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For more than 30 years, Passive House principles have been a valuable guide to making buildings energy efficient. But now, with steady improvements in our understanding of embodied carbon—the carbon emitted when building materials are created, transported, and installed—the overall carbon impact of Passive House construction has become a subject of concern.

Photo courtesy of NIGHTNURSE IMAGES/MAGNUSSON ARCHITECTURE AND PLANNING

DEKALB COMMONS, Magnusson Architecture and Planning's affordable-housing complex in Brooklyn, New York, will seek Passive House certification.

Just how much energy does it take to make the added insulation, extra layers of glazing, and other features required to meet Passive House standards, compared to how much energy those features might save over time? “A decade ago, we would talk about the tremendous benefits of operational-energy savings,” says Alan Barlis, a principal at BarlisWedlick, a New York–based firm that has completed about 25 certified Passive House buildings. “Today we tell the rest of the story, and a big part of that story is embodied carbon.”

A particular concern is that the large amount of carbon emitted by spray-foam insulation, which is used in some Passive House buildings, will cancel out the expected operational-energy savings. But proponents of Passive House standards say there are many other kinds of insulation, and that Passive House buildings need not be high in embodied carbon. Bronwyn Barry, a San Francisco architect who works pro bono as the policy lead for the New York–based Passive House Network (until recently called the North American Passive House Net­work), says, “We’re starting to pay close attention to embodied carbon. What we’ve seen from our early studies is that the choices homeowners make about things like square footage have a greater impact on embodied carbon than the decision to follow Passive House standards.”

Those standards, developed in Germany in the 1980s, require buildings to be heavily insulated and practically airtight, minimizing heating and cooling loads. They also mandate high-efficiency ventilation systems to circulate fresh air. Thousands of buildings have been certified by the international Passive House Institute, or PHI, and its competitor, the Chicago-based Passive House Institute U.S. (PHIUS), and the numbers are increasing sharply. Plus, experts say, for every building certified there may be a dozen or more that follow some or all of the Passive House principles but whose owners haven’t sought certification.

Despite the name, only some Passive House structures are houses. The principles can be applied to any building type. In New York, Architecture Research Office is designing a primary school and a high school that meet Passive House standards. In New Haven, a concrete office building by Marcel Breuer from 1968 recently reopened as the Hotel Marcel (RECORD, June 2022), which is expected to receive Passive House certification, in part because the building’s thick concrete walls provide thermal mass, helping stabilize indoor temperatures.

In terms of reducing operational energy, “Passive House has been transformative,” says Kate Simonen, chair of the architecture department at the University of Washington and director of the nonprofit Carbon Leader­ship Forum. But, she adds, “If you don’t do an embodied-carbon analysis, there could be serious unintended consequences”—that is, buildings using more energy, overall, than they would have if they weren’t built to Passive House standards.

A 2013, study of a single-family Passive House residence in Belgium found it used, in total, 3.8 percent more energy over an 80-year period than a standard house with the same geometry, structure, finishes, and number of residents, which the authors attributed to the energy used to make the Passive House building’s “large amount of insulation and the triple-glazed high-efficiency windows.” To make sure embodied carbon is taken into account, they argued, “current building-energy-efficiency certifications should widen their system boundaries.”

A more recent study considered several possible energy-saving retrofits to a 40-year-old house in Sweden. The study found that, compared to achieving the high level of insulation required under new energy codes, meeting the even stricter Passive House standards resulted in a tiny additional operational-energy savings but a huge increase in embodied carbon. The study’s authors concluded that to optimize energy savings, stopping short of strict Passive House rules might be the best solution. They also suggested that future building codes consider embodied as well as operational energy.

Photo courtesy of MAGNUSSON ARCHITECTURE AND PLANNING

DEKALB COMMONS — WINDOW JAMB