Development of cost distribution model for measured works components of building construction projects in Tanzania

Cost distribution models for building projects have been developed on various places of the world since 1950s; the models from developed countries are not applicable to developing countries like Tanzania due to differences in building requirements, resources availability, construction techniques and many other factors. Although the Ground Floor Area model is commonly used in Tanzania, it does not reveal the cost distribution on measured works components leading to underestimation or overestimation of building costs. A sample of twenty four (24) past projects executed by National Housing Corporation and Tanzania Buildings Agency was drawn from Dar es Salaam, Dodoma, Iringa, Manyara and Morogoro regions. Twenty one (21) projects were used to develop a cost distribution model and three (3) projects were used to validate the model. The PERT and Monte Carlo Simulation techniques were applied to obtain the model parameters. The developed cost distribution model on measured works components is comprised of substructure (14.74%), frame and walls (32.46%), doors and windows (14.51%), electrical installations (9.03%), roofing (3.13%), finishing (15.08%), painting and decorations (3.30%) and plumbing and drainage installations (7.75%). The weighted mean parameter has emerged to produce the best results as compared to arithmetic mean, median and mode parameters and the frame and walls has been found to be the best cost determinant component. The developed model has been recommended for use at both project initiation and tendering phases. The frame and walls should be used as a measured works cost determinant component at tendering phases and other components except the painting and decorations component may be used to estimate a measured cost at project initiation phases.