The development process at the site or building scale is a multiobjective process requiring the cooperation of many professions and other stakeholders. The addition of multiple sustainability objectives, often seemingly unrelated (economic versus environmental versus social) in a rapidly changing global urban context, further constrains and complicates the process. The MODESTT mapping approach was developed to elucidate the interdependencies, tensions, and trade-offs between different sustainability objectives for a given development, and to make explicit the points at which a single design decision may ‘lock-in’ or ‘lock-out’ various possible outcomes. In this article, we review and analyse existing models of the development process, illustrate the decisions and activities inherent in delivering a single element of a development (illustrated in this paper with the example of a roof); then apply the MODESTT analysis to three sustainability objectives. The analysis makes explicit the critical importance of sequencing of actions and decisions, and interdependencies between specific objectives that lead to tensions and trade-offs between the multiple sustainability objectives. We conclude by making recommendations for the generic application of the MODESTT approach to improve sustainability throughout the site development process. Regardless of the tools that are available in the UK or elsewhere for the development process and for sustainability proxies, it is the timing and sequencing of decisions (when data are collected or the tools are applied) that are important in delivering effective solutions. Keywords: sustainability, decision making, development process, sequencing, tensions, trade-offs, scale.