Start with the correct nation
England, Wales, Scotland and Northern Ireland have different rules. The questionnaire offers a conservative initial screen for England and sends other nations to their official guidance. A result is not consent or a certificate.
England: the main checks
For an incidental outbuilding at a house, the usual permitted-development checks include position, height and how much land is already covered. Listed buildings, designated land, restrictions on the property and the proposed use can change the answer.
- Keep it behind the principal elevation.
- A single-storey building normally needs eaves no higher than 2.5m.
- Within 2m of a boundary, the overall height limit is 2.5m. Otherwise the usual limit is 4m for a dual-pitched roof or 3m for another roof.
- Additions and other buildings must not cover more than half the land around the original house.
- Balconies, verandas and platforms over 0.3m require particular attention.
Use matters as much as size
Separate self-contained accommodation is outside the incidental outbuilding route. Sleeping accommodation, commercial use with visitors, or a bathroom proposal should be discussed with the authority in its full context. A toilet is not a shortcut to deciding the planning status either way.
Building regulations are a separate check
A planning exemption does not automatically remove building-control requirements. Floor area, sleeping use, distance to a boundary and construction materials can all matter. Electrical work has its own requirements. Check with the relevant building-control body before ordering a design.
Get evidence before you build
Confirm any planning conditions or restrictions affecting your address, check the measured proposal and discuss a lawful development certificate where appropriate. Keep the written advice, drawings and final approvals with your project records.