By Larry Peña | Video (above) by Matt Yoon

On an overcast day in Irvine, Calif., a gorgeous upscale bungalow sat on a bustling paved lot in Orange County Great Park. The house was low and angular, sheathed in a graceful lattice of redwood slats and wrapped with a spacious deck. Outside the building, a humming line of visitors stretched across the deck and down the ramp, doubling back on itself. Those visitors were eagerly waiting for the next tour of the house — and with it, a glimpse inside at the future of energy-efficient home design.

This was the U.S. Department of Energy’s prestigious Solar Decathlon 2015, a biennial competition in which 16 colleges and universities across the nation were invited to conceive, design and build a house that produces at least as much energy as it consumes. Cal Poly students from four different colleges came together over two years to create their entry, known as INhouse, as an example of how residential architecture can be both aesthetically pleasing and completely energy-neutral.

“The Solar Decathlon is an excellent opportunity for students to get their hands into the industry of net-zero design and renewable energy, to develop skills as emerging leaders in this area,” said Sandy Stannard, a Cal Poly professor of architecture and one of the project’s faculty advisors. “It gives them entry into a potential future career path, and it’s also a great opportunity for the public to see examples of great sustainable design that can perform in a net-zero future.”

This was Cal Poly’s second run at a competition that began in 2002, at a time when the potential of solar energy was just beginning to break through the clouds. Back then, installing solar panels was just about the most energy-efficient thing you could do to your home. Demonstrating how to incorporate solar power into residential construction was the main purpose of the competition. Things have come a long way.

“Now that solar is a lot more common and a lot less expensive, people already know about it,” said Lisa-Marie Mueller, a fourth-year architecture student and co-chair of the university’s decathlon team, Solar Cal Poly. “Energy efficiency is more than just putting solar panels on your roof. It starts with a really well-thought-out design.”

Even as energy regulating technology has improved, trends in energy-efficient home design have become less about installing the latest gadgets and more about smart design fundamentals that take advantage of the most basic resources already in place: the movement of the sun and the site’s climate. It’s a movement known as passive architecture, and while few outside the industry are familiar with this philosophy, it’s one that the Solar Cal Poly team has embraced.

“The basis of it is really just designing a space to respond to the way the sun moves around it throughout the day,” said team co-chair Alyssa Parr, a fourth-year architecture major. “Being able to understand the way the sun moves, positioning your house to make the best use of that energy, is the foundation of sustainable design.”

With that in mind, Cal Poly’s INhouse was developed to fit perfectly into its native environment on the California Central Coast. “In general, we tend to build despite climate rather than with climate, so we made this project very specific to our place,” said Eric Pinuelas, a fifth-year civil engineering major who led Solar Cal Poly’s construction team. “If everyone took that as a cue for climatic responsive design, designing for your place first and then adding in layers of comfort systems, we’d be a long way toward better-performing buildings overall.”

All that said, innovation still played a significant role in creating a space that was truly net-zero in terms of energy use. One of the best examples was the student-designed phase change material duct, an insulation system utilizing a core that shifts rapidly between solid and liquid at roughly room temperature. The system captures and stores excess heat energy for dispersal when it’s needed, helping the house avoid drastic temperature swings.

Another innovation displayed at the house, albeit a relatively low-tech one, is the graceful network of redwood slats that encases the entire structure. These slats form a shade screen that helps to modulate the inside temperature, while also giving the home its distinctive look.

And of course, it wouldn’t be a Solar Decathlon home without the eponymous solar panels. In the Cal Poly offering, half of those come in the form of bifacial photovoltaic panels that make up the roof of a partially enclosed deck area. “It’s my favorite space in the house,” said Mueller. “It’s a way to connect with the way your home is producing energy, while also providing a really nice indoor-outdoor space for you to enjoy.”

Of course, energy efficiency isn’t the only concern in sustainable home design, especially for a team hailing from a state still suffering the effects of a crippling historic drought. The house is designed to minimize water consumption, recycling grey water from sinks and laundry facilities to hydrate outdoor landscaping.

All these elements, whether passive or active, played a role in the final result of the competition, as each entry competed in a set of 10 measured or juried contests: architecture, market appeal, engineering, project communications, affordability, comfort, appliance efficiency, livability, commuting and energy balance. During the week in Irvine, Cal Poly students put the home through its paces, in challenges including charging an electric car for daily drives, washing loads of laundry and hosting dinner parties and movie nights.

At the end of the week, in a crowded auditorium not far from Solar Cal Poly’s beautiful, redwood-clad bungalow, the assistant secretary of the U.S. Department of Energy awarded Solar Cal Poly third place in the overall competition. INhouse did well across a broad range of contests, but its best scores came in two categories that are some of the most critical in gauging demand for sustainable home design: livability and market appeal.

“To be successful in this competition, you need to lay aside preconceptions in order to reimagine what a home can be in a way that still feels authentically livable and true to the American dream,” said Christine Theodoropoulos, dean of Cal Poly’s College of Architecture and Environmental Design. “At Cal Poly we achieve that.”

What makes the Solar Decathlon so important to Cal Poly students facing the beginning of their careers is that trends in energy-efficient design aren’t just aimed at making the future more environmentally responsible — they’re also meeting a very real emerging market demand. “I think there’s more awareness now of what you truly need to sustain yourself,” said Parr. “We’re starting to move from just wanting the hottest, newest thing on the market to being more aware of the energy those things are going to use, and trying to reduce those needs to sustain our planet.”