This paper discusses the advantages of using a coding interface both to describe form and run performance simulations in the context of architectural design. It outlines the relevance of combining recent interest in the design community for parametric scripting with available expert-level Building Performance Simulation. This approach enables designers to address performance-related design questions at the early design stage. Pitfalls when considering non-standard solutions and the potential of the approach to circumvent such difficulties are exemplified through a housing building case study, emphasizing the under-evaluated role of the analysis tool in steering design decisions. To circumvent the difficulty for non-expert users to interpret simulation results and transform them into design moves, the use of sensitivity analysis is proposed for its specific interplay with parametric scripting. Its potential for classifying parameters in order of importance is presented in the context of a design problem. The contribution outlines how providing designers with exploratory tools allows to consider sustainable construction in a systemic manner. (C) 2013 Elsevier B.V. All rights reserved.