Dynamic urban systems have altered human living environments. People have been compelled to live in tiny apartments due to the expansion of the urban population and the severity of socioeconomic issues, bringing about several issues, like water contamination and an urban heat island. Since natural or semi-natural green infrastructure strategies are frequently seen as popular ways to increase the amount of green in metropolitan settings, one of these methods to improve a variety of ecosystem services that naturally benefit the environment, society, and economy is the use of green roofs. These are widely recognised as a technology that can lessen urban areas’ intricate and numerous environmental issues by bringing vegetated landscapes’ natural cooling, water treatment, and air-filtering benefits. Although there are municipal and regional policies that support green roofs, installation costs are still high and discourage investment in this technology, specifically in developing nations leading to underutilisation on an urban scale. Considering the radical shifts in climate change and demand for Environmental, Social and Governance (ESG) in all sectors, espousing green roofs can be a key strategic instrument to develop resilient and sustainable cities.
What are Green Rooftops?
Green roofs, also referred to as “vegetated roofs” or “living roofs,” are ballasted rooftops that are covered in vegetation (plants), a growing medium (soil), and a waterproofing covering. Green roof systems can be modular, with drainage layers, filter cloth, growing media, and plants already primed in retractable, often interlocking grids, or loose built-up, with each system component installed individually. These can be installed on various buildings, from industrial facilities to private residences.
What are the Benefits?
Urban greening has long been marketed as a simple and successful method for improving the built environment. Green roofs improve a building’s appearance. If properly planned, the roof might serve as a getaway for the building’s occupants or even a playground for kids. They provide a peaceful and tranquil sanctuary above traffic noise and immediate air pollution.
Most urban and suburban areas have paved or constructed surfaces that prevent stormwater from soaking into the ground. Excess runoff degrades water quality by introducing pollutants into waterways. Green roofs can reduce stormwater runoff from a roof by up to 65% and delay runoff by up to three hours (GSA, 2021). The substrate stores water, which is then taken up by the plants and returned to the atmosphere via transpiration and evaporation. Green roofs retain between 70% and 90% of the rainwater in summer and 25% and 40% during the winter (Green Roofs, 2022). In addition to collecting rainwater, green roofs also serve as natural filters for any water that may flow off and help to keep the water’s temperature in check. They lessen the quantity of stormwater runoff and prolong the time it happens, reducing the strain on sewage systems during times of high flow.
Saves Operational Expenses
Green roofs help regulate the building’s temperature by adding more insulation, which, in turn, lowers heating and cooling expenditures after the initial installation costs. By lowering the roof’s exposure to the weather, green roofs can also lengthen their lifespan and prevent replacing the roof assembly too soon, as greenery serves as a barrier, preserving the waterproof membrane below and extending the useful life of the rooftop. According to the GSA green roof report, green roofs on commercial and public buildings have a payback period of approximately 6.2 years, based on 50-year average yearly savings, an internal rate of return of 5.2%, and an ROI of 224%, based on a net present value of $2.7/square foot (GSA, 2021).
Enhances Air Quality
Air pollution remains a prominent issue in urban areas, attributed to 11.65% of deaths annually (Ritchie & Roser, 2021). An eco-friendly roof contributes to better air quality in general. According to a study, green roofs can lower sulphur dioxide emissions by up to 37%, nitrous acid emissions by 21%, and dust particles by 0.2 kg per square metre annually (green roofers, 2021). The vegetation on green roofs can filter harmful gases, airborne contaminants, and atmospheric deposits. Green roofs’ ability to regulate temperature can lessen the load on power plants and possibly lower the amount of CO2 and other air-polluting byproducts produced.
Restraint of Urban Heat Island Effect
When cities replace the natural land cover with dense clusters of pavement, buildings, and other surfaces that absorb and hold heat, urban heat islands are created. Plants on vertical and horizontal surfaces can cool cities during the hot summer and lessen the Urban Heat Island (UHI) impact through the dew and evaporation cycle. Otherwise, the light absorbed by vegetation would be converted into heat energy. Green roof temperatures can be up to 30 to 40 degrees Fahrenheit lower than those of conventional roofs, and they can also cool the city’s air by up to 5 degrees (EPA, 2022). UHI is also reduced by covering some of the city’s hottest surfaces, such as black rooftops, reducing dust and particulate matter distribution throughout the city and smog production. This can help reduce greenhouse gas emissions and adapt urban areas to warmer climates.
