Amalgamation: Converting flats into a house (Deconversion)

Amalgamation is the process of merging self-contained flats into one home. If the property used to be one house or a large flat but was subsequently converted to two or more flats, then the process of turning back to what it once was is known as deconversion.

There are many reasons for wanting to deconvert flats. Maybe you currently own one flat and you are considering purchasing another and merging the two. Perhaps you wish to increase the size of your home, but you live in an area where it is hard to find suitable houses, or you just love the building and want to restore it to its former glory.

Whatever the reason, converting flats into a family house may seem like a relatively straightforward task. However, there are many things to consider when undertaking a deconversion in order to recreate a large house.

Keep reading to learn more about what the planning rules say about restoring one home from multiple self-contained flats. We’ll also discuss the design choices you’ll have when taking on a project like this.

If you are considering attempting to amalgamate two or more flats into one home, then you are probably wondering, “Do I need planning permission? After all, I’m just restoring a house to its original state.” Well, this depends on a couple of things.

One of the best ways of creating large houses is to allow the amalgamation of smaller flats within properties which were originally built as a single dwelling.

Before you start, it is worth checking with the local council to see the current planning status of the house. Why? It turns out that many Victorian and other older houses have been unlawfully converted and therefore are still officially single homes.

If that is the case with your property, then as far as the paperwork is concerned, this is the problem solved for you. No matter how many front doors or kitchens the property has, officially it is still one home and no planning permission is needed.

(Quick note, you will still need building regulations approval if you’re going to be stripping out those redundant kitchens and knocking through walls. And removing a doorway might need planning permission, especially if you are in a conservation area.)

However, if the planning department believes the property is separate flats, a little more work will be required.

The 1990 Town and Country Planning Act states that the amalgamation of two or more dwellings into one is not usually considered “development” and, therefore, would not need planning permission if all the works are internal. However, since the year 2000, councils have had to consider the loss of housing from the amalgamation of flats.

So now, the outcome of your planning application may depend on the housing needs in the area. But don’t despair, as this does not necessarily mean that your project is doomed.

The number of separate homes being "lost" will be a major factor here - three into one might be possible, five into one is very unlikely to get permission. If you do get a refusal from the council, possible grounds for appeal are:

To further complicate matters, these policies will change depending on your location. Even across London, the rules depend on the borough. In Kensington and Chelsea, the council views the amalgamation of flats as a material change requiring planning permission.

Since 2019 they have defined this further, stating that the council would only allow a merging of two apartments based on square footage and that planning permission would still be needed.

Camden takes a slightly more flexible approach, allowing the amalgamation of up to two dwellings into one without requiring planning permission. The most common method for securing approval is through obtaining a Certificate of Lawfulness, although some may opt to submit a full planning application instead.

In Westminster, the development of super-sized homes - which they define as homes measuring more than 200 sqm - is restricted, but losing one smaller unit to provide a family-sized house through deconversion is permitted. Smaller conversions may only need a certificate of lawfulness, and larger ones will require an application for planning permission. So, the success of your project may depend on your postcode.

Elsewhere in the UK, deconversion will fall under local restrictions, and so thorough research is always recommended before you undertake any significant works.

Even if you are sure that your council isn’t asking you to apply for planning permission for what you want to do, but that it does think that it is currently more than one home, it’s important to get the new situation documented. Why?

Mortgage lenders and future buyers will want to be sure that what you believe is the case is also what the local government agrees is the case.

In order to do this, you should apply for a Certificate of Lawfulness for Proposed Use or Development. This differs from one for existing use, which we will discuss later. Applying for one of these certificates is very much like applying for planning permission - however, there should be a minimal chance of rejection as long as what you are suggesting meets council rules. A decision is usually made within eight weeks, and fees are often half the price of full planning permission.

As you have probably realised, the issue of planning permission is a complicated one. Even if the original building was one house, you might need to apply for planning permission, and your application may be rejected. However, not all scenarios are equal here.

You stand a better chance of deconverting a house than amalgamating purpose-built flats. If the building only contains two self-contained homes, your chances of being able to carry out the work are even higher. It is really all down to whether your project is classed as “development” or not, and this can depend on an individual interpretation of current legislation.

The 1990 Town and Country Planning act defines development as “the carrying out of building, engineering, mining, or other operations in, on, over or under land, or the making of any material change in the use of any building or other land.”

However, it is not always the case that a planning application is required to carry out development. Some development may be permitted under national permitted development rights, but these rights are subject to limitations and conditions that control aspects of the build.

