Annexe planning policy: ancillary use and the condition

An annexe is either part of your house or it is a separate dwelling, and every question about annexe planning permission policy follows from that one distinction. If the accommodation is ancillary to the main house, it forms part of the same planning unit and the council can approve it as an extension or outbuilding. If it can function independently, it is a new dwelling, and it is assessed against the local plan's policies on new housing, which in a village or the countryside may mean refusal.

Councils control the difference with a condition. Understanding what that condition does, and what it stops you doing later, matters more than the design.

Ancillary annexe or separate dwelling

The test comes from the planning unit case law, and Burdle v Secretary of State for the Environment is the decision officers still work from. The question is whether the annexe has a separate and independent use, judged on the facts rather than on what the application form says.

Officers weigh a familiar set of factors:

• Whether there is internal access between the annexe and the main house, or only a separate front door.
• Whether the annexe has its own kitchen, bathroom, utilities and postal address.
• Whether the garden and parking are shared or physically divided by a fence or wall.
• The distance between the annexe and the host dwelling.
• Whether the occupants share meals, care arrangements or day-to-day life with the household.

No single factor decides it. A self-contained kitchen does not automatically make a separate dwelling, and an internal connecting door does not automatically prevent one. What matters is whether the unit could be occupied by someone with no connection to the main house without any physical change.

The local plan policy usually mirrors that. Most authorities carry an annexe or ancillary accommodation policy asking for subordinate scale, a functional relationship with the main house, and no permanent physical separation. Some also carry a neighbourhood plan policy on the same subject, and those sit in the development plan too, as our note on when neighbourhood plans outrank the local plan explains.

Where permitted development stops

Class E of Schedule 2 Part 1 of the General Permitted Development Order 2015 allows outbuildings within the curtilage of a house, but only where they are required for a purpose incidental to the enjoyment of the dwellinghouse as such. Incidental is a narrower word than ancillary, and it has been read as excluding primary living accommodation.

A garden building with a bedroom, kitchen and bathroom is therefore very unlikely to be permitted development, whatever the supplier's brochure says. A gym, a home office, a store or a garage is a different matter.

An annexe formed inside the house, or in an extension built under Class A, can be permitted development, because the use stays residential and no separate planning unit is created. The moment the accommodation becomes independent, the change of use falls outside Class A altogether.

Where you want certainty before spending money, a lawful development certificate for proposed works is the mechanism, and our note on proving works are lawful sets out the evidence that persuades. Building a garden annexe on the assumption that it is incidental is a common and expensive mistake.

The condition that ties the annexe to the house

Where permission is granted, expect a condition along the lines that the annexe shall be used only for purposes ancillary to the main dwelling and shall not be occupied as a separate dwelling. Some councils go further and tie occupation to a dependent relative or to a member of the household.

Three things follow.

Letting the annexe out on an assured shorthold tenancy breaches the condition, and breach of condition is enforceable. The council can serve a breach of condition notice, against which there is no appeal to the Planning Inspectorate.

Selling the annexe separately is not possible while the condition stands, which affects mortgageability and value. Lenders ask about it.

A condition can be varied or removed by an application under section 73 of the Town and Country Planning Act 1990, but that application reopens the merits. If the site is one where a new dwelling would be refused, removing the tie is unlikely to succeed.

A personal condition, naming an individual occupier, has to be justified under the six tests in national guidance and is used less often than it once was. Where one is proposed, ask what happens when that person no longer lives there.

Kitchens, access and independent facilities

The design decisions that shape the planning judgement are made early, and a few are worth getting right.

Keep an internal connection between the annexe and the house wherever the layout allows. A lockable door is fine. A shared entrance hall is better.

Share the garden. A fence dividing the plot into two curtilages is the single most damaging feature on an annexe drawing, because it shows physical separation.

Share the parking and the bin store, and do not create a second vehicle access.

A kitchen is not fatal, and for an elderly relative it is often the point of the annexe. Describe it as a kitchenette, size it accordingly, and explain the care arrangement in the supporting statement.

Council tax and utilities are treated as evidence of separate occupation, so a separate supply and a separate band will be noticed if the use is ever questioned. That is a matter for the council's own records rather than for the planning application, and it is worth checking the position before installing anything.

Green Belt and countryside annexes

In the Green Belt, the exceptions to inappropriate development include the extension or alteration of a building, provided the addition is not disproportionate to the original building. An annexe attached to the house can fall within that exception. A detached annexe is a new building, and new buildings in the Green Belt are inappropriate unless a specific exception applies, which means very special circumstances have to be shown.

In open countryside outside the Green Belt, the constraint is the policy against isolated new homes. An annexe that is properly ancillary avoids that policy because it is not a new home. One that reads as an independent dwelling runs straight into it.

Both positions turn on the same ancillary judgement, which is why the description of development and the drawings carry so much weight in rural applications.

What to submit and how to describe it

Describe the proposal as an annexe ancillary to the existing dwelling, name the host dwelling, and keep that wording consistent across the form, the drawings and the statement.

1. Existing and proposed floor plans showing the internal connection and the shared entrance.
2. A site plan showing one curtilage, shared garden, shared parking and no dividing fence.
3. Elevations showing subordinate scale and matching materials.
4. A short supporting statement explaining who the annexe is for, the care or family arrangement, and how the household will function as one unit. A Planning Statement is the place for the policy comparison where the site is in the Green Belt or the countryside.
5. A draft condition you are content with, offered up front.

One financial point is worth checking early. The Community Infrastructure Levy regulations contain an exemption for a residential annexe within the curtilage of a main dwelling, and it has to be claimed and granted before development starts. Missing that step can be costly, and the claim is straightforward if made in time.

If you want to see which supporting documents your site's constraints are likely to trigger, 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.