As mentioned in the last post the visible IFC structure is based on clearly defined spatial containers: IfcProject, IfcSite and IfcFacility (usually IfcBuilding), which are populated with data from the project information when exporting from Revit.
IfcBuildingStorey is building up on this structure and represents the building levels. When exporting from Revit, these are reduced to the Revit levels that are flagged as a building story in Revit:
If an element in Revit belongs to a level that is not flagged a building story and is therefore not exported to IFC, this element is assigned to the next lower assigned (if not possible, the next level above will be used).
However, this assignment can also be made manually overwritten with the parameter IfcSpatialContainer . The possible values are either the name of the desired level, or IfcBuilding / IfcSite - in this case, the components are assigned directly to these spatial containers (and not to a level!).
Example in Revit:
Result in IFC:
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