Measuring installation productivity in prefabricated timber construction

A problematic issue for new approaches to prefabricated timber construction is simply that there is insufficient productivity measurement data to assist estimation of resource usage, speed onsite and best practice. A lack of information potentially results in increased pricing behaviour which may slow the uptake of prefabricated construction. The purpose of this paper is to measure installation productivity onsite for prefabricated timber floor cassette panels and develop sufficient understanding of the process to suggest improved practices.

A time and motion approach, paired with time-lapse photography was used for detailed capture of prefabricated cassette flooring installation processes onsite. An emphasis was placed on work flow around crane cycles from three case study projects. Time and date stamping from 300 crane cycles was used to generate quantitative data and enable statistical analysis.

The authors show that crane cycle speed is correlated to productivity including gross and net crane time scenarios. The latter is refined further to differentiate uncontrolled outlying crane cycles from normally distributed data, representing a controlled work process. The results show that the installation productivity rates are between 69.38 and 123.49 m²/crane-hour, based on normally distributed crane cycle times. These rates were 10.8–26.1 per cent higher than the data set inclusive of outlier cycles. Large cassettes also proved to be more productive to place than small.

The contribution of this research is the focus on cranage as the lead resource and the key unit of measure driving installation productivity (in cassette flooring prefabricated construction), as distinct from past research that focuses on labour and craft-based studies. It provides a different perspective around mechanisation, for resourcing and planning of work flow. Crane cycles provide a relatively easy yet reliably repeatable means for predicting productivity. The time-lapse photographic analysis offers a high degree of detail, accuracy and objectivity not apparent in other productivity studies which serves to enable quantitative benchmarking with other projects.