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Passive Solar House

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By Amara Rose

“The Passive House standard is the most rigorous building energy standard in the world.” —Graham Irwin, Essential Habitat

Brrrr. It’s mid-winter, and heating a house in the North Bay can be expensive. Especially if you live in a mid-century, ranch-style home built on an uninsulated concrete slab, with lots of windows. But even on the coldest day of the year, Sonoma homeowner Catherine O’Neill can heat her entire 2,300-square-foot house with the energy equivalent of a hair dryer.

Catherine O’Neill lives in a Passive House.

“Passive House” is a voluntary, ultra-low energy building standard that creates structures so efficient they don’t require typical heating or cooling systems. The term originated with Dr. Wolfgang Feist, a physicist and cofounder of the German-based Passivhaus Institut. (Dr. Feist, in turn, was inspired by physicist Amory Lovins of the Rocky Mountain Institute in Colorado.) As the first Certified Passive House in California and the first Passive House retrofit in the United States, the O’Neill residence is a model for North American environmental architects and builders.

Developed over the past 20 years, Passive House has become “the benchmark for sustainable construction,” says Rick Milburn, the first builder in California to be certified by the Passive House Institute U.S. (PHIUS). His company, Napa-based Solar Knights Construction, collaborated with Certified Passive House consultant Graham Irwin of Essential Habitat in Fairfax and architect Jarrod Denton of LDG Architecture in St. Helena to retrofit the O’Neill residence.

Passive House versus passive solar

When people initially hear about Passive House, they tend to think of passive solar, but there are several crucial distinctions. While both passive solar and Passive House construction make use of the sun and southerly exposure, Passive House relies on maximum insulation and exceeds LEED (Leadership in Energy & Environmental Design) requirements. “Passive solar is a design approach that requires solar exposure; it’s not a performance standard,” says Irwin. “Passive House is a performance standard that recognizes and can use passive solar gains, but doesn’t require them.”

A Passive House must meet three rigorous standards:

•     Air leakage. The home must pass a physical test on air leakage to meet the exacting German standard, which permits only a fraction of the leakage common to typical American construction.

•    Heating/cooling allowance. The average new home built to current code requires nearly 10 times more energy to maintain interior comfort than the Passive House standard.

•     Energy use. The maximum allowable energy use can’t exceed 11.1 kilowatt hours per square foot, which is less than half (in some cases, one-third) of normal home energy consumption.

“Many of the traditional passive solar homes were like ‘energy sieves,’ with a tide of heat that washed in and out every day, creating huge temperature fluctuations. Passive House is more like a thermos bottle, maintaining indoor comfort with a high-performance shell,” explains Irwin.

“Basically, passive solar is an approach to building that uses heat from the sun to directly heat a building, whereas Passive House is a performance standard, based around long-standing principles, carefully analyzed and modeled for cost optimization, that produces a building that’s largely balanced with its environment rather than reliant on large, mechanical equipment [such as a typical furnace or air conditioner]. A Passive House, once constructed, is energy-efficient and saves you money forever.”

Using the energy modeling software program called Passive House Planning Package (PHPP) to determine how best to meet the Passive House standard, Irwin, who has an engineering and physics background (he also studied architecture at UC Berkeley), conducted an integrated design process with Milburn and Denton to identify, analyze and optimize the efficiency measures for the O’Neill residence retrofit. It took 76 iterations to get there.

The highest point of inefficiency was the slab-on-grade (the uninsulated concrete foundation), notes Irwin. Other challenging factors included a spread-out floor plan, lack of precedent and the project team’s commitment to using materials with the lowest possible environmental impact.

“The Passive House standard is the most rigorous building energy standard in the world,” says Irwin, who, in addition to Passive House design, advocacy and education, trains Passive House consultants in support of PHIUS. “While it’s just catching on in North America, Passive House has been widely adopted for both new construction and retrofits of all types of buildings in Europe. The German word ‘haus’ means ‘building.’”

“Passive House is a quantum leap in performance, not in what it takes to get there,” Milburn emphasizes. “In Europe, there are already more than 25,000 Passive House structures, both commercial and residential. California is leading the United States in the green energy push, but it’s almost like we’re trying to reinvent the wheel when a viable model already exists.

“We have a state mandate to be net zero by 2020 in residential construction; 2030 for commercial properties,” he continues. “Passive House gets us there that much faster. Between Passive House and renewable energy, we can meet those goals today.”

A house that breathes

While a Passive House is exceptionally airtight, it also “breathes,” rendering it closer to nature in construction than more conventional homes, says Denton. When the architect speaks about Passive House, it’s with the passion and reverence of one who’s found his calling. “Inspire,” literally, means “breathe into,” and a Passive House both breathes and enables its inhabitants to breathe more easily.

“Proper ventilation is extremely important. The Energy Recovery System (ERV) serves as the lungs of the house,” Denton explains. Drastically smaller than a typical HVAC system, the ERV, discreetly tucked into O’Neill’s pantry ceiling, operates at very low volume: no heat blasts from vents.

Instead, air comes into the house through a diffuser and “waffles” through the home, mixing with the existing air and maintaining an even temperature throughout. Return diffusers are located in moist areas (such as the bathroom and kitchen). If all the windows are closed, every spot in the house is designed to stay the same temperature regardless of season: a comfortable 68 to 74 degrees. Yet opening the windows, even at night, doesn’t affect the Passive House ventilation system.

In the O’Neill residence, an eco-friendly ethanol fireplace in the living room needs no chimney. And the number of air exchanges per hour is six times what’s required by building code, which translates into fresh, clean air—a haven for people with allergies—and a quiet system that’s 92 percent efficient.

