Passive house (PH) building design is challenging, meticulous and energy-focused. It began as a niche approach to deliver serious energy efficiency for single-family construction. Now gaining traction across the United States, “house” is a bit of a misnomer; PH has scaled up to include multifamily, high rises, schools and offices.
The basic elements of passive design include a tight building envelope supported by thicker-than-average walls; continuous insulation and air tightness, preventing outside air leaking in and inside conditioned air leaking out; high-performance doors and windows; balanced heat- and moisture-recovery ventilation and downsized HVAC; and managed solar gain using the sun. While the majority of PH projects are new construction, retrofits exist as well.
PH design emerged in the 1970s in Canada and through funded research by the U.S. Department of Energy (DOE). Germany embraced the concept, resulting in the German Passivhaus Institut (PHI) in the 1980s helping popularize adoption in Central Europe. The Passive House Institute US (PHIUS) officially formed in 2007. In March 2015, its PHIUS+ 2015 Passive Building Standard helped make PH workable across climate zones, moving a boutique energy performance design approach toward broader adoption. The PHIUS Technical Committee and Building Science Corp. developed the standard under a U.S. DOE Building America grant.
PHIUS+ Certified and precertified projects represent 1,200 units nationwide, more than 1.1 million square feet. They have bettered energy performance by 60–85 percent (depending on climate zone and building type) compared to code-compliant buildings (International Energy Conservation Code 2009).
“The green building communities, American Institute of Architects and others have taken notice,” said Katrin Klingenberg, executive director for PHIUS, and co-founder with builder and developer Mike Kernagis. “In this year alone, we will have 400 or so certified and precertified projects (completed or substantially completed). If you add in submittals not under construction, that brings numbers to 700-plus. PH is another way to get to building sustainability, resiliency and low-carbon operation.”
PHIUS has incorporated DOE’s Zero Energy Ready Home (ZERH) protocol into the PHIUS+ Certification program.
“Passive design leaves you with the smallest gap you need to close to get to net-zero and do it affordably,” Klingenberg said.
ZERH certification also requires buildings to be Energy-Star certified. PHIUS-2015 buildings earn the Environmental Protection Agency’s Indoor airPLUS label, as well.
Klingenberg said the integrity of the passive design falls on electrical contractors.
“The envelope is so good that it can hold the heat if you lose power or keep the house cool in summer,” she said. “Air-tightness is super important. Fewer building penetrations are essential and must be thoroughly sealed. You don’t want to diminish the integrity of the building skin introducing failure of the passive design.”
Multifamily PH design
New York City Mayor Bill de Blasio has cited PH as one tool in his “One City: Built to Last” plan promoting building sustainability and reduced energy use. The goal is to reduce citywide greenhouse gas emissions 7 percent by 2035, leading to an 80 percent reduction by 2050. In new construction, Passive House design and its deep energy-reduction capability is aligning with the city’s commitment to affordable multifamily housing. The demand has created a competitive market among PH developers and builders.
“NYC was the first city [where] we held Passive House training back in 2009,” Klingenberg said. “Essentially, bigger is better in passive design. You take advantage of the compactness of the build with one unit benefiting from the heat of another; internal heat sources from people, appliances, HVAC. In general, larger buildings don’t need an excess of insulation. Because multifamily structures are internal-load dominated, heating is not a problem. Overheating, however, can be based on solar gain from larger structures. Lower solar gain windows and shading devices help regulate this issue.”
The Bluestone Organization, based in Jamaica, N.Y., has developed Beach Green North, a passive-designed seven-story, 101-unit building. Completed in 2017, the PHIUS+ 2015 precertified project features a building envelope with insulated concrete; energy-recovery ventilation; variable refrigerant flow central air source heat pumps for heating and cooling; rooftop solar; and a natural-gas-fired co-generation system that will produce electricity, supply hot water, and serve as a backup emergency generator.
“We have been building to a higher energy efficiency standard for a long time,” said Eric Bluestone, Bluestone Organization partner. “Eight years ago, our Norman Towers project taught us that using different techniques for better thermal mass, insulation and air-tightness was not as difficult as we imagined. We were able to do so without adding a lot of cost. That moved us to tackle a complete passive design with Beach Green North. Key components to a successful PH include well-thought-out air-sealing details, implementation and progress inspections, as well as special attention to minimizing or eliminating thermal bridging.”
