Consumers and businesses are adding green roofs to houses and buildings at a rapid pace. And the benefits are more impressive than you may think.
Between 2020 and 2025, the green roof market is expected to grow at a CAGR of more than 14 percent, accelerating the sector to nearly $9 billion, as consumers and building owners seek out ways to make increase sustainability while reducing energy costs.
“As people become more aware of the benefits of green roofs and living walls, there is definitely an increase in demand that increases year to year,” Gennaro Brooks-Church, Founder of Eco Brooklyn, told Ethos via email.
Eco Brooklyn is known primarily for its living walls, which allow plants to grow in a shallow, vertical medium. But this technique is not exclusive to walls; it’s being used on rooftops alongside solar panel installations and rainwater catchment systems.
What is a green roof?
There’s no official definition of a green roof, but typically they involve plants either for harvesting, providing cooling effects, or home for pollinators and other wildlife. Often, they’re a mix of all of those things.
Green roofs can be flat, as is often the case on commercial buildings, where there can be garden beds, sitting areas, and even beehives. But sloped and slanted roofs can be covered in greenery just as easily, and with many of the same benefits.
“A green roof uses layers of material to allow the plants to live in an environment that typically would be too hostile for them,” says Brooks-Church. “These layers can vary but they typically have a root barrier, water retention layer, drainage layer and growing medium. These layers make it feel to the plants that there is a lot more depth than there really is. The layers might only be a few inches deep but it allows for plants that might traditionally need, say, a foot of depth.”
According to the U.S. government’s General Services Administration, green roofs deliver measurable benefits. It says that based on 50-year average annual savings, green roofs save about 6.2 percent nationally, with 224 percent ROI at $2.7 per square foot. GSA alone manages nearly 2 million square feet of green roofs across the country, but there are countless more.
In dense urban areas like Singapore, Hong Kong, and New York, particularly where there’s more concrete than greenery, the green roof trend is proving promising—they can often pay for themselves with rooftop garden operations, and they support healthy pollinators and ecosystems impacted by the buildings and concrete.
There are barriers, though. Green roofs aren’t cheap, for one; they cost on average twice as much as a traditional roof for residential buildings. But the cost may be worth it; they may also extend the life of your roof. According to GSA, on average, a green roof is expected to last twice as long as conventional roofs. And when you factor in the energy savings as well, it may come out cheaper than a conventional roof.
Improperly installed green roofs can be harder to fix than conventional roof issues. And there are codes and regulations that factor into rooftop gardens and a green roof setup, but within that framework, there’s quite a bit of wiggle room. From gardens like Gotham Greens in New York, which built its second location on top of Whole Foods Market’s flagship Brooklyn store, to the bee hives the Waldorf Astoria brought to its New York rooftop in 2015.
“The care for a green roof is pretty minimal,” says Brooks-Church. “You might need to weed it every couple of months. The care for an outdoor living wall is a little more involved. You need to watch the irrigation closely because if it fails the wall will die pretty quickly.”
Green roof benefits
A study published last year in Australia found that green roofs made solar-outfitted rooftops more efficient. According to the findings, the green roof improved the solar panel performance by as much as 20 percent at peak times and 3.6 percent in total over the experiment length. Part of the benefit comes from the cooling effects of the plants. Solar panels work better when they’re not too hot, and the plants help keep them cooler.
Researchers from the U.S. National Renewable Energy Laboratory estimate there are more than eight billion square meters of roofs in the U.S. suitable for solar panels—enough to produce nearly 40 percent of the total electricity used in the country. Many of those roofs are also well-suited to become green roofs.
In the Australia study, over an eight-month period, the green roof generated more than $2,500 worth of renewable energy than the roof without greenery. In light of the recent IPCC Sixth Assessment report that called for at least a 30 percent drop in emissions including carbon and methane, both of which are byproducts of the energy industry, solar-outfitted green roofs may play a key role, particularly in new developments.
Tesla’s solar energy is playing a key part of the forthcoming Panther National golf course and development coming to Florida. Hollywood’s Sunset Strip will soon have a new home for the popular nightclub Viper Room, which will be on the ground level of a sustainable hotel that boasts a large rooftop garden.
In London, Room2, which says it’s the world’s first net-zero hotel, also has a green roof. It serves as a home for pollinators as well as a way to help absorb CO2 emissions. That rooftop garden can also discharge as much as 50,000 liters of rainwater, serving as a crucial function in reducing localized flooding.
The Australia study measured CO2 absorption and rainwater run-off in its research, noting that a green roof absorbed nearly nine tons of greenhouse gases during the study period. The researchers found significant reductions in stormwater runoff as well.
“We’re looking at 600 litres per second sequestered into the green roof as opposed to going into the system,” study author Peter Irga from the University of Technology Sydney, said last year.
World Green Roofs Day
In June, the third World Green Roofs Day was celebrated across the globe in 60 countries. The initiative was dreamed up by U.K.-based green roof builders Dusty Gedge and Chris Bridgman.
“We saw worldwide participation from GRO members and their sister companies, including Sempergreen, Optigrun, Zinco, Bauder, and BMI Group who launched a series of campaign videos in 19 different languages. Green roof federations from around the world also brought green roof owners, designers, manufacturers and growers together to celebrate,” the founders said.
The celebration showcases the benefits of green roofs from climate action and biodiversity to energy savings, among other benefits.
But according to Brooks-Church, it may not be the energy savings, the cooling benefits, or the sequestering of carbon or water that makes green roofs so appealing. At least, not entirely.
“The biggest benefit is psychological,” he says. “People really appreciate an increase in greenery. It is calming and beautiful.”
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