Roofs filled with foliage and vegetable gardens are taking root in cities across North America and Western Europe. Otherwise known as green roofs, these increasingly popular components of the urban landscape are associated with lower energy costs, better health and wellbeing, and other benefits. Their emergence also reflects that over 80% of the world’s population now reside in urban environments engineered to cope with the demands of modern living.
Are green roofs easily transferable to the Middle East and other regions characterized by harsh desert climates? The answer to this and other questions can be found in the following interview with Dr. Sami G. Al-Ghamdi, Assistant Professor of Sustainable Development at Hamad Bin Khalifa University’s (HBKU) College of Science and Engineering (CSE).
What, exactly, is a ‘green roof?’
Green roofs contribute to wider efforts to reduce the negative impact of buildings on human health and the natural environment. Their design encourages efficient use of energy, water and land while simultaneously reducing waste and pollution. Green roofs particularly help to tackle the ‘heat island effect,’ which occurs when urban environments have higher temperatures than surrounding rural areas.
Beyond environmental benefits, green roofs also provide entrepreneurial opportunities for city dwellers, ranging from food and plant sales to creating urban wildlife habitats. To this end, they are widely thought to boost productivity, improve physical health, and create a greater sense of local community.
Are green roofs on the agenda of Qatar’s central planners, government departments etc.?
Qatar’s Public Works Authority (Ashghal) has a number of projects that divert treated sewage effluent (TSE) water into green structures such as Khalifa Avenue. For its part, Qatar Foundation aided the development of Northwestern University’s (NU-Q) green roof at Education City. The construction complies with multiple categories in the US-based Leadership in Energy and Environmental Design (LEED) green building rating system. These include Energy and water efficiency, material selection and indoor environmental quality.
As things stand, legislation does not require developers to incorporate green roof technologies into Qatar’s new properties. However, some rules and regulations governing water and energy supplies – most notably efficient usage – indirectly encourage the development of green roofs.
Does it necessarily follow that Qatar’s new buildings are ideal for developing green roofs? Are older buildings better candidates?
Both are promising, however, the design of some green roofs are not easily transferable to older buildings. In both instances, the structure needs to be strong enough to cope with the extra weight resulting from the installation of a green roof.
The type of building also goes a long way to determining what type of roof can be developed. There are two main types of green roofs: intensive roofs with a lower thickness of plant-growing medium that, thanks to inadequate infrastructure, are inaccessible to inhabitants; and extensive roofs, which have a greater thickness of growing medium, as well as infrastructure that supports public access.
What type of technologies and adaptations are required to make a green roof happen?
The challenge is to design, install and maintain green roofs that work in tandem with key features of the building. These include heating, ventilation and air conditioning (HVAC) systems and solar photovoltaic (PV) panels. A deep understanding of modern design and construction principles – not to mention familiarity with the local climate and environment – will also go a long way to creating a green roof in tune with its surroundings.
What might some of the technical features of a ‘typical’ Middle Eastern green roof look like?
The region’s efforts to develop more green walls may provide a useful insight. These are created by planting climbing plants at the base of a wall. They have been around for centuries and are widely acknowledged to reduce wall and building temperatures. The Sustainable Built Environment Research and Education Lab (SBE) at HBKU is exploring the potential for incorporating greywater-recycling systems (i.e. primarily from showers and bathtubs) into green walls and roofs. To date, studies have focused on the performance and design required for integrating green walls with greywater treatment facilities. However, adjusting prototype solutions to reflect the needs of green roofs is by no means impossible.
How does pollution affect the development of green roofs? For instance, does it influence the choice of plants that can be grown?
Thanks to rising population levels, urbanization is set to increase dramatically over the next 30 years. This will have a profound impact on a range of public health issues, including air quality, waste disposal, and the provision of safe water and sanitation. Elevated temperatures, more automobiles, increased reliance on air conditioning, and greater industrial emissions create the ideal conditions for smog. Air pollution created by smog is a major cause of poor respiratory health, especially asthma in children. Poor urban air quality accounts for an estimated 800,000 deaths per year.
Green roofs help to tackle the above challenges by reducing a building’s heating and cooling loads. More energy and water efficient buildings reduce demands on power and desalination plants thereby decreasing emissions of carbon dioxide and other harmful byproducts. Plants also help to improve air quality by capturing airborne pollutants on leaf surfaces and filtering noxious gases.
Of course, some plants are better at carrying out these tasks than others. For example, a 1996 urban forestry study determined that 2,000 m2 of uncut grass could remove up to 4,000kg of particulate matter (PM) by trapping it on its foliage. Another study analyzed the effects of six vegetation scenarios on air contamination in midtown Toronto. It concluded that varying amounts of grass, shrub and trees planted on green roofs could significantly mitigate air contamination, particularly when it comes to PM10 and carbon monoxide.
How is HBKU contributing to the study and development of green roofs?
The Sustainable Built Environment Research and Education Lab (SBE) at HBKU’s College of Science and Engineering conducts multidisciplinary research on the built environment in order to develop innovative solutions that improve quality of life. One of its leading projects evaluates the impact of climate change on residential building energy consumption in hot desert climates. The project also considers the potential for reduced energy demand through building renovation work, with a particular focus on the integration of green roofs and walls. This research compares quantifiable impacts of green roofs with common building insulation measures.
So when it comes to Qatar and the wider Middle East, are green roofs possible and practical?
Possible, yes, however, the jury is still out on whether green roofs are practical. For instance, plants that tend to do well in extreme climates lack dense foliage meaning that they are of limited use for reducing energy demands and removing pollutants. Using nonnative plants under such conditions is possible but requires a significant amount of irrigation. Conversely, countries with coastal desert climates such as Qatar use desalination to produce tap water. This environmentally intensive process has the potential to offset the energy saving benefits of all green developments.
The Communications Directorate at Hamad Bin Khalifa University (HBKU) submitted this article on behalf of Dr. Sami Al-Ghamdi. The views expressed are that of the author’s and do not necessarily reflect the university’s official stance.