Combining two houses or flats: do I need planning permission?

 

Combining two houses or flats into one is not automatically development, but neither is it automatically outside planning control just because the physical works are internal. Internal building works may themselves fall outside the definition of development, yet the resulting amalgamation can still be a material change of use if the loss of housing has planning consequences of sufficient significance. That is why the answer varies between sites and authorities. So please read on!

You might also want to check any covenants or previous planning permission on the properties to see if they might prevent you from trying to combine two into one.

Splitting one home into two or more is treated as development, because s55(3)(a) TCPA 1990 says the use of a single home as two or more separate homes counts as a material change of use. But an amalgamation from two units into one is only development if it is a material change of use. This is important. 

 

 

In 2024 the High Court rejected an appeal made by the London Borough of Lambeth against the decision by an inspector to grant a certificate of lawfulness to allow the amalgamation of two flats into one at Peninsula Heights, 93 Albert Embankment, London SE1. Lambeth had refused the application for a Lawful Development Certificate on the grounds that it did not comply with the Lambeth Local Plan. The Inspector decided that the net loss of a single dwelling unit did not have a harmful effect on the housing supply and was therefore not development. The council argued that the London Plan, and therefore its local plan, restricted amalgamations; any such amalgamation must therefore be material. The Inspector and the court said the London Plan does not prohibit amalgamations but counts them as housing losses.

The applicant, Kathryn Van Rooyen, wanted to combine her long-term home (Flat 27) with the flat next door (Flat 26), which she had recently bought, to make a larger four-bedroom home for her elderly parents. Lambeth refused both the certificate and planning permission, saying the loss of a self-contained flat went against Policy H3 of its local plan and that nothing exceptional justified it.

 

Key legal issues and findings

 

1. Material change of use: the High Court upheld the Inspector’s conclusion that, on the evidence and policy context before him, the loss of one dwelling did not have planning consequences of sufficient significance to make the amalgamation a material change of use. That is a planning judgment on the facts, not a rule that the loss of one home can never be development
2. Policy interpretation: neither the Lambeth Local Plan nor the London Plan actually forbids combining homes, they simply count the result as a housing loss, which mattered here because the floorspace did not change
3. Planning judgment: whether losing one home significantly affects the borough’s housing supply is a judgment for the inspector on the facts of the area, and the court would not interfere with a rational one
4. Previous decisions: Lambeth complained that the inspector had ignored earlier appeal decisions refusing similar schemes, but the court held he was not obliged to consider decisions nobody had put in front of him

 

Read the full judgment at London Borough of Lambeth v Secretary of State for Levelling Up, Housing and Communities [2024] EWHC 1391 (Admin)

A useful 2026 Camden appeal shows the same fact-and-degree approach from a different angle. At 47 Dartmouth Park Road, an internal staircase and dual-lockable door physically connected two self-contained homes, but both retained their own kitchens, bathrooms, entrances and independent living facilities. The Inspector found that the physical connection did not, on the evidence, amalgamate the two planning units into one dwelling. Future occupation as a single home was a separate question rather than something to assume from the works alone. Our Camden flat amalgamation report explains the appeal; you can also read the Inspector’s decision.

An earlier Kensington & Chelsea certificate appeal also rejected the idea that an amalgamation is automatically lawful merely because the resulting accommodation remains within Use Class C3. The same-use-class provision does not answer the separate question whether losing a dwelling has planning consequences significant enough to amount to a material change of use.

Local housing policy can be decisive, and there is no single “London rule”. The planning consequences of losing homes must be assessed in the context of the authority’s evidence and development plan.

Current policies illustrate the difference. The Royal Borough of Kensington & Chelsea’s 2024 Local Plan, Policy HO1, expressly protects existing market homes by not allowing the amalgamation of existing self-contained C3 homes. Richmond-upon-Thames adopted a new Local Plan in October 2025 with Policy 14 addressing loss of housing. Camden takes a different approach: Policy H3 accepts a net loss of one home where two dwellings are amalgamated into one, while generally resisting larger net losses unless one of its stated exceptions applies.

The Lambeth judgment confirms that policy is relevant to the material-change-of-use assessment, but it is not a simple tick-box exercise. Earlier certificate and appeal decisions also show that significant planning consequences can be relevant even where a policy does not expressly prohibit the particular amalgamation. And this is not only a London issue: a South Hams appeal reached the conclusion that an amalgamation there was material development.

