Rooftop escapes are nothing new in urban settings. The image of a solitary soul or impassioned couple seeking solitude on top of a tall city building is almost a cliche.
But, today, instead of being surrounded by industrial equipment and utilitarian surfaces, rooftops can offer a cooling green environment, offering a true respite. As a bonus, these aesthetic islands in the sky also provide stormwater management and buffer cooling and heating costs. What’s not to love about a rooftop garden?
A little history
People have been planting rooftops since the beginning of recorded history. The earliest records go back to the ancient ziggurats of Mesopotamia, built between 4,000 and 600 B.C. The Hanging Gardens of Babylon are probably the most famous ancient plantings, with landscape terraces boasting trailing plants reaching a planted roof that was 75 feet above the ground. This living mountain in the desert was an engineering marvel.
One of the first designed landscapes was a roof garden commissioned by Pope Pius II in Pienza, Italy, in 1463. In the U.S., rooftop gardens became popular in New York City in the 1890s. In fact, that’s where Madison Square Garden got its name.
Fast forward to the late 20th century. Although rooftop gardens were planted and enjoyed mainly as a novelty for the wealthy, in the mid-1970s a new system was developed in Germany. “The popularization of green roofs began in the early 1970s in Germany when the first green roof systems were developed and marketed on a large scale,” says Paul Kephart, president of Rana Creek, Monterey, California. The company has designed and installed a wide range of residential and commercial rooftop gardens. “Unlike former ‘green roofs,’ this first approach offered reliable technology that provided sophisticated irrigation and protection against root ingress for rooftop gardens.
“The second big step was the development of extensive green roofs in the late 1980s,” Kephart continues. “The goal was to create lighter and cheaper systems that could be applied to large, flat roofs. The main motivation for extensive green roofs was the restoration of nature and protection of the roof membranes from the elements and temperature fluctuations.”
Green roof? While some use the terms “rooftop gardens” and “green roofs” interchangeably, others point out a difference. “There’s definitely an overlap,” says Greg Raymond, owner and founder of Ecogardens in Chicago. Since 2003, Raymond has been considered a trailblazer in urban green roofs. “Green roofs are typically thought of as environmental features. They are designed to slow storm runoff to minimize urban flooding. Roof gardens are more amenity spaces and tend to invite some sort of interaction with people.”
“Actually, the newest term is ‘living roof,'” says Casey Lyon, president of Habitat Gardens in Pacific Grove, California. Lyon has built more than 150 native gardens and living roofs. “That’s because rooftop plantings can go dormant and don’t necessarily need to be green all of the time.”
“In Portland, they are called Ecoroofs. In California, they are called living roofs. In most of North America, green roofs apply,” Kephart explains. “Garden roofs tend to be inhabited; green roofs are rooftops partially or completely covered in vegetation.”
Whatever you call them, green roofs represent a new service (and profit center) for companies both small and large. Although there is much more to a green roof than planter beds and low-maintenance greenery, there are countless resources that offer education and training in the field.
First and foremost, an engineer is required to determine load capability. Like almost any project, it’s easier to design the green roof and the building at the same time. However, rooftop gardens can be installed on just about any structure if it will handle the load.
“There has to be a structural engineer involved in any process,” says Raymond. “We contract that out. We have a couple of engineers who know what we are looking for and understand green roofs.”
“We recommend a structural engineer be retained to determine the existing, or required, load capacity of the roof,” says McRae Anderson, president of McCaren Designs, one of the leaders in green roof design in Chicago. “Also a mechanical engineer should be required to discuss integration with existing and proposed rooftop mechanical equipment, electrical and drainage needs.” Anderson literally wrote the book on green roofs, producing a specification manual that covers the gamut on design, installation and even maintenance.
“Typically, I will get a call from an architect who is interested in installing a green roof, and he’ll ask me about the type of garden I recommend,” says Lyons. “My first question is, ‘What does your engineer say?’ The capacity of the roof dictates the design of the garden.”
Once the capacity is determined, the design process can begin. Depending on capacity and the desired finished product, planting areas can be as shallow as a few inches to massive containers for large trees.
Charlie Miller is considered a green roof guru. His company, Roofmeadow, based in Philadelphia, has landscape architects, civil engineers, horticulturalists and construction specialists who have been working to produce award-winning, sustainable green roofs since 1997.
“Our company is a landscape design and engineering consulting firm, and our primary client groups are architects, owners and developers,” says Miller.
“Green roof landscapes are as varied – or even more varied – than landscapes on the ground, ranging from thin layers of engineered media that support groundcovers to massive landscapes with large trees, elaborate masonry construction, water features and even lawns,” Miller notes. “The choice of green roof type depends on the goals of the owner.”
“We have done biomimicry on a rooftop that would mimic the surrounding landscape, and we have done linear plant layouts and formal designs on rooftops,” says Lyons. “It completely depends on the design or vision and the expectations of the client.”
“Every conceivable style of green roof is being installed today at every scale throughout North America,” says Kephart. “Roofs for parks, golf ranges, corporate retreats, recreation, wildlife habitat and private gardens are all possible.
