October 9, 2019 • 6 mins
Planting gardens, grasses, or wildflowers on urban roofs can solve a lot of problems, but it can cause a few along the way. Learn more about green roofs in this episode of BrainStuff.
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Episode Transcript
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Speaker 1 (00:01):
Welcome to brain Stuff production of iHeartRadio, Hey brain Stuff
Lauren vocal Bam. Here. For people living in cities plagued
by the heat island effect, air pollution, stormwater, and all
of the psychological and physical effects of living in a
crowded concrete environment, turning the rooftops of big buildings into
living gardens and parks seems like an ingenious way to
(00:23):
mitigate some of those problems, and green roofs aren't exactly
a new idea. According to Graham Hopkins and Christine Goodwins
book The Living Architecture Green Roofs and Walls, the earliest
green roofs were the hanging gardens of Babylon and other
roof gardens on stone temples, created around six b C.
But modernly green roofs began to catch on in Europe
(00:46):
in the nineteen sixties, and it wasn't until the two
thousands that the movement began to take root, so to speak,
in North America. In Seen alone, there were more than
one thousand green roof projects completed in thirty nine U
S States and five Canadian pro pances, covering nearly five
point four million square feet. That's about five thousand square
meters of rooftop space with soil and plants. At least
(01:08):
twenty five North American cities, including San Francisco, Washington, d C.
And Chicago, have an acted legislation that either requires green
roofs on buildings or provides incentives to create them. And
there's growing scientific evidence that green roofs are beneficial, with
studies showing that they lower street level temperature and reduce
fine particles of air pollution, as well as reduced and
(01:29):
delay runoff from rainstorms. And then there are the mental
health benefits of more exposure to green space and plants.
A study published in in the Journal of Environmental Psychology
found that simply spending forty seconds gazing at a rooftop
flowering meadow helped to restore experimental subjects attention, and that
those who had such a view made significantly fewer errors
(01:50):
and performed better on tasks than their counterparts who only
got to look at a bare concrete roof. At this point,
you might be wondering, if green roofs so many benefits,
then why aren't even more cities sprouting greenery on their rooftops.
While green roofs make sense in a lot of ways,
requiring their installation isn't as simple as it might seem.
(02:12):
The city of Denver, Colorado, learned that lesson after its
voters decided in by a fifty four to vote to
pass the nation's most aggressive green roof ordinance. It mandated
that all new buildings over two square feet an area
that's around two thousand three square meters, devote at least
a portion of their roof surface to vegetation, and required
(02:33):
some existing buildings to go green whenever they replaced their
roofs as well. Businesses, real estate developers, and Denver Mayor
Michael Hancock all opposed the measure, but pro green roof
activists utilized social media and quote a lot of community
meetings to build popular support. That's according to Brandon Rethheimer,
the initiatives lead organizer. After the election, Reetheimer joined a
(02:55):
city task force set up to figure out how to
implement the new requirements, and the groups soon discovered problems.
Three separate engineering evaluations of Denver's building stock revealed that
nine of existing large buildings would have to be exempted
from the green roof requirement. That's because their structures weren't
capable of handling the additional weight of adding a rooftop
(03:16):
membrane at least several inches of soil and vegetation, which
worked out to about eight pounds per square foot. Another
problem was that the ordinance allowed buildings to combine solar
panels with plants to meet the green roof requirement, which
might have resulted in less vegetation on rooftops than proponents
had envisioned. That, in turn, would mean that green roofs
wouldn't provide as much relief from the heat, island effect, pollution,
(03:38):
and stormwater runoff as hoped. Eventually, the task force decided
that the best solution was to write a new ordinance
to replace the one voters had approved. That measure, which
was approved by the city Council, includes more flexible requirements
and additional options. Instead of everyone having to put in
a green roof, buildings would have the option of installing
a cool roof that wouldn't absorb as much sunlight and
(04:00):
combining that with more vegetation on the property at ground level,
or other similar measures. As a result, the amount of
total green space required is higher for new construction, with
provisions for multiple paths to meeting the requirement. While some
supporters who voted for green roofs might be disappointed. A
Retheimer said, when people see the benefits at the end
(04:21):
of the day, it's much better. He remains confident that
many buildings still will opt for green roofs. We also
spoke with Jennifer Boslot, whose name I hope I'm pronouncing
correctly and who is an assistant professor in the Department
of Horticulture and Landscape Architecture at Colorado State University. She
also served on the task force. She said, it sounds
like it's stepping back, but it really was for the
(04:42):
greater good. While balancing the realities aside from structural limits,
cost is another challenge US. A Lot says that putting
a relatively shallow installation of a few inches of soil
could cost between fifteen to thirty five dollars per square
foot in the Denver area. A deeper layer capable of
growing drew plants and retaining more moisture would be even
more costly. The revamped ordinance produced that economic pressure could
(05:06):
train a man again. Energy efficient Buildings lead for the
City of Denver told US via email that compliance costs
would be reduced and that the cost of new construction
would rise by just one percent or less under the
new rules. But even though Denver had to loosen its
stringent green roof requirements, Boslot still sees green roofs as
the future, both in the Mile High City and elsewhere.
(05:29):
As more green roofs are built, the cost will drop,
She says, a quote. We're urbanizing at such a rate
that we have no other option. If we're going to green,
We've got to green our roofs. Today's episode was written
by Patrick J. Kaiger and produced by Tyler Clang. Brain
Stuff is production of iHeart Radio's How Stuff Works. For
(05:50):
more in this and lots of other growing topics, visit
our home planet, how stuff Works dot com. And for
more podcasts from my heart Radio, visit the iHeart Radio app,
Apple Podcasts, or wherever you listen to your favorite show.
