by housing policy, heritage constraints, leasehold complications and borough-specific judgment.

You may be looking to buy the flat next door to create a larger family home, or to restore a building to its original use as one house after it was subdivided years ago.

Either way, the key questions usually go far beyond design alone. The real issue is often whether the council will accept the loss of one or more self-contained units, and on what terms.

In this guide, we look at when planning permission may be required, what you need to be aware of before starting, and how borough-specific policy can affect the prospects of success.

We will also specifically assess in detail the following councils:

But before we move into that borough-by-borough comparison, let us first clarify the definition of amalgamation and deconversion, and then look at the planning position that sits behind them.

To understand how these projects are assessed, it helps to start with a clear distinction between amalgamation and deconversion.

Amalgamation is the process of combining self-contained flats into a single home, often merging two or more purpose-built flats into one.

This might involve buying the flat next door, combining upper and lower maisonettes, or reconfiguring neighbouring units to create a larger and more practical home. In planning terms, the key issue is often not the physical works themselves, but whether the council is prepared to accept the resulting loss of one or more housing units.

Deconversion is about ‘undoing’ a previous flat conversion to return a larger dwelling back to its original state. 

Imagine a Victorian property originally built as a single dwelling that was later divided into three flats. Deconversion is the process of reversing this conversion, and restoring the property back to its original form as one home.

Now that the distinction is clear, let’s look at how councils approach it in planning terms.

Under the 1990 Town and Country Planning Act, planning permission is required where works amount to “development”, including a material change of use. The legislation is clear that subdividing one dwelling into several is development, but it is less direct on combining dwellings. For that reason, flat amalgamation has often been treated as not requiring permission where works are entirely internal.

That is the legal starting point. In practice, however, it is rarely that simple. In London, the safest assumption is usually that the borough’s housing policies will matter, even where the works are entirely internal.

Since the Richmond case in 2000, councils have been entitled to consider the loss of housing units when deciding whether a proposal amounts to a material change of use. The focus is no longer just on the works, but on whether reducing the number of homes has a real planning impact.

In practical terms, a council may conclude that merging two or more flats into one does involve a material change of use, even if the works are internal. This is particularly relevant in boroughs under housing pressure, where policies strongly resist the loss of units.

The correct route therefore needs to be judged carefully. Some boroughs accept the certificate of lawfulness route for genuinely internal amalgamations where the planning consequences are limited. Camden is a clearer example of this approach in practice. Others, such as Westminster, have taken a more cautious position and may require a full application depending on the housing implications.

For that reason, the route should never be assumed. It needs to be tested against the approach of the specific borough.

So although the legal framework begins with the 1990 Act, the practical answer usually turns on local planning judgment. Some schemes can proceed through a certificate of lawfulness. Others will require a full application because the council treats the loss of units as a material planning issue.

Before doing anything, establish the planning status of the property.

Many older London houses, particularly Victorian ones, were converted into flats decades ago without clear planning consent. That matters. If the existing arrangement is not lawful, the starting point is not amalgamation. It is regularisation.

In those cases, you may need a certificate of lawfulness for existing use to confirm that the current flats are legally established before you can even consider merging them back into a single dwelling. Until that position is clarified, any further application sits on uncertain ground.

In our experience, this is commonly missed. We receive many enquiries where earlier advice did not correctly establish the planning status of the existing flats, even though this can have a major impact on the strategy.

We have worked on flat amalgamation proposals across many London boroughs, and one point has become very clear: these projects are highly borough-specific.

While some councils can be supportive where smaller flats are combined to create a genuine family-sized home, others take a much more restrictive view because of concerns about housing loss, housing mix and the creation of oversized dwellings.

In our experience, the central issue is rarely just whether the works are internal. More often, it is whether the council is willing, under its own local planning policies, to accept the loss of one or more self-contained homes.

Below, we set out our observations on ten London councils we have most commonly dealt with in this area, and explain what their approach tends to mean in practice.

