Several research initiatives in the field of product modelling have produced static descriptions of the architectural and geometrical objects capable of describing architectural design projects. Less attention is paid to the development phase in which these static models are transformed into workable architectural design environments. In the context of the IDEA+ research project (Integrated Design Environment for Architectural Design), we use the object-oriented analysis method MERODE to develop and describe both an enterprise (or product) model and a functionality model. On the one hand, the enterprise model defines the architectural and geometrical objects, their methods and their relation with other objects. On the other hand, the functionality model organizes the functionality objects - ranging from single-event objects to complex-workflow objects - in a layered and easily expandable system. The functionality model is created on top of the enterprise model and closes the gap between the static enterprise model and the dynamic design environment as a whole. After a short introduction of the envisaged design environment and its underlying enterprise model, the paper will concentrate on the presentation of the higher-level functionality model. Elaborated examples of functionality objects on the different levels will clarify its concepts and proof its feasibility.