When going green means aiming for the skies

Imagine a forest stretching not across the distant horizon, but up toward the sky, in the middle of a city. Instead of glass façades, skyscrapers are covered in vines, grasses and even large, woody trees. Birds flit from one green balcony to the next. For some people, these are offices; for others, this is home. And the best part: these buildings and structures actively clean up air pollution.

It may sound like fantasy, but these radical green architecture designs are already springing up around the world, including a “vertical forest” in the heart of Milan.

In the 20^th century, cities competed against one another to lay claim to building the tallest skyscrapers. They still do, but now the competition has expanded to having the “greenest” buildings, precipitating a bloom in far-out architectural projects that decrease pollution, conserve energy and promote biodiversity — even in the most densely populated urban environments.

“The issue of sustainable building design has become much more mainstream than it used to be,” says John McMinn, a Toronto-based architect who teaches at the University of Waterloo School of Architecture. He attributes the increased interest in eco-friendly architecture to the public’s growing awareness that “the idea of climate change is not a question mark anymore, but reality.”

The newest frontier in green building goes far beyond simply making conventional materials more energy-efficient by adding extra insulation, open-able windows, cleaner-burning boilers and the like. Instead, it seeks to transform the building materials themselves — a radical but new and untested approach that is already taking root in Europe, but has been slower to catch on in the U.S. and Canada.

McMinn believes that new ways of measuring the effects of green designs have made sustainable designs — even experimental ones — more popular among architects and clients alike. Vincent Callabaut Architecture’s Asian Cairns are futuristic “farmscrapers” that use solar panels, wind turbines, vertical organic gardens, carbon-absorbing algae panels and water recycling systems to reduce carbon footprints to a drastic minimum. The PH Conditioner Skyscrapers, designed by three Chinese architects, are conceived as jellyfish structures that float in the air and actively purify acidic chemicals from urban air.

Unfortunately, most of these technologies are either still in a conceptual stage or are many years away from being feasibly built. Two exceptions, however, have already seen the light of day: titanium dioxide coatings, which can be integrated into building materials or be installed separately, and “green walls,” groundcover plants grown up the side of a building. They illustrate both the promise and uncertainties of these new architectural materials, many of which are still highly experimental and untested in real-world settings.

There are many approaches to integrating titanium dioxide into building designs. One of the stranger-looking examples of these next-generation approaches is the Prosolve 370e tile. Developed by the German company Elegant Embellishments, the honeycomb-shaped module can be fitted upon a flat wall, allowing for easy retrofits of older buildings.

The key to the module’s design is its unique surface coating, explains Allison Dring, an architect and co-founder of Elegant Embellishments. Exposure to sunlight activates the titanium dioxide coating, triggering chemical reactions that break down toxic nitrogen oxides and other organic pollutants found in air. The nitrogen oxides are converted into nitric acid and neutralized by calcium carbonate in the coating, yielding trace amounts of harmless calcium nitrate, plus carbon dioxide and water.

The curved shape of the tile increases the surface area exposed to sunlight and creates turbulence that slows down wind speeds, making pollutants easier to catch. The modules are “particularly good for schools, hospitals and car parks,” Dring maintains.

Field tests have been encouraging. The module is based off the “Manila Trial,” the results of which were announced at the 2010 Transportation Research Arena Conference in Brussels, Belgium. In that study, more than a dozen high-traffic locations in Manila, Philippines were installed with titanium dioxide coating. Compared to control locations, concentrations of toxic air pollutants were 26 percent lower in areas where the coating had been used.

Prosolve 370e has been most prominently featured at the Torre de Especialides, a hospital in Mexico City. Based on the results of the “Manila Trial,” Elegant Embellishments estimates the modules situated there reduce the smog produced by nearly 1,000 cars driving by each day.

New designs like these can sometimes exhibit unintended consequences. A study conducted by Indiana University researchers found that in areas of a certain humidity range, titanium dioxide could degrade airborne ammonia and lead to the formation of more nitrogen oxides, which have been linked to serious health problems, including breathing difficulties and heart and lung disease.

Jonathan D. Raff, a coauthor of the Indiana study, suggests that previous titanium dioxide studies like the Manila Trial may not have been run in conditions of typical humidity. He and his team found that the most ammonia conversion to nitrogen oxide occurred at 40–50 percent humidity, or “close to the average relative humidity you would find on a spring afternoon in New York City.” The findings are worrisome, he said, but still require further testing.

A more natural form of green architecture is the green wall. Growing groundcover plants upwards against building walls is not a new concept, but it’s only recently that environmental engineers and architects are using green walls to fight pollution. They can absorb air pollutants through leaf pores, as well as capture harmful particle dust on wide leaf surfaces. Green walls also help cool the buildings on hot days.

Thomas Pugh, a biogeochemist at the Karlsruhe Institute of Technology in Germany, made the scientific case for green walls in a paper published last year. He and his colleagues used computer modeling to determine that applying green walls to “street canyons” — roads bordered by rows of tall buildings — could reduce urban pollutants like nitrogen oxides and particle dust by up to 30 percent.

The study is “just a fleshing out of the hypothesis using a computer model” and is still very much conceptual, Pugh acknowledges. Still, the results “highlight a large potential in green walls that hasn’t really been investigated or applied yet,” he asserts.

One famous example already in place is the green wall designed by French botanist Patrick Blanc for the Museé du Quai Branly, a museum in Paris that explores indigenous cultures from around the world. On his “Vertical Garden” website, Blanc argues that as long as they get enough water and nutrients, many plants don’t need soil and can grow instead on designed structures. The plants on the walls of the Museé du Quai Branly, for example, grow on a lattice composed of metal, plastic and felt.

A more audacious follow up to the green wall concept is Italian architect Stefano Boeri’s Bosco Verticale (Vertical Forest) design in Milan. A canopy of trees will cover a pair of urban residential towers currently under construction. Shrubs and groundcover plants on each unit’s terraces will help cool the interiors by shielding them from direct sunlight. More than 2.5 acres of forest — comprising roughly 800 trees, 15,000 groundcover plants and 4,000 shrubs — will be planted on the towers, which are 260 and 360 feet tall.

The glass façades that cover 90 percent of the tall buildings in the world are unsuitable for accommodating different climate conditions, Boeri says. Glass is inefficient as a temperature control system; it exacerbates heat gain in the summer and heat loss in the winter. A design emphasizing leaves, by contrast, would help control temperatures by providing shade in the summer and reducing cold air flow in the winter. Leaves would also reduce carbon dioxide and absorb soot particles.

When the Milan complex is finished next year, there will be more than 100 kinds of plants, including more than 20 tree species, 30 types of brush and 50 kinds of groundcover — a wide enough variety to attract many kinds of nesting birds.

While this type of design is cutting-edge, its green effects are still untested. Pugh acknowledges that “there’s still a lot of uncertainty,” about how effective green walls can be, and stresses the need for real world testing. “It would be dangerous to take numbers from our study and expect them with complete confidence,” he says.

Boeri has high hopes for the Bosco Verticale, but nevertheless believes it should still be considered “an experiment”. Until it’s finished and the air is tested, there will be no way to know how much — if any — it has improved air quality.

So far, Europe has been the torchbearer for many of these radical approaches. Compared to the United States, standards of building performance are higher and so are energy costs, increasing the incentive to try innovative designs, according to McMinn, the Toronto architect. As a result, he says, architects in Europe simply assume that sustainability concerns are paramount, while their U.S. and Canadian counterparts must actively choose to go green.

Still, McMinn is optimistic that North America can and will do better. “It’s easy to persuade people for a higher initial investment when you can explain they will reap benefits over time.”