Eco-conscious architects are feeling optimistic these days. Green building programs are off to a solid start, offering tech support and a stamp of approval for homes that adopt environmental measures. The gap between good looks and sustainability is narrowing too. Shimmering solar panels and planted roofs now bestow a hip aesthetic among in-the-know homeowners. As green goes mainstream, more clients want to participate. Yet there's one thing many of them don't want to sacrifice, and that is the pleasure of living large. Despite the recent spate of interest in not-so-big houses, Americans haven't fully assimilated the less-is-more attitude. They still want indulgences like home theaters, heated swimming pools, and three-car garages—particularly the subset that can afford an architect. That leaves architects with environmental records pondering the ethics of going green on a grand scale. Does a conservation agenda justify more than 3,000 square feet for a family of four?

It's a conundrum, because a large house violates the first premise of resource stewardship—not just in the collective energy used to build and operate a house but also to furnish and maintain it. Limiting one's carbon footprint is, by itself, a green strategy. On the other hand, what's wrong with a 5,000-square-foot house that produces 100 percent of its electricity? Lance Hosey, AIA, LEED AP, a director at William McDonough + Partners, Charlottesville, Va., thinks a lot about this tension between large and small. His tiny, gas-fed Smart car, for example, is more fuel-efficient than the gas-electric hybrids simply because there's less weight to carry around. The same analogy could be used for a single-family house: In the grand scheme of things, green gadgets don't necessarily cancel out square footage. But he envisions a time when building materials will be made and disposed of cleanly. “In the environmental movement, we talk about emulating nature,” Hosey says. “We don't accuse a sequoia of being unnatural. The smarter buildings become about how they use resources; size becomes less of a factor.”

small is beautiful Until that zero-energy, dust-to-dust house is within reach, however, can clients have their cake and eat it too? For many green architects, the short answer is no. “On principle, I'm very skeptical when people put a geothermal heat pump in a 20,000-square-foot house and call it green,” says Brian MacKay-Lyons, FRAIC, Hon. FAIA. “I'm skeptical even of active rather than passive solar, because I think 80 percent of the value to be had in solar is passive, not photovoltaic panels.” In 30-odd years of practice, he says his Halifax, Nova Scotia-based firm, MacKay-Lyons Sweetapple Architects, has done maybe one house bigger than 3,000 square feet. MacKay-Lyons also views outsized materials—salvaged or not—as irredeemably wasteful. “I actually get nauseous when I see these big West Coast houses with humongous timbers holding up something that could be held up with a 2x4,” he says. “The size thing and the material thing are connected by the culture of conspicuous consumption that we're in—the biggest house with the biggest chunks of wood.”

Susan Maxman, FAIA, design principal of Philadelphia's Susan Maxman & Partners, also believes a sprawling footprint is inherently unsustainable. “I feel people really should look at space differently if they're going to be sustainable,” she says. “The house has to suit the program, obviously, but if you look at size in terms of conservation, you develop a whole different idea of what's big and what's small.” As a sailboat owner, she has found that one actually needs little space to live, as long as it's efficient. Maxman and her husband are building a 1,900-square-foot house in the Bahamas that will double up on room functions to accommodate visits from seven children and 14 grandchildren. She's also excited about a potential client who wants to build a 900-square-foot house among megamansions on Long Beach Island, N.J. “If a client came to me asking for a 7,000-square-foot house, I would not do it,” Maxman says. “You can build really nice small houses if they have well-proportioned rooms and big windows and if circulation spaces are minimized.”

But even purists allow that there are countervailing principles in this debate. It's not just a building's bulk that determines whether it's wasteful but also its formal complexity; the goal is to capture the maximum volume with a minimal amount of materials. “You can build a big, simple volume economically or build a smaller building that's really formally complex and has way too many bumps,” MacKay-Lyons says. He points out that a complex form also has a poor surface-to-volume ratio, making it more costly to heat and cool.