Design space explorers are computer programs that play on an exploration metaphor to support design. They assist designers in creating alternative designs by structuring the process of design creation in a space of alternatives. Subsidiary metaphors relevant to design space explorers are generation, navigation, and reuse. This paper introduces, in two sketches, typed feature structures as a formal system in which a design space explorer and its knowledge level might be implemented. First, informal and abstract properties of typed feature structures suffice to build a sketch of the behavior of a design space explorer. Second, using an example based on single-fronted cottages (a common Australian housing type), we outline the typed feature structure machinery most relevant to design space exploration.