Tower of tomorrow

(Fortune Magazine) -- When Fortune invited my design firm, which specializes in sustainable architecture, to share our vision of a building of the future, we decided not to guess about conditions decades or centuries away. Instead, we looked at the possibilities that exist now.

Buildings consume 40 percent of our energy and can have life spans longer than humans. Because we live, work and associate with others in buildings, they form part of the fabric of human life - and thus have an enormous effect not only on the quality of individual lives but also on the state of the earth.

In the photographs that that follow, we have configured a structure that is not just kind to nature; it actually imitates nature. Imagine a building that makes oxygen, distills water, produces energy, changes with the seasons - and is beautiful. In effect, that building is like a tree, standing in a city that is like a forest.

William McDonough, founder and principal of William McDonough & Partners, built the first solar-powered house in Ireland in 1977 and designed the first "green office" in the U.S. in 1985.

The building of the future will not just sit on a lot. It will be productive. From solar panels that produce power to tree-filled terraces that recycle water, the building will work, quite literally, from the inside out. How distant is this prospect? Hard to say. All the technologies mentioned are "state of the shelf": That is, they already exist, although not all are economically practical. But architecture and design are crafts for the long term. This tower shows the way urban centers can get closer to nature - and in the process keep neighborhoods and cities vibrant and healthy.

Curved forms increase structural stability and maximize enclosed space; this reduces the amount of materials needed for construction. The shape is also aerodynamic, diffusing the impact of wind.

Traditional rooftops, covered in asphalt and tar, create heat-absorbing surfaces that contribute to the "urban heat island" effect - higher temperatures that can alter weather patterns and intensify smog. A layer of ground cover on this building's roof helps to regulate temperature, protects waterproof coatings, and absorbs and cleans storm water.

The western side of the building is a series of three-story atrium gardens. The greenery brings the outdoors inside, providing a breath of nature. Plants clean the interior air, and as leaf colors change, the building reacts in step with natural cycles. The north façade (unseen) is clear glass covered with positively-charged mosses that absorb particulates of the air.

Water is recycled in the building several times over. Greenhouses treat wastewater from sinks and bathtubs for reuse as irrigation in the building's gardens, a process made possible when nontoxic cleaning products are used. Cleansed by the gardens, the water can be used again as non-drinking water - for example, in toilets.

After a close study of the sun and shadows, the shape and orientation of the building are tailored to the site. This building faces south toward a park, so it can capture maximum sunlight, and its irregular form allows more daylight to reach the street. Gardens circle the base, contributing to the quality of life at street level.

The southern façade, made of about 100,000 square feet of photovoltaic panels that convert sunlight into electricity, collects enough energy to provide up to 40 percent of the building's needs. Costing at least 20 cents per kilowatt-hour - several times as much as coal or natural gas - solar PV is expensive today. But the trends are good: Solar is getting cheaper, and the relative economics will improve as more states and countries regulate the production of greenhouse gases.

The structure is built up in layers of materials that perform different functions, from weatherproofing to insulation to transparency. These surfaces are becoming thinner, lighter, and smarter.

Under-floor air distribution improves air quality. Flexible communal spaces replace fixed individual stations. Chairs and workstations are ergonomic. Smart monitors detect the presence of people and adjust temperature, light, air and sound as needed. This allows individuals to control their environment. Our motto: "We don't heat or cool ghosts."

In nature, nutrients are cycled and recycled endlessly. "Eco-effective design" seeks to mimic those cycles. All products, from building materials to furnishings, are designed to return safely to the earth or to be reused - like office chairs that can be disassembled into components and sent back to the manufacturer to become another product.

They account for almost 30 percent of a building's energy use. By transferring heat between the building and the earth using a system that circulates heat-absorbing liquid through underground wells, a building can reduce energy usage. A combined heat-and-power plant, fueled by natural gas, operates at up to 90 percent efficiency and supplies the power that the solar panels cannot.

What is a tree?

Take away the poetry, and it is an exquisitely productive organism. That is the model we keep in mind when we design. The building on the preceding pages aspires to this: Not only can it be used for either business or housing, it also works hard. Among other things, it is purifying the air, making oxygen, sequestering carbon and drawing energy from the sun. Just as a tree does, we want our structure to filter light down to the ground while optimizing its surface area to the sun. This building, planted like a poplar, reaches up to the sky. It honors the sky and what it means to scrape it.

For a building like this, the context is probably that of a city. There is a larger truth here: Structures and places need to work together, and buildings need to be flexible for cities to endure. Look at SoHo in New York City. The buildings in that neighborhood were designed as warehouses and factories. Then they became artists' studios and galleries, and finally offices and sought-after apartments. The transitions worked because the buildings in SoHo have characteristics - tall windows, high ceilings - that make them livable.

We also need to consider how cities evolve. For example, we're developing a conceptual design for a new, 120,000-person city outside Liuzhou, in southern China.

At its current rate of urbanization, China will lose 25 percent of its farmland in the next 15 years. As designers, we want to respond to that challenge. So we're proposing a 22-square-mile community that uses its roofs as farmland. Instead of being hot and unsightly, the city's rooftops will host productive gardens and farms that will also clean its air and water - a huge plus considering China's dire environmental straits.

Looking ahead, we see new materials that will make buildings even more productive, such as intelligent glass that is self-shading. We're looking at carpets and fabrics that clean the air, and photovoltaic coatings that can be applied to steel. We are intrigued by the lotus effect: If you take a lotus leaf and put axle grease on it, the grease slides off. We are working on coatings that mimic that, so that none of the dust and grime of urban life sticks.

A self-cleaning building is a beautiful prospect, shimmering and bright. Every time it rains, it gets washed. Just like a tree.

CONTRIBUTORS William McDonough & Partners: William McDonough, Kevin Burke, Lance Hosey, Matthew Winkelstein, David Johnson, Andres Pacheco, Christopher James, Emily McGlohn, Neal Harrod, Kyle Copas and FORTUNE: Eugenia Levenson contributed to this article.