A building is listed in its entirety. There is no such thing as a listed interior, exterior or single facade.
The definition of a listed building includes all of the building and also any structure or object fixed to it, for example an attached outbuilding or garden wall. The definition also includes other objects or structures, constructed before 1948, that are within the what is called the 'curtilage' of the building.
The 'curtilage' is often quite difficult to define but means the building itself as well as any associated buildings, such as garages or stables. It also includes any garden or land associated with the building and any fences or walls around the land.