The 2024 Green Roof Global Market report from Research and Markets notes that the green roof market will grow to $2.11 billion in 2024, and is expected to reach an astounding $3.9 billion by 2028. In line with this development, we’re continuing to see a steady increase in the number of roofs with greenery and vegetation (particularly in urban areas) aimed at revitalizing some of these metropolitan areas’ most underutilized spaces. While rooftops in these locations account for nearly 25% of horizontal surface area, New York City is home to only 730 buildings with green roofs — a meager 60 acres of the 40,000 acres of rooftop space available (or less than 0.1% of NYC’s 1 million buildings). The lack of such spaces boils down to a few key factors, including the complexity of implementing the necessary structural requirements. That said, the benefits of green roofs far outweigh the effort needed to successfully implement these concepts.
A study conducted by Geotab, which divided the amount of green space equally per resident in numerous major metropolitan areas, noted that each New Yorker would only be allotted 146 square feet of green space. Despite efforts to increase accessibility to parks and green spaces throughout the city, statistics like these demonstrate why these areas are still highly sought after. The amount of green space currently available for use pales in comparison to the city’s ever-growing population — which strengthens the case for the continued design and implementation of green roofs. Making use of the city’s underutilized surface area presents a pragmatic opportunity to increase the amount of greenery available to each resident, which studies have shown can ultimately benefit the emotional well-being of inhabitants.
Sustainable Design
In addition to simply increasing access to green spaces, vegetative roofs offer an aesthetically pleasing opportunity for sustainable design interventions that benefit the environment. The Urban Heat Island (UHI) effect describes the phenomenon in which urban spaces experience significantly higher temperatures than adjacent areas. This comes as a result of the way in which streets, sidewalks, and buildings absorb and retain heat, in addition to the added conditions of higher population density, increased use of vehicles, and general infrastructure. UHI is also a proven contributor to global warming, and has been shown to worsen the quality of both air and water in these urban areas. Since natural surfaces formed from greenery tend to absorb far less heat, green roofs help to cool down our cities and work to improve the air quality within them. Vegetation captures airborne pollutants, filters noxious gasses, and cleans the air through plant respiration. Easing the strain on city infrastructure and HVAC systems, these spaces further help to lessen the drain on power plants and natural resources, while enhancing waste diversion efforts by mitigating the overuse of heating/cooling equipment and increasing the lifespan of roof membranes.
One of the most positive aspects of green roofs lies in their capacity to assist with storm water management. It is not uncommon for cities to experience flooding, improper drainage, or runoff that overwhelms the urban infrastructure. This leads to erosion, water contamination, and other forms of costly damage. Buildings equipped with vegetative roofs help to alleviate municipal storm systems, which are often supercharged with runoff as a result of the large number of impervious surfaces in urban environments. Reaching 70-90% absorption of precipitation in summer and 24-40% during the winter, these green spaces aid the storm water system by way of their moisture-retention layers, greatly reducing the flow of water directed to drains. In the same way that their implementation reduces air temperature, they also regulate the temperature of storm water, while simultaneously serving as a natural filter for runoff. These roofs address a host of issues caused by excess storm water in cities, creating a more sustainable and resilient urban environment in the long term.
Taking into account other concerns raised by the elements, fire resistance is a benefit of green roofing that is often overlooked. While it sounds counterintuitive at first, a properly designed green roof will contain appropriate greenery and growing media, which in most cases will retain adequate moisture to achieve notable benefits in mitigating the spread of flames. This makes them not only environmentally beneficial, but also a practical addition to urban structures where fire safety is a critical concern. Despite these benefits, designers should consult with local building codes to ensure the system and components all comply with required fire protection standards.
Going Vertical
Beyond the horizontal or angled application of greenery on roofs, the application of greenery on vertical surfaces is becoming an increasingly common development in the world of vegetative roofing. Facade greenery can be equally beneficial to a building, serving not only as insulation but also to manage acoustic absorption while providing additional shade. These surfaces absorb soundwaves, serving as a form of acoustic insulation that can have a tangible impact on the city’s overall noise levels, subtly improving quality of life for residents and pedestrians alike. These installations are often met with growing levels of enthusiasm for their unique aesthetic appeal and sense of novelty.
The expansion and integration of green roofs in urban environments offers a variety of benefits that go far beyond the aesthetic; from fostering emotional well-being of inhabitants, making cities more sustainable, and easing strain on urban infrastructure. With so much unutilized horizontal space across not only New York City, but throughout the entire country, stakeholders now have the opportunity to create healthier, more sustainable urban environments. Designers, owners, and developers should work in tandem to overcome perceived barriers to implementing vegetative roofing, striving to transform urban landscapes into vibrant, eco-friendly spaces that contribute to the well-being of city dwellers and the planet itself.
For more information on key considerations for the implementation of green roofs, you can view Katz Architecture’s recent white paper, titled “A Root Over Your Head: A Study of Green Roofs.” The white paper is available at katzarch.com/resources.
About the author: Julia MacKenzie, a graduate of the University of Pennsylvania, is a project architect at Katz Architecture in New York. For more information, visit katzarch.com.
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