Developing Appropriate Labour Constants for Building Construction Processes in Nigeria

Abstract

Labour is one of the key components of unit rates for bill of quantities items. One of the major challenges facing estimators when pricing bills of quantities for tendering is their inability to quickly lay hands on proper information about labour thereby resulting in high variability of tender prices among contractors bidding for building contracts in Nigeria. These information are the standards, usually given as constants in the form of time necessary for the manual completion of a defined quantity of work (standard time (st), or in the form of unit output, standard output (sop) for a specified working time). The aim of this study was to improve the reliability of tendering among contractors and assist in effective project planning and control. Consequently, a survey was carried out in ten organized building sites in the south east states of Nigeria with a view to evolving appropriate labour constants for building processes (concrete work and block work). The sites were selected using purposive/judgmental sampling technique. Work study was used to evolve appropriate labour constants and this involved a full scale time study for each of the operations that make up the activity for a process. This was done by observing and recording the operations using stopwatches; the start and finish durations of each operation per shift for different cycles as well as measuring the quantity of work carried out by each gang for eight-hour working day. A three-time estimate using the formula for most probable time to complete each operation that makes up an activity relative to the quantity of work performed. Students t-statistic and mean score index were used for the analysis. The tradesmen were also required to estimate their outputs in selected tasks. The evolved labour constants were more realistic and appropriate for pricing than the claimed outputs by the tradesmen and, therefore recommended as veritable tools for realistic pricing. This will reduce the level of variability in tender sum among contending contractors. It will further assist in effective project planning and control through realistic determination of optimal labour force in the execution of building projects.