Cornwall Council assesses an annexe by asking whether it remains ancillary to the principal dwelling or would operate as a separate home. The Council’s guidance describes local planning expectations for ownership, access, layout, and occupancy. It is a local planning guide, not a decision about a particular proposal or a general rule for England.
Show how the annexe remains linked to the home
The Council expects an annexe to have a functional link with the principal dwelling. Its occupants should rely on facilities in the main house or the households should need to support one another. The annexe should remain in the same ownership, sit within the principal dwelling’s curtilage, share its vehicular access, and have no separately defined garden area. The Council also expects the building to remain subordinate in scale and well related to the main home.
When applying, Cornwall asks for a supporting statement that explains who will occupy the annexe, their relationship with the household in the main dwelling, which rooms or facilities will be shared, and how the proposal meets the Council’s criteria. The Council says proposals with more than one bedroom will normally be refused unless a specific and compelling reason supports the extra room; it gives live-in care and accommodation for children as examples. A floor plan should not make later room subdivision possible.
Check the countryside and detached-building guidance
For a countryside site, the Council says an annexe should be a physical extension to the main dwelling if possible. If a separate building is proposed, the application should justify that choice. As a guide, the annexe should not exceed half the existing dwelling’s footprint and should show how it could be incorporated into the main home when it is no longer needed as an annexe.
The application route can depend on the design and degree of self-containment. Cornwall distinguishes incidental buildings, ancillary rooms without all facilities of a dwelling, and self-contained outbuildings; it says detached self-contained outbuildings require a full planning application. The Council may impose a condition limiting an annexe to ancillary use and preventing occupation as a separate residential unit. The exact application and any condition depend on the proposal and the Council’s decision.
Before relying on an annexe status, check the current local guidance, the planning application and drawings, the decision notice and its conditions, and the property’s ownership and access. Planning permission does not itself establish compliance with building regulations, lawful occupancy, or a separately transferable title.