Posted on 19 February 2024 by Guest Author

This is a re-post from Yale Climate Connections by Sarah Wesseler

Imagine a home so efficient that it could be heated with a hair dryer.

That’s the promise of a passive house, a design standard that’s becoming increasingly popular in the architecture community for its benefits to occupants and the climate.

In passive house buildings, an airtight facade prevents unwanted flows of energy between the interior and exterior — a marked break with typical structures that let heat in during the summer and leak it out during the winter.

“Passive house is the most reliable, cost-effective, and healthiest way to reach superb energy performance in architecture,” said Sara Bayer, the director of sustainability at New York City design firm Magnusson Architecture and Planning.

Some policymakers are taking notice.

Buildings are a major source of planet-warming emissions. Reducing the amount of energy needed to maintain comfortable temperatures, keep the lights on, and provide other critical services is vital to meeting governments’ climate goals.

In recent years, Massachusetts has become a leader in promoting passive house design. The standard is a natural fit for the government’s building efficiency push, said Beverly Craig, a program director at the state-run Massachusetts Clean Energy Center.

“We can be sure when we build to passive house standards that we’re going to get 40 to 60% less energy use per square foot than what we traditionally have for [building] code,” she said.

Heat your home with a hair dryer

Despite the name, passive house design can be used for any building type, from hospitals and schools to high-rises. It can also be used on both new and existing buildings, as well as in any climate.

Passive house buildings feature thicker-than-normal insulation, energy-efficient windows, and a continuous membrane that prevents thermal bridges — spots on the facade where energy can leak through. (Think of wearing a warm coat without any gloves on a frigid winter day, Bayer said: Your hands are thermal bridges letting body heat escape.)

Together, these measures greatly reduce the need for energy-intensive heating and cooling, which together account for the majority of emissions from building operations. In fact, passive house advocates say that a typical-sized home can be heated with the energy equivalent of a hair dryer.

Thermal image from Nuremberg, Germany, showing heat escaping through the facade of a standard building in the background while the passive house in the foreground maintains a more consistent temperature. (Image: courtesy of the Passive House Institute)

And though many passive house buildings have mechanical heating and cooling systems, they’re typically smaller than their counterparts in standard buildings, thereby requiring less energy to manufacture and use. In addition, these appliances often aren’t needed for months at a time; like a thermos, a passive house can maintain internal temperatures for long periods.

Critically, the standard also calls for testing while the building is under construction to confirm that the facade is as airtight as intended. This step isn’t included in many other sustainable building methods, which can lead to significant differences between the energy efficiency levels the designers intend to achieve and the reality after occupants move in. With passive houses, “you have a verified and tested [building] enclosure, so your mechanical [heating and cooling] systems are definitely going to operate with the energy use that you’re expecting,” Bayer said.

Highbridge, a tower being designed by Magnusson Architecture and Planning, is aiming for passive house certification. When complete, the building will offer a mix of affordable and supportive housing, as well as a family shelter, in the Bronx. (Image: Rendering by Nightnurse. Courtesy of Magnusson Architecture and Planning)

How passive house could ease the way for a cleaner power grid

If adopted at scale, passive house could have major benefits for decarbonizing the electricity grid, said Lisa White, the associate director of Phius, a nonprofit focused on the standard.

“The electric grid essentially operates in order to feed the [energy] load that buildings have,” she said. “Whatever energy a building needs, the grid must sustain that, right?” In particular, the grid needs enough energy in the system to meet demand during the peak times for heating and air conditioning.

The move toward electric-powered building systems such as heat pumps complicates this by increasing reliance on the grid. Another challenge comes from the fact that solar and wind energy are produced intermittently, making it difficult to align supply and demand for round-the-clock building operations.

Passive house reduces these challenges by dramatically lessening buildings’ energy needs. “The lower peak load in the building, I think, is kind of the No. 1 thing a building can do to speed up the renewable transition,” White said. “If you can reduce the amount of renewable energy needed to power the building, right there you’re cutting costs and complexity.”

Graph of the annual load profile for typical buildings versus passive house buildings, showing lower annual energy consumption. (Image: courtesy of Lisa White, Phius)

Health and resilience benefits of passive house design

The airtight facade required by passive house necessitates another major break with standard buildings: a mechanical ventilation system providing a continual supply of filtered fresh air. (Occupants can also open windows whenever they choose.) This system also transfers heat between incoming and outgoing air to help maintain comfortable indoor temperatures while conserving energy.

