Importance of capacity constraints to construction cost and schedule

This paper makes a practice-based critique of the assumptions behind network planning methods from the perspective of subcontractors and suppliers. In the context of a case example, the time-cost trade-off and its resource-oriented extensions are critiqued as being incapable of representing the capacity costs and constraints of subcontractors and suppliers. These methods are also critiqued as being incapable of representing the effects of site conditions on productivity, which in turn affects the capacity choices of subcontractors. Restricting the focus to the general building industry, case findings from 15 subcontractors and suppliers are presented. The case research indicates that capacity constraints systematically affect subcontractors and suppliers and that site conditions affect the productivity of subcontractors. Moreover, it is found that these firms consistently take action to mitigate the impact of capacity constraints and site conditions on cost. This second finding suggests that not only do network planning methods fail to account for the costs of capacity constraints and site conditions, but also that the schedules generated by network techniques will be inaccurate. Hence, the research implies that much of the current basis of construction costing and control is inadequate to its task, and that new methods must be developed that more realistically represent the needs of construction subcontractors and suppliers.