Heading down a narrow street in the Mission Hills neighborhood of San Diego, you might assume the house set low in a wooded canyon is a meticulously updated example of mid-century modern design. Brothers Soheil and Nima Nakhshab are delighted that the dwelling they conceived, engineered, and built might trigger a case of mistaken identity. Notes Soheil, “We love this era of architecture, so it’s a huge compliment when someone thinks we remodeled an existing home.”

But rather than slavishly re-create an architectural classic, the two have produced a house that crisply articulates mid-century ideals, while anchoring it firmly in the 21st century. (It’s the first single-family LEED Gold–certified residence in San Diego.) Still, Shayan House might never have come to be had Soheil and Nima not seen past the location’s challenges. For nearly 13 years, the steep canyon lot sat undeveloped. But the Nakhshabs, who have designed other properties in the area, were undaunted. Says Soheil, “We love these sloped sites.”

As the principals of an eponymous San Diego–based design-build firm that they founded in 2003 with their father, Sasan, and mother, Mitra, the brothers have been making a name for themselves with their sustainable designs. From the start, their objective with Shayan House was to create a home that was not only green but that would also comfortably accommodate three generations of the family: Sasan and Mitra as well as Soheil, his girlfriend, Susana Mora, their son, Shayan, and infant daughter, Sofia. “We created multiple living spaces so that we could each have our own private area without getting in each other’s hair,” Soheil says.

Sasan Nakhshab first came to the United States from Iran to attend college. After earning a master’s degree in structural engineering from the University of Southern California, he returned to Tehran, where he became a prominent developer. But as the political climate in Iran became increasingly unstable, he, Mitra, and their toddler sons fled briefly to Italy before settling in Southern California.

Combining three generations under one roof might seem to some like a recipe for disaster, yet family is the heart and soul of Shayan House. “The only way you can survive in this world is to stick together,” says Soheil. “My brother and I grew up in a household where our parents were very liberal and accommodating; our home was always a hub of activity.” The tradition continues at Shayan House, which is regularly filled with friends, family, and music. Household clutter may be stowed neatly behind the walnut paneling, but Shayan’s trains are right at home skittering across the living room floor and into the kitchen.

Thanks to the brothers’ thoughtful planning, the 5,679-square-foot structure doesn’t overwhelm its 50-by-100-foot lot. “We wanted a big home to accommodate our needs, but the question was how to do it so that it wouldn’t look out of proportion,” Soheil explains. A two-story structure was in order, with the partly subterranean lower level abutting the slope. Rather than stairs to descend the 25 or so feet from the street, the Nakhshabs cut a switchback to allow for a driveway and level parking pad off the entrance, made possible by a city easement.

Soheil and Nima oriented the house to maximize passive lighting and ventilation. Atop the roof, 21 photovoltaic panels supply an annual energy offset of nearly 40 percent. “The structure was constructed to be 23.7 percent more energy efficient than required by California standards, which are already the most ambitious in the nation,” Soheil says.

The primary common spaces are upstairs, dominated by the open-plan living and dining areas and the kitchen. Soheil and Nima popped up the roof in the living area, where 13-foot-high windows flood the space with light. A deck off the dining area offers views down the canyon and to the bay beyond. Continuing the sustainable theme, refurbished furniture coexists easily with Persian rugs and pieces like a George Nelson Marshmallow sofa, an Eames dining table, and Bertoia chairs.

An open stair leads down to the family room and the bedrooms, which include a suite for Soheil, Susana, and Sofia and another for Shayan—each fitted with an accessible bath and sliding doors that open outside. Sasan and Mitra’s 1,000-square-foot suite combines an airy bedroom and sitting area, a spacious bath, and a large walk-in closet.

Throughout, finishes are simple and minimal: polished concrete floors, gallery-white walls, Caesarstone counters, walnut cabinetry, and white-painted cinder block. Where natural light is in short supply, ten-foot ceilings, judicious window placement, and a light palette ensure an open feel, while 36-inch doorways and generous hallways, along with zero-threshold showers, ensure accessibility for years to come. There’s even space for an elevator.

“Making a house accessible costs the same; you just need to think of it before you pour the concrete,” Nima says.

The creation of Shayan House was a collaborative effort. “Everyone had a say,” says Soheil. “We’ve had some battles,” interjects Nima with a smile, “though sometimes it’s about whoever gets to Mom and Dad first.”

While Mitra was the driving force behind the furnishings, many found in San Diego’s secondhand and vintage stores, Sasan inspired the addition of the “hidden” music and screening room, accessed through what looks like a cinder-block wall downstairs. “Growing up, we always had a music area in our home, and we started putting in studios about 12 years ago,” Soheil says. While each family member plays an instrument or two, the elder Nakhshab also composes music set to the words of 13th-century Sufi mystic Rumi and others.

Shayan House is proof that multigenerational living can energize and enhance the lives of its inhabitants, but Soheil and Nima believe it can do the same for the larger community. They’re now at work on other multigenerational dwellings, a trend they hope continues. Observes Soheil, “We’re at the forefront of something different."