While more expensive to deploy than their traditional counterparts, prefab units can achieve huge savings in construction costs by cutting down on work schedules.
A pioneering study by engineers from the University of Colorado Boulder has found that the use of prefabricated elements cut the cost of building a new hospital in Denver by millions of dollars and slashed more than two months in work days from the total construction time.
The new study by Matthew Morris and doctoral student Eric Antillon from CU-Boulder's Department of Civil, Environmental and Architectural Engineering examined the impact of using prefab parts on the costs and scheduling for the construction of Denver's new 831,000 square-foot Saint Joseph Hospital.
Their research was undertaken in collaboration with the builders of the project, Mortenson Construction, and is believed to be one of the first academic efforts to quantify the costs and benefits of employing prefab parts in large-scale building projects.
While prefabrication is renowned for its ability to save the time required for project completion, much uncertainty continues to surround its actual impact on costs. Building prefab units off-site can entail greater expense because of the transportation costs incurred conveying the these components to the construction site itself.
According to Morris, the direct cost of the prefab units can be as much as six per cent more expensive. The trick then is to ensure that the savings achieved by reduced building times outweigh the additional expense of the prefab parts. This is hardly a challenge, however, given the exorbitant costs associated with the construction process.
"If you save three months on the schedule, that's three months when you don't have to pay for all the things you need to run a job site," said Morris, who teaches construction engineering and management. "This reduces your cost of big-ticket items such as supervision, equipment and your field office."
For the building of the Saint Joseph Hospital, Mortenson Construction chose to use prefabricated parts for broad range of purposes, including exterior wall panels, bathroom pods, the headwalls of patient rooms, and the utilities running above hospital corridors.
According to the CU-Boulder study, this extensive use of prefabrication resulted in a reduction of the construction schedule by 72 work days, cutting construction costs by a hefty US$4.3 million.
Morris points out that pre-fabrication has the greatest potential for cost and time savings in larger projects such as hospitals, where the same components are employed repeatedly for the same types of units and greater economies of scale are achievable. The Saint Joseph Hospital is just such a project, with Mortenson prefabricating a total of 440 bathroom units and 376 patient room headway.
"This isn't the solution for every project,' said Morris. "It takes a particular type of project with repetitive work and an owner and design team that are willing to be completely onboard."
The study also found the use of prefabricated units increased safety and provided a more controlled environment on building sites by increasing the convenience of utilities installation and reducing the number of different tradespeople required at any given time. According to Morris and Antillon's research, the use of prefabricated utility racks in corridors as well as other prefabricated parts permitted as many as seven safety incidents on site to be averted.