Establishment of prediction system for cost of defect liability phase in construction project

What is it about?

Purpose – This study aims to establish a new system to predict the DLP cost using the Six Sigma methodology, which investigates sources of variations and reduces the error level to 3.4 per million through five phases: Define, Measure, Analyze, Design, and Verify. Design/methodology/approach – After the initial handover of the construction project, the defect liability phase (DLP) follows the practical completion. During this stage, the contractor is responsible for the remedy of any defects that appeared in the project. Many researchers have studied defect reasons and their associated costs in different industries, while the construction industry remains a green field for this kind of research. The objective of this study was to develop a model to predict the DLP cost. The research methodology adopted the five stages of the Six Sigma cycle: defining objectives, measuring the data, analyzing performance, designing the model, and verifying the results. Twenty factors were identified as potential factors affecting DLP cost. Factors were categorized into two main clusters: project data and organization data. Interviews were conducted with 42 project management experts, who have 8 to 35 years of experience in construction project management, to rank the 20 factors based on their importance. Simo's procedure was used to obtain the weight of each factor affecting the DLP cost based on the opinions of the experts. The Pareto principal was used to select the “Vital Few” factors affecting the DLP cost, and six factors were selected. The design of experiments was used to establish a dynamic model to predict the DLP cost using a sample of 41 construction projects obtained from the above mentioned 42 project management experts. The model accuracy was verified using data obtained from a different sample of five construction projects, which were not used to establish the model. Findings – The results showed that among the 20 factors, only six were found to have a cumulative impact of 50% over the cost of the DLP: (1) type of project; (2) project contract value; (3) nationality of the employer; (4) project manager experience; (5) defect liability phase duration; (6) sector of the employer. A model was established through the design of experiments to predict the DLP cost using the values of the aforementioned factors. Originality/value – A dynamic model was established to predict the DLP cost using the design of the experiments. The new model was validated, and the prediction error ranged from -18% to +21%.

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