A quantitative study of post contract award design changes in construction

Abstract

The investigation reported forms part of a wider study into the applicability of design for manufacture (DFM) thinking to the total construction process, and the ways in which this could be implemented. Historical data from change order request procedures were examined for several case studies which were considered to be successful projects. These procedures are intended to capture information about design modifications, and thus can be considered to be analogous to the rework procedures used in manufacturing. It was found that in monetary terms alone, the direct cost of post contract design changes amounts to 5.1-7.6% of the total project cost. Although the case studies used here were a convenience sample, the typical financial opportunity for controlling design changes better is likely to be considerably greater than this. Frequently cited reasons for design changes included: employer has changed his requirements, designer's omission in tender documents and new information on existing site conditions. Little commonality between case studies was found at the work package level. In contrast to manufacturing, the availability and accessibility of data relating to rework is problematic.