PH requires educating potential owners, the lending community and mechanical engineers. Explaining the concept, showing demonstrable energy cost savings through monitoring and tours of PH buildings featuring the smaller mechanicals, are necessary steps to introduce what is a new concept to most.
“The building envelope and mechanicals for Passive House multifamily show obvious economic benefits for building operation,” Bluestone said. “The savings in utility bills is especially keen for tenants with limited income living in affordable housing.”
Bluestone Organization is breaking ground on two new PH projects. Tree of Life in Jamaica is set for 12 stories, while 42 Broad Street in Fleetwood, N.Y., will climb 16 floors. The firm is also serving as construction manager for the first PH condo building in Manhattan, set to be six stories with six units. Collectively, Bluestone Organization has developed passive multifamily for affordable housing, but also mixed income and market rate.
Passive House design has expanded to commercial and institutional buildings. The Center for Energy Efficient Design in Franklin County, Va., is the first Passive House public school (K–12) in the United States.
“If you can rent with your utility costs less than a third of renting in another building, it is going to be a draw,” Bluestone said.
The sky is the limit
Hank Keating, former vice president of design and construction for Trinity Financial in Boston, and now consultant for the real estate development firm, wanted to learn firsthand about passive house. So, he designed one: his retirement home. From that experience he helped guide Trinity Financial into applying PH techniques. The multifamily Bristol Commons and Lenox Green projects in Taunton, Mass., are two examples that in 2016 bested energy performance by an average of 84 percent against LEED Gold townhouses of similar size.
The planned 425 Grand Concourse in the Bronx, a mixed-use affordable housing building, will be the first Passive House high-rise to reach 27 stories.
Now, Trinity Financial is shooting for the sky. The planned 425 Grand Concourse in the Bronx, a mixed-use affordable housing building, will be the first 27-story PH high rise. The current tallest and the first U.S. passive-designed high rise is part of the Cornell Tech campus on Roosevelt Island and features 352 units.
PH design wasn’t required in the “425” request for proposals, but Trinity Financial has integrated it into the skyscraper that will house 277 subsidized affordable rental units, including the first three stories set to include a school, a healthcare center, cultural center/meeting space, and retail space. The project is being developed with New York-based Dattner Architects and the MBD Community Housing Corporation.
“While I’ve found six to 12 stories very reasonable for a passive house, a 27-story building can be a challenge,” Keating said.
Skyscrapers create what is called the “stack effect.” The taller the building, the stronger the air current that rises up stairwells and elevator cores, akin to a chimney effect pulling up warm air. In PH, you can mitigate this effect with good air sealing, but can’t eliminate it. Trinity Financial developed a solution for 425.
“We will locate central energy-recovery ventilators [ERVs] on a lower roof feeding up and others on the upper roof feeding down through duct risers and supplying the units through CAR dampers,” Keating said. “Having centralized ERVs allow for easy service access and filter cleaning. The ERVs feature reheat and cooling coils served by electric heat pumps. We try to keep our PH buildings all electric to avoid fossil fuels.”
Keating said that New York City now requires PH design in recent multifamily requests for proposal.
“I see this segment leading in passive multifamily housing,” he said. “Public policy can influence what developers do as is happening in NYC. Another example is the Pennsylvania Housing Finance Agency. It has completed two competitive funding rounds where they offered 10 incentive points for PH projects. You can argue it’s more expensive to build passive with its 24/7 ventilation, need for more insulation, but obviously there is a payback as you use far less energy.”
Bluestone Organization found there can be costs beyond materials.
“On our projects, we’ve used a Passive House consultant for modeling and oversight, and a building envelop consultant to make sure a building is thoroughly thermally isolated and sealed,” Bluestone said. “We have one staff member who is PHIUS-certified and another pursuing certification.”
The importance of ECs
“Mechanical and electrical [contractors] play integral roles in meeting stringent PH energy-efficiency goals,” Keating said. “Passive is squarely on the electric side. Electricity is almost a given for source pumps for heating and cooling. Ventilation systems are all electric. Making everything electric is the goal where feasible. On a large multifamily apartment building, you are measuring overall energy use to help meet passive design, especially certification.”
Adding lighting control and refinement, managing ghost loads, installing solar, and implementing a monitoring system could all be part of an energy-efficiency strategy. However, ECs cannot come into these projects without being well-educated.
“One of our projects uses co-generation,” Bluestone said. “The broader, more varied the expertise of an electrical contractor the better for passive projects.”
Visit phius.org to learn more about passive building. PHIUS also has a new website for multifamily, which is available at multifamily.phius.org.