The absolute quiet of the home may be its most striking feature. The ventilation system, blown-in batt insulation and super-sealed joints combine to give a sense of deep serenity, as though one were on retreat in the middle of a private forest.

“Aesthetics and comfort are as important to sustainable architecture as energy conservation,” observes Denton. “A Passive House acts as an integral system, combining maximum insulation, optimal solar orientation, shading, air tightness, a well-balanced ventilation system, energy-efficient appliances and lighting fixtures to create a symbiotic system. Carbon neutral and net zero are achievable realities for both new construction and retrofits.”

The O’Neill renovation was especially challenging, Denton allows, because the 50-year-old house was an awkward configuration consisting of two structures on uninsulated concrete pads, connected by a breezeway. (In the redesign, the breezeway evolved into an open kitchen, the home’s centerpiece and gathering place.) In addition to the inefficient design and insulation typical of the time, there was no street entry, and the orientation of the rooms was predetermined.

Today, a large, covered porch creates a warmly inviting entry and shades the home from summer sun. Triple-pane windows promote passive solar gain. A blanket of insulation rests between the concrete slab and a gleaming, wide-planked, reclaimed wood floor.

Up on the roof, three Heliodyne solar water panels and 10 Sanyo photovoltaic panels provide all of the supplemental energy needed under normal weather conditions. In the event of extended winter storms, a Rinnai on-demand water heater provides backup.

Passive House doors and windows are also unlike conventional ones, which act as “thermal bridges,” meaning they extract heat from your body when you stand next to one on a chilly winter night. In contrast, the Passive House Optiwin windows and doors installed at the O’Neill residence let all the light, heat or cooling in, but perform more like the adjacent insulated walls. The design team used Argon between the glass panes of a 16-foot sliding glass door—which is North-facing to boot—and still conformed to the stringent Passive House standard.

“Passive House is all about optimization,” says Denton. “In a Passive House, the whole works better than the sum of its parts. This is a key concept: The house, as a unit, is more efficient than any single component.”

The O’Neill project has been selected as a participant in the U.S. Department of Energy’s Building America Research Program as a prototype home and is being monitored by the Lawrence Berkeley National Laboratory to verify the deep energy savings of the Passive House standard.

Passive House is also being implemented successfully in multiple commercial applications, with noteworthy results. For example, German studies have found that students in German schools built to the Passivehaus Institut standard perform significantly better than their counterparts enrolled in ordinary school buildings—possibly because they’re more alert due to improved air quality.

The fundamentals of sustainable shelter

O’Neill first became interested in remodeling her home to the Passive House standard when she read a New York Times piece about a Berkeley home that failed to meet the Passive House certification requirements. Intrigued, she then read Homes for a Changing Climate, coauthored by Katrin Klingenberg, Mike Kernagis and Mary James. (Klingenberg and Kernagis also co-founded PHIUS.) O’Neill had purchased her Sonoma property in 2008 as a retirement residence, to be closer to family members. Wanting to remodel it green, she approached Rick Milburn and asked what he thought about the Passive House concept.

Galvanized by possibility, Milburn invited Denton to accompany him to Germany. The pair flew to Frankfurt in April 2009 to attend the 13th annual Passivehaus Conference. Says Milburn, “During the first day of Passive House training, I was seated between a NASA scientist and a University of Illinois professor. That’s when I realized this wasn’t just another ‘green pipe dream.’”

Around the same time, O’Neill was on a flight back to Sonoma County and struck up a conversation with her seatmate, a civil engineer. He explained how the Passive House concept could work with an existing structure and, by the time the plane touched down, she felt a retrofit was a realistic goal. She called Solar Knights and said, “Let’s do it.”

Like most innovation, Passive House design and construction tends to cost a bit more than a conventional home. In Germany, a retrofit is typically 5 percent more expensive than new construction; the O’Neill residence ended up being 15 percent above what a standard remodel with the same finishes would have cost.

The long-term value, however, far outweighs the upfront expenditure, Denton points out. “I like to think of a Passive House as a ‘legacy home’: high quality, durable and built to last a century, so you can pass it on to future generations. A typical tract house, by today’s standards, is made to last just 28 years.”

Passive House is also a step in the direction of what social scientist Duane Elgin calls “voluntary simplicity.” He says, “The world is moving into a new era where the human community must work together if we are to realize a future of sustainable prosperity. This transition represents both a great challenge and an extraordinary opportunity. We are being called to make a shift toward green lifestyles, guided by the collective wisdom of science and spirituality.”

Denton concurs. A Passive House will enhance your health as well as Earth’s health, he reminds. “A home is supposed to represent relaxation, not the constant whoosh! of mechanical systems. The utter quiet of a Passive House is very appealing.”

At the 13th International Passive House Conference in 2009, Professor Ludwig Rongen termed the Passive House standard “sensible beauty.” His words echo those of eco-philosopher and living systems activist Joanna Macy, author of World As Lover, World As Self: Courage for Global Justice and Ecological Renewal: “For me, beauty resides in authenticity. Those people whom I most admire have turned away from the super-fluidity and cluttered materialism and returned to the beauty of the natural world and objects made by human hands, the texture of wood, the woven basket, the mixing of compost into soil in the back garden, a good soup cooking on the stove, an evening around the table with family and friends. Rediscovering this kind of beauty involves a slowing down, doesn’t it? And it certainly involves listening to the priorities of the heart.”

Passive House is an architectural return to the priorities of the heart and soul. It’s a true Aquarian Age model that lets humans live in harmonious relationship with Mother Earth, embracing the principles of deep ecology.