Prefabrication's Green Promise

When it comes to green building, prefabrication promises three major benefits: reduced waste, more durable and energy-efficient construction, and reduced transportation during construction. According to manufacturers and prefabrication supporters, the industry realizes these benefits along with reduced costs compared with site-built homes. But few of these benefits have been measured directly, and most vary based on the conditions in the factory and the location of the building site.

As with any manufacturing industry, cost-cutting drives waste reductions in prefabricated housing. Not only do housing companies design homes around standard material sizes; they also save and sort scrap materials for later use, whether in the homes themselves or for packaging and transport. Factories tend to have high recycling rates to avoid disposal costs. Although production builders do mostly the same thing, the factory setting makes it simple to collect and segregate materials for recycling and to monitor the production line.

The waste savings in a factory setting can be remarkable. According to Thayer Long, executive vice president of the National Modular Housing Council, there are no firm numbers on waste savings across the industry, but he says of manufacturers: “They’re not filling up dumpsters, they’re filling up trash cans.” Some green-focused firms have quoted waste reductions of 70 percent or more. These figures may not reflect the practices of the prefabricated housing industry as a whole, but most  manufacturers are striving to reduce waste as disposal fees rise and environmental responsibility becomes a more mainstream idea.

Supporters of prefabrication also tout the durability of the final product, thanks to the factory environment. Materials are stored and assembled indoors, where they are less likely to be damaged. Quality-control measures are easier to implement. Modular homes are also built to withstand the stresses of transport, which advocates say makes the homes more robust once they are placed on site.

But the type of over-building that allows a home to survive highway transport does not necessarily translate to resilience against on-site conditions. It does mean that a modular home is built with more material than a similarly sized stick-built home. Although manufacturers are moving away from this practice, many modules are shipped with both a floor and a ceiling even when they will be stacked on top of each other, or with all four walls, which leads to thick “marriage walls” where two modules meet side-by-side. Panelized construction and kit homes are not subject to the same transportation stresses, making such overbuilding unnecessary.

The controlled environment and quality-control measures typically found in a factory may lead to higher quality building envelopes that are also more durable and energy-efficient. Because they build a home from the inside out, workers can more easily insulate properly around electrical outlets and other openings. Supervisors are always “onsite” in the factory, able to inspect work and fix problems before they are sealed behind walls. However, the overall performance of a home is only as good as the finishing work performed on site when contractors “button up” the house, joining modules or panels together to create a tightly sealed envelope. Convincing clients to move beyond the basics to extra insulation or other energy-efficiency measures can also be a challenge. Says Long, “It’s very difficult for a buyer to understand that a $2,000 investment up front is going to equal greater savings down the road.”

To date, no one has examined the transportation impacts of prefabricated housing as compared to those of site-built housing, so no hard numbers are available. Contractors travel to and from site-built house sites just about every day. In some areas, workers can use public transportation or carpools, but they often arrive on site separately in individual vehicles. With remote sites, the energy used for these commutes can add up, especially in older and larger vehicles, which are common. Materials must also be delivered, usually on multiple occasions, often on large vehicles that are not fully loaded.

Prefabricated construction can in many cases shorten those commutes with a factory located near a skilled workforce. KieranTimberlake Associates of Philadelphia, Pennsylvania, looked at two of its projects, comparing a site-built dormitory in Middlebury, Vermont, and a prefabricated dormitory in New Haven, Connecticut. They found that the project in Vermont required 1.8 million more commuting miles than the New Haven project, although their calculations did not include commutes to the New Haven site to finish the building. There are transportation benefits for materials, too, since they are delivered for several projects at once, typically arriving on a fully loaded vehicle. A smaller transportation footprint during construction, however, may be offset by the energy used to get the completed house—whether in modules, panels, or precut pieces—to the site.

Each form of prefabricated housing has its drawbacks when it comes to transportation. Modular units take up lots of truck space and require that a crane be brought onsite, but the few workers that travel to the site only need to make the trip a handful of times. Panelized homes take up less truck space and typically need a smaller crane (if they need one at all), but more workers are needed on site for longer periods of time, meaning more commuting.

Fredrick Zal of Atelier Z in Portland, Oregon, has worked with both modular and panelized construction, sometimes in the same project. For most purposes, he favors panelized construction. “If you panelize, you’re shipping less air, which makes your carbon footprint smaller,” he says. He argues that the largest energy use in transportation is the starting and stopping of large trucks, so fewer trucks going to the site means less energy consumed. Modular does have its uses, however, especially for portions of a house requiring plumbing or for shapes that would be difficult to construct on site.

The Reality of Green

Mainstream prefabrication companies, particularly modular manufacturers, claim that their product is already green: it is both energy-efficient and durable, and the manufacturing process harnesses the efficiencies of mass production to reduce material waste and the carbon footprint of the final product. But incorporating many green features, such as extra insulation or low-emitting materials, often results in hefty customization fees, moving higher performance homes out of reach. In addition, many stock plans are not designed to respond to opportunities for passive-solar heating or other site-specific conditions.

