The nD modelling research agenda is looking at how information technology can help to improve the efficiency and effectiveness of the building design and construction process. Building design is a complex task as there are different, sometimes conflicting, factors to be considered. One of the key challenges for nD modelling is the integration of these factors into the design decision-making process. This paper reports on a collaborative research project that has developed HyCon—a design support tool that allows users at the conceptual design stage to carry out ‘what-if’ analysis in a virtual reality environment to consider various hybrid concrete alternatives against a range of ‘hard’ and ‘soft’ performance criteria. The ‘hard’ criteria allow contractors and designers to assess initial and whole lifecycle cost and production duration implications. The ‘soft’ criteria encourage the whole project team to assess and prioritize the importance and performance of design alternatives against criteria such as physical form and space.