Before turning to each one individually, the overall pattern is this: councils are usually more receptive where amalgamation creates a well-proportioned family home, does not result in the loss of scarce family accommodation, and avoids producing an oversized luxury dwelling at the expense of several smaller units. The more a proposal appears to reduce housing choice without a clear planning benefit, the more difficult it usually becomes to justify.

Westminster is one of the clearest boroughs in London when it comes to flat amalgamation. It is also one of the most controlled. The council does not treat the merging of flats as a neutral internal exercise. It assesses proposals directly through housing delivery, housing protection and its long-standing resistance to very large homes replacing multiple smaller units.

In policy terms, Westminster allows the reconfiguration of smaller, non-family homes into a family-sized dwelling. That is the main route through which amalgamation can be supported. However, this sits alongside a strong expectation that new homes should not exceed 200 sqm gross internal area unless there is a clear site-specific justification, most commonly linked to heritage constraints.

In practice, this creates a very defined planning envelope. A proposal that combines two smaller flats into a well-proportioned three-bedroom family home may be acceptable. A proposal that results in a significantly oversized dwelling is much more likely to be resisted, particularly if it appears to prioritise luxury floorspace over housing need.

Heritage can also play an important role, especially in listed buildings or historic townhouses. Where amalgamation restores a more coherent original layout, that can strengthen the case. But heritage is not a shortcut. It still needs to be demonstrated clearly why the building itself justifies any departure from the usual size expectations.

The strongest Westminster applications are tightly controlled, policy-led and carefully sized. The key is not simply to show that the final home is better. It is to show that the loss of one unit is justified and that the resulting dwelling aligns with the borough’s wider housing objectives.

Kensington and Chelsea is one of the most challenging boroughs in London for flat amalgamation. The council is particularly sensitive to the loss of smaller homes and has a long-standing concern about the steady reduction of housing units through these types of proposals.

The policy approach has consistently been restrictive. Amalgamations are generally resisted unless the loss of units is very limited and the resulting home remains within a tightly controlled scale. Even within those limits, the council has identified a pattern of housing loss, which continues to influence decision making.

In practice, this means the focus is not just on the quality of the proposed home. The council will examine whether the proposal removes useful housing from the stock without sufficient justification. A well-designed outcome alone is not enough to outweigh that concern.

Heritage is often a factor, particularly in listed buildings and conservation areas. Restoring an original house layout can support the case. However, heritage does not override the issue of housing loss. It strengthens the argument but does not replace it.

This is a borough where tightly framed proposals perform best. The strongest applications are modest in scale, clearly justified and directly aligned with policy. Broader or more speculative proposals are far less likely to succeed.

Camden takes a more nuanced approach than many central London boroughs. It does not rely on a single rigid policy on amalgamation. Instead, outcomes often depend on how the proposal is classified and the route that is taken.

One of the key distinctions in Camden is between proposals that require full planning permission and those that may be approached through a certificate of lawfulness. Where works are internal and there is no material change of use, amalgamation may fall outside the need for a full application. That procedural choice can be critical.

However, Camden remains strongly housing-protective. The borough seeks to safeguard its housing supply and will assess whether the proposal results in a meaningful loss of units. A two-into-one scheme may be acceptable in principle, but it still needs to be justified in terms of housing impact and overall planning logic.

Heritage is often central to these schemes. Many properties are listed or located within conservation areas. Reinstating an original house layout can strengthen the case, but it may also introduce additional consent requirements and constraints on internal alterations.

Camden often rewards a well-considered strategy. The strongest projects are those where the correct route is established early and the planning case is built around the specific characteristics of the building.

Hammersmith and Fulham is a borough where the direction of policy is becoming more restrictive. While the adopted Local Plan is relatively dated, emerging policy clearly signals a tighter approach to flat amalgamation.

The council is moving towards supporting amalgamation only where it results in a family-sized home. At the same time, there is a clear intention to resist the creation of oversized single dwellings from multiple smaller units.

In practical terms, this means proposals are now being scrutinised more closely. The council is increasingly focused on whether the scheme serves a clear housing purpose rather than simply improving internal space for one household.

