Cornwall Council’s annexe guidance distinguishes an extension to a home, an incidental outbuilding, an ancillary outbuilding, and a self-contained outbuilding. The proposed use and facilities affect both the application route and the planning fee. The fee examples below are the Council’s amounts stated as correct from April 2026; confirm the current schedule and classification before applying.
| Proposal described by Cornwall Council | Example application route | Planning fee stated from April 2026 |
|---|---|---|
| Annexe extension related to the existing dwelling | Householder application | £548 |
| Incidental outbuilding, such as a garage, shed, home office, or gym | Householder application | £272 |
| Ancillary outbuilding with living or sleeping space that is not fully self-contained | Full planning application | £548 |
| Self-contained outbuilding with bedroom, living room, bathroom, and kitchen | Full planning application | £610 |
These are planning-application fees, not building-control charges or a complete project cost. The Council says annexe proposals should remain functionally linked to the principal dwelling, in the same ownership and curtilage, share access, and avoid a separate garden boundary or subdivision. It asks applicants to explain the intended use and how the proposal relates to the main home. In the countryside, its guidance generally prefers an extension where feasible and asks for justification where a separate building is proposed.
The Council may impose a condition that keeps an annexe ancillary rather than allowing it to operate as a separate dwelling. Its guidance also says proposals with more than one bedroom will normally be refused unless a specific and compelling reason is established. These are local planning considerations, not a decision on a particular site. Confirm the application form, current fee, planning conditions, and any separate building-regulations or other approvals with the relevant authority.