What makes an annexe 'self-contained'?

A self-contained annexe has its own kitchen (with cooking facilities, sink and food storage), bathroom (WC, basin, bath or shower) and a separate entrance that does not require going through the main house. Self-contained annexes may attract separate Council Tax and require planning permission as a separate dwelling unit.

Will I have to pay separate Council Tax on an annexe?

Possibly. If the annexe is self-contained, the Valuation Office Agency may assess it for separate Council Tax. However, if it is occupied by a relative, many councils apply a 50% discount on the annexe assessment. Non-self-contained annexes are typically included in the main property assessment. Contact your local council before building.

Do I need planning permission for an annexe?

In most cases, yes. A new build annexe or converting an outbuilding to self-contained living space requires planning permission. The annexe must be ancillary to the main dwelling — it cannot be used as a separate, independent dwelling or holiday let without further planning consent.

What is the minimum size for an annexe?

Under the national space standards (not mandatory in all areas), a one-bedroom annexe for one person should be at least 37m² and 39m² for two people. A two-bedroom annexe should be at least 61m². Ceiling height must be at least 2.3m for habitable rooms. Your local authority may have additional requirements.

Can I rent out an annexe?

Not without planning permission for a change of use. An annexe granted planning permission as ancillary to the main dwelling must remain ancillary — typically occupied by a family member or dependent. Renting to a non-family member would constitute a change of use requiring separate planning consent. Short-term holiday letting may also need planning permission.

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Annexe Calculator — Self-Contained Requirements & Planning

Assess annexe self-contained requirements including kitchen, bathroom and separate entrance, plus Council Tax implications and planning considerations.

Annexe type

Floor area

Bedrooms

Kitchen included

Bathroom included

Separate entrance

How We Calculate This

This calculator assesses annexe requirements based on configuration, self-contained status and compliance needs.

Self-contained assessment

An annexe with a kitchen, bathroom and separate entrance is self-contained. This triggers potential separate Council Tax and affects planning requirements.

Space standards

Minimum floor areas follow the national space standards: 37m² (1-bed, 1-person), 39m² (1-bed, 2-person), 61m² (2-bed).

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.