Annexes for a dependent relative and the planning unit
An annexe for a relative is lawful as part of the house while it remains ancillary. Access, kitchen provision, garden division and separate services decide whether a second planning unit has been created.
An annexe for a dependent relative stays lawful as part of your house for as long as it remains ancillary to it. The moment it can function as an independent home, the council is entitled to treat it as a separate dwelling, which changes the application, the levy position and what happens when your relative no longer needs it. Annexe dependent relative planning cases turn almost entirely on one question: has a second planning unit been created, or is there still one dwelling with an extra set of rooms?
Ancillary use against a separate dwelling
A dwellinghouse is identified by its ability to provide the facilities required for day-to-day private domestic existence. That formulation comes from Gravesham Borough Council v Secretary of State for the Environment [1982] and it is still the starting point. Cooking, washing, sleeping and living, in a unit that someone could occupy without needing anyone else's space.
An annexe that provides all four and is physically separate, separately accessed and capable of separate disposal is a dwelling, whatever the family intends. An annexe that shares the main house's entrance, has no separate garden, relies on the main house's utility supplies and is connected internally is part of the single dwelling, even if it has a bedroom, a bathroom and a kettle.
Intention is the weakest factor in the analysis. Councils have heard it many times, and it carries almost no weight against a plan that shows a self-contained flat.
The links that decide it
Officers assess physical and functional separation together. These are the features that move the answer.
| Feature | Points towards ancillary | Points towards a separate dwelling |
|---|---|---|
| Access | Shared front door or internal connecting door | Own street door, own path, own gate |
| Kitchen | Kitchenette, or no cooking facilities | Full kitchen with the usual provision |
| Garden | Shared, undivided | Fenced and allocated to the annexe |
| Parking | Shared driveway | Separate allocated space |
| Services | Supplied and billed through the main house | Separate supplies and separate billing |
| Postal address | Same address | Separate numbering applied for |
| Disposal | Could not be sold separately | Could be sold or let on its own |
No single row settles it. An internal connecting door between the annexe and the house is the strongest single indicator of ancillary use, and it is the cheapest change to make at design stage. A door that is kept locked still counts, provided it exists and is usable.
Physical proximity matters too. An annexe formed by converting part of the house or by a rear extension is far easier to argue as ancillary than a detached building at the bottom of the garden, which is covered in our note on why front extensions are harder than rear ones for a related reason: siting is read as a statement about how the space will function.
Which application you need
Internal reorganisation of a house to form an annexe is not development at all, because there is no material change of use and no building operation requiring consent. Knocking two rooms together and adding a shower room for a parent needs no planning permission.
An extension to form an annexe may be permitted development under Class A of Part 1, provided the extension stays within the dimensional limits and the enlarged building remains a single dwellinghouse. Where the result would be a self-contained unit, Class A does not apply, because the right permits enlargement of a dwellinghouse rather than the creation of a second one.
A detached annexe is the difficult case. Class E of Part 1 covers only buildings incidental to the enjoyment of the dwellinghouse, and sleeping accommodation is treated as primary rather than incidental, so a detached annexe with a bedroom falls outside it. That means a householder or full application, with a short Planning Statement addressing the ancillary relationship directly rather than burying it.
Within the curtilage of a listed building, add listed building consent and a Heritage Statement to the list, and expect the conversion of an outbuilding to be assessed on its effect on the building's significance.
Converting an outbuilding
Converting an existing garage, stable or barn in the curtilage into an annexe is the most common route and the one most likely to be refused. Three issues recur.
The building's existing lawful use is the first. An outbuilding erected under Class E as incidental accommodation cannot simply become sleeping accommodation, because that is a material change of use of the building. A garage built as part of the original house has the same problem.
The second is residential amenity and separation. A building 20 metres from the house, with its own door facing the lane and a window overlooking a neighbour, reads as a cottage. Officers will say so.
The third is what the building is like to live in. Head height, daylight, insulation, means of escape and ventilation all become Building Regulations questions under Approved Documents B, F, L and M, and heating usually means an air source heat pump, whose own permitted development conditions are set out in our note on air source heat pumps and the conditions attached.