Applicants should be cautious about relying solely on the adopted policy framework. Emerging policy can carry weight, especially where it reflects a consistent direction of travel. Ignoring this can lead to difficulties later in the process.

A strong application will demonstrate that the proposal creates a genuine family home, remains proportionate in scale and aligns with the borough’s evolving housing strategy.

Lambeth is more supportive of flat amalgamation than many central London boroughs. However, that support is clearly conditional. The council allows the loss of smaller units where they are combined to create a family-sized home, typically three bedrooms or more.

This creates a clear opportunity. The borough recognises that merging smaller flats can help meet demand for larger homes, particularly in buildings that were originally designed as single dwellings.

At the same time, this is not a free pass. The proposal must clearly read as a family-housing solution. If the outcome appears to be an oversized or purely value-driven dwelling, the case becomes weaker.

The quality of the final layout is important. The council will expect a coherent and usable family home rather than an arrangement that simply increases floor area.

Heritage may assist where the proposal restores the original character of the building. However, the planning argument must still address housing policy directly.

The strongest Lambeth schemes are clearly family-led, well proportioned and grounded in a logical reconfiguration of the existing building.

Southwark does not rely on a single, clearly defined policy on flat amalgamation. Instead, it assesses proposals through broader policies that protect existing housing and resist unnecessary loss of units.

This can be misleading. The absence of a specific rule does not mean the borough is relaxed. Southwark remains cautious and will examine whether the loss of homes is justified.

In practice, the outcome depends heavily on how the proposal is framed. Removing good quality smaller flats to create a much larger dwelling is likely to face resistance. Improving poor layouts or restoring a building to a coherent family home may be more acceptable.

The borough’s wider housing pressures are also relevant. Southwark has a strong focus on maintaining and increasing housing supply, which influences how these proposals are assessed.

Heritage can support the case in period buildings, particularly where original layouts are reinstated. However, it does not remove the need to address housing loss.

Success in Southwark usually depends on presenting the proposal as a sensible housing and building improvement rather than simply a reduction in the number of homes.

Islington takes a cautious approach to flat amalgamation. The borough does not prohibit it outright, but it places strong emphasis on protecting existing housing stock.

Policies are particularly focused on preventing the loss of multiple units and safeguarding larger family homes. This means that even relatively modest proposals need to be carefully justified.

A two-into-one scheme may be acceptable in principle, especially where it results in a well-designed family home. However, the council will closely examine what is being lost. Where existing units are of good quality or include family accommodation, the proposal becomes more difficult.

Changes in the number of flats are often treated as a planning matter in Islington, which means a full application is usually required.

The strongest applications are modest, clearly justified and aligned with the borough’s housing objectives. Once more than one unit is lost, or where family housing is reduced, the case becomes significantly weaker.

Wandsworth has one of the clearest policy frameworks in London for flat amalgamation. The council allows the merging of no more than two non-family-sized dwellings into a single family home, with the resulting property generally limited to around 130 sqm.

This clarity is helpful because it allows early assessment of whether a proposal is likely to comply. However, it also means there is very little flexibility.

If a scheme falls within these parameters, it can be considered on its merits. If it falls outside them, it is likely to face direct policy resistance.

The approach is designed to support family housing while preventing the creation of very large single dwellings at the expense of smaller units.

Design and heritage considerations still apply, particularly in conservation areas. However, the primary test remains the policy framework.

In Wandsworth, small changes in floorspace or unit numbers can determine the outcome. Careful measurement and early policy testing are essential.

Richmond does not operate a single explicit policy on flat amalgamation. Instead, its approach is shaped by a broader focus on family housing and housing mix.

Across much of the borough, policy supports the provision of family-sized accommodation. This can work in favour of amalgamation, particularly where a building is restored to a single-family use.

However, this varies depending on location. In more central or mixed-use areas, there may be a stronger expectation for smaller units. As a result, the same proposal may be viewed differently depending on its context.

The loss of housing units still needs to be justified. The council will consider whether the proposal contributes positively to the overall housing mix.

