Climate change is happening and predictions of the future climate show that the city of Austin is expected to get warmer in the near and distant future. Green roofs, a growing phenomenon, could help alleviate extreme heats in the Texas capital city.

Green roofs are simply rooftop gardens. In the downtown areas of urban cities, like downtown Austin, climate change takes a greater toll on the environment with what is known as the “urban heat island effect”. Climate experts and environmental experts say green roofs could help cool down quickly heating cities.

“[Green roofs] capture carbon, are pollinators and hold rainfall. No singular green roof is going to fix [the urban heat island effect] but the cumulative effects with larger-scale implementation of green roofs could help combat some issues of climate change,” said John Asher environmental designer at the Lady Bird Johnson Wildflower Center.

According to the Environmental Protection Agency, the term “heat island” means built-up areas that are hotter than nearby rural areas. This is more prevalent in urban areas because of the congestion and amount of concrete and asphalt. The EPA says this urban heat island effect can cause temperature differences as much as 5.4 degrees Fahrenheit in heat islands than in rural areas. The consequences of this are increased demands in energy, air condition, more air pollution, more greenhouse gas emissions, decreased water quality, illness and mortality.

The EPA says green roofs reduce temperatures by removing heat from the air. Benefits of having one of these include reduced energy use, reduced air pollution, improved human health, enhanced storm-water management and better water quality, according to the EPA.

The EPA recommends installing green roofs to reduce the heat and provide an array of environmental benefits. Several Austinites have already hopped on board with rooftop gardens and the popularity is increasing among homeowners and building owners.

“Some clients come to us for the visual appeal, but there are other benefits,” said Asher, who has been involved with six successful green roofs in Austin. Asher said the Wildflower Center started looking at green roofs years ago and they are now a hot item among architects. The Wildflower Center consults with clients, designs and builds green roofs.

Some of their successful green roof projects include the Dell Medical School green roof and the Edgeland House green roof.

The Dell Medical School green roof at the University of Texas-Austin was planted in July 2016. The building is still under construction, but, once finished, patients in the clinical and oncology areas will be able to overlook this greenery with the city in the background.

Chris Brown is an Austin resident who had a green roof installed on his house by the Wildflower Center. His house, known as the “Edgeland House” was built in 2011 and the green roof was installed in 2012.

“I live on an edgeland– with urban factories on one side and the Colorado river on the other side,” Brown said. “My house is the transition between industrial and nature.”

Brown said the land his house is built on was a “brownfield”, formerly contaminated with a pipeline that has since been removed. He wanted the green roof for both design and environmental reasons.

“I wanted my house to be buried [with greenery] and wanted the green roof for energy efficiency,” he said. “It’s a miraculous thing that anybody cold do. [Green roofs] have the power to radically transform our city to be more ecologically healthy.”

Casey Boyter is another Austinite who has been working with green roofs for several years. Since 2005, Boyter said she has successfully installed about three-dozen green roofs in Austin. Boyter, like Asher and the Wildflower Center, typically installs green roofs for the aesthetic appeal clients want, but she recognizes the environmental benefits of them and potential to help the urban heat island effect brought on by climate change.

“We have solid statistics that show obvious benefits of green roofs in a sea of concrete,” Boyter said. “Green means cool.”

Asher said at first it was difficult to make green roofs work in a climate like Austin, but after years of research the Wildflower Center has learned how to successfully install them both in downtown Austin and other areas.

Green roofs typically work well in temperate regions, like Germany, Britain, or France, said Asher. Successful green roofs can be seen in American cities like Chicago or New York. He said in semi-arid regions like Texas, installing green roofs is much more difficult. When green roofs first came to Austin more than a decade ago, designers and builders tried using non-native species but this proved to be a failure because Central Texas was too hot and the climate did not meet the needs of the plants. When temperatures are too hot, plant growth fails and the plants eventually die. According to U.S. climate data, the average high temperatures for Austin in the summer are in the upper 90s, whereas in Chicago and New York they are in the low to mid 80s.

What worked for successful green roofs in Chicago and New York, could not work in Austin, said Asher.

Asher said the Wildflower Center examined failed green roofs and, after some research, learned what kind of plants worked to make a successful green roof in Austin. There are two types of plant pallets the Wildflower Center uses: A prairie mix of native grasses and wildflowers and a cacti and succulent mix with a hint of flowers for color and aesthetic. Asher said the cacti mix, which is on the Dell Medical School, is perfect for clients who don’t want to do much upkeep of the green roof and don’t want to use a lot of water. The prairie mix green roofs require more maintenance and watering to stay alive.

The Dell Medical Center green roof has a succulent mix with a bit of prairie grasses. The cacti require less water and less maintenance than other native plants. In light of spring, bluebonnets have bloomed across the roof.

In addition to the plant pallets, Asher said there are two types of green roofs– intensive and extensive.

Intensive green roofs can be up to three feet thick, which allows more room for plant roots to expand and more volume for the material to hold in moisture, such as rainwater. These types of green roofs are heavy, which requires structure to be added to the building, which adds to the expense of installation. However, Asher said this type of green roof is easier to do than extensive.

Extensive green roofs are much thinner, typically from 3 to 12 inches. He said they are cheaper to install and more practical for clients, but offer more challenges for creating an environment that plant life can thrive in, with less than a foot of soil and material.

Asher said from consultation to completion, a green roof usually takes about six months.

“We are installing an ecosystem, putting a grassland on top of a building,” he said.

Boyter said she looks forward to green roofs being installed in Austin on a larger scale. “I’m talking acres of green roofs,” she said. “Texas needs bigger projects– Like a green roof on a Target or on a Home Depot. That’s where we will see the real big benefits.”

She said in the last decade plus since she’s been doing this, she has seen green roof popularity in Austin grow.

The Austin City Hall green roof was installed in 2005. Since then, green roofs have been popping up throughout the city of Austin.

However, even with the growth of green roofs being installed in Austin and adding the potential to help cool the city down, the city of Austin has only partially gotten involved– while it encourages developers to install green roofs and acknowledges the environmental benefits, the city does not offer any monetary benefits or rebates to Austinites who have green roofs on their homes or buildings, and does not initiate green roofs being built in the city.

Matt Hollin with the watershed department said the city of Austin formed a green roof advisory group in 2009 because a city councilmember was interested. The group came out with a report in 2010 and 2011 about green roofs, which acknowledge the issue of the urban heat island effect and offered green roofs as a possible solution.

The council also developed a green roof website, created a database for registering green roofs and did several case studies.

The only incentive offered to build green roofs is bonus building area depending on the amount of green roof a building will have. For example, instead of a seven-story tall building, the city might allow developers to build a nine-story tall building because of green roof space.

“We are very concerned about climate change increasing heat and we think natural systems, like adding a green roof, will be a big part of the future,” Hollin said. “We want to live in a healthy city with a good quality of life. We want the city to stay beautiful and green.”

In addition to the heat island benefits, Hollin said green roofs can also help stormwater management and reduce flooding in the city because the vegetation will capture much of the rainwater. Green roofs can even help solar panels do better because they help with absorbing the heat from the sun rays, which are also picked up by solar panels on the roof, he said.

Although green roofs are great for the environment, Hollin acknowledged the fact that installing them is expensive and leaves a carbon footprint.

“It would be interesting to see a study about the carbon expended from making green roofs,” Hollin said. “However, it’s more interesting to live in a place like this than a place with boring asphalt roofs and no environmental benefits.”


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This article was written in April, 2017 for “Reporting on the Environment” at the Univesity of Texas, taught by Dr. Kris Wilson.

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