Purpose The purpose of this paper is to identify the main reworks and their causes in a case study of the ongoing mass housing project in Iran. Using the real data captured from the project, the most important causes for reworks have been computed and prioritized. Design/methodology/approach More than 900 non-conformance forms filled in the construction site have been used to categorize reworks. Then, the frequency and cost of each rework group in the project have been estimated. Finally, using these data, the primary classification and sorting of the main causes of reworks have been specified. Findings Results show “Poor site supervision and inspection” with 24 percent of costs had the most impact and “unclear project management process” with about 6 percent of costs had the least impact on the formation of non-conformances. “Cost of each incidence” (COI) ranged from 0.67 for “The need to categorize the complicated operations” to 1.86 for “Unclear project management process.” Research limitations/implications The causes of rework which are not in contractor’s hand (like change orders from the client) have not been considered in this study. Originality/value Although some works have been done in rework causes, the key elements and causes of reworks in mass housing projects in developing countries have not been yet fully specified through the real data. Knowing the root causes of reworks can help project managers to remove them and reduce reworks costs in future projects. COI which is defined here for the first time and computed in a relative concept could be a good criterion to compare rework causes between two or more similar projects.

Reducing the cost of quality in mass-housing projects can reduce the overall cost and can also result in increasing profitability or the possibility of getting more projects due to the lower price offered in the tenders. The first step to reduce the cost of quality is to identify different elements, determine their impact on the final product quality and then prioritize them. In this study, questionnaires and structured interviews with experienced construction professionals were employed to identify and prioritize the fundamental elements using the P-A-F (prevention, evaluation, and failure) method, one of the most well-known methods for categorizing quality costs. The results indicate a high impact of preventive activities and the low impact of external failure activities on final product quality. According to the results, the use of experienced specialists and skilled workers is more effective than in-service training of inexperienced forces. Corrective actions of non-conformities and design improvements have a significant impact on final product quality. The new approach to COQ elements ranking, used in this research, can help decision-makers to prioritize the most effective activities in construction projects to increase final quality with an optimum quality cost.