Situated in the epicenter of Silicon Valley, Cupertino is home to Apple, where many a well-heeled tech professional lives in a green McMansion. "There are houses in the hills nearby trying to get the highest LEED-Platinum rating, huge houses with five-car garages," remarks William Leddy of Leddy Maytum Stacy Architects. In sharp contrast, Leddy's design of the 2,245-square-foot Vai Avenue house for his clients, David and Stephania Kaneda, was undertaken from a decidedly different perspective—the team sought a contemporary interpretation of the inexpensive and efficient "case study house," popularized on the West Coast during the post-World War II residential boom, with the added directive of net-zero energy. "This is a small house that has a two-car garage only because the city required it—otherwise we'd have a carport. The modest scale is an important part of the story," says Leddy.
Location Cupertino, California (San Francisco Bay watershed)
Gross area 2,245 ft2; city-required garage, 494 ft2
Annual purchased energy use 0 kBtu/ft2 (0 MJ/m2)
Annual carbon footprint 0 lbs. CO2/ft2 (0 kg CO2/m2)
Program Three bedrooms, three bathrooms, home office, family room/guest room, living/dining room, pool
TEAM & SOURCES
Cladding Certainteed Corporation, weatherboard fiber cement siding
Sloped roofing Berridge Manufacturing Company, preformed Energy Star-rated standing seam
Windows Bonnelli, aluminum frame windows
Occupying net-zero-energy offices designed by EHDD in 2007, the Kanedas own an engineering firm called Integrated Design Associates (IDeAs), which focuses on sustainable design. It comes as no surprise then that a client so thoroughly committed professionally to green buildings would want the same for their family of four.
The team set out to accomplish this goal by dismantling and recycling 90 percent of the materials from the poorly constructed 1950s dwelling that originally sat on the one-third-acre property in this medium-density suburb. The Kanedas' Asian sensibilities (David is Japanese-American and Stephania was born in Hong Kong) influenced their aesthetic choices, and the mild Bay-area climate contributed too. Taking cues from the mid-century case study model, the architect wove high performance into the house's contemporary design in an indoor/outdoor setting.
The rectilinear front facade of the house, accented with a bright orange door and FSC-certified cedar trim, makes subtle references to the spare aesthetics inside. In the front yard, the drought-resistant landscape is sustained with drip irrigation from gray water, reducing potable water consumption to more than 50 percent below baseline. Inside, a central flexible living/dining room/kitchen space with floor to ceiling glazing faces onto a backyard with a swimming pool.
Bookending the multipurpose space, three bedrooms, a home office, and the garage are on one side; a family/guest room and bath are on the other.
All the water used in the house, including the swimming pool, is heated by a solar thermal collector and stored in two tanks. A 6.4-kW roof-mounted photovoltaic array provides 100 percent of the home's electrical needs, with space available for future electric-vehicle charging capacity.
In a mild climate like California's, an electric boiler or a ground-source heat pump with the related expensive drilling costs doesn't make sense, but an electrically powered air-source pump run by PVs does. Implementing this strategy turned out to be troublesome. The contractor went through four iterations before getting it right. "We started with an air-source heat pump that never went into production; an alternative air-source heat pump was implemented, recalled, and removed; then an inefficient electric boiler was installed as a temporary fix. Finally, a high-performance air source heat pump was installed last November, about one year after we moved in, remedying the situation," explains Kaneda. Due to the series of snafus, a full year of energy performance data is not yet available, but the HVAC system now performs as it should, helping to move the energy balance to the goal of net-zero.
Exceeding California's strict energy code by nearly 40 percent, the stick frame construction of the envelope was beefed up with soy-based foam insulation, a framing module to reduce waste, and sealants and membranes to minimize air infiltration. "There were a couple of construction methods we looked at early on, including prefabrication and the then-emerging passive-house technology," says Leddy. But the team decided to take a conventional approach to see how far they could push it. "The most efficient way to innovate is often to build on existing practices rather than inventing entirely new technologies and retraining an entire industry," he continues.
Manually and mechanically controlled flushing at night cools the house. "A fan on a timer with a thermostat draws air through the house, which exits via grills," explains Kaneda. Abundant high-performance glazing with manual and automatic shading controls sunlight, and reflective solar tubes enhance light entering from skylights. Artificial lighting is efficient and sensor-controlled; appliances are Energy Star; and low-flow faucets and dual-flush toilets modulate water for the graywater system. Rapidly renewable materials, FSC-certified lumber, non-VOC paints, locally manufactured materials, as well as those with high-recycled content, round out the green checklist, putting this house on track for a very high LEED-Platinum level. Still, Leddy points out that the team was not trying to set a world record. Complications in final commissioning of the solar thermal/heat pump system in the first year of the house's life stalled the LEED certification process, soon to be remedied now that the house performs as it should.