Community-gardening advocates have sold urban farming as a sustainable local alternative to industrial-scale farming and as an educational platform for healthier living. And municipalities are buying in, adopting urban ag to transform vacant lots into productive civic assets. In the last two or three years, however, entrepreneurial urban farmers have opened a new frontier with a different look and operating model than most community gardens. Their terrain is above the ground, not in it. Working with help from engineers, architects, and city halls, they have sown rooftops and the interiors of buildings worldwide. “There’s a lot of activity right now, and there is huge potential to do more of it,” says Gregory Kiss, principal at Brooklyn-based architecture firm Kiss + Cathcart.

Exploiting the wide-open technology and design potential of these vertical farms—as building-based agriculture is increasingly known—should make them “more energy- and water-efficient and better integrated with their host buildings,” says Kiss.

The simplest vertical farms are soil-based agricultural extensions of the green-roof concept. Rather than covering rooftops with drought-resistant sedums to help control stormwater runoff and combat the urban-heat-island effect, they grow edible herbs and vegetables that deliver additional benefits. These roofs create jobs, provide fresh produce, and raise consciousness to combat the rising incidence of obesity, diabetes, heart disease, and other diet-related illnesses.

Adding a greenhouse, meanwhile, can add another level of verticality, in which the well-protected crops are stacked to multiply the growing area. Further enhancing output are high-tech additions such as automated conveyance systems, supplemental lighting, and hydroponics, which substitutes nutrient-enriched water for soil. Eliminating soil—which can weigh 50 pounds or more per square foot—slashes structural costs. And all these enhancements boost the output of fruit, vegetables, and herbs, creating additional revenue to finance the capital-intensive installations.

The most innovative vertical-farm designs are expanding urban ag’s potential by moving high-tech growing systems below the rooftop. Some current and future schemes include exploiting space deep in the belly of buildings, substituting grow lamps for sunlight, and encasing buildings in hydroponic greenhouses. Such projects would feed people more sustainably than current industrial practices, in the view of vertical-farming advocates. If they are right, these farms could feed the world’s growing population while shutting down many of today’s mega-farms.

As Kiss explains this most utopian view of vertical farming’s potential: “You eliminate the enormous pollution from agricultural runoff and pesticides, monoculturing of ecosystems, and water-usage problems, and allow land to return to nature, which restores habitats and sequesters carbon. It is a radical view of how the food system ought to be.”

FROM CONCEPT TO REALITY

The term “vertical farming” and the concept of farming within buildings are often credited to Columbia University microbiologist Dickson Despommier and the graduate seminar on medical ecology he began teaching in 1999. His first class examined rooftop gardening’s potential impact on New York City’s food supply. When the students were disappointed by their estimate that rooftop farms could feed just 2 percent of the city’s population, Despommier suggested adding multifloor gardens within abandoned buildings. “Food was being grown indoors already in greenhouses,” he says. “It wasn’t much of a stretch to ask, ‘What happens if you stack them up?’”

Posting the seminar’s ideas online in 2005 sparked a global conversation. That same year, vertical farming got its poster-child design and entered architectural consciousness with Paris-based SOA Architectes’ Tour Vivante—the winning entry in a design competition for an integrated commercial and residential building proposed by the Urbanism Information Center of the city of Rennes. SOA’s hypothetical scheme delivered on the mandated uses and added a third programmatic element: hydroponic production of tomatoes, salad greens, and strawberries via more than 75,000 square feet of greenhouse growing area spiraling up the 30-story, 540,000-square-foot tower.

Vertical farms are now more than unrealized proposals. While Despommier could find none in operation when he completed his 2010 book The Vertical Farm: Feeding the World in the 21st Century, he found three farms in three countries to add when the paperback edition appeared the following year. Since 2011 a profusion of projects has blossomed worldwide.

Most of the first-generation vertical farms are rooftop greenhouses employing some form of hydroponics. Greenhouses provide protection from harsh and variable environmental conditions and enable stacking, while hydroponics cuts weight and boosts productivity.

