An Article 4 Direction is the Local Planning Authority’s way of removing Permitted Development rights, when the character of an area of acknowledged importance would be threatened by the proposed development. This will mean that you have to submit a planning application for work which normally does not need one.
Article 4 Directions are most common in Conservation areas.
As a property owner you will probably know if your property is affected by such a Direction. It is always best practice to check with the the Local Planning Authority before commencing works that are generally considered as Permitted Development.
