There are different suggestions in the standards (for thermal building simulation):
You may find more information about so-called space boundaries in this paper. Unfortunately, it’s in German, but you can use DeepL or other tools to translate it:
Geometrische Transformation von IFC-Raumbegrenzungsflächen für die normkonforme thermische Gebäudesimulation (Geometric transformation of IFC room boundary surfaces for standard-compliant thermal building simulation)
In: Proceedings of 33. Forum Bauinformatik : 07.- 09. September 2022
doi:10.14459/2022md1686600
Link: https://mediatum.ub.tum.de/doc/1686600/1686600.pdf (Page 283)