When architect Cass Calder Smith first met with his client to discuss replacing her cramped beach house, she took him for a canoe ride along the adjacent lagoon to check out the neighborhood. As they paddled past the eclectic cottages (studded with a few higher-profile hangouts by Joe Esherick, Stanley Saitowitz, and William Wurster), she shared some of her requirements: “To be able to see the top of Mount Tamalpais from my living room, to have lots of usable outdoor space, and to push it to be as environmentally responsible as possible.”

The original house—nestled in a gated community in Stinson Beach, 45 minutes north of San Francisco—was a view-eviscerating, tile-roofed, arch-windowed affair the owner referred to as the “Taco Bell house.” She had purchased it seven years earlier due to its location across the street from her husband’s vacation home. When the time came to design the replacement, many of the 25 extended family members who drift between the two houses—her children, her husband, his children, and a passel of grandchildren—had a say. “One of her sons worked for the Nature Conservancy and was very focused on finding green solutions,” Smith recalls. He adds wryly, “The other is a project manager for an affordable-housing development organization, so yes, there was an unusual amount of give and take.”

One of the first decisions Smith and project architect Dera-Jill Lamontagne made was to reduce dependence on fossil fuels. Photovoltaic panels generate all of the electricity—powering the HVAC and radiant-heating systems—and provide backup on cloudy days for the solar hot-water system, which is powered by two thermal panels.

Though not fully energy independent, the house actually feeds the grid, giving surplus power back to the community. “We’re all used to thinking that electric houses are expensive to heat,” says Smith, “but when you have a little power plant sitting on the roof, and you’re using the house four days a week, it’s ideal.” Apart from a 50-gallon propane tank that fuels the cooking range, the home’s energy consumption works out to net zero. Though the initial investment was higher—the homeowner estimates $30,000—a state refund check for $9,000 arrived soon after construction was complete.

The house’s layout is designed to help regulate comfort levels naturally while forging a connection to the outdoors. Because FEMA regulations require new construction to be at least three feet above grade, Smith approached the house as if building a dock. Two large ipe decks, big enough to ride a tricycle on, flow from the great room in front and to the back, where bleacher-style steps descend to the lagoon. When slid open, the double-glazed glass doors make the room essentially disappear, inviting cooling cross drafts. All of the skylights open, and a large overhang on the south side shields the house from the sun.

On cooler days, the Boffi ceiling fan reverses direction to circulate warm air, and the hanging fireplace orb rotates out from the living room to take the chill off the deck. Low-maintenance materials allude to the outdoors, including the cerulean blue of the sealed MDF cabinets, whose strips of mirror pull in the view even when one’s back is turned; the sand-colored tiles; and the honed concrete floor, whose pebbled appearance echoes the sand of the nearby beach.

Because the primary goal was to provide a large social place, the sleeping zone—a hallway off the great room—is relatively spartan. There’s a small bedroom at either end, two baths, and an even smaller children’s room (90 square feet) in the middle equipped with bunk beds. Pocket doors in the hall can be left open, or closed for en suite bathrooms. “It’s like a precise Japanese box. Everything fits in just so,” says the owner, describing the challenge of working within the 1,900-square-foot limit imposed by the neighborhood association.

Allowing that she ended up with everything on her list and more, she adds, “You can sit in any part of the house and feel this exquisite harmony. And it’s nice to know that in the future, my children and their children will be treading gently on nature—and won’t have to pay any utility bills!”