Big family compound or intimateretreat for two? The owners of this Cape Cod property wanted a net-zero beach house that was both of those things.

“In listening to them describe the way they would use the house, we realized they almost needed two homes,” says Stephanie Horowitz, managing director at ZeroEnergy Design (ZED), the firm that masterminded this home’s clever architecture. “You had the two of them as a couple, but then the large, combined family was almost a Brady Bunch situation with seven adult kids, all of whom had significant others and an exponentially growing number of grandchildren. This was the place they would all come together for holidays and summer vacations.”

ZED responded to this seemingly impossible paradox with a 6,200-square-foot plan that is split into two volumes. The “living bar” side contains common hangout space, a master suite, and a kitchen—everything a couple would need for a weekend getaway. The “sleeping bar” on the other side is essentially an expansion module (containing five additional bedrooms on the lower level, plus a second master suite with a study above) that can be completely decommissioned when not in use.

From there, the team used energy modeling to factor in other constraints and arrive at the best combination of systems for net zero. Located on a bluff 115 feet above sea level, the site had a magnificent west-facing view, which was great for aesthetics but not so good for energy efficiency. Large expanses of glass to capture the sunset were a no-brainer, but even with Arcadia low-E, double-pane, thermally broken aluminum windows, the envelope and mechanical systems needed bolstering to offset that west-facing heat gain. Builder Silvia and Silvia used staggered double-stud framing with a 2x10 top and sill plate, which proved advantageous from a couple of stand­points. The wall thickness allowed for a continuous, uninterrupted layer of foam insulation, improving the thermal envelope. Plus, it improved the home’s interior architecture and sight lines by allowing steel beams [required per structural code to withstand 120 mph winds] to be hidden inside the walls.

Net Zero Housing

“We didn’t want columns and soffits all over the place, and with this solution, there is no visual evidence of that steel cage on the front of the house,” Horowitz says.

Other energy-conserving features include water-saving plumbing fixtures, hot water on demand, native landscaping, geothermal heating and cooling, and a heat recovery ventilator. The house uses propane for cooking and keeps its rooms comfortable—even the great room, where the roof peaks at 18 feet—with radiant floor heating, which, Horowitz notes, “heats the people, not the space.”

All told, the house uses two-thirds less energy than your standard code-built home, offsetting its minimal energy consumption with a south-facing rooftop photovoltaic system. Its HERS rating is 33.