A building’s energy performance goes hand in hand with its design. In the United States, LEED has set the standards and certifications that many developers, architects, engineers, and builders aim to hit in each project they construct. Since the classification system’s rollout in 1993, thousands of buildings worldwide have earned official LEED ratings, and “achieving LEED certification” has become a talking point so well known that it’s commonplace even in popular culture. Yet LEED, which stands for Leadership in Energy and Environmental Design, is hardly the only standard in green building, and one in particular is on the rise: Passive House.
Passive House (sometimes spelled the German way, passivhaus), is a building standard that, although it shares its main goal with LEED—to help create a more sustainable world by reducing architecture’s impact on the natural environment—predates the USGBC’s prescriptive system. Its origins can be traced back to superinsulated homes developed in the US in the 1970s. To date, 30,000 buildings worldwide have been built to its strict energy performance specifications. It’s the go-to standard for green building in Europe, but stateside, it’s just now picking up steam.
Two primary institutions are responsible for developing the tools and applications central to Passive House construction. In Europe, the Passivhaus Institut (PHI), headquartered in Dormstadt, Germany, has been officially studying building practices and materials performance since 1996, using their findings to outline the Passive House building code. While other Passive House certifying organizations do exist in Europe, it is the PHI that sets research standards. In the United States, the Passive House Institute US has been adapting this code for the past seven years, taking the European principles and refining them so that Passive House buildings can optimally function in the varied American climatic zones. “It’s just in its infancy here in the US,” says Julie Torres Moskovitz, author of the 2013 book The Greenest Home: Superinsulated and Passive House Design and the principal of Fabrica718, which designed Tighthouse, New York City’s first certified Passive House project. “It took 15 years in Germany for Passive House to take off. Here, it’s just getting started.”
To anchor the movement stateside, PHIUS has laid out a set of straightforward Passive House characteristics. According to the published standards, Passive House buildings “achieve overall energy savings of 60 to 70 percent and 90 percent of space heating without applying expensive ‘active’ technologies like photovoltaics or solar thermal hot-water systems.” Their designs incorporate “superinsulation, airtight envelopes, energy recovery ventilation, [and] high performance windows” to accomplish this drastic energy reduction. Unlike with LEED, energy performance can be precisely predicted because energy consumption and output is carefully calculated for each Passive House structure using Passive House Planning Package (PHPP) software, a program developed initially in Europe. Designers deploy PHPP in the early design phase, making energy performance central to each Passive House building. “It’s similar to Excel,” Torres Moskovitz says of the software. “It’s all plug-ins and formulas that relate to building science. When you use it, you input all the details—a structure’s materials, its design, its local weather—and PHPP runs the details and gives you a model that tells you about building decision trade-offs.”
“It’s really useful,” she adds, “because you instantaneously see a building’s performance results.” Armed with the PHPP predictive model, designers can make informed decisions about each element that goes into a building’s total design. And as a project evolves, different decisions can be made to counteract any other design changes that would otherwise increase energy output or consumption.
It’s a smart checks and balances system of building, and it’s been consistently proven to work. “Passive House is very simple because it’s numbers based, so you have to be accountable,” says Tim McDonald, a Passive House specialist whose firm, Onion Flats, developed the Belfield Avenue Townhomes, Philadelphia’s first certified Passive House project. To McDonald, the numbers-don’t-lie approach pushes architects to engage the question, “How do we get buildings to sustain themselves and hit net zero?” And when it comes down to actually answering that question, the extensive training required to become a Certified Passive House Consultant (CHPC) certainly makes architects, builders, and craftsmen well acquainted with all the numbers that go into a building’s energy calculations.
PHIUS divides the rigorous CHPC program into two learning phases. Phase one requires 24 hours of classroom instruction, and introduces participants to heat transfer, air tightness, thermal bridge free detailing, superinsulation, highly efficient ventilation, and moisture control principles. Phase two teaches participants how to use the PHPP software via case studies that model real Passive House buildings. A final software-competencies exam and take-home modeling case study compose the certification exam. “Learning how to track your work from the design side makes you rethink the process of how things get structured on the outside in relationship to the inside,” McDonald says. More than one CPHC can work on a project, and often designers team up with other CPHC engineers and builders, minimizing the chance that a Passive House project will compromise its design intent.
Torres Moskovitz prefers this method of building a CPHC team. “I always want to work with a CPHC engineer because they understand the smallest ins and outs of the software,” she says. “When it comes to building, I like to work with CPHC builders and tradesmen, too. It just makes accomplishing your Passive House goals that much easier when everybody understands why we’re working toward Passive House certification on a project and how, when building, we can actually adjust the design to get there.” Her point is a good one: a Passive House predictive model is only good if the Passive House building is actually built so that it can achieve its reduced energy numbers. Strong communication among the entire building and design team is essential. “When we were building Tighthouse, we put up a sign that said, ‘Report any air penetration to the outside to Julie,’” she says. “It was a simple approach, but it helped everybody stay on track. I could tweak the design, and we could all work together to solve materials and construction problems so that we could make an airtight building.”
