Flats and permitted development: what is and is not available

Flats permitted development rights are far narrower than most owners expect, and the reason is a single definition. The General Permitted Development Order 2015 defines a dwellinghouse so that it does not include a building containing one or more flats, or a flat contained within such a building. Schedule 2 Part 1, which carries all the familiar householder rights for extensions, outbuildings, roof alterations and porches, applies only to dwellinghouses. So none of it is available to a flat or to the building that contains it.

That is the whole answer to most questions on this subject. What is left is working out which other parts of the Order still apply, and what to do where none does.

Why Part 1 does not apply

Part 1 is headed development within the curtilage of a dwellinghouse. Every class in it, from Class A rear and side extensions through to Class H satellite dishes, is drafted around that word. The 4 m and 3 m rear extension depths, the 50 per cent curtilage rule for outbuildings, the roof volume allowances: all of them are dwellinghouse rights.

A ground floor flat with its own front door, its own garden and no shared parts is still a flat, because the building contains more than one dwelling. Ownership makes no difference. Freehold ownership of a converted flat does not convert it into a dwellinghouse for the purposes of the Order.

Where the curtilage question arises for a house rather than a flat, the 50 per cent curtilage rule for garden outbuildings sets out how that allowance is measured.

The definition in the Order, read carefully

The interpretation provision excludes a building containing one or more flats and a flat within such a building. It does not exclude a building that merely has a flat somewhere nearby, and it does not exclude a house with an annexe that remains part of the same planning unit.

Two practical consequences follow. A house that has been divided into two self-contained flats loses Part 1 rights for both units from the moment the division is lawfully made. And a house with a lawful self-contained annexe may or may not have lost them, depending on whether the annexe is a separate dwelling or remains ancillary, which is a question of fact and degree rather than of labels.

A lawful development certificate is the only formal way to confirm that works or a use are lawful, and on this particular question it is money well spent before anyone starts building.

Maisonettes and converted houses

Maisonettes are flats. The arrangement over two floors, with its own street door and its own stair, feels like a house and is not one, because the building contains more than one dwelling.

Converted Victorian and Edwardian houses are where most disputes arise. An upper flat owner who wants a rear dormer, a lower flat owner who wants a conservatory, and a freeholder who owns the structure all discover the same thing at once. Each of those works needs planning permission, and each also needs the agreement of whoever owns the relevant part of the building.

What rights do apply

Each of those classes has its own limitations, conditions and exclusions, including on designated land, and several require prior approval rather than being automatic. Read the class text rather than a summary, including the conditions at the end of each class, which is where most of the traps sit.

The commercial to residential route is the one landlords ask about most, and the vacancy and continuous use conditions under Class MA are the gateway test for it.

Communal areas, ownership and who may apply

Anyone may apply for planning permission on land they do not own. What they must do is serve notice on the owner and complete the correct ownership certificate with the application under the Development Management Procedure Order 2015.

For a flat that means identifying who owns the roof, the external walls, the forecourt and the rear garden. In a converted house the lease often demises the rear garden to the ground floor flat and leaves the roof with the freeholder. Get the title plans before drafting the certificate, because an incorrect certificate can invalidate a permission.

A Planning Statement should set out the ownership position plainly where the works affect communal parts, since the case officer will otherwise raise it as a validation query.

Leasehold consent is a separate matter

Planning permission does not override the lease. Most residential leases require the landlord's written consent for alterations, and many prohibit structural alterations outright. Consent for improvements is subject to statutory controls on unreasonable refusal in some circumstances, but the starting point is the lease itself.

Treat the two tracks as parallel. Obtaining permission for a loft conversion in a converted house, and only then discovering that the roof space is not demised to the flat, is a common and expensive sequence.

Rooflights, windows and cladding

Works affecting only the interior of a building, or which do not materially affect its external appearance, are not development at all under the 1990 Act. A like-for-like window replacement in matching materials usually falls within that, and an internal reconfiguration almost always does.

A new rooflight, a new window opening, a change of window material that reads differently from the street, external cladding or insulation, and a replacement front door of a different design all materially affect external appearance and so need permission. In a conservation area the threshold for what reads as material is lower, and Article 4 directions may remove rights that would otherwise exist.

Routes where no right exists

Three options, in order of cost. A prior approval application where the works fall within Part 20 or Part 3 and the conditions are met. A full planning application, which for a single flat extension is a householder-scale exercise in all but name and fee. Or a lawful development certificate where you believe the works are not development at all.

Support a full application with drawings that show the whole building rather than just your flat, a Design and Access Statement where the authority's validation list requires one, and evidence that neighbouring flats have been considered on daylight and overlooking. And start the leasehold consent conversation on the same day you start the planning one, because that is the track that usually runs longest.

To see which documents your application needs, enter your postcode on PlanScope.

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.