The 50% rule for permitted development is a guideline within UK planning regulations that dictates the extent to which you can extend or build on your property without needing formal planning permission. This rule states that the total area of extensions or other buildings on the property must not exceed 50% of the land surrounding the original house. This limit includes all buildings, such as existing and proposed outbuildings, as well as any existing or planned extensions to the house. While the area occupied by the original house is excluded, any subsequent extensions or detached buildings are included, even if they were built before 1948 or, if the house was constructed after that year, built concurrently with the house, such as a detached garage or garden shed. If your plans exceed this limit, you will need to apply for planning permission from your local authority.