Conditions, council tax and the levy
Where permission is granted, expect a condition. The usual wording restricts occupation of the annexe to use ancillary to the main dwelling and prevents it being occupied or disposed of as a separate dwelling. Some authorities go further and restrict occupation to a member of the household or a dependent relative, which is harder to justify against the tests for conditions and harder still to enforce.
A condition preventing separate disposal is the one worth agreeing to, because it survives a change of occupier. A condition naming a particular relative does not, and it creates a problem for you the day that person dies or moves into care.
On the levy, the Community Infrastructure Levy Regulations 2010 provide an exemption for residential annexes. It is available where the annexe is within the curtilage of the main dwelling, the main dwelling is the claimant's sole or main residence, and the annexe is not a new dwelling for levy purposes in its own right. The exemption has to be claimed, granted and a commencement notice served before work starts. Miss that sequence and the exemption is lost with no discretion to restore it.
Council tax runs on different rules. The Valuation Office Agency may band a self-contained annexe separately, and a separate banding is sometimes produced by objectors as evidence of a separate dwelling. The tests are not the same, and a separate band is not determinative in planning, but it is awkward to explain away.
Illustrative example: a 1930s semi where the family converts the integral garage and adds a 3 metre rear extension to form a ground-floor annexe for a parent, with a shower room, a kitchenette with no oven, a connecting door to the hall and no separate external door. No garden division, shared drive, services through the main house. The council accepts it as ancillary and conditions it against separate occupation. The annexe exemption from the levy is claimed before commencement. The details are illustrative rather than drawn from a real case.
What happens when the relative leaves
Nothing automatic. The permission and its condition remain, so the annexe stays part of the single dwelling and can be used by the household as extra bedrooms, a study or a guest suite.
What you cannot do is let it. Separate occupation by someone outside the household, on a tenancy, is a material change of use to two dwellings and a breach of the condition. If that is the long-term plan, apply for it properly at the outset or apply later under section 73 to vary the condition, with the evidence a fresh dwelling application would need: parking, amenity space, separate bin storage, daylight and the policy position on subdivision in that area.
Three documents are worth keeping from the start: the approved plans showing the internal connection, the levy exemption paperwork and commencement notice, and a note of the services arrangement. They are what you will be asked for if the council receives a complaint in five years' time.
Enter your postcode on PlanScope to see which documents an annexe application in your area is likely to need.
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.
Frequently asked questions
Does an annexe need planning permission?
Internal reorganisation of a house to form an annexe is not development. An extension to form one may be permitted development under Class A of Part 1 provided the result remains a single dwellinghouse. A detached annexe with sleeping accommodation falls outside Class E, because sleeping accommodation is not incidental, so it needs an application.
What makes an annexe a separate dwelling?
The ability to provide the facilities required for day-to-day private domestic existence independently, a formulation drawn from Gravesham Borough Council v Secretary of State for the Environment [1982]. A full kitchen, its own external door, a fenced garden, separate parking, its own utility supplies and the ability to be sold separately all point that way.
Does an internal connecting door help?
Yes, it is the single strongest indicator of ancillary use and the cheapest change to make at design stage. A door that is kept locked still counts, provided it exists and is usable. Combine it with shared services, an undivided garden and a shared drive and the ancillary case becomes straightforward.
Is an annexe exempt from the Community Infrastructure Levy?
The Community Infrastructure Levy Regulations 2010 provide a residential annex exemption where the annexe is within the curtilage of the main dwelling and that dwelling is the claimant's sole or main residence. It must be claimed, granted, and a commencement notice served before work starts. Missing that sequence loses the exemption with no discretion to restore it.
What happens when the relative no longer needs the annexe?
Nothing automatic. The permission and its condition stand, so the space stays part of the single dwelling and the household can use it as bedrooms, a study or a guest suite. Letting it to someone outside the household is a material change of use to two dwellings and a breach of the condition.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.