This ventilation process has benefits for occupant health, according to Ken Levenson, executive director of The Passive House Network, a nonprofit dedicated to promoting the building method. In typical buildings, breathing air comes from the leaky facade, meaning “you have polluted exterior air moving through the building unfiltered and little real control over any indoor air pollutants or the quality of the indoor air,” he wrote in an email. “By contrast, passive house ventilation provides a baseline of very high quality, healthy indoor air.”

Architect Greg Fisher’s passive home in Fort Collins, Colorado. (Image credit: Sierra Ann Photography)

This baseline is particularly important as climate change increases the risk of wildfires, said Greg Fisher, an architect who designed his own passive house home in Fort Collins, Colorado. A tightly sealed envelope can help keep smoke out, while the filtration system brings in clean air.

As extreme weather grows more common, passive house’s ability to maintain comfortable indoor temperatures during power outages is also important, Fisher said. On two occasions, the heating and cooling system in his home failed during periods of extreme outdoor temperatures — and at first, the change was imperceptible. “We didn’t realize it for two days in both cases,” he said. “It was a really good illustration of the resilience of the home, that you can survive several days without radical changes in the inside temperature relative to the outside temperature.”

How did passive house design get started?

The Homes at Anne M Lynch Old Colony Phase 3C, a multifamily residential building in South Boston that was awarded $220,000 as part of the Massachusetts Clean Energy Center’s Passive House Design Challenge. (Photo credit: Ed Wonsek)

Passive house’s origins lie in the U.S. energy crisis of the early 1970s when an embargo on oil imports from members of OPEC led to skyrocketing prices. In response, a group of building professionals affiliated with the University of Illinois designed a home that used extensive insulation to drastically reduce energy needs. Other designers and researchers in the U.S. and Canada built on this innovation.

But as oil prices dropped and the demand for conservation fell, the nascent North American movement faded. Germany eventually emerged as the new hub for the standard.

Today, Europe leads the world in the deployment of passive house buildings. This success can be traced in part to ambitious policies developed in different parts of the continent. In 2007, the regional government of Brussels, Belgium, achieved impressive gains by launching a competition to spur the growth of a passive house market, then capitalizing on this momentum by changing its building code in 2009, requiring all new developments to adopt a passive house framework. (In 2019, New York State launched a climate-friendly buildings competition inspired by the Belgian capital’s example.)

Another leading city in passive house design, Frankfurt, Germany, passed a law in 2007 requiring that all new buildings follow the model. At the national level, Scotland announced in early 2023 that it will require that new housing be designed to passive house standards.

Though North America lags behind Europe, governments in some areas have made significant commitments to the standard in recent years — and seen a notable return on investment.

In Massachusetts, a suite of programs designed to transform the multifamily residential market has led to “a hockey stick of adoption” since it was started in 2017, said Beverly Craig. As of 2020, the state had only one multifamily passive house. Today, 119 buildings that have received financial and technical support under the Mass Save passive house incentive program are scheduled to achieve official passive house certification by 2026. In addition, 30 communities accounting for approximately 25% of the state’s population have opted into a higher-tier building code that mandates this certification for buildings of more than 12,000 square feet.

North Commons at Village Hill Passive House in Northampton, Massachusetts, a winner of MassCEC’s Passive House Design Challenge. (Image credit: Community Builders)

Similar results have been seen in other areas that have supported the standard. In a 2022 report, The Passive House Network found that, in general, places with government engagement on passive house had seen a much greater amount of development using the method. “The notable lead by New York, followed by British Columbia, and trailed closely by Pennsylvania, indicates a strong correlation with clearsighted policies (and funding support) laid down in these three regions,” wrote author Bronwyn Barry, an architect specializing in passive house design.

For another report released earlier this year, Barry described policies that have been shown to increase adoption across different geographies, from providing incentives to developers, designers, and building owners to incorporating passive house outcomes in building codes.

Barry now uses these findings to lobby policymakers across the country as the head of the Passive House Network’s policy committee. “We figured out which policies are working at what level, so when we go to city policymakers, we take them city policies that are working elsewhere,” she said. “And when we go to the state level, we know there’s a certain number of things that the state level policymakers can actually effectively action.”

“It’s been a very clarifying journey,” she said. “It’s helped to get us all really focused, and also to not waste time on trying to invent some new policy that may or may not be actually effective.”