Permitted development after a house is split into flats

Convert a house into two flats and the whole building loses its householder permitted development rights. Schedule 2 Part 1 of the GPDO 2015 applies only to a dwellinghouse, and the Order's interpretation excludes a building containing one or more flats, and a flat within such a building, from that term. So no rear extension under Class A, no loft dormer under Class B, no garden outbuilding under Class E and no hard surface under Class F, for either flat or for the freeholder.

Landlords discover this at the wrong moment, usually after a tenant has asked for a bike store or an agent has suggested a loft room. The rights do not come back until the building is lawfully a single dwellinghouse again.

Why Part 1 applies to dwellinghouses only

Part 1 is titled development within the curtilage of a dwellinghouse, and every class in it is framed around "the dwellinghouse". The Order defines the term so that it does not include a building containing one or more flats, or a flat contained within such a building.

The logic is straightforward once you see it. Part 1 rights assume one household controlling one building and its garden. A building in multiple occupation has shared structure, shared access and competing interests, and the national grant of rights would be unworkable.

The trigger is the lawful conversion, not the physical appearance. A Victorian villa that looks identical to its neighbour has no Part 1 rights if it was lawfully converted to flats, while the neighbour next door retains them in full. That asymmetry across a party wall is the single most common source of confusion in a terrace.

One further point to settle early: a maisonette is a flat for these purposes. Having its own front door at ground level and its own garden makes no difference if the building contains more than one dwelling.

What a flat retains and what it loses

The loss is specific to Part 1. Other Parts of Schedule 2 are drafted differently, and several of them expressly cover blocks of flats.

Check the wording of the specific class each time rather than relying on a general rule. The renewables and charging classes have been amended repeatedly, and the limits on siting, size and noise differ between the dwellinghouse and block of flats versions.

Works to a building containing flats

So a bike store, a bin enclosure, a rear extension to the ground-floor flat or a dormer to the top-floor flat all need planning permission. That is a householder application in form only. The fee category depends on the nature of the works, and the authority will assess the proposal against the same design and amenity policies it would apply to any alteration.

Two features of these applications are worth anticipating. Authorities frequently resist extensions to one flat within a converted building where the effect is to take garden space that serves the other flat, so the application needs to show the amenity space remaining for each unit against any adopted standard. And a dormer or roof alteration raises the question of who owns the roof space, which is a lease question rather than a planning one but which the authority may raise through the ownership certificate.

Where the building is in a conservation area or is listed, add the heritage assessment, and remember that the loss of Part 1 rights means you cannot fall back on the argument that the works would have been permitted anyway.

Communal areas and the freeholder position

Ownership and planning run on separate tracks, and both have to be satisfied.

The applicant must serve the correct ownership certificate. Certificate A applies where the applicant owns the whole of the application site. Where part of the site is owned by someone else, including the freeholder or another leaseholder, Certificate B and notice to that owner is required, and an owner for these purposes includes a person with a leasehold interest with at least seven years unexpired. Getting this wrong is a validation problem and, if discovered later, can undermine the permission.

Separately, the lease will usually require the freeholder's consent for alterations, and the works may need a licence to alter. A planning permission confers no right to carry out works the lease forbids. Where the building has a residents' management company, expect that process to take longer than the planning application.

For a rear extension to a ground-floor flat, the practical sequence is to agree the lease position first, then apply, because an approved scheme the freeholder will not license is worthless. Our note on the 50 per cent curtilage rule for garden outbuildings explains the test that applies instead once a building is back in single occupation.

Rights under other Parts that survive

Several useful routes remain open.

1. Part 2 covers gates, fences, walls and means of enclosure, with the usual limits of 1m where adjacent to a highway used by vehicular traffic and 2m elsewhere.
2. Part 2 also covers electric vehicle charging points, including classes framed around the curtilage of a block of flats, subject to size and siting conditions.
3. Part 14 covers microgeneration, with classes addressing solar photovoltaics and solar thermal on a block of flats and air source heat pumps, each with its own conditions on siting, scale and noise.
4. Part 20 provides routes for additional storeys on existing buildings, including blocks of flats, by prior approval rather than full application, subject to substantial limits and conditions.
5. Part 3 may be relevant where a change of use is proposed rather than building work.

Part 20 deserves a closer look on any converted building with a flat roof or a shallow pitch. It is procedurally demanding and the prior approval considerations are extensive, but it is the route that can add value without a full application. Our note on Class Q structural works and what is reasonably necessary shows how tightly the Order's limits on building operations are read in the comparable prior approval classes.

Where a building reverts to a single dwelling

Combining two flats back into one house is itself a change of use that normally needs planning permission, because the number of planning units changes. Authorities in areas with pressure on small units sometimes resist the loss of a dwelling, and a local plan policy on the retention of housing stock may apply.

Once the building is lawfully a single dwellinghouse, Part 1 rights apply to it again. The coverage test under A.1(b) and E.1(b) then measures the curtilage and the buildings within it as they stand at that point, so extensions built under planning permission during the flat period count towards the 50 per cent, and the original dwellinghouse is still the building as first built or as it stood on 1 July 1948.

That sequencing is worth modelling before you amalgamate. A building that has gained two extensions by application while in flats may revert to a single dwelling with very little Part 1 headroom left.

Checking the lawful configuration first

Before advising on rights, establish what the building lawfully is. The questions to answer:

• what does the planning history show, and is there a permission for conversion to flats
• if there is no permission, has the conversion become immune from enforcement, and on what evidence
• how many separate dwellings exist as a matter of fact, with separate access, facilities and council tax entries
• do the titles and leases match the physical arrangement
• are Part 1 rights removed or restricted by condition on any relevant permission, which matters for the reversion scenario
• is there an Article 4 direction in force over the area

An unlawful conversion is the awkward case. The building may be a dwellinghouse in planning terms while functioning as flats, which means Part 1 rights exist on paper but relying on them risks compounding a breach. A certificate of lawful development under section 191 of the Town and Country Planning Act 1990 is the only formal way to confirm the existing lawful use, and it is the right first step before any works are designed.

Where an application is needed, a short planning statement setting out the lawful configuration, the policy position on amenity space and the design response is usually enough for a minor alteration. Our notes on Class MA vacancy and continuous use conditions and garden offices and the separate planning unit problem cover adjacent traps for conversion investors.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.