A 2026 Camden LDC appeal provides a useful modern example of the factual side of this test. An internal staircase and lockable connecting door did not, on the evidence, amalgamate two self-contained homes where both retained their own kitchens, bathrooms and entrances. The physical connection was relevant evidence, but it did not decide the planning-unit question by itself. Read appeal APP/X5210/X/25/3372706.

Read the current local plan before you start work. If the position is genuinely uncertain, a certificate of lawfulness of proposed use may be the cleanest way to establish whether planning permission is required. If an application is needed, Planning Geek can provide a fee proposal.

If the amalgamation has already taken place and you want formal confirmation that the resulting use is lawful, the appropriate route is normally a certificate of lawfulness for the existing use or development. Before carrying out a proposed amalgamation, use the proposed certificate route where appropriate.

If the flats are within a listed building, listed building consent is required for internal or external alteration works where they would affect the building’s character as a building of special architectural or historic interest; it is not triggered by every internal alteration automatically. In a conservation area, removing or altering an external entrance can also raise separate planning and heritage issues, so check the particular works rather than assuming the amalgamation question settles them.

 

Combine three flats into one and the answer changes

 

The Lambeth case involved the net loss of one home, but the important point is not the number one. The Inspector assessed the planning consequences in Lambeth’s housing and policy context and concluded they were not significant enough to make the change material. The High Court held that he was entitled to reach that planning judgment.

There is no statutory rule that two homes into one is acceptable but three into one is development. A larger net loss can plainly make the planning consequences more significant, but the answer still depends on the facts, the scale of the loss and the development-plan policy applying in that authority.

If you want to turn three or more homes into fewer units, do not assume either that a certificate will succeed or that a full planning application is automatically required. Check the local housing-loss policy first and assess whether the proposed amalgamation amounts to a material change of use on the evidence.

 

Councils that limit how many homes you can combine

 

Councils take quite different approaches to amalgamation. Some policies resist the loss of even one self-contained home; others expressly allow two homes to become one but resist a larger net loss; some build in exceptions for family-sized housing, affordable housing or sub-standard existing units. That is why the current local plan matters more than a generic rule of thumb.

The exceptions are the part people miss, because they tend to be about where you are rather than what you are building. A council may accept losing homes to create one big family house, but only in the particular wards where big homes are already scarce. One side of a ward boundary gets permission and the other side gets a refusal.

Camden is the clearest example. Its policy resists the loss of two or more homes unless the scheme creates a large home in a part of the borough with few large homes, adapts affordable homes to the sizes most needed, or enlarges homes that fall below the space standards. The council treats the first of those as meaning four named wards and nowhere else.

Two appeals show how hard that is to shift. At 37 Estelle Road an owner wanted three flats back as one house, and argued that his own street was almost all flats so large homes were scarce there. The inspector dismissed the appeal in January 2023, saying he could not be sure one street reflected the whole ward, and that the council’s published ward list was recent enough and specific enough to rely on. At 33 Ferncroft Avenue the owner of a listed building wanted four flats back as one home, with real heritage gains that the council’s own conservation officer supported. That appeal was dismissed too, in July 2025, because losing three homes outweighed the benefits.

Read the council’s policy, and any ward list sitting behind it, before you buy rather than after you apply.

 

What it costs, and what happens if you are refused

 

If you do need permission, the application carries the nationally prescribed fee. A certificate of lawfulness has its own fee, but it only helps where combining the homes genuinely is not development in the first place; it is not an alternative route to a planning permission. See our planning fees page for the current position.

If the council refuses, you can appeal. One change matters a great deal here. Most section 78 appeals relating to applications made on or after 1st April 2026 initially follow the Part 1 written-representations procedure. Under that procedure the appellant cannot introduce evidence at appeal that was not previously considered by the LPA when it determined the application. The Planning Inspectorate can transfer a case to Part 2, a hearing or an inquiry where appropriate, but the practical lesson is the same: if you need to make a housing-need, policy or factual case for amalgamation, put it properly before the council at application stage.

It is also worth asking whether you need to go all the way. Where a plan allows the loss of one home but not two, turning three flats into two homes can be permitted where three into one is refused. You keep most of the space and you keep the council on side.

 

 

 

Page Updated: 20th September 2026

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