IfcSpace modelling

[Erik Bjornhage]

Sooo...

I have recently had a discussion about IfcSpaces and what is the best way to model them in order to maximise the use for other disciplines.

Looking at the semantic definition and the BaseQuantities of IfcSpace it is clear that the IfcSpace starts at the level of the construction slab and ends at the underside of the construction slab on the story above. However, this is not how we ususally model spaces (zones) as we normally start at the finished floor level.

I know that there is the parameter in the zone to set a value for subfloor thickness - but if we are to model zones "correctly" there should also be a parameter for ceiling height (which exists in the SpaceBaseQuantities). 

So, two questions:

1. Has any had experience of modelling this way or are we all modeling the "architecture" way?
2. Is there a parameter for FinishCeilingHeight hidden somewhere in Archicad? I have not found it...

Operating system used: Windows 11 Pro 24H2