Annexe for a relative: planning conditions and council tax

An annexe for a parent or an adult child is granted, in most councils, subject to a condition that it is used only for purposes ancillary to the main house and not as a separate dwelling. That single condition governs almost everything that follows: whether you can let it out, whether the Valuation Office Agency bands it separately, and whether the property can ever be split.

The planning question, the council tax question and the design question are the same question wearing different clothes. Is this one home or two.

This is general guidance rather than legal advice. Check the position with your local planning authority and, for the tax, with the Valuation Office Agency.

The condition councils use to tie an annexe to the house

The standard wording runs along the lines that the accommodation shall be occupied solely for purposes incidental or ancillary to the enjoyment of the main dwelling and shall not be occupied as a separate independent unit of residential accommodation.

It is imposed because the planning merits are different. A council that would refuse a new house in your back garden may readily accept extra accommodation for the household, and the condition is what keeps the second thing from turning into the first.

Breach of condition is enforceable. Councils act on annexes that appear on letting sites, and neighbours report them. A breach of condition notice carries no right of appeal on planning merits, only compliance or prosecution, so this is a condition worth taking seriously at the design stage.

Occupancy wording and dependent relative restrictions

Some councils go further and restrict occupation to a named category: a dependent relative, a member of the family occupying the main dwelling, or a person employed at the property.

A dependent relative condition is more restrictive than it sounds. When the relative moves into care or dies, the accommodation cannot lawfully be occupied by anyone else in the same way, and the family is left applying to vary a condition at exactly the moment they have least appetite for it.

If the officer proposes that wording, ask for the simpler ancillary condition instead, and explain why. Councils frequently agree where the annexe is physically connected to the house and shares its garden, because the ancillary condition already achieves the planning purpose.

What makes an annexe a separate dwelling

The condition does not decide this on its own. Planning looks at the facts on the ground, and a building that operates as an independent home is a separate planning unit whatever the decision notice says.

The factors that push towards independence:

• A self-contained kitchen as well as a bathroom.
• A separate entrance not reached through the main house or its shared garden.
• A garden area fenced off for the annexe alone.
• Separate utility meters and a separate postal address.
• A physical separation from the house, particularly a detached building at the end of the plot.
• The ability to sell or let it without altering anything.

The factors that keep it ancillary: shared access, shared garden, shared parking, a connecting door or a short link, shared services, and use by a member of the same household.

None is decisive by itself. A detached annexe with a shared garden and a connecting path can be perfectly ancillary. A converted garage with its own fenced yard and gate can be a separate dwelling. The same reasoning applies to the ancillary test applied to garden rooms, and it is the test to design against.

Council tax banding and the annexe discount

Council tax follows a different assessment, made by the Valuation Office Agency rather than by the planning authority. The Agency asks whether the annexe is a self-contained unit, which broadly means it has its own facilities for living, sleeping, cooking and washing.

Where it is, the annexe gets its own band and a second bill arrives. Two reliefs matter:

1. A discount of half the annexe's bill applies where the annexe is occupied by a relative of the person liable for the main dwelling, or is being used as part of the main home.
2. An exemption applies where the annexe is occupied by a dependent relative, with the qualifying categories set in the regulations, broadly older people and people who are substantially and permanently disabled or severely mentally impaired.

Two consequences worth knowing before you draw the kitchen. A separate band is not evidence that the annexe is a separate planning unit, and councils sometimes suggest otherwise. And leaving out a full kitchen, providing a kitchenette without a separate hob and oven arrangement, sometimes keeps the accommodation out of separate banding altogether.

Separate access, curtilage and the severance risk

Officers look hard at anything that would make the annexe saleable on its own.

A new vehicular access serving only the annexe raises the question immediately. So does a boundary fence across the garden, a separate bin store on the frontage, and a driveway divided by a kerb. None of these is fatal on its own, and all of them make the case harder.

Keep the curtilage single on the drawings. Show one garden, one bin store, one parking area, and a path from the main house to the annexe door. If the plot is large enough that severance would be physically easy, expect the condition to be tightly worded and the officer report to dwell on it.

Where the annexe is a converted or new outbuilding, check the outbuilding limits under Class E as well, since a building providing primary living accommodation generally falls outside those rights and needs permission in its own right.

Varying the condition later

Circumstances change. Removing or varying a condition means an application under section 73 for planning permission without the condition or with different wording, and the council reconsiders that condition afresh.

Success turns on the ordinary planning merits of a separate dwelling on the plot: access, parking, amenity space, overlooking, and whether the site is a sustainable location for an additional home. In a village with a settlement boundary drawn tightly, the answer is usually no.

Long-standing breaches raise the question of immunity. Enforcement time limits were extended by the Levelling-up and Regeneration Act 2023, so check the current periods and the commencement provisions before assuming anything about lawfulness, and take advice. A lawful development certificate is the only way to have the position confirmed formally.

Building Regulations and the levy exemption

An annexe is habitable accommodation, so Building Regulations apply in full: insulation and heating, ventilation, escape windows or protected routes, and sound insulation where it adjoins the house. A detached annexe brings its own drainage connection, and sometimes a separate electricity supply.

For the levy, an annexe within the curtilage of the main dwelling can qualify for the residential annex exemption. The sequence is strict: assume liability, claim the exemption, receive confirmation, serve the commencement notice, then start. Disposing of the annexe or the main dwelling within the clawback period brings the charge back.

Put the ancillary case in writing when you apply. A short Planning Statement explaining who will live there, how the accommodation relates to the house and why the plot cannot sensibly be split answers the officer's main question before it is asked.

Work out which supporting documents your council expects for a householder application first. You can enter your postcode on PlanScope to see which reports your site is likely to need.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.