Summary
Planning designations can change what you are allowed to alter, extend or replace. Conservation areas, Article 4 directions and listed buildings can all add extra checks before you rely on normal permitted development assumptions.
Definition
An Article 4 direction is a local planning measure that removes specified permitted development rights in a defined area or for a defined type of development. A conservation area is an area of special architectural or historic interest where local planning controls aim to preserve or enhance character. A listed building is a building of special architectural or historic interest with legal protection. Before buying with plans to extend or alter, check the local planning authority map, Article 4 directions, conservation area appraisal, planning history and the National Heritage List for England where relevant. Do not assume that replacement windows, roof changes, extensions, demolition or boundary works are allowed just because similar work might be permitted elsewhere.