Why flats and maisonettes have no Part 1 permitted development

Flats have no permitted development rights under Part 1 of the GPDO, and the reason is a definition rather than a policy. Schedule 2 Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015 grants rights for development within the curtilage of a dwellinghouse, and article 2(1) of the same Order says that dwellinghouse does not include a building containing one or more flats, or a flat contained within such a building.

So the rear extension, the loft dormer, the garden room and the hard surfacing that a neighbouring terraced house can build without an application all require planning permission when the property is a flat or a maisonette.

The definition that does the work

A flat, in the Order, is a separate and self-contained set of premises constructed or adapted for use as a dwelling and forming part of a building from which it is divided horizontally. The word horizontally is the whole test.

A terraced house divided from its neighbours by vertical party walls is a dwellinghouse, however narrow. A ground floor maisonette with another maisonette above it is a flat, however generous, and so is the upper one. A house converted into two units with one above the other stopped being a dwellinghouse on the day the conversion happened, and Part 1 rights went with it.

Note the second limb. The building containing flats is also excluded, so the freeholder of a converted terrace cannot use Part 1 either. Nobody in the building holds those rights.

What that removes

The list is long, and it covers most of what householders think of as permitted development:

• Class A rear and side extensions
• Class AA additional storeys on a dwellinghouse
• Class B and Class C roof alterations, including dormers and rooflights
• Class D porches
• Class E outbuildings, garden rooms and swimming pools
• Class F hard surfaces within the curtilage
• Class G flues for biomass or combined heat and power
• Class H microwave antennas within the curtilage of a dwellinghouse

Every one of those needs planning permission on a flat. A Planning Statement becomes worth preparing for what would otherwise have been a permitted development project, because the application is now assessed against local plan policy on amenity, design and, in a converted building, the effect on the other flats.

What still applies to a building containing flats

The position is not as bleak as it first looks. Several Parts of Schedule 2 operate on buildings or land generally rather than on dwellinghouses, and they survive.

Part 2 covers gates, fences and walls, the painting of the exterior, and the electric vehicle charging outlets and upstands in Classes D and E, which apply to areas lawfully used for off-street parking rather than to dwellinghouses.

Part 14 includes rights for solar equipment and for microwave antennas that are expressed to apply to a block of flats as well as a dwellinghouse. Read the Class carefully, because the limits differ from the dwellinghouse version.

Part 3 change of use rights apply to the building by reference to its use class, so a ground floor commercial unit under flats keeps whatever Part 3 rights that use attracts.

Part 16 covers electronic communications equipment, and Part 11 covers demolition subject to prior approval.

Part 20 upward extensions: the real exception

Part 20 is where a block of flats gains something a house does not. Class A permits the construction of new dwellinghouses on top of a detached purpose-built block of flats of three or more storeys, subject to limits on the number of additional storeys, the resulting height, the age of the existing building and a list of excluded locations.

It is not a light-touch route. Prior approval is required and the matters for approval are extensive, covering transport and highways impacts, air traffic and defence safeguarding, contamination and flood risk, external appearance, provision of adequate natural light to all habitable rooms, impact on the amenity of the existing building and neighbouring premises, and construction management.

Two practical points. Structural capacity governs everything, and a Structural Survey of the existing frame and foundations should come before the design rather than after prior approval. And the natural light requirement is a genuine constraint, since a new top storey commonly deepens the plan or introduces single-aspect units.

Related Classes in Part 20 cover upward extension of terrace buildings and of buildings in commercial or mixed use, and Class ZA covers demolition and rebuild. Each has its own qualifying conditions and none of them is a substitute for reading the Class.

Leasehold consent is a separate hurdle

Planning permission does not give you the right to build. For most flats the physical works also need the freeholder's consent under the lease, and the lease usually prohibits alterations to the structure, the exterior and the common parts outright.

Where a management company or a residents' association holds the freehold, works to the structure may trigger consultation obligations with other leaseholders before costs can be recovered. Where the works affect a party structure, the Party Wall etc. Act 1996 procedure runs alongside and independently of both planning and the lease.

Sequence it as consent, then design, then permission, then Building Regulations. Applicants who obtain permission first and discover the lease bars the works have bought an expensive piece of paper.

Internal works and the conversion trap

Works affecting only the interior of a building, or which do not materially affect its external appearance, are not development under section 55(2)(a) of the Town and Country Planning Act 1990. So reconfiguring a flat internally is usually outside planning control, subject to the lease and to Building Regulations.

Subdividing one flat into two is a different matter. That is a material change of use creating an additional dwelling, it needs planning permission, and it is assessed against space standards, amenity, refuse storage, cycle parking and parking stress. Councils in high-demand areas resist it firmly.

Combining two flats into one also needs permission in most cases, because it results in the loss of a dwelling.

Confirming the position before you build

Where there is any doubt about whether a property is a dwellinghouse or a flat for GPDO purposes, a Lawful Development Certificate for proposed development under section 192 of the 1990 Act is the only formal way to confirm that works would be lawful. It is charged at half the equivalent application fee and settles the point in writing.

Illustrative example: a two-storey Victorian terrace converted into upper and lower maisonettes in the 1980s. The lower maisonette owner wants a single-storey rear extension across the full width. It looks identical to the extension the neighbouring unconverted house built without an application. It is not. The property is a flat, Part 1 does not apply, and the works need planning permission, the freeholder's consent under the lease, and a party wall award with the adjoining terrace.

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This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.