Consider Local Garden, a 5,700-square-foot greenhouse completed in February by clean-tech firm Alterrus atop EasyPark, a municipal parking garage in downtown Vancouver, British Columbia. Alterrus offered to rent roof space on the long-underused garage to build a farm that would demonstrate its automated hydroponic technology—a system that supports vegetables on standardized rotating trays to maximize exposure to light and reduce waste of nutrients and water.

Alterrus claims to deliver 20 times the yield per growing area compared to land farming with just 8 percent of the water use. Atop EasyPark the company expects to produce 150,000 to 200,000 pounds of leafy greens per year. This hyperlocal food is sold in nearby shops, which means negligible transportation costs and energy input, and fresher food on the shelf, according to Sadhu Johnston, Vancouver’s deputy city manager for environmental and emergency affairs. He cites broader civic benefits, including local jobs and a high-profile symbol for eating fresh foods.

There is plenty of open skyline for more developments. The greater challenge is convincing building owners to try something new, according to Kubi Ackerman, an urban ag expert and project manager at Columbia University’s Urban Design Lab. “The real barrier is getting agreement or even arousing the interest of the property owner,” says Ackerman.

Realizing the Alterrus rooftop farm required new ways of thinking for the city of Vancouver: “They had to drill holes through floors of the garage and store water there,” says Johnston. “There were a lot of new things that required a very different mindset for managing that property.”

FARMING WITHIN

If rooftop greenhouses have an Achilles’ heel, it is temperature regulation. Kiss, whose firm designed the educational greenhouse on top of Public School 333 on Manhattan’s Upper West Side, which was New York City’s first hydroponic rooftop farm when it opened two years ago, cites the heavy heating load required to produce tomatoes over the winter as one example. Doing so could, he says, consume as much energy as importing tomatoes from warmer climes, if not more. Readily available solutions such as opaque blankets that cover the glass at night are underused because, he says, “energy is cheap enough that it doesn’t yet pay.”

SOA takes a different tack in its latest vertical-farm design: a set of rooftop greenhouses as part of the renovation of a public-housing complex in the Paris suburb of Romainville. The project is awaiting financing from the French state. SOA’s multistory greenhouse additions would be heated only by the sun, requiring a shift to cold-resistant crops in the winter, such as the presently in-vogue oyster leaf, a member of the borage family.

Ultimately, rooftop greenhouses could procure heat more sustainably by absorbing exhaust from a building’s occupied space. Concerns about crop contamination via airborne microbes currently prevent this integration of airflows, but vertical farmers say filtering can ensure safety. SOA co-founder Augustin Rosenstiehl says the multilevel, soil-based growth system the firm plans to use at Romainville could do just that. He argues that growing in soil produces tastier and more nutritious food, much as terroir—which includes soil as well as climate and geography—defines the quality of a region’s wines. But, he says, the soil could also serve as a medium for filtering microbes out of warm, CO₂-rich air.

Growing inside a building offers a more definitive solution to vertical farming’s winter heating challenge and simultaneously multiplies growing potential. Of course, interior farms introduce a new energy load: lighting. While rooftop farms such as Local Garden have lights to provide supplemental illumination, interior farms are wholly dependent on electric lighting.

Vertical farms in the Chicago area are the first in the U.S. to begin testing this trade-off. The largest, FarmedHere, occupies one-fifth of a previously vacant 90,000-square-foot warehouse in Bedford Heights and looks like a marijuana grow-op on steroids. Layers of trays and fluorescent lamps stacked five or six levels high nearly reach the 24-foot ceiling, sandwiching an armada of basil and arugula plants whose roots dangle from reusable sheets of polystyrene. The farmers—many of whom are at-risk youth trained by a local nonprofit—tend the crops from moving platforms.