Heritage can also be relevant, particularly in period buildings. Restoring original layouts can strengthen the case, but it must be supported by a clear planning rationale.

Richmond is best understood through its wider housing strategy. The strongest proposals are those that align with local character and support the borough’s family housing objectives.

Hackney takes a more case-by-case approach to flat amalgamation. It does not rely on a single clear rule. Instead, decisions are shaped by a combination of housing policies, design standards and heritage considerations.

The borough places strong emphasis on protecting family housing and managing how residential buildings are reconfigured. This means proposals are assessed within a wider planning framework.

In practice, this creates both flexibility and uncertainty. There is scope to build a case around the specific building, particularly where the proposal improves layout quality or restores a more coherent form. However, outcomes can be less predictable than in boroughs with clearer rules.

Design quality is an important factor. The council expects well-considered layouts and a strong relationship between internal spaces.

Heritage can also play a role, especially in conservation areas. Where relevant, it can support the case, but it must be part of a broader planning argument.

A strong Hackney application brings together housing policy, design quality and building logic. It is not a borough where a simple policy check is enough.

The key point is that postcode matters. In London, the same proposal may be encouraged in one borough and resisted in another.

In a conservation area, even relatively minor changes can trigger planning control.

This can include not only external alterations, but internal changes where they affect the character of the building. Councils may expect key elements of the existing layout to be retained, including staircases, entrances or room divisions, even where they are no longer functionally necessary.

There is also a clear expectation around design approach. Proposals that read as sensitive and coherent tend to perform better. Schemes that appear overly modern or disconnected from the building’s character are more likely to face resistance.

It is also important to check whether an Article 4 Direction is in place. This can remove permitted development rights and bring changes that would normally be allowed firmly within planning control.

The key point is this: restoring a building to a single home is not automatically seen as neutral. It still needs to be justified.

For listed buildings, the position is more controlled.

Listed Building Consent will almost always be required, even for internal alterations and even where the intention is to reinstate the original layout. The focus is on preserving the building’s significance, not simply returning it to a previous state.

In practice, this means:

Listed Building Consent is assessed in great detail, with strict criteria that (again) can vary between councils. Therefore, the best approach is to work with a chartered architect and heritage consultant who understands the nuances of historic building restoration.

The strongest applications do not just show a better home. They explain clearly why the council should accept the loss of one or more units.

In practice, councils usually focus on a small number of core issues. How many homes are being lost, what type of homes are being lost, what kind of dwelling is being created, whether the proposal fits local housing policies, and whether the building’s character or history supports the case.

To improve the chances of success, the submission should make a clear and well-supported case around the following points:

Although every flat amalgamation project should be assessed on its own merits, and councils consider each application on its own facts, the factors outlined above have played an important role in helping our practice secure planning permission for a number of successful property conversion projects across London.

If your application is refused, the first step is to understand the reason for the decision.

In most cases, refusals are not about internal layout design alone. They are usually linked to housing policy, the loss of housing units, heritage considerations, or the way the proposal has been presented against the council’s local policies.

In practice, the best way forward is often either a revised application with a stronger planning case, or an appeal where there are sound grounds to challenge the decision. Much depends on whether the refusal arises from a genuine policy conflict, weak supporting evidence, or an overly rigid interpretation of the proposal.

Whether you are preparing a revised application or considering an appeal, there are usually three points that deserve particular attention:

If a refusal has been issued, there is still a right of appeal, and the Planning Inspectorate can overturn the council’s decision where there are valid planning grounds to do so. However, it is important to approach appeals carefully.

For most written representation planning appeals relating to applications submitted on or after 1 April 2026, the appeal will follow the Part 1 written representations procedure. Under that route, there is no separate Statement of Case, and the Inspector will rely heavily on the material submitted with the original application.

That makes the quality of the original submission especially important.

In many situations, the better route will be a revised application that deals more directly with housing policy, justifies the loss of units more clearly, and strengthens the evidence base. Where the council has taken an unduly rigid view, an appeal may still be appropriate. The key is to identify the underlying issue and respond with the right strategy, rather than treating every refusal in the same way.

