Determining optimal proportion of design in design-build request for proposals

The design-build (DB) system is a popular and effective delivery method of construction projects worldwide. After owners decide to procure their projects through the DB system, they may wish to determine the optimal proportion of design to be provided in the DB request for proposals (RFP), which serves as a solicitation for design-builders and describes the scope of work. However, this presents difficulties to DB owners and there is little, if any, systematic research in this area. This paper reports on an empirical study in the United States entailing both an online questionnaire survey and Delphi survey to identify and evaluate the factors influencing owners' decisions in determining the proportion of design to include in DB RFPs. Eleven factors are identified, i.e., (1) clarity of project scope, (2) applicability of performance specifications, (3) desire for design innovation, (4) site constraints, (5) availability of competent design-builders, (6) project control requirements, (7) user group involvement level, (8) third-party requirements, (9) owner experience with DB, (10) project complexity, and (11) schedule constraints. A statistically significant agreement on the 11 factors was also obtained from the (mainly nonowner) Delphi experts. Although some of the experts hold different opinions on how these factors affect the proportion of design, these findings furnish various stakeholders with a better understanding of the delivery process of DB projects and the appropriate provision of project information in DB RFPs. Because the result is mainly industry opinion concerning the optimal proportion of design, in addition and for completeness future studies should be conducted to obtain a big picture of the optimal proportion of design by means of seeking owners' inputs.