At Tighthouse, hitting the Passive House numbers meant thwarting as many thermal bridges between inside and outside as possible—a common goal for all Passive House projects. The home is actually a retrofit of an old Brooklyn brownstone, and large doors and windows and doors puncture both its front and rear façades. Its design required taping around as many joints as possible so that the home could remain superinsulated. “We taped everything—especially around the windows—on every overlapping surface so that nothing was leaking,” Torres Moskovitz says. The windows themselves are a tilt-and-turn model commonly used in Europe. Torres Moskovitz sourced them from a European company and had them imported because similar American-made models weren’t available.
Which is common. Because Passive House building design is still relatively young in the US, architects and builders are forced to source PHI-approved materials from Europe. However, American building materials manufacturers are beginning to come to market with products certified by PHIUS. In 2013, Marvin Windows and Doors, based in Warroad, Minnesota, earned the PHIUS stamp of approval for its Ultimate Casement window. “It’s been in the works for some time,” says Christine Marvin, director of marketing for the family-owned business. “Marvin has always been focused on the voice of the customer. Years ago, we heard about Passive House from our customers, and we knew we had to respond with product options and find solutions to meet their needs. We also anticipated that the movement would pick up momentum in the US.”
“We’ve been approached from Georgia to Portland,” adds Brenda Brunk, a Marvin product planner behind the Passive House Ultimate Casement project. “People are very passionate about getting American products for Passive House projects.” Working in tandem with PHIUS, Marvin’s research and development team learned how to refine its traditional Ultimate Casement window design in order to meet the Passive House materials certification benchmarks. The Passive House Ultimate Casement model meets the standards for the climatic conditions of US Zone 3 and Marine South, and it’s available in triple and quadruple glazing.
As American-made products arrive on the market, architects can achieve Passive House designs that don’t sacrifice style, an issue that’s often raised as one of the standard’s drawbacks. “There are many beautiful Passive Home buildings around the world,” McDonald says. “One of the problems [in the US] is that there just aren’t enough excellent architects designing Passive House buildings yet. But you really don’t have to compromise style for a Passive House. It’s a symbiotic relationship between one’s design and the Passive House parameters.”
Regardless of architectural style, the mechanical nuts and bolts of each Passive House project remain relatively constant. Unsurprisingly, superinsulated buildings require high performance insulation that keeps heat transfer to a minimum; for most of the US, a Passive House thermal envelope typically requires at least twice the R-value as required by the building code. Superinsulated Passive Home projects, since they are so well sealed, also require a special ventilation system—what McDonald refers to as a “lung” for the building—that also provides energy recovery. The energy recovery ventilator, or ERV, works by bringing in fresh air from the outside, while exhausting stale air out. “The air from the outside absorbs the heat from the exhaust air as it’s vented into the house, leaving the air that’s vented outside a cooler temperature,” McDonald explains. This, of course, reduces energy losses to the exterior, and the constant air exchange works in tandem with the superinsulation so that buildings do not need to be heated and cooled to such extremes. The goal is to construct a structure that’s so well insulated and regulated that it remains a constant temperature, even when heating and cooling are cut.
McDonald used an ERV in his project, but Torres Moskovitz used a heat recovery ventilator (HRV) in her project, which is similar and can become an ERV by just switching out a part. The energy reductions in both projects’ PHPP models have so far proven accurate. “The Tighthouse owners are amazed by their utility bills,” Torres Moskovitz says. “In that project, we literally monitor the electrical load of every circuit so we can adjust anything that’s off.” McDonald’s experience has been similar in the Belfield Townhomes, where he also monitors all electrical circuits and compares electrical usage across the three-unit complex. “Since we have a multifamily complex, we like to show each of the families and the landlord all the statistics so they can see and compare how they’re using energy,” he says. “The key to all of this is to educate people about value of understanding their energy consumption, something that’s not common in this country.”
It’s this clear, results-oriented approach, coupled with the movement’s scalability and long-term financial practicality, that’s inspiring architects and builders to adopt Passive House practices. “The amazing thing about Passive House is that it works,” McDonald says. “You design a building, run it through the software, build it, and it just works. Occupant behavior, however, is the greatest variable, but this comes with education.”
Both architects are hopeful for the Passive House movement’s success, and they’re confident that it won’t take much more time to really take off. “More young people who are designing homes or who are having them designed are moving toward Passive House because they see it as a tool, not as a hindrance,” Torres Moskovitz says. “As a designer, once you’ve done one Passive House project, it’s hard to go back. You can’t help but apply its techniques to all your projects in the future.”
McDonald phrases this idea a bit differently, but the sentiment is the same. “Passive House is a standard that really allows buildings to be what I call ‘Net-Zero-Energy-apable,’” he says. “And if you look at a project holistically, as we do, they don’t have to cost any more money. If you can design and build a building that can achieve net-zero energy at a zero premium, there should be zero debate.”
This is the ultimate Passive House goal, and as the building industry continues to green itself, it’s a safe bet that many will do so through the calculated, cost-effective strategies outlined by the Passive House standard.
For more, read Q&As with Lukas Armstrong and Vahid Mojarrab and an op-ed by Passive House Institute US executive director Katrin Klingenberg.