Smoke
Welcome to brain Stuff production of iHeartRadio, Hey brain Stuff
Lauren vocal Bam. Here. For people living in cities plagued
by the heat island effect, air pollution, stormwater, and all
of the psychological and physical effects of living in a
crowded concrete environment, turning the rooftops of big buildings into
living gardens and parks seems like an ingenious way to
(00:23):
mitigate some of those problems, and green roofs aren't exactly
a new idea. According to Graham Hopkins and Christine Goodwins
book The Living Architecture Green Roofs and Walls, the earliest
green roofs were the hanging gardens of Babylon and other
roof gardens on stone temples, created around six b C.
But modernly green roofs began to catch on in Europe
(00:46):
in the nineteen sixties, and it wasn't until the two
thousands that the movement began to take root, so to speak,
in North America. In Seen alone, there were more than
one thousand green roof projects completed in thirty nine U
S States and five Canadian pro pances, covering nearly five
point four million square feet. That's about five thousand square
meters of rooftop space with soil and plants. At least
(01:08):
twenty five North American cities, including San Francisco, Washington, d C.
And Chicago, have an acted legislation that either requires green
roofs on buildings or provides incentives to create them. And
there's growing scientific evidence that green roofs are beneficial, with
studies showing that they lower street level temperature and reduce
fine particles of air pollution, as well as reduced and
(01:29):
delay runoff from rainstorms. And then there are the mental
health benefits of more exposure to green space and plants.
A study published in in the Journal of Environmental Psychology
found that simply spending forty seconds gazing at a rooftop
flowering meadow helped to restore experimental subjects attention, and that
those who had such a view made significantly fewer errors
(01:50):
and performed better on tasks than their counterparts who only
got to look at a bare concrete roof. At this point,
you might be wondering, if green roofs so many benefits,
then why aren't even more cities sprouting greenery on their rooftops.
While green roofs make sense in a lot of ways,
requiring their installation isn't as simple as it might seem.
(02:12):
The city of Denver, Colorado, learned that lesson after its
voters decided in by a fifty four to vote to
pass the nation's most aggressive green roof ordinance. It mandated
that all new buildings over two square feet an area
that's around two thousand three square meters, devote at least
a portion of their roof surface to vegetation, and required
(02:33):
some existing buildings to go green whenever they replaced their
roofs as well. Businesses, real estate developers, and Denver Mayor
Michael Hancock all opposed the measure, but pro green roof
activists utilized social media and quote a lot of community
meetings to build popular support. That's according to Brandon Rethheimer,
the initiatives lead organizer. After the election, Reetheimer joined a
(02:55):
city task force set up to figure out how to
implement the new requirements, and the groups soon discovered problems.
Three separate engineering evaluations of Denver's building stock revealed that
nine of existing large buildings would have to be exempted
from the green roof requirement. That's because their structures weren't
capable of handling the additional weight of adding a rooftop
(03:16):
membrane at least several inches of soil and vegetation, which
worked out to about eight pounds per square foot. Another
problem was that the ordinance allowed buildings to combine solar
panels with plants to meet the green roof requirement, which
might have resulted in less vegetation on rooftops than proponents
had envisioned. That, in turn, would mean that green roofs
wouldn't provide as much relief from the heat, island effect, pollution,
(03:38):
and stormwater runoff as hoped. Eventually, the task force decided
that the best solution was to write a new ordinance
to replace the one voters had approved. That measure, which
was approved by the city Council, includes more flexible requirements
and additional options. Instead of everyone having to put in
a green roof, buildings would have the option of installing
a cool roof that wouldn't absorb as much sunlight and
(04:00):
combining that with more vegetation on the property at ground level,
or other similar measures. As a result, the amount of
total green space required is higher for new construction, with
provisions for multiple paths to meeting the requirement. While some
supporters who voted for green roofs might be disappointed. A
Retheimer said, when people see the benefits at the end
(04:21):
of the day, it's much better. He remains confident that
many buildings still will opt for green roofs. We also
spoke with Jennifer Boslot, whose name I hope I'm pronouncing
correctly and who is an assistant professor in the Department
of Horticulture and Landscape Architecture at Colorado State University. She
also served on the task force. She said, it sounds
like it's stepping back, but it really was for the
(04:42):
greater good. While balancing the realities aside from structural limits,
cost is another challenge US. A Lot says that putting
a relatively shallow installation of a few inches of soil
could cost between fifteen to thirty five dollars per square
foot in the Denver area. A deeper layer capable of
growing drew plants and retaining more moisture would be even
more costly. The revamped ordinance produced that economic pressure could
(05:06):
train a man again. Energy efficient Buildings lead for the
City of Denver told US via email that compliance costs
would be reduced and that the cost of new construction
would rise by just one percent or less under the
new rules. But even though Denver had to loosen its
stringent green roof requirements, Boslot still sees green roofs as
the future, both in the Mile High City and elsewhere.
(05:29):
As more green roofs are built, the cost will drop,
She says, a quote. We're urbanizing at such a rate
that we have no other option. If we're going to green,
We've got to green our roofs. Today's episode was written
by Patrick J. Kaiger and produced by Tyler Clang. Brain
Stuff is production of iHeart Radio's How Stuff Works. For
(05:50):
more in this and lots of other growing topics, visit
our home planet, how stuff Works dot com. And for
more podcasts from my heart Radio, visit the iHeart Radio app,
Apple Podcasts, or wherever you listen to your favorite show.
Smoke
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