Driven by our interest in sustainability, the vernacular architecture of Wales and a preference for ‘rational’ over wilfully expressive form, the determination to ‘build simply’ has become an abiding aspiration in the work of the Design Research Unit (dru) at the Welsh School of Architecture, Cardiff University. Established in 1998, dru aims both to apply the School's wider research to architectural commissions and to develop design as a medium of research in its own right. In this paper, various themes that recur in the Unit's recent work are discussed in the context of two current schemes that exemplify this research-based approach to design.