An alternative approach to conceptualizing and measuring the built environment is developed which forms the basis of a new assessment tool. The role of buildings is reframed to consider what capabilities for sustainability a building can provide to the inhabitants and local community. This capability to support sustainability is defined as the ability to improve the local quality of life (Human Development Index) whilst remaining below the environmental carrying capacity (environmental footprint). This approach has clear implications about the role of buildings in enabling residents and users to achieve these targets and outcomes. This shifts the focus of net-positive development toward configurations and characteristics of the built environment that are appropriate for a particular context. A Built Environment Sustainability Tool (BEST) is presented that defines and assesses these configurations and characteristics. Assessments can be conducted by measuring the extent to which required configurations and characteristics exist (i.e. 'the capability of the built environment to support sustainability'). BEST is compared with other green building rating tool approaches in order to review the methodology critically and to evaluate this as a means of improving built environment sustainability performance.