(a)Erection, re-erection, addition to, or alteration of, any internal partition wall, or a parapet wall or a cornice or chajja within the boundaries of the site and not over-hanging a street, so, however, that the total height of the parapet wall, shall not be more than one hundred twenty centimetres and the width of a cornice or chajja, shall not be more than fifty centimetres: