Under the terms of ordinance SIA 416 of the Swiss Institute of Engineers and Architects, the usable space (Nutzfläche - "NF") constitutes part of the net floor space (Nettogeschossfläche - "NGF"). It includes the main or primary usable space (Hauptnutzfläche - "HNF") and the ancillary or secondary use space  (Nebennutzfläche - "NNF").