We’ve mentioned that houses have often been converted into flats without getting the correct planning permission. But the reverse can also be true: the property could be multiple homes according to the council records, but has been in use as a single unit for some time. If that period of time is more than four continuous years* – and you have the evidence to prove that – you can get what’s known as a Certificate of Lawfulness of Existing Use or Development (or, more simply, a lawful development certificate). This establishes the current arrangement as the official one. From that point on, the council has to accept that this is one home.

Why would you choose a certificate of lawfulness over retrospective planning permission? Firstly, it's about half the cost, but you'd also choose it if you thought that according to the council’s policies, the loss of a housing unit would be unacceptable. With a four-year rule application, the council’s view of this loss becomes irrelevant because the new use has been going on for long enough to become the legal one. But be aware, you do need to have very solid evidence for this.

*A note on certificates of lawfulness and enforcement: the four-year rule was replaced by a ten-year rule on 25th April 2024. This means that moving forward, any works completed without the required planning permission will need to demonstrate ten years of continuous use rather than four - a far more arduous task.

However, there are some transitional provisions and if your project was “substantially completed” before April 25, then the new time limit may not apply to you. The definition of  “substantially completed” is vague and will likely be further clarified and defined over the next few years through consequential appeals and court interpretations.

In the meantime, the Royal Town Planning Institute (RTPI) has offered the following transitional guidance in their most updated Enforcement Handbook: “Substantial completion is not always clear and is a matter of fact and degree. A building is complete when it is complete for the purposes for which it was intended.”

Additionally, the RTPI makes a note that when buildings are built in stages, the clock can be restarted if lawfulness of a previous stage has not been accrued and demonstrated. This will similarly likely be tested through the legal system over the coming years.

If you have any questions, please get in touch with our team.

If you don’t need planning permission, then this should be relatively straightforward, but please pay close attention to council policies anyway.

If you do need planning permission, then you should ideally be able to argue that:

Even if you don’t need to apply for planning permission, you may still need to apply for other permissions before carrying out any work. These include:

In some cases, it is worth seeking planning permission even if you don’t think your project needs it, as planning permission gives you more scope to do the work you need to make the new, larger home convenient and comfortable. If your project is found to be in need of planning permission after you start the work, it may lead to enforcement action, which will require you to reverse any changes.

On the plus side, many deconversions won’t affect the exterior of the building, which is favoured when doing any building works. But your local council may have to decide whether the amalgamation is deemed a material change of use, and they will need to assess the impact on the local housing situation.

Of course, you can avoid a lot of confusion by consulting with a reputable architectural firm. They will be able to inform you about any local restrictions and have working knowledge regarding how likely a successful application would be. At Urbanist Architecture, our architects and town planners have real-world experience of local building regulations and can give you the best advice for your situation.

Once you’re confident that you are going to be able to merge the properties into one home, whether through planning permission, a certificate of lawfulness, or clarification that neither of these is needed, you are ready to start planning your deconversion. But where to start?

When undertaking a reverse conversion of flats into a single house, the instinct is to use the original layout of the home and restore it to how it was before.

Restoring a Victorian home to its original state can be extremely rewarding and opening up a pokey flat into a few large rooms will breathe fresh air into the house.

Restoration may also be the most straightforward route, as flat conversions often involve putting up stud walls that are easily removed. Victorian properties may also retain original flooring and other features that a restoration can uncover and embellish.

However, restoration is not your only option, and restoring the building to its original condition may not be the best use of space. Getting an architect to have a look at the space before you start designing can help you get the best out of your building. Don’t think that you are obliged to put it back as it was, as there are many ways you can fully utilise the space. Building and design have come a long way since most of these properties were built, and you may be surprised when exploring the possibilities.

Many buildings that were previously converted into flats are Victorian, and these houses hold endless possibilities in terms of renovation and extension. Victorian houses will often have the option to extend to the rear of the property.

Side-return extensions are also popular and an excellent way to utilise the wasted space on the side. While you can choose to match the existing brickwork and blend the extension into the original, there are many examples of modern materials used to great effect.

Glass and wood feature heavily in many contemporary extensions, and these materials can bring warmth and light to the back of the house whilst still expanding the living space dramatically.

Loft conversions are also hugely popular in this style of house and made possible by the steep sloping rooves. You can easily turn the loft into a master bedroom or office to increase the home’s square footage. You may be concerned about storage, but the eaves can be sectioned off and turned into cupboards. This touch will square off the room and give you valuable storage space.

