New modular systems, lower-cost products, and consumer interest in energy efficiency are bringing a 30-year-old German-based construction method into the mainstream. While its early adherents may have been thought of as eco-warriors intent on saving the earth, the Passive House technique is no longer on the fringes of residential building. In fact, driven by strict energy codes, the practice is on track to become commonplace in some parts of the country like California, which faces a residential net-zero mandate in 2020.
Among sustainable building advocates, Passive House represents the gold standard for its demanding requirements and rigorous verification process. Launched in Germany as Passivhaus, the approach was inspired by energy-efficient, passive-solar homes built in the U.S. in response to the 1970s oil crisis. The first Passivhaus homes were built in 1990; since then, more than 2,000 certified buildings have been constructed worldwide, according to the International Passive House Association.
The building system uses very low amounts of energy for heating and cooling, which it achieves with a tightly sealed building envelope, high levels of insulation without thermal bridging, high R–value windows, and mechanical ventilation. The passive approach has a notably high requirement for airtightness, a maximum of 0.6 air changes per hour (0.6 ACH 50). Because of its exceptional efficiency, it makes getting a home to net-zero energy that much easier and minimizes the need for heating, which accounts for about 40% of residential energy use and causes seasonal spikes in energy consumption—making a passive home intrinsically more sustainable.
According to the Passive House Institute US (PHIUS), homes built to passive standards use 50% to 70% less energy than typical houses. They are also known for their high comfort levels, since they maintain a consistent temperature while providing a steady supply of clean, fresh air. Due to their tight envelopes, the homes can also stay comfortable even during extended power outages. (Click here for more on passive's resilient benefits.)
About 1,000 U.S. professionals have been trained to design and/or build Passive House–certified homes, PHIUS says. Some have made it the cornerstone of their practice, like Mela Breen, founder and principal designer at Atmosphere Design Build in Nevada City, Calif., whose projects are located mainly in the state’s mountainous Gold Country. The firm has completed one official Passive House–certified home and uses the principles to guide all of its projects. (As with LEED, it is possible to use the passive approach without actually pursuing certification.)
In another sign that the technique is becoming more accepted in the U.S., its tenets are sanctioned by the U.S. Department of Energy. “We are big fans of Passive House,” says Sam Rashkin, chief architect of the Building Technologies Office at the DOE. “It represents the highest level of energy-efficient enclosure that you can build.” In fact, the DOE has aligned its own standard for energy-efficient homes, called Zero Energy Ready, with Passive House. Zero Energy Ready is now a prerequisite for gaining Passive House certification in the U.S., and encourages builders to continue on to the next step. Zero Energy Ready itself requires a well-insulated, tightly sealed enclosure; Passive House adds a higher standard for airtightness and a whole-house ventilation system.
With a sharp focus on low energy usage, Passive House principles also have gained increased acceptance with U.S. multifamily builders and developers. The 26-story House at Cornell Tech, a student housing project completed in 2017 in New York City, is the tallest and largest residential Passive House high-rise in the world. And in San Francisco, the Passive House–certified Sol Lux Alpha condo runs completely off the grid, producing enough energy on-site to power the entire building.
COSTS COMING DOWN
Building a house that is comfortable year-round and uses a minimum of energy for heating and cooling is not significantly more difficult or costly, according to experienced builders. As with any state-of-the-art building technique, there are extra costs involved—about 5% to 10% more, according to PHIUS. However, as Passive House builders tell their customers, the investment in the building is offset by reduced utility bills.
Rashkin breaks down the expense like this: “It costs roughly $4,000 to $8,000 more per home [to do Zero Energy Ready]. That results in a $20 to $40 increase in a monthly mortgage payment, but a $40 to $90 savings on the utility bill. So it’s truly cost-effective.”
Breen says there’s a misconception about passive construction being super-expensive, when it just takes commitment. “What makes it cost-effective is a simple design and buy-in from the builder and subs. If you look at other custom-designed houses with comparable finishes, we’re building them for the same price,” she says.
Depending on a builder’s current techniques, it might represent a relatively small step instead of a big leap, says Steve Bluestone, a builder and former partner at New York–based developer Bluestone Organization, which builds both multifamily and single-family Passive House–certified projects.
“If you are building a crappy building today that’s just energy-code compliant and you want to make it [passive], you have to do a lot,” Bluestone says. “Passive House is real simple—it comes down to insulation, air sealing, and ventilation. For one of our multifamily projects, our walls were already at that level. But instead of installing a $75 exhaust fan, we had to install an energy recovery ventilator that cost us $750 to $1,000 per unit.”
Meeting the blower door test can be tricky for builders who are accustomed to building with wood and materials that move and shrink and dry, because higher-performance homes have multiple layers and each step has the potential for failure, says Bluestone.
“The reason we were able to hit the standard for very little cost is almost entirely because we’ve been building with ICF [insulated concrete forms] since 2008. It’s the best bang for the buck for building up to 25 floors.” Bluestone, who uses forms from ICF Panels, is also a fan of using AAC (autoclaved aerated concrete) for building to passive requirements.
MORE CHOICES
A few builders have turned to prefabrication to make meeting passive standards cost-effective while improving quality. Leveraging their experience with stick-built passive homes, companies including Bensonwood, BuildSmart, Ecocor, and Threshold Builders have panelized the building envelope, producing Passive House–level insulated walls, floor, and roof components in their factories for quick assembly on site. The first three companies offer their panels to architects and builders as a commercial product, which are custom-built for a particular design and can be shipped to sites nationwide. (Click here for a story about panelized passive building techniques.)
“We’re taking advantage of best practices in the manufacturing industry as well as automobile and boat design, test, and fabrication,” says Sean Ritchey, co-founder of Threshold Builders in upstate New York, which launched its panelized system in early 2018. The company has panelized the hydrothermal envelope, foundation, walls, and roof, constructing them from standard off-the-shelf components such as wood studs and cellulose insulation.
“We can make a home passive for about 1% to 2% more than code-built, a price premium that can pay itself back in just a few years,” says Ritchey. “Using a 20-year financial model, Passive House is going to save the homeowner a shocking amount of money in this Northeast cold climate, because it’s so efficient.”
Other new building technologies promise to make Passive House–levels of performance easier and more cost-effective. For instance, new strides in air sealing are making a difference for passive building. Prescott, Ariz.–based Mandalay Homes is using a new air sealing process called AeroBarrier to reach passive airtightness levels in hours. The automated system uses a fine mist of caulking material that gravitates to air leaks and seals them off. In Arizona, where dust is a significant issue, the fine-grained air sealing also helps keep home interiors clean.
As passive building continues to grow in popularity and relevance, more cost-saving measures are sure to follow. The biggest innovation on the horizon, according to Rashkin, is a new triple-pane insulated window that offers R-5 and R-7 for only a slight price increase and a 50% performance gain from R-3. The window uses krypton gas and ultra-thin glass for the middle layer, allowing the triple-pane window to fit into the same extrusion as a standard window. Andersen Windows has committed to working with Lawrence Berkeley National Laboratory to bring the technology to market in a couple of years.
In the near future, all of these technologies and standards will result in a very self-sufficient home. Says Rashkin: “The buildings themselves need to be able to withstand a whole bunch of disaster events, have systems that can store energy and keep them operable afterward, and buy homeowners time by slowing infiltration by the weather.” B
