When Betsy Harper (MBA 1984) was shopping for real estate in Cambridge, Massachusetts, in 2018, she had some atypical requirements. Her dream house would have “enormous health problems.” The dark-gray house she eventually purchased in Observatory Hill was moldy, with terrible indoor-air quality and standing water in the basement. Over the last three years, Harper, through her company, Birchwood Sustainable Development, turned it into a beautiful bright-blue Victorian-style home. In its aesthetics, the five-bedroom, five-and-a-half-bath house matches its neighbors in the historic area; but in its construction, the building is an innovation—and a proof of concept that could ultimately spark a home-design revolution.

A Passive House is designed to be ultra-energy efficient. Some, like Harper’s Victorian, achieve net-zero-energy demand by pairing ultra-low energy use with solar panels for energy production. But Harper’s home goes even further than that select group—achieving net-positive-energy production—because the house uses so little energy that the solar production is designed to exceed the annual energy demand. The Passive House movement got its start in Germany in the early 1990s; by the mid-2010s, there were an estimated 60,000 Passive House buildings in the world. But many of those are boxy, modern structures. An ultra-energy-efficient house can’t leak air where walls meet, as typical houses do, which makes more traditional and elaborate creations a challenge.

Harper came to energy-efficiency development after a 20-year career in the financial industry. “As I contemplated what I wanted to do for the second half of my career, it became clear that I wanted to work on climate change issues and help us get to the US goal of zero-carbon emissions by 2050,” she says.

In the early 2000s, Harper moved into nonprofit consulting, working for clients such as the Appalachian Mountain Club and the Charles River Conservancy, and then into roles that concentrated on the growing field of sustainable building. According to the United Nations, buildings and their construction account for 39 percent of greenhouse gas emissions. It was the measurable impact of the work that attracted her. “I had used a lot of analytical tools in the financial industry, and suddenly these were made available in the building industry,” she recalls. She could, for instance, track the positive environmental impact of each dollar the Massachusetts Department of Housing and Community Development spent on retrofitting and installing renewable-energy technology in low-income housing during her tenure as the department’s sustainability program developer.

But the concept of building a Passive House from the ground up—the most cost-effective way to fully incorporate the newest building science—captivated Harper. She is herself the owner of a leaky, high-maintenance 130-year-old Victorian in Newton, Massachusetts, and thus knew well the difficulty of her undertaking in Cambridge, but she wanted to prove that the Passive House model could be implemented within a variety of architectural styles, opening the door to wider adoption. She launched Birchwood Sustainable Development in 2018 to take on the task.

The process began with a lot of education. Her Cambridge neighbors, unfamiliar with the Passive House concept, were initially skeptical of Harper’s plans, but two historical commission meetings and nine neighborhood meetings later, she was ready to start demolition. The design process was complex, and Harper worked with design-and-build firm Group Design Build to execute an exacting vision. Each bay and gable creates challenges for unwanted air leakage and heat loss. To dramatically decrease potential loss at the seams, the core shell was built in 90 panels at a factory in Maine and then craned into place on site. Factory construction enabled the six layers of insulation and air-resistant and moisture-wicking materials to be cut and adhered with precision. And the triple-paned windows and doors, manufactured in Poland, were installed with exacting tolerances to avoid the traditional problem of significant air leakage around window and door frames. An air-exchange system turns over the filtered air supply in the house every three hours, providing superior indoor-air quality and helping the house maintain a constant, comfortable temperature. The structure is so well insulated and air sealed, there is near silence inside the house. Heating and cooling is provided with nine heating and cooling zones from an ultra-high efficiency air source heat pump system­–completing the all-electric house which uses no fossil fuels.

The project itself was also an educational tool. Although the pandemic curtailed some of Harper’s plans, dozens of architecture professors and students, engineers, other developers, and government policy-makers toured the house during the building phase. Harper hopes more people will recognize the benefits of this approach to house design. Though a single-family Passive House can require 10 percent to 15 percent higher up-front investment, the lower energy and maintenance costs can offset the expense. And Harper estimates that larger dwellings can be built for a 0 to 2 percent premium. “The biggest market transformation is happening in large-scale multifamily buildings, particularly in low-income residences,” she observes. “At 25 units or more, you have real economies of scale.”

A higher-density project may be on the horizon for Birchwood Sustainable Development, says Harper. But for now, she is thrilled that her state-of-the-art home recently received multiple bids when she put it on the market in early June, selling within three days. “I had no idea of the true market demand for this type of product,” says Harper. “I’m very encouraged that home buyers are educating themselves about durability and indoor-air quality and are demonstrating a real interest in a lower-carbon lifestyle.”

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