There are many routes that you can take when converting two or more flats back into one house, and you can browse plenty of successful projects online. Depending on the terms of your mortgage, you may even be able to live in one flat and rent the other out for some time to build up funds for the project. Many people undertaking an amalgamation project choose to live in one flat while they carry out work in the other, allowing them to live comfortably on site.

Whatever your circumstance, working with an architecture firm specialising in planning from the start of your project can give you an invaluable insight into what lies ahead. Many companies will be able to provide you with a consultation when your project is still in its planning stages. By getting this initial consultation, you will be able to assess the viability of your project, as well as get an insight into any changes you could make to make the build more feasible and financially rewarding.

At Urbanist Architecture, we specialise in residential architecture and can give you a unique perspective on your plan. Our small but comprehensive team is experienced in offering exceptional solutions to unconventional builds and may be able to open up possibilities that you have not considered.

As well as helping with the layout and practical aspects of a build, experienced architectural firms will be able to supply you with comprehensive advice and assistance with the legalities of converting flats back into one property. Getting the job done correctly and legally is vital to save you any expensive complications, and it is essential when it comes to selling the property further down the line.

Hopefully, you now know a bit more about the process of reinstatement of flats into a single dwellinghouse. Although it may not be as straightforward as you initially thought, it could be the best way of obtaining the home of your dreams.

Another factor you will have to consider is whether your property is freehold or leasehold. Flats are often leasehold - by deconverting, you might become the sole freeholder. This issue can make securing a mortgage challenging as most lenders will require the deconversion to be complete before they agree to mortgage finances. However, specialist mortgage companies are out there that deal with precisely this type of scenario, so be sure to research mortgage brokers thoroughly.

There are many issues when it comes to financing a buy like this. Perhaps the value of the separate flats is greater than that of a single home, which would make lenders wary of the project. Especially when you take into account the expense of the renovation itself, which you may also need to get financed. Unless you are a cash buyer, you will probably need a bespoke financial solution rather than follow a traditional mortgage method.

Do note, though, that it is not always the case that the combined value of the flats will be greater than one home. Many deconversions have added value to the property by making improvements and extending. Victorian houses often have the potential for loft conversions and side return extensions, increasing the sq. footage of the finished home.

Before we move on, we wanted to share a recent high court decision that was quite significant in the planning world, and will no doubt be used as a precedent in future.

Strap yourself in for a wild ride…

Back in May 2022, property owner Kathryn van Rooyen attempted to gain a lawful development certificate (LDC) for the amalgamation of her flat with the flat next door. Unfortunately for her, the council rejected the LDC, suggesting instead that planning permission was required. 

So, van Rooyen pursued a planning application for the conversion, only for that application to then also be refused by the council. Frustrating, to say the least. 

When explaining the second refusal, Lambeth Council stated that the proposed amalgamation resulted “in the loss of an existing self-contained unit. No exceptional circumstances have been demonstrated, therefore the development fails to comply with Policy H3 of the Lambeth Local Plan (2021)". For context, Policy H3 relates to the protection of self-contained housing, meaning the key reason for the dismissal was the proposed loss of a unit of housing in the local area.

The next step for van Rooyen was to appeal this decision, which initially yielded quite positive results. The planning inspector overruled both of Lambeth Council’s refusals, stating that refusal A - the lawful development certificate - should have been granted, as the conversion of two flats into one "would not be a material change of use... [and] would not constitute development under [the Town and Country Planning Act 1990] and therefore would have been lawful at the date the LDC application was made". Then, in regard to refusal B - the loss of an existing self-contained unit - the inspector found that the "loss of a single unit, in the context of current housing delivery in the borough, would not be a planning consequence of significance."

A good result for van Rooyen, right? Not so fast. 

Lambeth Council then took the inspector’s report to the high court, believing his conclusions were contradictory. Here’s exactly what happened.

The council’s first issue was how the inspector could grant planning permission for refusal B when he had already decided in refusal A that the conversion would not constitute “development”. In other words, how could the loss of a single unit be insignificant if there was no “development” in the first place? To this, the judge replied: "If his (the inspector’s) conclusion on Appeal A were to be overturned on appeal, Appeal B would cease to be academic. The inspector probably ought to have included a sentence in his [decision letter] explaining that he was determining Appeal B, in the alternative, in case his decision on Appeal A was overturned on appeal. However, as both parties had adopted the same approach throughout, it is unlikely that they were in any genuine, as opposed to forensic, doubt as to the basis upon which he was determining Appeal B."