Green roofs contribute to smart growth precepts and positively impact the urban environment by expanding amenities and green space and decreasing community resistance to infill projects. Green roofs can be used for various purposes, including community gardens, commercial spaces, and recreational spaces. Also, new employment prospects in manufacturing, plant development, design, installation, and maintenance are brought about by the market expansion for green roofs.
Green roofs’ increased insulation can decrease the energy consumption required to maintain a building’s temperature, as roofs experience the most heat loss in the winter and the highest temperatures in the summer. For example, the National Research Council of Canada discovered that an extensive green roof lowered the daily energy needed for air conditioning in the summer by more than 75% (Green Roofs, 2022).
Today, most individuals are looking for ways to use sustainable living techniques to help the environment. A green roof can attract this group of potential tenants or buyers. Buildings with green roofs may be more marketable. They can serve as a motivator for individuals interested in the numerous advantages that green roofs have to offer because they are an instantly recognisable symbol of the green construction movement. Sales, lease-outs, greater property value due to increased efficiency, easier employee recruiting, and lower employee and renter turnover have all been linked to green roofs as a part of the green building movement.
What are the Drawbacks?
One of the most significant disadvantages of integrating a green roofing system is the expense, as they are more expensive than traditional ones. One reason is to compensate for the additional support required to handle the increased load. Other costs include the foundation, soil, vegetation, and installation. As a result, its benefits will be realised only after overcoming the challenges of installing this system.
Frequent Maintainance is Required
Keeping plants on the roof requires some work and attention to ensure the plants are doing well. This could be an advantage for some, but for many people, this would be a disadvantage. A green roofing system should be treated similarly to a garden. Weeding, watering, harvesting, and trimming are all common maintenance tasks to keep bare spots and an attractive appearance. Most of the time, this can be addressed more easily by hiring someone to manage the landscaping and upkeep, adding to the expenses.
Increasing Weight load
A green roofing system will be heavier than a typical roof and need more installation support. They often increase the weight of an existing building structure by 50 to 200 kg per square metre (Truong, 2020). Not all structures are sturdy enough to hold this roofing system. In contrast, lighter solutions, known as extensive green roofs, can range in price.
Although a green roofing system can improve a building’s beauty, there are still restrictions on the kind of vegetation that can be installed due to temperature, weather, and other considerations. A thick-growth media may sustain a wide variety of plants, including shrubs and small trees, for an intensive green roof system. However, thin, extensive green roofs can often only support a small number of shallow-rooted, drought-tolerant plants.
Although green roofing system has drawbacks, the benefits are multitude. Developing countries like Pakistan should invest in such sustainable practices owning to climate vulnerability, increasing urban floods, and expanding populations. It will help mitigate global warming, protect the environment, and transform traditional concrete jungles into sustainable green cities.
EPA. (2022, July 13). Using Green Roofs to Reduce Heat Islands. Retrieved from the United States Environmental Protection Agency: https://www.epa.gov/heatislands/using-green-roofs-reduce-heat-islands#:~:text=Green%20roofs%20provide%20shade%2C%20remove,effect%2C%20particularly%20during%20the%20day.
Green Roofs. (2022). About Green Roofs. Retrieved from Green Roofs for healthy cities: https://greenroofs.org/about-green-roofs
green roofers. (2021). Advantages and Disadvantages of Green Roofs. Retrieved from green roofers: https://www.greenroofers.co.uk/green-roofing-guides/advantages-disadvantages-green-roofs/#:~:text=Without%20doubt%2C%20one%20of%20a,conditions%20over%20the%20summer%20months.
GSA. (2021, November 15). Green Roofs. Retrieved from U.S. General Services Administration: https://www.gsa.gov/governmentwide-initiatives/federal-highperformance-green-buildings/resource-library/integrative-strategies/green-roofs#:~:text=Energy%3A%20Green%20roofs%20reduce%20building,and%20insects%2C%20thereby%20increasing%20biodiversity.
Ritchie, H., & Roser, M. (2021, January). Air Pollution. Retrieved from Our World Data: https://ourworldindata.org/air-pollution#:~:text=Summary-,Air%20pollution%20is%20one%20of%20the%20world’s%20leading%20risk%20factors,to%2011.65%25%20of%20deaths%20globally.
Truong, T. (2020, December 14). Pros and Cons of Implementing a Green Roofing System in a Building Structure. Retrieved from LinkedIn: https://www.linkedin.com/pulse/pros-cons-implementing-green-roofing-system-building-structure-trung/