Architectural researchers working in the field of building modeling have determined that one of the most critical attributes of a building model is integrity—the model should not allow you to create a "junk building." So far, no BIM application really meets this requirement (see my recent review of Revit Building 9), but ArchiCAD, with its near complete lack of modeling constraints, is very far from this goal. It might not be a critical issue right now, but it will be in the future, when the focus of BIM will increasingly be on analysis and simulation rather than on automatically generating construction drawings.
Also, as I pointed out in my review of Revit Building 9, all BIM applications need to rethink how they deal with spaces/rooms, as none of them have quite got it right yet in my opinion. This includes ArchiCAD with its zone element. To start with, it should make a distinction between rooms/spaces as commonly defined by a single enclosure, and a larger collection of spaces that can come together as a zone. Also, the very existence of walls should automatically define some kind of volume, whether fully or partially enclosed, and the application should be smart enough to determine when such a volume has been created. The user should not have to go through the additional step of explicitly creating and placing a room/space/zone element within a set of walls, as this subsequently creates problems such as keeping that element synchronized with the surrounding volume, as I pointed out earlier. ArchiCAD too does not automatically detect the vertical footprint of a zone by elements such as slabs and roofs but uses a numeric value instead, so that to calculate the true volume of a zone under a complex roof, you have to first specify its height to be greater than that of the roof and then trim the zone against the roof. Also, zones in ArchiCAD cannot be seen in sections at all, which is another unfortunate consequence of explicitly creating them rather than them being implicitly defined.
In conclusion, ArchiCAD 10 is right on track in providing users with what they critically need right now—more modeling freedom, improved ease of use, vastly improved training, and better integration of drawings with the modeling workflow. In the long term, more attention needs to be paid to the issue of model integrity by incorporating more intelligent modeling behavior that takes into account the physical properties of building elements and their relationship with other elements, so that the model can be free of modeling errors before moving to the analysis and simulation phase. How it can do this without detracting from the user experience represents the ultimate challenge—not only before ArchiCAD, but before any current-day BIM application.
About the Author
Lachmi Khemlani is founder and editor of AECbytes. She has a Ph.D. in Architecture from UC Berkeley, specializing in intelligent building modeling, and consults and writes on AEC technology. She can be reached at
lachmi@aecbytes.com.
This is a wake up call for me
