Due to recent advances in technology and consumer awareness, there has been much debate about the green advantages of off-site, prefabricated, and modular building systems.
According to Tom Hardiman, Executive Director of the Modular Building Institute, "One of the biggest changes over the past few years has been the increased market share of modular construction for permanent facility applications. No longer limited to relocatable buildings and temporary structures, the permanent modular construction industry has started to demonstrate its ability to live up to its label as the future of construction"
Because of the unique off site construction process, modular construction workers report to work at the same manufacturing facility rather than commuting to and from a typical building site. Multiple trades are capable of working simultaneously on a project in a factory, whereas on site, the process is more linear – that is to say, one task, or trade, or floor must be substantially completed before staring the second.
Materials can be purchased for multiple projects and stored in the manufacturing facility until needed, thus reducing the total number of material deliveries needed and greatly reducing the environmental impacts of material delivery. This safe storage demonstrates another benefit in that materials are not damaged, lost or wasted by inclement weather conditions.
Once a project is completed in the factory, the assembled building components are transported to the site for installation. And while this final delivery and installation process certainly requires energy and has an environmental impact, the debate continues as to whether this impact is more than offset by the efficient process itself.
A recent research project led by the University of Virginia School of Architecture and Yale University “Comparing Environmental Impacts of On-Site versus Off-Site Construction,” seems to confirm the theory that offsite construction has a lower environmental impact. The report states that the researcher team’s aim was to evaluate two methods of building construction in the United States, conventional construction and modular/off-site construction and attempt to determine which is more environmentally preferred.
The analysis showed that impacts from off-site construction were generally lower than those from on-site construction. For global warming potential, average on-site construction impacts were about 23 percent higher than off-site.
According to lead researcher John Quale, Associate Professor at the University of Virginia School of Architecture, “If you compare on-site and off-site projects, and if the construction time is shorter, the environmental impact from the shorter construction time will be reduced (assuming similar locations) there appears to be a relationship between reduced construction time and reduce environmental impact.”
It needs to be noted that each project has its own unique attributes and variables and that this research is still in its preliminary stages with results expected in the fall of 2010.
Another research project by the National Institute of Standards and Technology (NIST) titled “Advancing the Competitiveness and Efficiency of the U.S. Construction Industry” seems to add validity to the UVA hypothesis. The NIST report states:
Prefabrication, preassembly, modularization, and off-site fabrication involve the assembly or fabrication of building systems and/or components at off-site locations and plants. Once completed, the systems or components are shipped to a construction job site for installation at the appropriate time. One study that examined the relationship between changes in material technology and construction productivity based on 100 construction-related tasks found the following:
· Labor productivity for the same activity increased by 30 percent where lighter materials were used; and
· Labor productivity also improved when construction activities were performed using materials that were easier to install or were pre-fabricated (Goodrum et al., 2009).
Prefabrication and related techniques allow for the following:
· More controlled conditions for weather, quality control, improved supervision of labor, easier access to tools, and fewer material deliveries (CII, 2002).
· Fewer job-site environmental impacts because of reductions in material waste, air and water pollution, dust and noise, and overall energy costs, although prefabrication and related technologies may also entail higher transportation costs and energy costs at off-site locations;
· Compressed project schedules that result from changing the sequencing of work flow (e.g., allowing for the assembly of components off-site while foundations are being poured on-site; allowing for the assembly of components off-site while permits are being processed);
· Fewer conflicts in work crew scheduling and better sequencing of crafts persons;
· Reduced requirements for on-site materials storage, and fewer losses or misplacements of materials; and
· Increased workers safety through reduced exposures to inclement weather, temperature extremes, and ongoing or hazardous operations; better working conditions (e.g., components traditionally constructed on-site at heights or in confined spaces can be fabricated off-site and then hoisted into place using cranes) (CURT, 2007).
Prefabrication and related techniques are commonly used in the construction of industrial projects, but they are also used, if less frequently, for commercial and infrastructure projects.
The committee believes that greater use and deployment of these techniques (if used appropriately) can result in lower project costs, shorter schedules, improved quality, more efficient use of labor and materials, and improved worker safety.
Case study examples
A look at a few projects show some green advantages made possible through modular construction.
MBI annually hosts the Awards of Distinction, the premiere awards contest for the commercial modular construction industry. Included in the contest is a category for best “renovated reuse” of an existing building. Renovated reuse is defined as a reconfiguration of an existing factory-built commercial structure to meet the needs of an application that is different from its original design. MBI also hosts a category for best green building design.
The 2007 winner in the renovated reuse category was the Brookfield Homes Sales Office in Kona, HI. The original unit was a standard double wide with metal siding, VCT flooring, wood paneling, and modulux lighting. Due to the technical simplicity of the modular unit, the architect was able to freely design and accomplish all of the requirements by the owner. The modular provided a solid foundation to work from. The architect was surprised at the rigidity and quality of the framing and insulation. The a/c duct work and the electrical wiring was a cost that he could take out his estimate due to the extent of the modular’s pre-finished condition. The layout was designed to create the atmosphere and to showcase the quality of the homes being offered.
Brookfield Homes Sales Office by Hawaii Modular Space
The 2009 winner in the green building design category was High Tech High in Chula Vista, CA. The school is LEED® Gold certified with the USGBC. In addition, the school was submitted to the Collaborative for High Performance Schools program, a national initiative to improve student performance and the overall education experience by building the best possible school. The project includes 59 modular units totaling 32,807 square feet.
Various green materials were used to enhance classroom acoustics, day-lighting and energy efficiencies. The modular units feature various high-performance products including, dual pane windows with low-E coatings, acrylic skylights, light fixtures with motion controlled sensors and low volatile organic compound (VOC) paint. The project also incorporated renewable and recycled materials such as sealed lightweight concrete floors, Homasote 440 Sound Barriers, which are high-density fiberboards made from recycled newsprint that help to control acoustics in walls, and a sprayed polyurethane roof. All the materials, with the exception of the interior casework, were available locally, further reducing the carbon footprint of the project.
High Tech High by Williams Scotsman
Summary
While the debate will continue as to whether modular and off site construction practices are in fact more environmentally friendly, any process that can offer the promise of reduced materials waste, improved worker safety and a streamlined construction process certainly merits further consideration by architects, specifiers, and consumers.
About the Author
Tom Hardiman is the Executive Director of the Modular Building Institute (MBI). MBI is the international non-profit trade association representing commercial modular contractors. For more information, visit www.modular.org.
Sources:
University of Virginia/Yale University preliminary results of phase one research report, “Comparing Environmental Impacts of On-Site versus Off-Site Construction”
National Research Council/National Institute of Standards and Technology Report “Advancing the Competitiveness and Efficiency of the U.S. Construction Industry”
http://modular.org/marketing/documents/NRC_USConstructionIndustry_Report.pdf
Modular Building Institute, www.modular.org