PPS 6 Planning Archaeology and the Built Heritage·Page 49·C8
Relative Importance and Grading of Buildings
Buildings of importance to Northern Ireland are normally graded higher than those of local importance, and well-designed buildings by prominent architects are considered of higher status than modest vernacular buildings, unless vernacular losses increase the importance of survivors.
Buildings of importance to Northern Ireland will normally be graded higher than those of more local importance based on a narrower context e.g. the townland. Similarly a well-designed building by a prominent British or Irish architect will be considered of higher status than say a modest 19th century terrace house, unless the sheer number of buildings of a particular category being lost increases the importance of those that survive. Northern Ireland's vernacular buildings are a case in point.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/PPS 6 - Planning Archaeology and the Built Heritage.pdf