Prefabrication's Green Promise

Mass Production Offers Unique Opportunities For Customized Green Construction
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From GreenSource
Allyson Wendt

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."

 



Off-the-grid WeeHouses from Alchemy Architects start at around 350 square feet and cost $100,000. (top); A small wood stove provides all the heating necessary for the WeeHouse. (bottom)

Images courtesy Alchemy LLC

 

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.

Frederick 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.

 

 

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Originally published in GreenSource
Originally published in January 2009

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