Time-related and cost-related waste through design and construction phases of the Green Building (GB) project delivery process are much higher than that of Nongreen Buildings (NGBs). Although prior studies have identified some waste types and related root causes for GB projects, a comprehensive classification of process waste and root causes encountered in GB project delivery does not exist in the literature. The objectives of this study are (1)to identify and classify waste types and associated root causes observed in design and construction phases of GB project delivery process, and (2)to rank the classified waste types and root causes based on their effects on time and cost increases during design and construction phases. To achieve the first research objective, an extensive literature review and a case study with three GB projects were conducted, and the identified root causes and waste types were represented in an Ishikawa diagram. To achieve the second research objective, two rounds of the Delphi method were performed with 12 panelists who are qualified in GBs and accredited by various areas of expertise. The findings include the following: (1)6 major types of waste, and 4 types of primary root causes with 16 types of secondary root causes, (2)an Ishikawa diagram for representing the cause-effect relationship between waste and associated root causes, and (3)ranking of the identified waste types, and primary and secondary root causes in design and construction phases of GB project delivery process based on their significance. The contributions of this study are a comprehensive classification of waste and associated root causes for the GB project delivery process, a description of their relationships, and a ranking of waste types, and primary and secondary root causes in terms of their negative impacts on the GB delivery process in terms of time and cost. The findings of this study can be utilized for developing models and/or tools in the future that would allow the owners to detect existing root causes and potential waste in GB project delivery processes. (C) 2015 American Society of Civil Engineers.