Sustainability has become a driver of innovation in the built environment, but the affordability of sustainable building remains a significant challenge, according to developers, building owners, and design teams. This dissertation proposes a framework to understand how the characteristics of a project design team are influential cost drivers. We use empirical data to understand: (1) the sustainable building construction cost (SBCC) in relation to level of sustainability; (2) the influence on the SBCC of soft cost associated with the project design team; (3) the causal relation between project characteristics, project design team characteristics and construction cost of sustainable buildings. A mixed methodology is employed with four steps: research flow; a regression model and structural equation model in the quantitative research phases; and a comparative case study in the qualitative research phase. Altogether, thirteen project and project design team characteristics are studied, and ten hypotheses tested. The findings reveal: (a) the construction cost of studied sustainable building is comparable to conventional buildings, even lower; (b) the relationship between the construction cost and level of sustainability achieved is inconclusive; (c) among the project design team characteristics, skill and experience dominate, while communication, collaboration, and innovation are less influential; and (d) technical complexity is not always related to sustainability, hence the empirical data does not proved its influence. The proposed research contributes to research and practice at three levels: data, evidence, and methodology. The broad impact of this research is to advance an understanding of the SBCC cost as a means of promoting building green. The findings and methods resulting from this research project can empower architects, engineers, and developers to promote affordable sustainable building.