We use different zones for the 'usable space' square meters and the 'gross volume' (and quantity take off). Might not be what you like, but it works quite fast.
You can use 2d linework as a zone boundary and we use that to communicate where the 1.500 mm and 2.600 mm heights, that are of interest in determining the 'usable space' according to our building regulations, are anyway.
Erwin Edel, Project Lead, Leloup Architecten
www.leloup.nlArchiCAD 9-26NED FULL
Windows 10 Pro
Adobe Design Premium CS5