Two forms of hydroponics are in play. FarmedHere mists the arugula roots using a technique known as aeroponics, which reduces weight by eliminating water flows and boosts aeration to accelerate growth. Four varieties of basil, meanwhile, are grown via aquaponics: the water bathing their roots circulates through a tank of tilapia, whose droppings provide nutritional enhancement.

FarmedHere CEO Jolanta Hardej says a 5.5-ounce box of its arugula retails in local markets for $4.99, 50 to 75 cents more than imported organic arugula. Still, she says it sells out because it is fresher and tastier. “We harvest one day and deliver to stores the next day. Produce coming from California or Mexico may have traveled three days,” says Hardej. Growing in clean interior conditions also enhances flavor, she says, because the greens are marketed without washing, thus preserving essential oils on the leaf surface.

Controlled cleanliness is a selling point for the vertical farms that have mushroomed in Japan since the 2011 nuclear-reactor meltdowns that contaminated farms and fisheries. According to Despommier, there are now 211 vertical farms in Japan. Some of these, such as the 30,000-square-foot farm run by Kyoto-based Nuvege, have pioneered the use of efficient LED lighting. Powering lights accounts for 18 percent of FarmedHere’s operating costs, and Hardej expects that number to drop considerably as it transitions to LEDs.

FARMING FACADES

The breakthrough moment for architecturally ambitious vertical farms akin to SOA’s Tour Vivante could be a project awaiting municipal approval in Linköping, Sweden, where vertical-agriculture nonprofit Plantagon International has commissioned a 17-story office-farm hybrid one mile from downtown. CEO Hans Hassle hopes to clear permitting by early 2014 and complete the building one year later.

The $30 million tower, designed by Swedish engineering firm Sweco, will split vertically. Roughly 67,000 square feet of office space will occupy the northern half; vegetables will occupy a south-facing, 190-foot-tall growing space that is the architectural equivalent of a 60-foot-deep double-skin curtain wall. Within, trays of plants will take a slow-motion roller-coaster ride to maturity, rising by elevator to the top and then descending on a helical track over several weeks.

The plan maximizes energy efficiency via heat exchange between the office and the growing space. The vertical farm will also be integrated with industrial facilities nearby, using heat from a trash-burning plant that supplies district heating in downtown Linköping and accelerating harvests with carbon dioxide from a garbage-composting biogas plant (which will, in turn, take its organic leftovers).

Plantagon originally envisioned stand-alone glass towers and spheres that would maximize daylight exposure, but that turned out to be a tough sell, says Hassle: “It is easier to get investors if we combine vertical farming with other uses.” Kiss, meanwhile, sees growing food within as a way of boosting return on investment from double curtain walls, which rarely enhance efficiency enough to pay for themselves. Kiss’s firm has designed a vertical-growth system as part of a double-wall facade that also provides an adjustable shade and can be integrated with a building’s HVAC system to manage energy demand and enhance occupant comfort. Kiss + Cathcart hopes to incorporate the system into a community center it is designing in Maryland.

BOK CHOY FOR SWEDEN

Integration of vertical farming is an exciting prospect for architects, but the farming side must cover its costs if it is to thrive. This appears to be within reach. Hardej, for example, says FarmedHere is expanding from four growing lines to six and expects to be in the black when it has 24 lines. Pricier designs such as Plantagon’s may be able to recoup some costs by earning premium rents for their space.

While the high-end produce from such farms is better suited to feeding the upper-middle class than a hungry world, lessons from these first-generation growing systems could bring costs down and expand vertical farming’s impact.

Plantagon is already preparing to reach broad markets. At Linköping, the company plans to grow and sell 300 to 500 tons of an Asian vegetable that is high in fiber and protein but as yet unknown to most Swedish consumers: bok choy. “We have to show cities like Shanghai, Beijing, and Singapore that we can grow the food that they want,” says Hassle. He expects to be producing in China soon: “If we don’t have a building up and running in China within two to three years, we will be very disappointed.”