Could Green Roofs on Schools Be a Climate Solution?

More than 7,000 gardens rose from 2015 in US schoolyards. For decades, these green spaces have been hailed for their multifaceted benefits: providing children with hands-on experience growing fruits and vegetables, helping them develop a love of healthy foods, and providing teachers with a platform to explore STEM concepts. Representative Nydia Velázquez (D-NY) wants to move some of the world’s school gardens — to rooftops — and plant them next to meadows that also provide refuges for wildlife, reduce stormwater runoff and reduce urban heat islands.

HR 1863, also known as the Public School Green Rooftop Program Act, which Velázquez introduced in March, would authorize the Department of Energy to provide $500 million in grants to public schools to build and maintain green roof systems. That’s enough for about 14 million square feet of greenery — which by some estimates would hold some 154 million gallons of rainwater and 537 tons of carbon — prioritizing schools serving low-income students. Velázquez, backed by 20 (Democratic) co-signers and the backing of the National Resources Defense Council and other environmental groups, says such roofs will help pave the way to “cleaner, healthier communities.”[ies],” said a press release.

Science is on its side, though Pete Ellis, senior project manager for Restore green roofs, a Massachusetts-based company that has installed green roofs on about 20 school and college buildings and is an industry sponsor of the bill, says more needs to be done to quantify things like carbon sequestration potential, improving biodiversity and how much green roofs can do. reduce heating and cooling costs for a given building. Yet he says, “There are many things… strictly substantiated: improved air quality, lower ambient temperatures to reduce the effects of the urban heat island, and the ability to capture and retain rainwater.”

The roof of Saugus Middle-High School in Saugus, Massachusetts.

Ellis says green roofs are also a great way to “maximize the benefit of underutilized spaces – nothing against” [rooftop] solar panels, but if you’re looking for student engagement that’s all [environmental] boxes, there is no better way to go about this.” Added bonus: Certain types of green roof waterproofing membranes can have an average lifespan of around 40 years – in some cases this equates to a marked improvement over the 17 years a typical school roof membrane lasts before needing to be replaced.

There are numerous types of green roof systems and they implement different strategies to grow plants. And techniques differ depending on whether the roof is added to an existing building or becomes part of a brand new building, and how much structural load a building can support. In principle, however, insulation is spread over a roof and covered with a membrane and drainage material; a substrate of soil or soil-like material is added to all or part of the roof; then the flora goes in. Species of the shrubby sedum genus are the most common plantings — something that Ellis says is thankfully beginning to change in the US, thanks to a drive to implement more native plants with greater biodiversity to better support pollinators and other wildlife. On school roofs, this low-lying greenery can be accompanied by a separate farm or garden, with food plants growing directly in the substrate or in pots.

In all cases, the membrane absorbs and retains heat; the substrate absorbs rainwater and retains at least some amount of carbon, as well as particulate matter; evaporation takes place between the substrate and the plants to obtain a cooling effect. And of course, schoolchildren can grow things, conduct experiments and spend more time outside in nature, boosting both their emotional well-being and their safety. (These are both critical considerations, as the Delta strain of COVID continues to place people indoors close together at risk of infection and schools welcome students again this fall.)

A green roof installed in 2012 by Recover, at Massachusetts Natick High School, is actually not up to standard: It’s not meant to be hunted by students or anyone else. But in addition to its climate-limiting effects, it also offers another important advantage, which is that it can be seen from multiple classrooms. “There’s Been a Lot” Research around improvements to health and well-being when nature is visible,” explains Ellis.

A few hundred miles to the south, New York City has become home to an estimated 730 green roofs, according to 2018 data of the Nature Conservancy – including perhaps the most famous, the one on top of the Javits Convention Center. This 6.75-acre oasis has acted as a breeding ground for geese and gulls and has become home to honey bee hives. It now also absorbs 7 million liters of rainwater and reduces energy consumption by 26 percent per year.

The roof of Saugus Middle-High School in Saugus, Massachusetts.

There is no official count of the number of green roofs in NYC that have been added to new or existing public school buildings, although they are there and spreading, from Coney Island until Roosevelt Island and further. Vicki Sando, a green roof consultant, says the Department of Education has been pushing for solar on the roof lately. “But solar energy works better on green roofs – the transpiration” cools down the panels and makes them more efficient,” she says.

“Solar works better on green roofs – the transpiration cools the panels and makes them more efficient,” a benefit that will only become more necessary as temperatures continue to rise.

Sando was also a STEM teacher at PS 41 in the West Village, and she still volunteers to oversee the 15,000-square-foot green roof completed on the school in 2012. It was called the Green Roof Environmental Literacy Laboratory (GELL). contains (usually) inedible plants and is designed to help students better understand their role in protecting and improving wildlife and ecosystems.

Data collected in 2019 shows that the roof of the PS 41 contributed to a 32.7 percent decrease in greenhouse gas emissions and a 27.8 percent decrease in energy consumption in 2008; that it contains more than 180,000 gallons of rainwater annually; and that it is frequented by red-tailed hawks, kestrels, warblers, monarch butterflies, bats, and many other native and migratory animals. The school’s greenery has also become part of a nature corridor, connecting other nearby green spaces such as Washington Square Park, Union Square Park and the High Line. Perhaps best of all, a survey of the students themselves found that they expressed a wide range of positive feelings for their green roof: enjoying “free time with friends surrounded by plants”, “eating the chives”, “walking” .[ing] around pretending to be in a fairy garden,” and “check[ing] some bugs out.”

Sando hopes the current wave of enthusiasm for green roofs will extend beyond the high school and into many more and varied types of buildings in the city and country. That’s one of the biggest benefits of Velázquez’s bill: “Whether passed or not, it raises public awareness among the general public and elected officials and helps our cause, improving communities and combating climate change.” Sando says.

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