Buildings ancillary to flats or maisonettes
20. A detached single-storey building ancillary to and within the curtilage of a flat or maisonette. Except-A building exceeding 8 square metres in area. A building within 3 metres of the flat or maisonette or within 3 metres of any other part of the building containing the flat or maisonette. A building containing a flue, a fixed combustion appliance installation or sanitary facility. A wall or fence.