Prefab homebuilding is undergoing a revival, but it’s nothing like its predecessors. In its new incarnation, “green” prefab promises an efficient way of building a high-quality, energy-conserving home with smart, earth-friendly materials.
Architect Michelle Kaufmann’s foray into the world of prefabricated homes was purely practical. In 2001, she and her husband, builder Kevin Cullen, began searching for a modest home in the overinflated San Francisco Bay area real estate market. After six months of being unable to find an affordable, energy-efficient, eco-friendly home, they decided they needed a new approach—create their own.
They purchased a lot in a semi-rural town in Marin County, California, and worked to complete their green design—a home that would use less water, energy, and materials than a conventionally constructed home.
The result is a three-bedroom, 1,560-square-foot home designed for function and tailored to the climate. Strategically placed dual-paned windows and doors throughout maximize cross-ventilation and natural lighting while minimizing the need for artificial lighting and mechanical climate control. Exterior gliding wood shades help mitigate heat gain from the hot summer sun, while maintaining ventilation. The sloped roof of their “Glidehouse” facilitates hot air inside the home to move up and out of the house through small, operable clerestory windows. Oriented south, the roof also accommodates a 4.5-kilowatt solar-electric array. Inside the house, energy-saving LED and compact fluorescent lighting, and Energy Star appliances, help keep energy use low. Durable, low-maintenance materials, such as composite concrete countertops and weathering steel siding (alloyed for weather resistance by creating a thin rust sheen), were used inside and out.
Intrigued by their unique home construction project, friends and colleagues asked how they could have modern, green houses too. “People are desperately trying to find healthy, green, efficient homes for their families,” says Michelle. “However, the information and solutions are not always easy to find. People are uncertain of what to do and the best way to do it. People are busy, have budgets, and want simplicity. Where were the easy, affordable green solutions?”
When Michelle and Kevin were searching for a place to live, green home options were limited—and expensive. After their home-building experience, Michelle made it her professional goal to “marry good design with minimal environmental impact, and create ‘green’ homes that could be widely available.” She says that translated into “creating a prepackaged solution using the principles of mass production combined with sensible, uncomplicated floor and roof plans, eco-friendly materials, and low-energy options.”
“I soon realized I would have to start thinking less like an architect and more like a product designer,” says Michelle. “I began researching mass production and working on parallel tracks. Although we had used structural insulated panels (SIPs) in our home’s construction, I also researched how a factory could make the walls and roof, and how to calculate maximum dimensions for shipping a home module on flatbed trucks.”
Michelle’s persistence paid off when she found a prefab factory willing to give her a chance. The Kaufmann-Cullen home had taken 14 months to construct at a cost of $197 per square foot. The factory built an identical Glidehouse in less than one-third of that time for $40 less per square foot. Since then, Michelle has built 33 prefab homes for clients ranging from young, urban families to rural retirees. But those aren’t the most impressive numbers. She estimates that compared to conventionally constructed homes, these 33 homes together provide an energy savings of 1,934,000 kBtus per year, a water savings of 3,251,920 gallons per year, and annually save 594,000 pounds of carbon dioxide from being emitted.
Michelle is not alone in her quest to bring modern, green homes to mainstream markets. In the past few years, several architectural firms have started to green their scenes (see “Pushing the Envelope” sidebar).
While their design approaches may vary, the primary goal of green modern prefabs remains the same: reduce a home’s environmental impact by maximizing energy efficiency, reducing water use, and using eco-friendly materials, while making it a healthy, comfortable space for its occupants.
“The opportunity to do better seems extraordinary,” says Bill Haney, president of the Boston-based prefab design company, Blu Homes. “Other countries do better. The average footprint and the amount of space and energy costs for the average family of the same income in Europe is dramatically lower. Other countries make a lot of their housing in factories, so they are able to use fewer materials and be much more efficient—so they don’t have big waste. In Finland, about 70% of the houses are built in factories before they get to the site. In the United States, it’s more like 0.7%.”
Prefab proponents say that one of the main advantages of prefab over kit, panel, or site-built homes is the amount of work done off-site. Most of the home is factory built, from the shell down to the kitchen cabinetry and even lighting fixtures, allowing predictable time and cost estimates while maintaining quality. By decreasing on-site work and increasing factory assembly, prefab home providers say they have greater control over the quality, schedule, and cost of construction.
Because the site work and home construction can happen simultaneously, the overall construction schedule for modular homes can be shortened, and homes can often go up in a hurry. Besides offering potential time-savings, says Kaufmann, building in a factory nearly eliminates the uncertainties of scheduling that often plague traditional building projects, such as delays or damage due to weather.
