Green roofs are emerging technologies that can provide a wide range of benefits to communities interested in enhancement and protection of their environment. The major benefits of green roofs are reducing energy use as well as air pollution and greenhouse gas emissions, enhancing stormwater management and water quality, decreasing heat island effect by regulating temperature for the roof and the surrounding areas and providing aesthetic value and habitats for many species.
According to a 2013 MENA renewable energy status report, the Total Primary Energy Supply (TPES) in Middle East and North Africa has reached about 800 million tons of oil. This equates to a 15% increase in energy demand since 2007. Increased energy consumption in the region is due largely to population growth, with related increases in demand for liquid fuels and electricity for domestic use and devices, heating, cooling, and desalination of water. With heating and cooling being a reason for the increasing demand on fossil fuels, there is enormous opportunity for investment in green roofs as a way to stabilize or reduce energy consumption in the MENA region.
Enhancing Stormwater Management and Water Quality
Stormwater is rainwater and melted snow that hits impervious surfaces and runs off into streets, lawns, sidewalks, and other sites. The main concern with stormwater is it can pick up debris, chemicals, dirt, and other pollutants and flow into a storm sewer system or directly to a lake, stream, river, wetland, or coastal water. In many places around the world, including MENA region, anything that enters a storm sewer system is often later discharged untreated into a nearby waterway polluting the same waters we swim, fish, and drink from.
In addition, stormwater runoff can cause flooding and an overflowing of sewer sanitary systems causing serious water quality impairments. In developing countries like Morocco and Algeria, where countrywide stormwater management and municipal waste management systems are deficient, stormwater runoff is a big problem. Rainwater flows from roofs straight onto streets carrying things like petrol, household garbage, bacteria, fertilizers and pesticides to nearby receiving waters.
According to an EPA study, green roofs are capable of removing 50% of the annual rainfall volume from a roof through retention and evapo-transpiration. By reducing the amount of impervious surfaces within a developed zone, green roofs reduce the amount of stormwater runoff. Also, because green roofs absorb water, they delay the time at which runoff occurs, resulting in decreased stress on sewer systems at peak flow periods.
For conventional non-living roofs with a slope of 2%, a 96% runoff rate is observed. On the other hand, intensive green roofs may have as low as a 15% runoff rate. The benefits green roofs have regarding stormwater runoff could be amplified by more green roofs in a close-knit area and using green roofs with a deeper substrate layer. Nevertheless, if implemented, countries in the MENA region in which stormwater management systems are not in place could greatly benefit from the use of green roofs to help reduce hazardous runoff and subsequent contamination of water supplies.
Decreasing Urban Heat Island Effect
Since the built environment tends to be constructed from materials that are impermeable and non-reflective they tend to absorb a significant proportion of the sun’s radiation and release it as heat. Because urban areas are densely populated with buildings, they tend to be hotter than the surrounding areas, a phenomenon known as heat island effect. Urban heat islands have many negative impacts such as an in increase energy demand for cooling, an increase in air pollutants and greenhouse gas emissions, and impaired water quality.
The heat island effect causes internal temperatures of buildings to rise which subsequently increases the demand for air-conditioning to moderate the buildings internal temperatures. This in turn leads to higher emissions from power plants, as well as increased smog production as a result of warmer temperatures. Additionally, hot rooftop surfaces transfer their excess heat to stormwater causing the runoff water to be much warmer than the streams, lakes, and other waterways it enters. In many cases dealing with this rapid change in temperature causes stress to aquatic ecosystems.
Urban heat island effect is especially worrisome for areas like Middle East and North Africa, where out of a population of 300 million, 170 million people reside in urban areas. Furthermore, according to UN projections the MENA population will reach 430 million by 2020, of which 280 million are expected to be urban. In order to combat the potential for the heat island effect in the MENA region, communities can utilize green roofs.
The vegetative surfaces of green roofs utilize a relatively large proportion of the absorbed radiation in the evapo-transpiration process and then release water vapor into the air which helps to cool air temperatures. Additionally, the shade provided by trees and other shrubbery greatly helps to reduce the rooftop temperatures and the overall heat island effect.
Rooftop vegetation moderates the factors that accelerate a rooftops breakdown such as extreme temperatures, UV radiation, and cold winds, thus dramatically expanding the life of a roof. According to a study in Germany, a vegetated roof on average can be expected to prolong the service life of a conventional roof by at least 20 years. The result of this is not only cost savings to the building’s owner but also a reduction of landfill wastes.
Habitats for Species
One of the more altruistic aspects of green roofs is the creation of wildlife habitats. Green roofs can provide habitat (food, shelter, water and breeding grounds) for many different species. Because of their high density, cities severely restrict green space and threaten or destroy habitats so the creation of such green space assumes particular importance in these areas. Urban habitats are often seen as too degraded and depauperate to support biodiversity.
Various recent studies in Europe have indicated that green roofs in large cities have high potential as habitat for species negatively impacted by land-use changes. For example, in Basel, Switzerland, surveys of birds, spiders and beetles on green roofs found high diversity levels for all groups, including many species considered rare or threatened.
For modern Middle Eastern citiies like Dubai, Jeddah, Cairo, Beirut and Tehran, creation of habitats for species could be very valuable. Across the MENA region natural habitats are few and far, and green roofs can provide living space for plants and animals, especially for species such as invertebrates and birds.
Green roofs have the ability to significantly improve the beauty of buildings, the visual and environmental diversity which can have positive impacts psychological well-being. Studies across several countries have all shown the correlation between daily contact with nature and human well-being. In fact, the results of a large survey in the Netherlands showed that the amount of green space in the residential environment was positively related to the health condition people said they experienced in their daily life.
When people have contact with green space research has indicated a positive effect in levels of stress, health levels due to green space encouraging a higher level of use of the outdoor spaces, and mental well-being due to positive psychological effects plants and nature has on humans.
While green roofs in Northern Scandinavia have been around for centuries, in North America green roofs are still a relatively new technology. In Europe, these technologies have become very well established mainly due to governments and legislatives financial support. This support has led to the creation of a vibrant, multi-million dollar market for green roof products and services in Germany, France, Austria and Switzerland among others.
Currently, implementation of green roofs is rare in the MENA region. However, there is a definite market potential as the benefits of green roofs address many of the major environmental concerns of this area. Furthermore, the concrete architecture in the Middle East is ideal for a green roof implementation. The structural soundness of concrete buildings has the potential to support the weight load of both intensive and extensive roofs. The swift progress of green buildings industry in the Middle East promises a deeper penetration of green roofs in domestic as well as commercial constructions in the years to come.
However, one issue that may surface is that roofs are often fully accessible and are often used to dry laundry or to hold social events like weddings and other celebrations. This may pose an issue for home owners if their green roof takes up too much of their roof to perform their daily functions. An intensive roof may be more suitable for homeowners in this region as they lend well to daily visits and offer space to hold social functions.
Due to their extensive range of environmental and economic benefits, particularly their insulation and cooling properties, ability to significantly reduce rainwater runoff and urban heat island effect, as well as improve air quality and their value in promoting biodiversity and habitat in urban areas, green roofs have become important elements of sustainable and green construction in many countries. While the green roof industry is growing in popularity, the industry is still young with many areas needing advancement.
The major barriers to green roof expansion in the Middle East include a lack of governmental support, high installation costs, lack of awareness and education about green roofs, and limited data quantifying green roof benefits. However, with proper support these barriers can be easily overcome through research and innovation in design by the green roof industry.