Planning permission is only one part of the picture. Even where flat amalgamation does not require a full planning application, other approvals may still be needed before works can begin lawfully.

Depending on the property and its location, the following consents may also apply:

The key point is that securing planning permission, or confirming that it is not required, does not necessarily mean you are ready to start on site. A flat amalgamation project often involves a wider package of legal, technical and regulatory approvals, and these should be reviewed carefully from the outset.

In most cases, the work continues well beyond the planning stage, with the design being developed through RIBA Stage 3 and then technically coordinated at RIBA Stage 4 before the project is ready for construction.

Once you are confident that merging the properties into a single home is possible, the next step is to think carefully about the design. In our experience as residential architects the most successful amalgamation and deconversion projects are the ones that treat the building as a whole again, rather than simply removing the walls that once divided it into separate flats.

When converting flats back into one house, the instinct is often to restore the original layout. In many cases, especially with period homes, that is a strong starting point. It can help recover the proportion, flow and character that were often lost during conversion.

That said, the aim is not always to recreate the past exactly. The better approach is usually to create a home that feels coherent, comfortable and suited to modern life, while still respecting the original logic of the building.

A successful amalgamation or deconversion is not just about opening walls up. It is about making the property work properly as a single home again.

That means rethinking circulation, privacy, storage, natural light and the relationship between the main living spaces. One of the biggest opportunities is to remove duplication. Two kitchens, several small bathrooms, awkward corridors and disconnected reception rooms can often be reorganised into something far more generous, practical and enjoyable to live in.

These projects often depend on getting the fundamentals right. Entrances, staircases and servicing all need careful thought.

In some cases, one entrance may become redundant. In others, the challenge is how to rationalise plumbing, electrics and service runs so the new arrangement works efficiently as well as spatially. These are not secondary technical matters. They are often central to whether the final home feels properly resolved..

Amalgamation also creates an opportunity to improve light and ventilation, particularly where the original flats had compromised layouts.

Removing unnecessary walls, widening openings and reconsidering how rooms connect can make the house feel much brighter and more generous. Where parts of the property suffer from poor natural light, tools such as internal glazing, open-plan arrangements and light-reflective materials can help rebalance the space.

At the same time, it is important to preserve what gives the property its character. Original staircases, fireplaces, mouldings, floorboards and sash windows can all help maintain the identity of the house, particularly in older London terraces.

Where flats have been altered at different times, bringing consistency to materials, finishes and detailing is equally important so the final home feels intentional rather than pieced together. In our experience, the strongest schemes are rarely the ones that strip everything back. They are the ones that combine restoration with careful modernisation.

There is also often scope to expand the house further. Many amalgamation and deconversion projects involve Victorian house extensions, especially where the property has a generous rear garden or an underused side return.

Wraparound extensions can work particularly well because they allow the ground floor to be restructured in a way that feels much more natural for contemporary family life, while still respecting the proportions of the original house.

Fire safety also needs to be considered carefully. Buildings that were previously arranged as flats were often adapted to meet stricter separation requirements, including fire compartmentation, protected escape routes and fire-resistant construction between units. Reversing those changes is not simply a design decision.

It must be assessed properly against the Building Regulations, particularly Approved Document B. Depending on the scale and nature of the works, this may involve layout changes, upgraded construction, fire doors, detection systems or a revised escape strategy.

This is especially important in the current regulatory climate. In some cases, the role of the Building Safety Regulator may also become relevant, particularly where wider safety issues arise in more complex residential buildings. Even where that is not the case, the principle remains the same: moving from multiple units back to one dwelling should not weaken the safety standards of the building.

The strongest schemes also think ahead. Storage, flexibility, home-working space and long-term adaptability should be considered from the outset rather than added later.

Done well, an amalgamation or deconversion should not just produce a larger house. It should create a home that feels calm, coherent and properly resolved, as though it was always meant to be one.

Deconverting flats into a single home is as much a financial and legal exercise as it is a design one.

