An annexe is self-contained living accommodation. It can be attached to your property, or have a separate external entrance. Annexes are billed separately for council tax.
Annexes used by you and your family
If your annexe is only used by you and your family (the people who live in the main building) you may be able to claim a 50% discount on the council tax. If anyone who uses the annexe depends on you for care and support, or is not a member of your family, you can’t apply for this discount. It doesn’t matter if the annexe is furnished or not.
The discount can be in addition to other council tax discounts, such as single person discount. So for example, if the council tax bill is £1000 this becomes £750 when the 25% single person discount is applied, and then £375 when the 50% annexe discount is applied.