Green roofs can help cool cities in the summer heat, but building them is only the first step – many don’t survive
The success of green roofs depends on more than just good intentions and engineering – they need long-term love and care.
As summer temperatures continue to climb across the United States and Europe, cities are grappling with the serious issue of dangerously high heat levels. Record-breaking heatwaves strain power grids, force people to seek refuge in cooling shelters, and can render the upper floors of certain apartment buildings uninhabitable. One potential solution to this problem is the installation of green roofs – living rooftops covered in vegetation that can convert heat-absorbing surfaces into cooling systems.
Certain cities, like Chicago, offer zoning incentives to developers to encourage the construction of green roofs. However, simply building a green roof is not sufficient for it to be effective in cooling a city. Our research indicates that the maintenance of green roofs after installation is equally, if not more, crucial for their success.
Our findings reveal that many green roofs are abandoned and fail to thrive beyond a few years, often due to the expenses associated with maintenance. During economic downturns when building operational budgets are reduced, landscape elements such as green roofs are frequently neglected or maintenance is scaled back to save costs.
Green roofs are more than just decorative additions to buildings. They consist of various layers, including insulation, waterproofing, and drainage, which enable plants to grow on top of structures. Depending on their design, these roofs can support a range of vegetation, from low-growing sedums to shrubs and trees. For instance, Rockefeller Center's rooftop terrace gardens in New York City, established in the 1930s, featured trees, grass, shrubs, and seating areas that doubled as park-like respites above the city's traffic.
Moreover, these green roofs provide substantial environmental benefits beyond cooling. Plants absorb sunlight that would otherwise heat the building below, cool the surrounding air through evapotranspiration (the process through which they release water vapor), and reduce the energy required for heating and cooling. Additionally, green roofs capture rainfall, preventing it from entering storm drains, thereby decreasing flood risks and enhancing water quality in the community.
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