Posted: August 3, 2016 | Project Management
By Adrian Charest, PE, LEED AP BD+C
Construction productivity has been well-researched and can be calculated many ways.
The simplest method of determining productivity takes the amount of output and divides it by the number of hours that were expended into production. Simply stated:
Productivity = Output / Work Hours
Productivity is an important measurement to understand, mainly because labor represents a significant portion of construction costs, and there are many factors working against a productive workforce. A few examples of these factors include: delays in materials arriving on the job site, uninstructed or poorly informed crews, and unproductive time. These factors all contribute to lost time in the overall completion of a project.
This concept can be illustrated in the graph on page 45 that compares overall productivity rates. In the middle is an average project with a typical learning curve and rate of production, to the left is a project with a steeper learning curve and a higher rate of production, and to the right is a project with a low learning curve and a low rate of production. With this graph, it is easy to see how a project’s completion date (x) moves further to the right as its productivity decreases and, as a result, the duration of the project increases.
There are many industry guides assisting contractors with methods of measuring construction productivity. Most are trade specific and task specific – identifying the direct work elements, as well as the nonproductive time for the task at hand. Under “direct work” are the tasks related to the installation of an item. Productivity measurements can be performed on all aspects of building construction, such as formwork installation, concrete placement, and painting, with each trade providing unique characteristics of construction.
Published Productivity Studies
Many studies have been performed on construction productivity in an effort to improve results and decrease overall costs.
Research presented by Dozzi’s “Productivity in Construction” displayed productivity findings from a variety of sources to determine the actual time (as a percentage) that construction crews were productive on the job. According to his study, Civil Engineering magazine and S.B. Palmater found actual productivity to be 32% and 34.7%, respectively, at nuclear power sites.
Ying Zhao’s “Relationship Between Productivity and Non Value-Adding Activities” presented findings that were measured using video recordings and stopwatches at seven different construction sites. Zhao determined, “On average, workers spend only 46% of working time on the value-adding activities, 15% on the essential contributory ones, and the rest (39%) was spent on waiting and idling.”
“Productivity Analysis of Small Construction Projects in India” compared productivity of small construction projects in India to that of the United States. In this article, Yogendra Kumar conducted an in-depth study of productivity and defined direct work, indirect work, and no work for contractors performing brickwork, plastering, formwork, and reinforcement. Focusing on their research in the United States, the direct work productivity in Austin, Texas, had a consistent value of about 45% across the trades. Direct work productivity was found to be highest in reinforcement (24%) and lowest in plastering (15%).
“Applying Lean Techniques in the Delivery of Transportation Infrastructure Construction Projects” presented a study of work activities in regards to rebar installation for structural deck and asphalt paving. This study found direct work productivity rates of 32% for rebar and 35% for asphalt (averages to 34%), and nonproductive rates of 29% for rebar and 51% for asphalt (averages to 40%).
These results, and additional research, find an average minimum and maximum productivity rates of 63.7% to 84.7%, respectively. This is interesting, because it’s right in line with the six hours of an eight-hour working day rule that estimators frequently use (75%). Is it possible to increase construction production by decreasing waiting times through better planning?
"Capacity Utilization and Wait Time: A Primer for Construction" concludes this thesis and further explains that owners and contractors could increase productivity by reducing variability in work flows. The study also points out that a single construction activity is usually one part of an overall complex system of construction where multiple aspects are coming together and can be difficult to manage – work-force capacity and material inventory being a few of them. So yes, you can decrease waiting times, but it may be more difficult than it seems.
About the author: Adrian Charest, PE, LEED AP BD+C, is senior engineer at The Gordian Group who leads the development of their virtual building models. He has experience in construction, engineering, and estimating.