Some key technical lessons from the Green Building Challenge (GBC) process over the past four years are examined and the future direction of these developments is considered. The GBC assessment method consists of the definition, structuring and scoring of a range of collectively agreed performance criteria - the GBC assessment framework, and the development of a software version to operationalize the framework - GBTool. This generic assessment method is designed to be customized and applied to different building types and cultural contexts. However, its development and testing has exposed numerous important conceptual and technical issues related to building environmental performance assessment. Additional features introduced in GBC 2000 - normalizing for occupancy, making context an explicit part of the assessment process, and a set of absolute environmental performance indicators - show considerable promise. The transformation of the GBC assessment framework into a sustainability assessment tool represents the most important issue in its future development.

• sustainability, environment

1. Emerging trends in building environmental assessment methods
2. Green Building Challenge: the development of an idea