Net-Zero Mountain Home Relies on High-Performance Insulation

Originally published by: Builder OnlineJanuary 30, 2018

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A small cabin in rural Northern California is an example of what can happen when clients have high standards in both sustainability and design. The owners of the Nevada City home, parents of two young children, asked architect Mela Breen to focus on comfort, energy efficiency, and indoor air quality, but they wanted more than that. They had specific design goals centered on rustic living spaces set off against contemporary lines and modern materials.

To meet their green objectives, Breen suggested a Passive House approach that would keep the family comfortable year-round and incorporate mechanical ventilation strategies and low-emitting materials to keep them healthy, too. She relied on passive solar design, meticulous air sealing, triple-pane Alton windows, and high-performance insulation that reduces heating and cooling needs to a fraction of those of a typical home.

Since the owners moved in a year ago, a 7 kW rooftop PV array has more than met their needs and conforms to California’s looming Title 24 building standards that require new residential buildings to generate as much power as they use by 2020.

The 1,690-square-foot house is heated and cooled with one ductless mini split in the main living space, supplemented by an HRV that supplies a steady stream of fresh air. “Because the house is super-insulated and has a big open floor plan, as long as they keep the bedroom doors open, every room stays a nice, constant temperature, even in summer,” Breen says.

She sited the home to overlook and capture breezes from a nearby creek canyon. Warm-toned handmade materials, including plentiful reclaimed wood, provide a natural feel, while polished concrete floors give off an urban industrial vibe. “We tried to let the structural elements work as finishes,” says Breen, who has designed other homes to Passive House standards and finds that the approach allows for plenty of design freedom.

“One of the reasons we like the Passive House methodology is that it’s not super restrictive on design or how you meet its goals,” she says. “Ultimately it’s sort of a pragmatic approach with the goal of reducing energy consumption.”

As more California builders look toward 2020 they, too, will need to think about strategies for reducing overall energy use before deciding how to generate more of it, notes Breen. She recommends incorporating energy-saving strategies during the design phase.

“Net zero needs to be integrated in a thoughtful way to the overall project,” she says. “It’s a better approach than just putting a ton of PV on the roof of a house that’s using a lot of A/C.”

Although going for net zero added to the cost of the C.A.S.K. House—Breen estimates about 5% for the building envelope and sustainable materials and 2.5% for the solar panels, which qualified for a significant rebate—she says it also added value.

“The new code will add layers of cost on to building—you cannot get around that fact,” she says. “But the long view of it is that instead of paying utilities, homeowners can put the extra cost into their mortgage and put more value in their house.