For major cities and urban areas, incorporating green roofs, or roofs planted with gardens and vegetation, serves as a way to reduce energy use in buildings while giving people a glimpse of nature that they would rarely ever see. Putting gardens on the relatively unused space of urban building roofs is a surprisingly attainable goal.
A traditional roof is vacant, with the exception of air conditioning equipment, and constructed with asphalt, black tar, and other materials that are used to give it a stable construction. During warmer seasons, heat radiates off the black rooftops of high-rise buildings and skyscrapers, raising the overall indoor temperature of the entire building, which then needs to be reduced through electricity-generated air conditioning. Buildings with green roofs limit this problem, as the vegetation on the rooftop absorbs much of the heat and sunlight that is pouring onto the building, and uses it to support growth of its plants through photosynthesis.
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| Greenroofs over the Berlin cityscape |
Green roofs also absorb much of the rainwater that strikes the top of buildings. In major cities, managing the rainwater as it enters storm drains can be challenging. Since the majority of large cities are also major port areas, rainwater can introduce new pollutants into rivers and oceans. To manage this, places like New York City implement waste processing plants to safely introduce rainwater into large bodies of water. The absorption of rainwater makes green roofs reduce the water management pressures that are placed on governing bodies.
Major cities are prone to the urban heat island effect. This is characteristic of areas that in landscape differ greatly from the natural surface of the Earth, and makes large cities warmer than other places in the same climate region, especially in the spring and summer. This problem can be mitigated by introducing more parks and gardens into the area so that they can absorb the heat and sunlight. However, introducing more green spaces can be a challenge, since there is little available space in many major cities, in which 54 percent of the human population resides today. Green roofs lower the elevated urban heat levels without taking away any space that would be used for commercial and residential purposes.
In addition to the environmental and physical human health benefits that can come from green roofs, they can also help people’s emotional health. All humans have innate physiological responses to elements in nature, and in large urban areas where vegetation is not common, seeing anything that is natural and green can help to alleviate stress and even depression. Easy access to a green roof on the top of an urbanite’s residence can give him or her this benefit daily.
Green roofs and other green infrastructure are relatively new additions to American architecture, but they have been throughout Europe for some time now. They are so common and accepted that the city of Copenhagen has a policy mandating that new buildings with roof slope than less than 30 degrees must be green roofs. To gain the same benefits that many European cities have long been granted, major cities in the United States have taken measures to ensure for them a future in which green roofs are in abundance. In September 2010, the NYC Department of Environmental Protection issued a green infrastructure plan, which proposed spending $1.5 billion to significantly reduce the rainwater in sewer watersheds by 2030. Similarly, Chicago’s Department of Buildings provides incentives for building developers to install green roofs as part of their storm water management and climate change action plans.
The biggest challenge with green roofs is likely their installation process. Soil on the ground that can grow vegetation is rich in nutrients to support that growth, and green roofs need to give these same qualities to a surface that would otherwise just be plain roof material. While there is a great deal of variation in green roofs, since the term refers to any kind of roof with vegetation, all of them have five basic components: weatherproof membrane, root-protection barrier, drainage layer, growing medium, and the plants themselves. Installation involves determining the appropriate materials and plants needed to successfully lower the temperature in the building and the surrounding city while handling varying amounts of water and sunlight.
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| Green Roof Installation |
The average cost of green roofs in the United States is estimated between $15 and $20 per square foot. This makes for a mild expenditure that will lead to immense benefits, even without the tax credits, grants, and additional incentives that people can get. The Morgan Processing and Distribution post office facility is the site of the largest green roof in New York City. Since its installation in 2008, the building’s storm water runoff into the municipal water system has been reduced by 75 percent in summer and 40 percent in winter. In addition, it has been responsible for cutting the building’s energy costs by $30,000 every year. This serves as a great example on how green roofs can benefit large cities economically. It is a very realistic assumption to say that, from their benefits and favored response from the public and the government, green roofs will be spread throughout the country in the near future.
There is a variety of ASTM standards available on the ANSI Webstore for the construction and design of green roofs and related materials. These include:
ASTM E2777-20 – Standard Guide for Vegetative (Green) Roof Systems
ASTM E2397/E2397M-19 – Standard Practice for Determination of Dead Loads and Live Loads Associated with Vegetative (Green) Roof Systems
ASTM E2400/E2400M-19 – Standard Guide for Selection, Installation, and Maintenance of Plants for Vegetative (Green) Roof Systems
ASTM E2399/E2399M-19- Standard Test Method for Maximum Media Density for Dead Load Analysis of Vegetative (Green) Roof Systems
ASTM E2398/E2398M-19 – Standard Test Method for Water Capture and Media Retention of Geocomposite Drain Layers for Vegetative (Green) Roof Systems
ASTM E2788/E2788M-18: Standard Specification for Use of Expanded Shale, Clay and Slate (ESCS) as a Mineral Component in the Growing Media and the Drainage Layer for Vegetative (Green) Roof Systems
ASTM E2396/E2396M-19- Standard Test Method for Saturated Water Permeability of Granular Drainage Media [Falling-Head Method] for Vegetative (Green) Roof Systems
ASTM D7852-13(2022) – Standard Practice for Use of an Electrically Conductive Geotextile for Leak Location Surveys
SMACNA 1156-2011 – Building Systems Analysis and Retrofit Manual
