There have been a number of EXPRESS-to-OWL conversion procedures suggested in the past few years, aiming specifically at IFC and thus resulting in diverse ‘flavours’ of ifcOWL. It seems nevertheless useful to (also) have one common ifcOWL ontology which can at least be used as a reference ontology. In this research effort, such a common EXPRESS-to-OWL conversion procedure is devised and implemented, specifically targeting IFC. This converter is complemented with a corresponding IFC-to-RDF converter, so that fully detailed graphs can be obtained of 3D Building Information Models. Because of the DL basis of the ontology, these graphs can be used for advanced and logically sound reasoning and querying. This can lead to improved building performance checking (energy, acoustics, operation, …) and regulation compliance checking processes (urban regulations, fire safety regualtions, …). The results of this project are now proposed for recommendation by the BuildingSMART alliance.