Blu Homes is focused on making site work quicker and more efficient. “We really feel that customers suffer when they have site-cost overruns,” says Blu Homes’ Maura McCarthy. “Pier foundations, for instance, can save between $8,000 and $15,000 compared to conventional foundations, and also have positive benefits in terms of the environment, since the site is disturbed less and less material is needed for the foundation.” In some cases, McCarthy says, a hydraulic truck can be used instead of a crane to place the modules, which offers both savings and less disruption to the site. Blu Homes is also looking at ways to ship “more house on less truck” to minimize shipping costs and fuel use for transportation.
Modular homes all meet local and national building codes, but also can exceed them. Because they have to withstand the rigors of shipping and, possibly, being crane-lifted into place, modulars are typically built with more framing and strapping details to maintain their building integrity. According to Kaufmann, the additional materials for that extra strength can be offset many times over by the savings in construction waste achieved by prefabrication. Critics of prefab take issue with the “less waste” argument, considering that, in some areas, waste removal companies are available that will pick up on-site construction materials for recycling, making the comparison moot.
Jason Pelletier, founder of the eco-home improvement site Low Impact Living, says that a distinct advantage of prefab construction is that “hard-to-find green materials can be bought in bulk and used for many projects, minimizing delays and ensuring that no shortcuts are taken due to unavailable materials.” He points out that the opportunity for “bulk purchasing and the delivery of a small number of completed modules to the home site can dramatically reduce pollution from transportation to and from the site.”
McCarthy says that “there’s absolutely no doubt that you get efficiency of scale with large purchases or large products, and having them shipped to a factory,” and that using local factories to put together homes “reduces the amount of travel and shipping costs.” But, she says, focusing on the home’s embodied energy doesn’t give a true picture of the more important aspect—its performance over time. “When you look at a home’s embodied energy compared to its 50-year life-cycle cost, it’s miniscule. Over a home’s lifetime, the energy it consumes could be 30 to 50 times its embodied energy.”
Up-front affordability has always been the bane of modern homes, whether customized or prefab, and, many say, the jury is still out on whether prefab can bring modern to the mainstream (see “Cost of Going Green & Prefab” sidebar). But others argue that the more important consideration is long-term costs.
“If you’re the average family, you’re figuring out what mortgage payment you can make, and insurance is probably calculated into that mortgage payment, and probably property taxes are calculated into that,” says Haney. “Maintenance costs? That’s your own nickel. And energy? You’re all on your own. We’re trying to refocus the questions: What would it take to buy a house? How long will it be on site? What will it cost to operate it?”
Blu Homes puts their prefab designs through off-the-shelf and proprietary modeling software to get detailed estimates on how they will perform in various climates, and works with clients to tailor the envelope—insulation, framing, and window placement—to their specific climate and needs. “Just like you can find out a car’s fuel economy before you buy it, we think people should have a sense of ‘gas mileage’ for their homes before they buy,” McCarthy says.
Kaufmann agrees. “To avoid repeating the dire situation so many homeowners are in today, it is critical that our thinking evolve around home costs,” she says. “Once we start to equate monthly costs with the true costs of a home, the positive impact will reverberate among homeowners, who will be less likely to find themselves living in homes they cannot afford and more likely to choose green homes, which are often more affordable in the long term.”
In 2005, green homes made up just 2% of the market—but in 2008, they were expected to account for anywhere from 6% to 10%. By 2012, that market share is expected to jump to between 12% and 20%. Yet U.S. builders cite “consumer willingness to pay” as the second largest obstacle affecting green home-building growth, and say that the higher up-front costs of the “green premiums” attached to sustainably designed homes is a barrier to green building’s expansion into the mainstream. However, what people are realizing is that, spread out over the terms of a 15- or 30-year mortgage, these higher up-front costs can be easily absorbed and offset by lower utility bills and, to varying degrees, lower maintenance costs and higher tax deductions.
“If we can come up with a system that is more affordable for the average family to live in, is better for the natural world, is more healthful for them and their children—I think that’s the kind of thing the average family is looking for,” says Haney. “Working with the Massachusetts Institute of Technology and others on energy modeling software has convinced us that it’s not that hard to do.”
Managing editor Claire Anderson spends her spare time poring over green home designs and trying to master SketchUp.
Prefab Green by Michelle Kaufmann & Cathy Remick (Gibbs Smith, 2009)