A study into the effects of design parameters on building cost of public building projects in Kenya
This study looks at the effect of design parameters on building cost of public building projects in Kenya. Four elements have been selected for examination. The four elements are substructure, walling, roofing and finishes. The study has established that design parameters can be used to express building cost by elements and therefore can be used in cost advise in the early stages of design process. The design parameters considered in the study are size, storey height, total height, shape and specification and building cost index. Both correlation and regression analyses were used to test the strength of the relationships between the cost of buildings by elements and the design parameters. A total of forty three buildings qualified for study out of a population of two hundred and eighteen. Substructure exhibited strong correlation coefficient of 0.7295 with size of building at student t-test confidence level of 99'%. Roofing showed correlation coefficient level of 0.600 with building cost index and finishes recorded 0.5318 with size of building. The regression analyses showed even better results by including several design parameters in the equation. Substructure was better explained by size, building cost index and storey height, achieving a multiple correlation of 0.800. Similarly walling was explained by size and storey height giving a multiple correlation coefficient of 0.716. Roofing was explained by building cost index and storey height giving a multiple correlation coefficient of 0.69 and finishes was explained by size, storey height and building cost index giving a multiple correlation coefficient of 0.65. In determining which design parameter to include in the element cost equation, stepwise regression was used. Only those design parameters, which satisfied the criteria for selection using stepwise regression was included thus rninimising the standard error and increasing the strength of the relationships. The findings of this study show that building cost can be explained by their elements and the design parameters that affect the cost of the elements. In so doing vital information during design stage can be accessed in order to keep to the budget limits given by clients. This study is divided into five chapters. The first chapter o~ this study outlines the evolution of cost models in the evaluation of building costs over time, where we find traditional models being blamed for not controlling building cost. This problem can reasonably be reversed by introducing the concept of design parameters in the estimation of building costs at early design stages. The second chapter looks at the concepts associated with implementation of public building projects, cost control and cost planning together with design method and cost planning. Chapter three looks at cost consequences of building elements on design parameters and the study model. The design parameters considered are size of buildings, its shape, total height and storey height. Chapter four is on data analysis and presentation. It is concerned with the gathering of data, how it was transformed for analysis and finally how it was interpreted and presented. Finally, Chapter five covers conclusions and recommendations of the study together with recommended areas of further research.