An Empirical Study of the Accuracy of Elemental Cost Plans in Commercial Buildings in Lagos

Elemental cost planning is widely regarded as the principal technique for achieving cost certainty at the design development stage of commercial building projects. Despite its prevalence in Nigerian practice, empirical evidence on the accuracy of elemental cost plans relative to final accounts is scarce. This study examines the accuracy of elemental cost plans for commercial buildings in Lagos using a dataset of 45 projects completed between 2020 and 2024. A quantitative, archival and survey design was employed, with cost plan and final account records obtained from 18 quantity surveying firms supplemented by practitioner questionnaire data from 162 respondents. Deviation analysis, coefficient of variation, and multiple regression were applied. Results show that elemental cost plan accuracy, measured as percentage deviation from final account, averages 14.2% across the dataset, with structural frame, mechanical services, and external works elements demonstrating the highest individual inaccuracies. The study identifies poor design definition at cost plan preparation stage, inadequate use of up-to-date cost data, and exclusion of risk contingency as the strongest predictors of cost plan inaccuracy. Projects prepared by firms with dedicated cost data management systems show significantly lower deviation rates. Unlike prior studies that rely on perceived accuracy, this research uses matched cost plan and final account data, providing an objective accuracy baseline for Lagos commercial construction. Policy implications target curriculum development and professional practice standards. Keywords: elemental cost planning, accuracy, commercial buildings, Lagos, cost management