Design space exploration (Woodbury and Burrow, 2006) is the activity of discovering and evaluating design alternatives. While this is one of the long-standing motivating ideas underlying computer-aided design (CAD) research, it gains renewed interest in the current context of increased emphasis on building performance. In order to meet specific performance requirements, a designer has to create and evaluate possible design alternatives and their performance. Information systems that can support this task of generating design alternatives can be beneficial, because they allow the designer to quickly evaluate alternatives and freely proceed in an open-ended process of discovery.