EMPIRICAL DETERMINATION OF LABOUR OUTPUT FOR FLOOR SCREED AND TILE FINISHES FOR CONSTRUCTION WORK

There is dearth of information on output level of building operatives in Nigeria, consequently, the output constants currently used for preparation of construction estimates are remnants of British colonial heritage or derived from untested experiences. Therefore this study aims at empirically determining output constants for floor finishes (screeds and tiles) for building project in Abuja. The objectives are to identify the productivity factors related to Building Engineering Standard Method of Measurement 3 (BESMM3) and evaluation of their impact on the outputs of five work items of floor finishes. The procedure adopted field survey involving work measurement to observe and measure operatives output. Data was collected from 80 on-going construction sites with an average of 50 gangs of workers for each work item to establish the following average outputs per day; 25mm thick cement and sand screed (23.70), 44mm thick cement and sand screed (19.31), 400 X 400mm ceramic floor tile (27.38), 300 X 600mm ceramic floor tile (30.18) and 300 X 300mm ceramic floor tile (23.61). The study also revealed a significant difference on mode of employment and period of observation on the outputs of the workers. The results suggest that experience and negotiation as mode of employment affect output of workers to varying degrees based on the thickness of floor screed and unit area of floor tile. The study has recommended that the established output should serve as an effective baseline for efficient estimating process and be in compliance with the BESMM requirements.

The source of labour output used for estimation of construction cost has been a point of discourse and contention. This is because this involves the quantitative estimation of the labour rates while market survey research for materials prices are the basis for the material cost estimation (Ashworth, 2002). The high degree of inaccuracy found in BOQ estimates is mostly attributed to the uncertainty of the accuracy of the labour constants used in pricing labour costs. Ajia (2002) concluded that while most of the outputs used by estimators are the British originated constants, some contractors adopt outputs gotten from their experience and hence non-uniform outputs are widely in use.

The common method of generating cost estimates for construction projects involves the multiplication of unit rate by the measured quantities in the bill of quantities (Ashworth, 2002). The unit rate is a component of labour rate (obtain from the multiplication of labour constant by all-in rate) plus cost of material and percentage allowance for profit and overhead, while the measured quantities are obtained from drawings and specifications for the works rules specified by Building and Engineering Standard Methods of Measurement (BESMM). The inconsistency in application of a defined output constant for construction estimates has posed a serious challenge to the accuracy of estimates computed by quantity surveyors.

Labour being one of the important components of the construction industry productivity represents a considerable proportion of the final cost usually accounting for between 40 to 60% of building cost (Abdullahi et al., 2010 and Butchan et al., 1993).