A few architects have taken on the challenge of greening prefabrication, designing and building super-green prefabs. Most work with existing factories to create their product and offer differing degrees of customization. Others have started their own factories so that they can control the process and the quality of the final product. Unfortunately, these firms remain the exception in the industry, which remains devoted to the basic homes that have served it well over the past several decades.

Quincy Vale, president of PowerHouse Enterprises of Lawrence, Massachussetts, works with a handful of different factories in the Northeast to build the modular homes his company designs. Negotiating designs with outside companies can be difficult, he says, because “when they say [they can do] almost anything, there are actually a lot of things that they can’t or don’t want to do.” Among those are some of the greener aspects of construction. “We’ve spent a lot of time teaching these companies how to build a greener module,” Vale says, incorporating everything from added insulation to paints with low-VOC levels.

For a recent project in Cambridge, Massachusetts, PowerHouse worked with Epoch Homes, located in Pembroke, New Hampshire, to build two green modular townhouses for an urban lot. For some companies, the specifications for the PowerHouse project—designed to achieve a Platinum LEED for Homes rating—would disrupt the production line, resulting in additional fees. For Epoch, however, the project was business as usual, and part of the company’s overall move towards green construction. According to president and CEO John Ely, the company builds only custom homes, an increasing number of which are built to green specifications. Ely argues that building custom homes in this way is really no more difficult than building standard models: the company develops basic operating procedures for building elements and combines them to create the house.

Like many companies, Epoch has seen an increased demand for green homes in the last couple of years. Rather than picking a single green standard to build to, however, the company has chosen to let their customers decide. “There are a lot of different views right now on what green means. We try to respond to what the customer wants and give as much guidance as we can,” says Ely. He argues that this approach is more effective at introducing green building to the mainstream market than the practice of offering specific green home models or features. Many of the firms making green modular housing offer only a few models with several customizable options, he says, and “home-owners want more options than that.”

To really give the public what it wants, especially if those desires include green features, the prefabricated housing industry needs to change the way it operates. Green-housing manufacturers are leading this change—s some by starting their own factories and demanding more from their manufacturing partners, others by reimagining the entire housing industry.

Architect Michelle Kaufmann became interested in prefabrication when she moved to Northern California and found a dearth of affordable green homes. After designing and building her own home with a modular manufacturer, she started a company to design and build green prefabricated homes. Kaufmann’s firm has built more than 30 homes since its start in 2002, and plans to increase that number to at least 100 by the end of 2009. Michelle Kaufmann Designs, based in Oakland, California, offers seven basic homes that can be customized within certain limits, and also offers custom design-build services.

Faced with the challenges of working with existing manufacturers to meet the high green standards she sets for her homes, Kaufmann started her own factory near Seattle. This move allowed her to more closely control the quality of the homes she was selling and to develop a detailed protocol for building the homes. As the company looks at expanding its operations nationwide, it is considering partnering with manufacturing companies that can meet its specifications. Kaufmann’s company could pass on its own best practices, which would theoretically result in a greening of the partner factory’s operations. Such partnerships could, in time, change the industry standards for prefabricated construction, making green features standard rather than custom additions.

Architecture firm KieranTimberlake Associates has a more radical vision for prefabrication, believing that it could remake the construction industry in the style of the aircraft or automotive manufacturing industries. In this vision, a number of factories could construct portions of a home as stock parts and then deliver them either to a central factory or to the site, where they would be assembled. Although it’s not clear how the details of this model would work, it could take advantage of the efficiencies of prefabrication while offering aesthetic and site-specific options.

KieranTimberlake has begun experimenting with this model of prefabrication, incorporating elements of panelized and modular construction into its Loblolly house on Taylors Island in Maryland. The 2,200-square-foot house features an aluminum structural frame that was created to order and assembled on site. The frame holds floor and wall panels, called “cartridges,” that contain the electrical and plumbing runs needed for the home, including a radiant floor heating system. Modules containing the bathrooms and the mechanical room arrived on site fully constructed and were lifted into place by a crane. Exterior wall panels included interior finishing as well as insulation, windows, and exterior cladding. The house was assembled in six weeks on site, and can be disassembled quickly with simple tools. Parts of the house can be reused, while others are designed to come apart for easy recycling and disposal.

Making the Promise a Reality

To realize the environmental benefits of prefabrication, designers may need to combine elements, joining panelized construction with modular components and site-built finishes to create a structure that best meets the needs of the site and the client. As the industry continues to respond to client demand and green leadership, finding a manufacturer willing to work with green specifications will become easier. The promise of green prefabrication may soon become a reality. 

Allyson Wendt is Associate Editor of Environmental Building News, a monthly newsletter from BuildingGreen.

Prefabrication's Green Promise Originally published in the January 2009 issue of GreenSource McGraw-Hill Construction - Continuing Education

http://continuingeducation.construction.com/article.php?L=5&C=482&P=6

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