Green Roofs, Ecological Design and the Future of Urbanism

By William McDonough

I am strolling in a field listening to crickets and watching birds pluck insects from the dirt. Wildflowers bend in the wind. Warblers and thrushes flit about in tall native grasses and soar over the rolling terrain. The scene is rich, beautiful, lively, delightful—some might say wild. But this landscape is also a cultural space: I am standing on top of a building.

The building, the centerpiece of Gap Inc.’s corporate campus in San Bruno, California, is a pioneering office building with a green roof—and the rooftop is more than just a pretty patch of sod. Blanketed in soil, flowers and grasses, the roof’s undulating terrain echoes the ancient local landscape, reestablishing several acres of the surrounding coastal savannah ecosystem. The native plants and soil also absorb storm water, filter the air, and provide thermal and acoustic insulation. And from inside the building, one can look out the window at the rooftop grasses being tossed by the wind or enjoy a breeze scented with the living perfume of healthy plants and soil. In these and many other ways the roof makes the landscape an integral part of the building’s design.

This is rich, new territory and it has brought to the fore a whole realm of design questions not often considered by architects, planners and their clients. In addition to the obvious practical questions of good business, such as those relating to cost and scheduling, we began the Gap project also asking “What would native birds hope to see as they fly over the site?” and “Wouldn’t it be marvelous if the birds could see the habitat with which they evolved?” Questions such as these, in a quite literal way, change the nature of the design process, expanding its concerns into multidisciplinary terrain that includes ecology, botany, conservation biology, and environmental history. These disciplines offer a lens through which one can see the natural systems at work in a place—the landforms, hydrology, vegetation and climate of each particular locale—and, thoughtfully applied, they empower architects and planners to develop designs …