Green Walls and Their Environmental Merits

When it comes to creating the cities of the future, the latest buzzword often mentioned is “smart cities.” But what exactly makes a city smart?

 
 
Highlights:
  • Green walls can be used to increase biodiversity, reduce noise levels, lower the urban heat island effect, and also contribute to minimizing dispersion of particular matter from traffic and pollution.

  • Green walls consist of a variety of plants, pollinators, and invertebrates and also serve as habitat and nesting spots for many bird species.

  • Green walls may be a great factor in pollution reduction in cities by sequestering carbon dioxide, capturing particulate matter, and lowering extreme summer temperatures through evaporation of water in the plants’ medium.

  • Green walls also provide an opportunity for beautifying areas, urban agriculture, and natural healing.

 
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BY PETER NORMANN VANGSBO and LISSA BARROWS | March 14, 2014

There are many definitions of a smart city, and they all include concepts that are sustainable, liveable, intelligent, and green. Among the green concepts so-called green walls are becoming more and more popular as a pocket size remedy in a micro-urban environment, offering many social and environmental benefits for the general public. In addition to promoting a static growth of green spaces, smart cities can use those green walls to increase biodiversity, reduce noise levels, lower the urban heat island effect, and also contribute to minimizing dispersion of particular matter from traffic and pollution.

EFECTS ON BIODIVERSITY

Furthermore, green walls can greatly help counteracting the loss of biodiversity due to urbanization. Such green walls consist of a variety of plants, pollinators, and invertebrates and also serve as habitat and nesting spots for many bird species. Local plants or adapted plant species can be used for the green walls for maximum benefits and will vary based on the local environment. Often the walls include plants with strong root structures, such as grasses, vines, and other climbing plants. Compared to other plants, vines grow faster and are hardy and drought-resistant. Since vines use most of their energy to grow leaves rather than trunks, they sequester 60 to 100 times more carbon dioxide than trees. Vine systems do not have runoff issues, like rooftop grass, because their roots are retained in a planter. Vines are also cheaper than most other plants used for green roofs. Vines suitable for outdoor green walls include Queen's Wreath and Cat's Claw vines.

Musée du Quai Branly, Paris. Image Credit Bertrand Garbel, Hemis.fr/Getty Images

EFFECTS ON POLLUTION AND NOISE LEVELS

Green walls result in noise reduction and muffle high-frequency sounds. They can even block low-frequency noises when created with a substrate or growing medium support. The reduction of the heat island effect is another benefit of green walls as the vegetation in urban environments advances the naturally occurring cooling processes, including evapotranspiration and photosynthesis. Continuously recycled water systems can be integrated into green walls with built-in irrigation systems where the water is collected from the bottom of the wall and returned back to the top. Indeed, strategic placement of green walls cools down the air and also the buildings benefit from significant energy savings. They provide thermal insulation and reduce energy usage for heating or cooling, thus resulting in less pollution. Furthermore, they may be a great factor in pollution reduction in cities by sequestering carbon dioxide, capturing particulate matter, and lowering extreme summer temperatures through evaporation of water in the plants’ medium.

MANY CASES PROVE THE POINT

Many case studies reveal the benefits of green walls. A recent study from Karlsruhe Institute of Technology in Germany shows that green walls can possibly decrease air pollution in the corridor between tall buildings, called a “street canyon.” In a Western European city, the researchers developed a computer model of a green wall with generic vegetation and recorded the chemical reactions based on several factors, such as building placement and wind speed, and the simulation exposed an unmistakable correlation. In a street canyon, the green wall trapped or sequestered large amounts of nitrogen dioxide and particulate matter pollutants that are harmful to people.

At the Tempe Transit Center Covered in Green in Tempe, Arizona, green walls provide a buffer from the harsh sun and heat and facilitate cooling and shade for the surrounding areas through evapotranspiration. Queen's Wreath and Cat's Claw vines were used for the installation, and a rainwater downspout that conveys water into a bed of soil was also integrated.

In order to renovate a building from the 1960s, Arizona State University incorporated greenscreen green walls to cool the interior, clean the air, and support the design. The greenscreen includes desert-tolerant vines, grasses, and flowers, and they plan to add herbs and more flowers in the future. Moreover, the installation and greenery creates shade for the area and has become popular with students and faculty as a shaded space for lunch and socializing.

THE SOCIAL FACTOR

Besides environmental benefits, green walls offer societal benefits, including the opportunity for beautifying areas, urban agriculture, and natural healing. The greenery can visually enhance the areas outside as well as inside to naturally draw more people to locations. Green walls can also be used in forgotten spaces for vertical gardens of small fruits, vegetables, and herbs to benefit local communities and help alleviate food deserts. Additionally, through green walls, natural processes of healing can be facilitated in public areas, restaurants, and other institutions. In particular, greenery and green walls in hospitals can help to remedy patients and turn a dreary hospital into a paradise with the natural healing powers of nature. Green walls are a critical aspect of smart cities and a powerful micro-tool for contemporary urban built environments.