Speaker 1: Welcome to brain Stuff production of iHeartRadio, Hey brain Stuff
Speaker 1: Lauren vocal Bam. Here. For people living in cities plagued
Speaker 1: by the heat island effect, air pollution, stormwater, and all
Speaker 1: of the psychological and physical effects of living in a
Speaker 1: crowded concrete environment, turning the rooftops of big buildings into
Speaker 1: living gardens and parks seems like an ingenious way to
Speaker 1: mitigate some of those problems, and green roofs aren't exactly
Speaker 1: a new idea. According to Graham Hopkins and Christine Goodwins
Speaker 1: book The Living Architecture Green Roofs and Walls, the earliest
Speaker 1: green roofs were the hanging gardens of Babylon and other
Speaker 1: roof gardens on stone temples, created around six b C.
Speaker 1: But modernly green roofs began to catch on in Europe
Speaker 1: in the nineteen sixties, and it wasn't until the two
Speaker 1: thousands that the movement began to take root, so to speak,
Speaker 1: in North America. In Seen alone, there were more than
Speaker 1: one thousand green roof projects completed in thirty nine U
Speaker 1: S States and five Canadian pro pances, covering nearly five
Speaker 1: point four million square feet. That's about five thousand square
Speaker 1: meters of rooftop space with soil and plants. At least
Speaker 1: twenty five North American cities, including San Francisco, Washington, d C.
Speaker 1: And Chicago, have an acted legislation that either requires green
Speaker 1: roofs on buildings or provides incentives to create them. And
Speaker 1: there's growing scientific evidence that green roofs are beneficial, with
Speaker 1: studies showing that they lower street level temperature and reduce
Speaker 1: fine particles of air pollution, as well as reduced and
Speaker 1: delay runoff from rainstorms. And then there are the mental
Speaker 1: health benefits of more exposure to green space and plants.
Speaker 1: A study published in in the Journal of Environmental Psychology
Speaker 1: found that simply spending forty seconds gazing at a rooftop
Speaker 1: flowering meadow helped to restore experimental subjects attention, and that
Speaker 1: those who had such a view made significantly fewer errors
Speaker 1: and performed better on tasks than their counterparts who only
Speaker 1: got to look at a bare concrete roof. At this point,
Speaker 1: you might be wondering, if green roofs so many benefits,
Speaker 1: then why aren't even more cities sprouting greenery on their rooftops.
Speaker 1: While green roofs make sense in a lot of ways,
Speaker 1: requiring their installation isn't as simple as it might seem.
Speaker 1: The city of Denver, Colorado, learned that lesson after its
Speaker 1: voters decided in by a fifty four to vote to
Speaker 1: pass the nation's most aggressive green roof ordinance. It mandated
Speaker 1: that all new buildings over two square feet an area
Speaker 1: that's around two thousand three square meters, devote at least
Speaker 1: a portion of their roof surface to vegetation, and required
Speaker 1: some existing buildings to go green whenever they replaced their
Speaker 1: roofs as well. Businesses, real estate developers, and Denver Mayor
Speaker 1: Michael Hancock all opposed the measure, but pro green roof
Speaker 1: activists utilized social media and quote a lot of community
Speaker 1: meetings to build popular support. That's according to Brandon Rethheimer,
Speaker 1: the initiatives lead organizer. After the election, Reetheimer joined a
Speaker 1: city task force set up to figure out how to
Speaker 1: implement the new requirements, and the groups soon discovered problems.
Speaker 1: Three separate engineering evaluations of Denver's building stock revealed that
Speaker 1: nine of existing large buildings would have to be exempted
Speaker 1: from the green roof requirement. That's because their structures weren't
Speaker 1: capable of handling the additional weight of adding a rooftop
Speaker 1: membrane at least several inches of soil and vegetation, which
Speaker 1: worked out to about eight pounds per square foot. Another
Speaker 1: problem was that the ordinance allowed buildings to combine solar
Speaker 1: panels with plants to meet the green roof requirement, which
Speaker 1: might have resulted in less vegetation on rooftops than proponents
Speaker 1: had envisioned. That, in turn, would mean that green roofs
Speaker 1: wouldn't provide as much relief from the heat, island effect, pollution,
Speaker 1: and stormwater runoff as hoped. Eventually, the task force decided
Speaker 1: that the best solution was to write a new ordinance
Speaker 1: to replace the one voters had approved. That measure, which
Speaker 1: was approved by the city Council, includes more flexible requirements
Speaker 1: and additional options. Instead of everyone having to put in
Speaker 1: a green roof, buildings would have the option of installing
Speaker 1: a cool roof that wouldn't absorb as much sunlight and
Speaker 1: combining that with more vegetation on the property at ground level,
Speaker 1: or other similar measures. As a result, the amount of
Speaker 1: total green space required is higher for new construction, with
Speaker 1: provisions for multiple paths to meeting the requirement. While some
Speaker 1: supporters who voted for green roofs might be disappointed. A
Speaker 1: Retheimer said, when people see the benefits at the end
Speaker 1: of the day, it's much better. He remains confident that
Speaker 1: many buildings still will opt for green roofs. We also
Speaker 1: spoke with Jennifer Boslot, whose name I hope I'm pronouncing
Speaker 1: correctly and who is an assistant professor in the Department
Speaker 1: of Horticulture and Landscape Architecture at Colorado State University. She
Speaker 1: also served on the task force. She said, it sounds
Speaker 1: like it's stepping back, but it really was for the
Speaker 1: greater good. While balancing the realities aside from structural limits,
Speaker 1: cost is another challenge US. A Lot says that putting
Speaker 1: a relatively shallow installation of a few inches of soil
Speaker 1: could cost between fifteen to thirty five dollars per square
Speaker 1: foot in the Denver area. A deeper layer capable of
Speaker 1: growing drew plants and retaining more moisture would be even
Speaker 1: more costly. The revamped ordinance produced that economic pressure could
Speaker 1: train a man again. Energy efficient Buildings lead for the
Speaker 1: City of Denver told US via email that compliance costs
Speaker 1: would be reduced and that the cost of new construction
Speaker 1: would rise by just one percent or less under the
Speaker 1: new rules. But even though Denver had to loosen its
Speaker 1: stringent green roof requirements, Boslot still sees green roofs as
Speaker 1: the future, both in the Mile High City and elsewhere.
Speaker 1: As more green roofs are built, the cost will drop,
Speaker 1: She says, a quote. We're urbanizing at such a rate
Speaker 1: that we have no other option. If we're going to green,
Speaker 1: We've got to green our roofs. Today's episode was written
Speaker 1: by Patrick J. Kaiger and produced by Tyler Clang. Brain
Speaker 1: Stuff is production of iHeart Radio's How Stuff Works. For
Speaker 1: more in this and lots of other growing topics, visit
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