This paper illustrates our findings concerning space based design methodologies and interoperability issues for todays Building Information Modeling (BIM) environments. A method is elaborated which enables building designers to perform an automated energy use analysis, based on an Industry Foundation Classes (IFC) model derived from a commercial BIM environment, in this case Autodesk Revit 9.1. A prototype application was built, which evaluates the building model as well as vendor-neutral exchange mechanisms, in accordance with the Flemish Energy Performance Regulation (EPR) standard. Several issues regarding the need for space-based building models are identified and algorithms are developed to overcome possible shortcomings.