A prefab home completed by Bensonwood Homes of Walpole, N.H., for Unity College in Unity, Maine, has just been granted LEED Platinum designation by the U.S. Green Building Council. Designed for net-zero energy use, the house is actually performing ahead of expectations, even in Maine's severe winter weather. And its occupants are discovering the comforts of a net-zero life.

Known both as Unity House and as the OPEN_2 House, the home is the second designed and built as part of the Open Prototype Initiative (OPI), a partnership between custom timber-frame home builder Bensonwood Homes and the Massachusetts Institute of Technology's House_n Research Consortium. Based on performance models, the design team expected that the house's energy production would be negative from December 2008 through March 2009, but for the latter half of February and to date in March, the house's energy production has been positive, according to Tedd Benson, Bensonwood's founder and president.

Whether the house truly achieves net-zero energy goals will not be certain until the end of 2009, but early data are encouraging. Current projections are for the house to remain net-positive (producing more energy than it uses) through March, Benson notes. "Even in these colder months, they've been making quite a bit of energy. We're almost certain the net-zero goal will play out as well," he says.

The 1,930-square-foot prototype house is the second to be based on Bensonwood's Open-Built principles, using modular systems, panelized building components, and flexible assemblies. Like the first prototype house, OPEN_1 (2006), Unity House/OPEN_2 is primarily designed around principles of layering and disentanglement, which separate mechanical, plumbing, and electrical systems from the structure, granting greater flexibility and control for the occupants over the home's interior elements. Two types of demountable interior walls expand the living spaces to accommodate large gatherings. "It allows the footprint to remain smaller while it expands and contracts to meet various uses," Benson explains. (To read more about Open-Built principles, click here).

Proving the market viability of net-zero energy houses was a major goal for the OPI team, so the house incorporates many passive energy features to reduce its energy demands, including a super-insulated and tightly sealed building envelope; a finished concrete slab floor to provide a heat sink; triple-glazed fiberglass windows for passive solar heating; and a solar hot water system. An air-source heat pump supplies any remaining heating needs, which have been low (about 20,000 BTUs), and a photovoltaic system supplies most of the home's electricity, while feeding excess energy back into the utility grid.

Helping to earn the house its LEED Platinum rating is a range of recycled, recyclable, and low-VOC materials and finishes, many of which were sourced locally. Benson used some readily available, standard building materials in innovative ways as well, such as AdvanTech OSB panels, used in assembling some of the building components. After testing the concept in his own home, Benson used the AdvanTech panels as a finish material for some interior walls; he simply sanded them smooth and oiled them for a unique effect. Benson and his team also applied a locally sourced board product to the living room ceilings in a random pattern below a light source, creating squares of light every few feet.

Just as critical as the house's energy performance is the experience of living in it, Benson believes. Unity House/OPEN_2 is the on-campus residence of Unity College's president, Mitchell Thomashow, and his wife, Cindy. Since moving into the house last September, the couple have been blogging about life inside an Open-Built net-zero energy home and the house's energy use (click here).

One of the most important aspects of the house is the level of comfort and quality of life it offers its residents. "They're telling us it's been a joy for them, because it's so comfortable and in a passive way—without motors and fans running," Benson says. "They're really enjoying the unique finishes and bright light of the interiors."

Rather than being forced into a life of self-denial and sacrificing home comforts, the Thomashows instead simply have a heightened awareness of their energy use. Entries on their blog speak of the interior comfort of their home on days when the outside temperature drops well below zero; there are also detailed recordings of the surface temperature of the house's materials and furnishings and musings on how its design impacts its daily performance.

"As conscious as we are of the high-performance aspects of this building, the actual comfort and efficiency never cease to amaze me. This house is a masterpiece of intentional integration ... the ways in which each part supports the other is the secret to its success," Cindy Thomashow wrote in a Feb. 23 blog entry.

Unity House/OPEN_2 offers substantial proof that a net-zero home can deliver quantity as well as quality of life in terms of space, technology, light, and comfort.

Unity House turned out so well that Bensonwood Homes has decided to offer four net-zero capable variations on the design in its new Unity Collection, ranging in size from 994 square feet to just under 2,000 square feet; visit www.bensonwood.com. For more about Unity House from Unity College, visit www.unity.edu/NewsEvents/News/UnityHouse.aspx.