Flat amalgamation is not decided simply by asking whether two homes have been physically connected. A Camden lawful development certificate appeal shows how the actual use, facilities and relationship between the units still matter.
The proposal at 47 Dartmouth Park Road was for an internal staircase and lockable connecting door between a lower-ground-floor flat and the maisonette above. Both homes would retain their own kitchens, bathrooms, entrances and other living accommodation.
Appeal APP/X5210/X/25/3372706 was allowed on 18th September 2026 and a certificate was issued. A separate application for appeal costs was refused.
Two self-contained homes would remain
The building contains a two-bedroom garden flat at lower-ground-floor level and a separate three-storey, five-bedroom maisonette above. Each has its own external entrance.
The proposal was to install an internal staircase and a door connecting the two. The door was designed so that it could be locked from both sides.
The appellant occupied the maisonette and his mother-in-law occupied the garden flat. The explanation was straightforward: the connection would allow easier family movement between the homes without requiring someone to go outside, while each household could continue to live independently.
Internal building work was not itself development
Section 55 of the Town and Country Planning Act 1990 defines development. It also excludes building work that affects only the interior of a building from the meaning of development, subject to exceptions that were not relevant here.
That meant the physical staircase and door were not operational development requiring planning permission.
Camden’s concern was different. The council considered that making the connection would in practice amalgamate the two flats into one dwelling and therefore produce a material change of use.
Why the Inspector rejected flat amalgamation on the evidence
The Act expressly says that changing one dwelling into two or more dwellings is a material change of use. It does not contain an equivalent rule saying that combining two dwellings into one is always a material change.
Whether amalgamation amounts to a material change of use is therefore a matter of fact and degree. The character of the use and the planning consequences both matter.
Here, the application did not propose to remove either kitchen, bathroom or entrance. Both units remained capable of independent occupation. The lockable connecting door also meant that neither household automatically gained unrestricted access to the other home.
The Inspector concluded that the physical connection did not, on the evidence before him, change the character of the two planning units so that they became a single dwelling.
Future occupation was a different question
Camden was concerned that the door might later be left open or future occupiers might use the building as a single home.
The Inspector treated that as speculative. A lawful development certificate for the proposed works had to be decided on the proposal and evidence before him. If a later pattern of occupation produced a material change of use, that would be a separate planning question and could be investigated at that time.
This is why the decision should not be read as saying that a staircase or connecting door can never contribute to amalgamation. Physical changes are part of the factual picture, but they do not replace the planning-unit and material-change-of-use analysis.
Why Camden’s costs decision went the other way
The appellant sought a full award of appeal costs, arguing that Camden had wrongly treated the works as amalgamation and persisted despite legal advice and decisions elsewhere.
The Inspector refused costs. Camden was entitled to reach its own planning judgment on a fact-and-degree question. Advice obtained by the appellant and decisions by other councils did not bind Camden, and the fact that the Inspector ultimately disagreed did not make the council’s behaviour unreasonable.
What this flat amalgamation appeal means in practice
A physical connection between dwellings is evidence, not a legal shortcut. Ask what facilities remain, how the homes can be occupied, whether each retains practical independence, what the planning units are and whether the character of the use has materially changed.
Planning Geek’s existing guide to combining houses and flats explains the wider case law, including the significance of housing-loss policies. Our lawful development certificate guide explains the certificate process.
Appeal decision: APP/X5210/X/25/3372706, 47 Dartmouth Park Road
Costs decision: costs application relating to APP/X5210/X/25/3372706
Report published: 20th September 2026
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