This paper focuses on three different aspects in which the IDEA+ core model differs from many other product modelling research initiatives: the systematic approach in the construction of the model, the respect for the evolutionary nature of architectural design, and the use of actual and complete design cases to test the model. Key words: CAAD, product modelling, integrated design environment, MERODE 1 The IDEA+ project: towards an integrated design environment In spite of the extensive use of all kinds of hardware and software in the architectural offices, the use of computers still does not contribute essentially to better architecture. For the CAD packages on the one hand, they have proven to be an efficient alternative for the traditional drawing board. Yet they fail in the early conceptual stage of design where creativity and exploration play the leading role. For computational tests and analysis tools on the other hand, they can hardly handle the typical absence o