The first question is ownership. Most flats are leasehold, which means you do not own the building outright. If both flats share the same freeholder, the process is usually more straightforward. If not, you may need to negotiate with multiple parties or acquire the freehold, which can add time, cost and complexity.

Financing is often less straightforward than a standard purchase. Many mainstream lenders are cautious, particularly where the combined value of the separate flats exceeds the value of the completed house. In many cases, funding is arranged through specialist lenders, bridging finance, or a bespoke mortgage solution via an experienced broker.

Lease terms also need close attention. Amalgamation may require a Deed of Variation to permit the works and reflect the new single dwelling. If the lease is approaching 80 years, extending it early is often sensible, as costs rise significantly below that threshold.

Service charges and ground rent may not automatically reduce once two flats become one. Some freeholders continue charging as though both units still exist, while others recalculate the position. This is something worth clarifying at the outset.

If the building was originally a single house, there may also be scope to acquire the freehold and remove leasehold constraints entirely, depending on the freeholder’s position and the cost involved.

Beyond acquisition, you will need to budget for construction costs, architect fees, legal fees, planning application costs and any refinancing. Structural alterations, service integration and layout changes can all increase the overall budget, so it is important to understand the full financial picture from the beginning.

The key point is simple: amalgamation is not just about combining space. It also requires careful coordination of ownership, finance and legal structure from the outset.

Before we conclude, it is worth looking at a recent High Court case that has become highly relevant to flat amalgamation proposals in London. It is useful because it highlights the legal distinction between whether amalgamation amounts to development at all, and whether a council can still rely on housing loss policies to resist it.

The case concerned the proposed amalgamation of two adjoining flats at Peninsula Heights, Albert Embankment, into one four-bedroom home. No external works were proposed. Lambeth refused both a lawful development certificate and planning permission, arguing that the scheme involved a material change of use and conflicted with Policy H3 of the Lambeth Local Plan because it would result in the loss of an existing self-contained unit.

On appeal, the Inspector allowed both appeals. He found that the proposal would not amount to a material change of use and therefore would not constitute development under section 55 of the Town and Country Planning Act 1990. He also found that even if planning permission were required, the loss of one unit in the context of Lambeth’s housing delivery would not be a planning consequence of significance.

Lambeth challenged those decisions in the High Court. However, the court dismissed the claim. The judge held that the Inspector had been entitled to determine the planning appeal in the alternative, in case the lawful development certificate decision was later overturned. The court also accepted that Lambeth’s Policy H3 did not amount to an outright prohibition on amalgamations, and that the significance of losing one unit had to be judged on the facts of the particular case.

The importance of the judgment is not that amalgamations must now be approved. It is that whether a proposal amounts to a material change of use, and whether the loss of a housing unit is significant, remains a matter of fact, degree and local policy context. It is also a reminder that local plan policies must be interpreted by reference to their actual wording, not by assuming they prohibit more than they say.

This case does not create a general rule in favour of amalgamation. What it does show is that a refusal is not always the end of the story, particularly where the proposal is limited in scale, the policy wording is less restrictive than the council suggests, and the evidence has been prepared carefully.

For applicants, the practical lesson is straightforward. A strong amalgamation case needs to be built around the correct route, a clear explanation of why the loss of a unit is acceptable, and robust evidence on local housing context and the quality of the resulting home. Where those points are addressed properly, the proposal may be in a much stronger position than the refusal notice first suggests.

Flat amalgamation projects often look simpler than they are. In reality, they sit at the intersection of housing policy, heritage, design, leasehold constraints and technical coordination. Getting the strategy right early on can make the difference between a straightforward approval and a long, expensive detour.

At Urbanist Architecture, we bring together chartered architects and chartered town planners to assess these projects as one joined-up exercise. That means helping clients choose the correct route from the outset, whether that involves a certificate of lawfulness, a full planning application, listed building consent, or a wider design and planning strategy.

If you are considering merging flats into a single home, we can help you assess whether the proposal is likely to be supported, what risks need to be addressed, and how to shape the strongest possible application.