A Study into Pre-Design Construction Project Cost Prediction in Ghana

Most often than not, prospective clients rely on the building professionals to determine the feasibility and viability of a proposed project. This they do by asking for designs and subsequently the probable costs. If this initial cost is too high it will discourage the client from proceeding further with the scheme and so the potential commission is lost and if it is too low, it may result in abortive designs, dissatisfaction on the part of the client and shoddy works. In an attempt to arrive at this initial estimate within the shortest possible time, certain cost predicting methods are normally used, these methods often than not result in large variations and deficiencies which ultimately affect the accuracy of our initial cost estimates. The objectives of this research are to identify these existing methods, assess their effectiveness and above all attempt to develop a mathematical cost model for estimating the initial cost of building projects. In order to achieve these objectives, there was the need to review relevant related research works of other authors. This review of literature, informed the design of the research. A field work was carried out by administering twenty-eight well-structured questions to eighteen practicing building consultancy firms with good standing in five regions of Ghana namely Ashanti, Greater Accra, Brong Ahafo, Upper West and Northern, during the process of which personal interviews were conducted to further solicit the views of these professionals. A detailed cost analysis on twenty-five (25) completed building projects was done and the results were used to develop a cost model using SPSS12.0 which states that Total Cost = -203,688 + 99.15 (Floor Area) + 43,919.71(Building Height).Among the key findings were that floor area and total building height contribute 36.4% of the cost of building. Cost models were found not to be in use in cost estimating in Ghana hence, there is no interest in the development of such models by building professionals. It was established that the most commonly used cost predicting methods were cost per square metre of floor area, unit and elemental cost methods with the former dominating. It was realised that quantity surveyors and architects most often do not visit proposed sites before designs and cost estimating and this has significant effects on initial cost. It was found out that condition/nature of site causes the highest variability between initial and final construction costs with time overrun being the least. It was therefore recommended that more research work be done on the floor area method of cost prediction so as to correct the deficiencies associated with its usage. Quantity surveyors should have elemental cost analysis and cost plans of various types of projects executed before in their respective offices for easy cost comparisons with proposed projects since cost planning is more appropriate method for cost estimating. It was further recommended that there must be cost data publications of all past projects of various kinds in the different regions in Ghana stating their actual costs of construction and time of completion which will serve as a guide when estimating for such similar types of projects. Architects and quantity surveyors must endeavour to visit proposed sites, have the designs evaluated before arriving at the final decision. Professionals must develop the interest in cost model development to derive the benefits that accrue from their use.

Source: KNUST