“But there are two main types of green roofs,” Kephart continues. “An intensive roof is more traditional with a thicker, heavier growing medium and can support a larger variety of plants, such as small trees and shrubs that have a more extensive root systems. However, as the name implies, it is more intensive to maintain, requiring an irrigation system and regular feeding and maintenance. For this reason, intensive roofs are often designed more like parks with easy access.
“Extensive roofs are lighter with a thinner layer of growing medium, such as specially formulated compost,” Kephart explains. “They are designed for limited maintenance and may only require once yearly weeding and a slow release fertilizer.”
Pros… and pros
Outside of the cost to the client, there are few, if any, drawbacks to a properly designed and installed green roof. As far as cost goes, “Installation costs may range from $6 a square foot to $200 a square foot,” says Miller. Keep in mind that those are strictly installation costs, not counting design services.
“Realistically, for a simple green roof with about 6 inches of growing media, the price should be $15 to $25 per square foot,” says Raymond. “Although it could be less. We’ve done some for as little as $8 a square foot.”
Over on the West Coast, Kephart quotes simple projects for $18 per square foot to $100 per square foot and more for those with amenities, while Lyons estimates about $20 to $30 a square foot. In other words, it can be a profitable venture, but quality and due diligence are a must.
There are several advantages to green roofs. “There are two very distinct benefits to urban rooftop gardens,” Lyons says. “The first is the slowdown of stormwater runoff and discharge into the urban stormwater runoff system. The other is simply an increase in valuable real estate. With so many buildings in such small spaces, there’s just not enough green space for people to enjoy.”
“The No. 1 benefit is stormwater management,” says Raymond. “But any greenery on a roof will also help mitigate heat. Plants, especially the sedums that are often used, absorb the sun’s energy during the day and release it back when things cool down at night. This means traditional HVAC systems and solar panels work better and more efficiently.”
“According to a study conducted by Environment Canada, installing a green roof can result in a 26 percent reduction in cooling needs and a 26 percent reduction in heating costs,” says Kephart. “Plus, a properly installed green roof can increase your roof’s life span by as much as two to three times according to a Penn State University green roof research center.
“Other benefits include habitat restoration, filtration of acid rain and air pollutants, noise pollution reduction, and the therapeutic effects found from being in the presence of nature,” Kephart concludes.
A growing trend
Green roofs are on the grow. “Green roof sales have doubled every year for the last 12 years,” says Lyons. “The new Facebook and Apple campuses will have huge, intensive green roofs. The new 49er stadium has a huge green roof. The biggest roof we have coming up is on a church in Walnut Creek this July that will be an intensive green roof that’s over an acre.”
Projects running an acre or larger are business as usual for Rana Creek, where Kephart and his staff have designed and installed enormous projects, such as rooftop gardens on the Vancouver Convention Centers; the California Academy of Sciences; and the Croton Water Treatment Plant in the Bronx, New York, which is incredibly topped with the Mosholu Golf Course. “The forecast for the North American roofing market is an anticipated worth of $18 billion by 2015,” says Kephart.
In Chicago, once considered the hot spot for green roofs, Raymond still sees some growth, although “the craze has leveled off,” he says. “There used to be subsidies and grants available, but a lot of those have dried up. Cities such as Portland and the District of Columbia are taking the lead nowadays. It’s ironic because the city of Chicago is requiring green roofs in many instances, but isn’t offering any financial assistance anymore.”
Green roofs do not have to be enormous creations to be profitable and ecological. “We’ve designed roofs for chicken coops and dog houses,” Lyons says. In Philadelphia, Miller’s company won awards for their designs of green roofs for bus shelters.
A newer product offered by several companies is pre-planted trays that can make green roof installation easier and more efficient for smaller companies. However, Lyons points out that these can be expensive, similar to installing a lawn with sod vs. seed. “Plus, you will still have succession, and some plants will die out while others will take over,” he says.
One of the hottest trends in rooftop gardens is edible landscapes. Urban farming is catching on across the nation, and, with limited space, a rooftop is a perfect place to grow food. “The latest trends in rooftop gardening are urban food production, aquaponic greenhouses and large-scale park lands,” says Kephart. “The innovation of these roofs is where stormwater and grey water is reused for irrigating rooftop vegetation.”
“Rooftop agriculture is definitely the buzz in the industry nowadays,” agrees Raymond. “If you have a large building that has the capacity to hold growing media, why not grow produce or other edibles to feed the local crowd?”
“I just had a conversation with a potential client who was very happy with his landscape of California natives, but wanted to grow vegetables as well,” says Lyons. “His roof was the only space he had left.”
Finally, maintenance can’t be forgotten. “Specialized professional maintenance is essential to maintain successful green roofs,” says Miller. While some simple green roofs might only need quarterly or even annual visits, rooftop amenity gardens will need at least weekly maintenance to look their best.
Green roofs are a great way to benefit both the environment and your bottom line. There are many educational opportunities available. A good place to start is Green Roofs for Healthy Cities.
Don’t be afraid to experiment. As Paul Kephart notes, “If you can sow it, you can grow it.”
Editor’s note: This story was originally published in April 2015.