Building codes are both an index of social values and a strategy to enforce those values. On these grounds an examination is made of the emergence of green building codes in North America as a category of building codes that is particularly important for sustainable development. The classical definition of sustainability proposes that multiple, competing frames of interpretation--economic development, environmental protection and social equity--can, in theory, be balanced. It is found, however, that in practice equity is generally ignored. Through historical and theoretical investigation, it is hypothesised that codes which are successful in incorporating equity as a criterion emerge from public talk and social learning, not abstract speculation. The paper concludes by articulating a change-oriented research design for an ongoing project to test this hypothesis. 10.1177/0042098009346327