Study of Cost Estimation Accuracy in Residential Building Projects in Plateau State

Accurate cost estimation is critical to the financial viability of residential building projects, and understanding the accuracy of estimates produced in Plateau State, North Central Nigeria, provides important guidance for quantity surveying practice. This study examined cost estimation accuracy in 40 completed residential building projects in Jos North, Jos South, and Barkin Ladi Local Government Areas of Plateau State. Project data including tender sum, estimated cost, and final account value were collected from quantity surveying firms, building contractors, and private developers. Cost performance was measured by the percentage deviation of final account from tender sum and from the original estimate. Factors influencing cost estimation accuracy were assessed through questionnaires administered to 45 quantity surveyors and project managers. Results showed that tender sums exceeded original estimates by a mean of 18.7% and final accounts exceeded tender sums by a further mean of 24.3%, yielding an overall cost escalation of 46.2% from initial estimate to final cost. The primary factors reducing estimation accuracy were identified as price fluctuations in building materials (cited by 89% of respondents), inadequate site investigation data (72%), and design changes during construction (68%). Shortage of current bill of quantities data in the North Central region was identified by 61% of professionals as a systemic challenge. The study recommends establishment of a regional building cost database and quarterly price indexing for materials in Plateau State.

Keywords: cost estimation, residential buildings, cost overruns, quantity surveying, Plateau State