This paper describes the usage of parametric design and evolutionary optimisation techniques in architect-engineer collaborations. It discusses the apparent challenges in setting up a trans-disciplinary working-platform that cuts across profession-specific boundaries and negotiates between the otherwise distinct work-methodologies through the use of intelligent CAAD applications. Two approaches to architectural form finding have been combined in this research. The first, parametric design, uses a proprietary package as a key element to the organisation and reorganisation of architectural design. By doing so, it is providing it with intrinsic flexibility allowing designers to go beyond form and accommodate performance data for versioning. The second, ESO (Evolutionary Structural Optimisation), is an engineering tool based on the use of finite element analysis (FEA) capable of optimising the formal geometry of an object to obtain minimum volume under even stress-distribution through an iterative design process. In undertaking this research it became apparent that different levels of resolution need to be addressed in the form-finding process in order to investigate the full potential of the interactive use of parametric design and evolutionary optimisation. The case studies reflect this diversity and demonstrate more successes, limitations and future challenges within the transdisciplinary, collaborative effort.