Recently, we have noticed projects exporting IFC files incorrectly; specifically with missing content. Wether this is due to changes to ARCHICAD from IFC2x3 to IFC4, or if it is just a modeling error on our part, is difficult to pinpoint at this time. What we have determined is the issue is the result of Element Classification going missing.
The Element Classification is the little drop down at the bottom of the settings dialogue for each model element. You can locate this within the Categories and Properties tab of the element settings.
It can be easy to ignore this setting, since it really doesn’t impact our typical model or document process. But for IFC coordination this setting is critical. If this goes missing, the element will not save out.
So a missing or undefined classification can get in the way of effective collaboration, but so can an incorrect classification. An example I have seen is doors that were used as gable end vents/walls. Because the door’s classification was left as “Door”, it was read as a door on the Revit side. This resulted in the door and the wall were defined as an opening that penetrated the roof; the engineer had to ask for a correction from our end.
IFC Classifications can seem a little confusing, given the unclear and vague terminology used in describing each classification. But fortunately Bond Bryan has already done the leg work to define each element classification and what is included. I have in turn reinterpreted this list in our BIM Manual for our calibre of projects; you can view this Dictionary of Element Classifications under Collaboration > IFC Classification in our BIM Manual. Or for a more complete list of building components and their Classifications, see Rob’s list here.