Energy Equilibrium

David Baker’s Zero Cottage is a passive house in a dense urban area.

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It’s one thing to build a solar-paneled, green-roofed building supplied by rainwater and relying on open ventilation in the middle of a wide-open field with full access to all of nature’s offerings, and quite another to do the same in a heavily populated, hyper-dense city. But Baker wanted to try. The structure combines tried-and-true strategies, like reusing wood from another project his firm had done in Oakland, with brand-new ideas like a rain screen made from movable tiles that clip into a curtain-wall structure and can be taken down, rearranged, or replaced with planters. That screen adds to the house’s most remarkable feature, which is its air- and temperature-control system. “It’s a super-insulated building and it basically doesn’t have heat,” Baker says, describing a heat-exchange air system and a recovery ventilator that extracts energy from, for instance, the heat produced when he or his partner, Yosh Asato, takes a hot shower. The ventilators aren’t currently used much in the United States, but Baker likes them for both the distance they take him toward net-zero and the healthfulness of the air they circulate. “You don’t get any mustiness because every part of the house is getting tempered—you get fresh air at this super-low volume.”

The green roof includes succulents growing in recycled tires.

Courtesy Matthew Millman

The cottage wouldn’t be as efficient a building without a green roof, but Baker took a slightly different approach from the typical one. He points out that many green roofs  are actually energy losers once you factor in the plants raised in New Jersey and then shipped in from, say, warehouses in Chicago (an example he gives based on research into what’s typically used). His roof, filled with native and nonnative succulents tucked into repurposed scooter and motorcycle tires to control erosion, required no warehousing or air-freighting. These thoughtful tactics made all the difference in Baker’s breakthrough— if you want to build net-zero in a city, no detail is too trivial.

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