“She was a nice, conservative lady who wanted a new house.” That’s how 86-year-old San Francisco architect George Homsey—an assistant in famed Bay Area architect Joseph Esherick’s office in the early 1950s—remembers Louise Hewlett Nixon. But that description of Nixon barely flicks at the whole story behind the redwood-shingled marvel Esherick would design for her at the crest of the Berkeley Hills.

By the mid-1950s, Esherick was a rising star on the San Francisco design scene, with homes scattered across the region, and a handful of what Homsey recalls as “rustic, elegant buildings up in Lake Tahoe.” Nixon, then single and a Stanford University–trained psychiatrist, was in the market for a house in nearby Berkeley—ideally something with an Asian influence. Esherick’s design offered a T-shaped layout, clad in a Japanese-inspired shingling technique, typical of Berkeley buildings of the era. The home also came equipped with arresting views of nearby Tilden Regional Park’s grassy slopes to the north and a vista all the way to the distant Golden Gate Bridge to the west.

The house was completed in 1954 and included another marker of midcentury California cool—a landscape designed by Lawrence Halprin, a young lion of American modernism. His vision for the grassy outdoor “room,” nestled in the eastern crook of the T, was an alpine meadow, replete with a small stream and charming pond.

“It was very much a house for a single person,” says Eric Gimon, Nixon’s great-nephew. In 2004, a year after Nixon died, Eric and his wife, Emma, bought the house. Nixon, who married in 1967 but had no children, inhabited the home’s small upstairs bedroom for nearly half a century. But the Gimons needed more space. They would soon count children Luc, five, Paul, two, baby Louise, and their dog, Nefi, among the residents of Esherick’s wood-paneled wonder.

“We’d talked about expanding the house out,” says Emma, “but worried the new space would either be squeezed in, or that it would mess with the architectural lines of the Esherick house.” With Halprin’s landscape in some disrepair—Emma suspects it was never fully realized—the couple elected for a more significant update of the property in 2009: two new structures and a recast landscape, all working in concert with the original house.

To achieve this, the Gimons leaned on architect Kate Simonen. She’d worked on a small renovation of the house in 2004, and by the late 2000s was collaborating with architects Benjamin Parco and Phil Kaefer on a new prefab design system. The couple hired the trio, along with landscape architect Gary Roth—who worked closely with Halprin for years before the master’s death in 2009—to reimagine life at their lush spot in the hills.

After much discussion, the team lit upon the idea of reserving the old house, with its updated kitchen, ample social space, and grand deck, as the home’s public zone. Then, at the end of the day, the five Gimons would travel across a pair of footbridges and through an open “tearoom,” cocooned by two Japanese maples and a dogwood tree, before finally arriving in a new sleeping pavilion, hugging the yard’s southern edge. The pavilion itself—two prefabricated, off-center rectangular volumes beneath a butterfly roof half clad with solar panels—now hosts the family’s private lives. A small master bedroom with vast windows and a modest porch overlooks Tilden Park; a pocket door separates Paul and Luc’s bedrooms; a library faces the yard; and red tiles from Heath Ceramics enliven the kids’ bathroom.

The couple initially considered a modular prefab, but getting the necessary crane up to the top of the hill and onto the site proved too tricky. But because the panelized wall and roof system that the team devised was very straightforward, the frame was erected in just five days.

Simplifying the prefabricated panels was key, and by drastically reducing the amount of electrical work and lighting in the structure’s frame—“getting the junk out of the walls,” Parco calls it—assembly was especially quick. By shifting key lighting elements and storage into large, locally made chests; moving electrical sockets into the floor; and installing programmable wireless light switches, the team made the set-and-connect walls extremely flexible and easy to install.

“This project is all about scale,” explains Parco, “the scale of the new spaces in the landscape, the roof shape and siding. It’s also about restraining ourselves from being overbearing architects,” he continues. “Not everything has to be a manifesto. How about respecting the amazing house that’s already there?”

Honoring the environment was another key concern. Emma, who has a Ph.D in structural engineering and used to work at the global engineering firm Arup, and Eric, a former UC Berkeley physicist and fellow at the Department of Energy, and currently a technical adviser to the advocacy group the Vote Solar Initiative, collaborated with their architects to bake an enviable array of green features into the home. An Altherma air-to-water heat pump by Daikin runs off electricity generated by the solar panels; in-floor radiant heating helps conserve energy; and Eric keeps a close watch on how the green gizmos are faring, thanks to a monitoring system that allows him to check on things such as how much energy the solar array is collecting.

Though finding architectural sympathy between the new home and the old was much of the team’s task, it fell to Roth to fasten a revamped landscape to the buildings on-site. “The concept grew out of the original design and the clients’ needs,” he says.

Now, a pool of water off the sleeping pavilion’s deck takes the lead in an aquatic loop around the property. Runoff from the roof courses through the runnel, around the back of the house, and eventually into Halprin’s original stream that runs out to the pond.

The pond itself—stocked with goldfish and frogs—is fed seasonally by rainwater from the roof of the house. During the summer months, the runnel acts as a conduit for filling the pond, exposing the release of precious water from an upstream valve.

“We didn’t try to be overly literal in jumping off from Larry’s design,” Roth explains. “We took his vocabulary and then integrated it into the new buildings and landscape.”

By giving a nod to, but never slavishly copying, what came before, the Gimons—nice, conservationist people who wanted a new house—are writing the next chapter of an evolving exemplar of Bay Area design.

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A Modern Prefab Addition to a Midcentury California Classic