So far, so good for van Rooyen. 

The second ground Lambeth took issue with was that the inspector didn’t properly acknowledge Policy H3 of the Lambeth Local Plan’s role in protecting existing housing stock and, therefore, the area’s restriction of amalgamations to the extent allowed for by the London Plan. To this ground, the judge asserted that the inspector interpreted the policy correctly, stating that he found "there were no policies that prohibited amalgamations. However, he also recognised the policy imperative in London Plan Policies H1 and H2 to increase the supply of housing, and the policy to 'safeguard existing self-contained C3 housing' in Lambeth Local Plan Policy H3, which required consideration of the planning consequences of the net reduction of one unit from Lambeth's housing stock.”

The next pain point highlighted by Lambeth was that the inspector "made an irrational decision, or failed to take into account material considerations, when he treated the effect of the proposed net loss as an insignificant planning consequence". To this, the judge essentially said that Lambeth Council was being too stringent in its safeguarding of existing properties, and that while the council held that the approval of this project could have a cumulatively negative impact, the inspector was entitled to draw the conclusion he did, based on the reasons he gave.

Ultimately, all of Lambeth Council’s grounds for challenge were dismissed by the judge and van Rooyen’s amalgamation was approved at last in June 2024. If you’re compelled to comb through the judge’s findings, head here.

So, what does all this mean?

Firstly, if you have the financial means (and the time) to argue against planning decisions you believe are incorrect, then you can escalate them to the highest level and potentially win your case. 

Secondly, any London Borough that successfully meets its 5-year housing supply will struggle to argue that the loss of a single unit would be significant enough to affect the current supply. To help you figure out where your application may stand, it is always advisable to double check if your local authority is constantly meeting its target or if it is on the right track to build homes. This can be done by reviewing your council’s annual Housing Delivery Test results, which is measured by calculating the total homes delivered over three years, divided by total number of homes required over that period.

Of course, gaining approval based on your council’s healthy housing supply isn’t a guarantee you will gain permission for an amalgamation. As always, there are many elements at play. For example, what type of unit is your proposal adding or subtracting from the local housing stock? If what you’re proposing is required in the area (let’s say there’s a need for more two-bed homes over one-bed homes and that’s what your proposal is both adding and removing from the area), then it’s more likely to be approved. To help you establish where you stand, you can review your LPA’s housing needs by referring to the Strategic Housing Market Assessment, a tool that outlines which accommodation sizes are required in the area.

The last thing to note is that the loss of a single unit is likely to be viewed differently to the loss of multiple units. If you’re trying to turn four flats into one, for example, that is obviously a significantly greater loss of housing than a single unit and is, therefore, less likely to gain approval. Again, how this is viewed will vary from council to council. Lewisham Council recently approved an amalgamation that resulted in the loss of three units, while Hackney Council recently dismissed a similar proposal and doesn’t generally approve of these amounts of housing loss. 

The key takeaway? Councils will rarely draw the same conclusions, as each is operating within the unique contexts of their setting and the needs of their locality.

Merging several dwellings is not just about knocking down a few walls. You will have to consider issues with council tax. Even if you do not need planning permission to complete the work, you will still need to get the finished property reassessed to update the council tax band. You can contact the Valuation Office Agency to determine how any proposed changes will affect your council tax band.

Utilities are another matter that will need to be addressed, as separate flats will have their own meters for gas and electricity. Removing one set of meters may involve having to dig up pipes or cables that have been laid under the pavement, and the disconnection will have to be undertaken by a reputable utility company.

Buying two properties and combining them may also create issues regarding stamp duty, as you may have to pay a “higher rate for additional dwelling” stamp duty surcharge on one of the flats. This surcharge is added because you will technically be buying a second property, even though the intention is to merge it into one. It may be tempting to think you can get around this by having you purchase one property and a partner purchasing another.

However, by taking this route, you will run into complications down the line regarding your mortgage and the tenure of the property. Having said all that, you may be entitled to a refund on the surcharge after the work is completed. As with any dealings with HMRC, it’s best to avoid any issues and just pay what’s asked.

If all this hasn’t put you off undertaking a conversion of flats into one property, then keep reading to find out more!

Urbanist Architecture is a London-based RIBA chartered architecture and planning practice with offices in Greenwich and Belgravia. With a dedicated focus in proven design and planning strategies, and expertise in residential extensions, conversions and new build homes, we help homeowners to create somewhere they enjoy living in.

If you would like us to help you with your deconversion, please don’t hesitate to get in touch.