Metaphor is a fundamental heuristic supporting cognitive and communicative requirements in design problem solving. This reasoning mechanism helps structure how architects reason about problems, and how they approach design situations from novel perspectives. This paper investigated empirically the use of metaphors during the conceptual front edge design, known as the most creative stage of the process. Figurative phenomena were analyzed in their original context of occurrence. Emerging metaphorical expressions generated during communication interactions maintained by sixty architects were identified and examined based on protocol analysis approach. Metaphors were further categorized according to main experiential domains at different levels of detail, as well as in terms of image and conceptual descriptions. The study contributed to gain a deeper insight into the rhetorical potential of metaphor during design problem solving, and to strengthen its centrality in architecture.