This paper explores and explains the relationship between interorganizational sustainable innovation processes and the elements of a national sustainable innovation system in building. The literature proposes that this relationship is characterized by mutual reinforcement. This paper integrates the interorganizational innovation process- and the national innovation systems-approach into a new model. A case research project, that covers a sixteen-year period of sustainable innovations in the Dutch residential building industry, investigates the interplay between process and systematic sustainable innovation within the structure of the model. The research project indicates, illustrates, and explains how interorganizational sustainable innovation processes and a national sustainable innovation system in building co-develop in an interactive and mutually reinforcing process. In this process, the national system for sustainable innovation in building provides the structure in which the interorganizational sustainable innovative building processes develop. Simultaneously, the interorganizational sustainable innovative building processes stimulate the development of a national system of sustainable building innovation.