An example of a green wall (Picture of a Green Wall in Paris: MUSEE DU QUAI BRANLY)
Definition
Green walls are vertical structures that have different types of plants or other greenery attached to them. The greenery is often planted in a growth medium consisting of soil, stone, or water.
Green walls differ from facades, which are often seen climbing up the outside walls of buildings, using them as structural support. In green walls, the growth medium is on the surface or structure of the wall, whereas facades are rooted in the ground. Moreover, the greenery of facades can take a long time to grow enough to cover an entire wall, while green walls may be pre-grown.
Maintenance of green walls
The higher the wall, the trickier it gets to maintain it.
In order to stay healthy to serve their purpose, both green walls and smart and active green walls need upkeep. Like all living plants, greenery in plant walls requires periodical replacements to compensate for plant loss.
In loose and structural media solutions, replacing plants is generally straightforward. In mat media systems however, replacing plant matter is more problematic: lost sections often have to be cut off. Removing these sections may cause extra plant loss due to greenery having spread their roots into the removed area.
Moreover, water is vital for the survival of the plants, which is why most plant walls have integrated irrigation systems to make it easier to take care of the plants. The plants also need basic nutrients, which are usually received through irrigation.
The irrigation systems are typically either recirculating or direct systems. A recirculating system circulates the water, pumping and distributing it from a built-in tank. The tank can be either filled manually or connected to a building’s water supply.
Meanwhile, a direct irrigation system gets the water from an external water source. Whereas recirculating systems collect excess water for reuse, direct systems send the excess water to a sewer drain.
For a green wall to function as it should, all of its mechanisms need to work properly. In addition to plants, irrigation, and growth media, the remote monitoring systems may also need maintenance at times in case of an error. This is why regular maintenance is needed to make sure everything runs smoothly and effortlessly.
Applications of Green walls
Green walls can be an opportunity to contextualize urban design contents and strategies, moving into the direction of integration and sustainability of all city elements, such as buildings, public spaces and greenery. The scientific research on green walls systems and their benefits in the environment of the cities is still in the development stage. The most common knowledge about the applications in this field is associated with new or existing buildings, which are seen as landmarks in the urban fabric, such as the CaixaForum in Madrid or the Citi Data Center in Frankfurt. Despite of these very well-known buildings, the fact is that green walls have been rarely used as elements of urban design, and urban fabric composition, either in new urbanizations or in the rehabilitation of historical places. As shown by the presented examples, their use can play a decisive role in the composition of the city’s shape and in the qualification of the urban image, in matters such as the regularization of different buildings heights and alignments, in the camouflage of blank walls or in the qualification of small places. In summary, the use of green walls as elements of urban regeneration and cities design continues as a challenge, of linking the buildings to the urban environment and to the nature. Thus, is in this context that their application should be encouraged, as part of basic urban homeostasis, i.e. the ability of the city to stay in balance. Green walls can be an ingenious way of greening the historic areas of cities, which otherwise would remain void of biodiversity.
Effect of green walls on humidity and temperature:
When plants transpire, they become miniature humidifiers—when grouped together the relative humidity is increased, benefiting all plants around. Green walls often have an advantage of higher humidity due to many plants together in close proximity. Grouping plants together can be beneficial; however, if pests or disease are prevalent, plants should be spaced properly to allow air flow. Green walls also reduce the ‘urban heat island’ effect in cities. They also act as insulation helping to regulate a building’s temperature, keeping it warmer in Winter and cooler in Summer. In some cases the use of living walls has even allowed for a reduction in air conditioning requirement.
Effect of green walls on air pollution:
Planting trees isn’t always the best way to reduce air pollution on city streets, a new study says. In some cases, more trees could even make the problem worse. Instead, “green walls”—blanketing sides of buildings with grass, ivy, or other plants—might be the most effective solution.
In a new study, a team took a closer look at a common feature of the urban landscape: the street canyon. Street canyons are roads surrounded by tall buildings, where air tends to linger.
The researchers ran computer simulations to determine how green walls and roofs might affect pollutant concentrations at street level. Adding plants to walls would cut nitrogen dioxide levels by 15 percent and small particulate matter by 23 percent, the authors estimate. In areas with little wind, those numbers could reach 40 and 60 percent. Green roofs didn’t perform as well because they don’t directly affect the air near the street.
Trees also help reduce air pollution and clean the air, but they can keep street-level air from mixing with the air above. At low-to-medium pollutant levels, planting trees will still reduce air pollution, the team predicts. If a city is very polluted, however, trees could actually increase nitrogen dioxide levels near the street. “By not considering the adverse effects of tree planting on canyon ventilation, urban greening initiatives that concentrate on increasing the number of urban trees, without consideration of location, risk actively worsening street-level air quality,” the authors warn.
The advantages and disadvantages
Everything has a negative and positive side and is the same for the Green Walls.
The green walls have a lot of advantages but also some disadvantages .
Advantages:
- That you can save space
Now-a-days most of us don’t have outdoor spaces to go for a garden, people are living in an apartment and could give only a limited area of their balcony for gardening.
A vertical garden uses a very limited space for planting, you can have piles of plants vertically arranged one by one or hanging one above the other. But keep in mind that they need enough sunlight.
- Keeping your Diversity of plants:
You can even experiment with growing diversities of plants like decorative and vegetable plants row by row to give an aesthetic to the garden.
- It’s a protective shield:
Everybody knows that plants absorbs pollutants and harmful compounds, so when we grow plants vertically in a compact way, it acts as a protective shield and gives you a pure environment to breath in.
- It protects your building:
Your green wallsdo not only absorb the air pollutants but also the heat, noise, harsh weather and UV rays. It regulates temperature through transpiration.
- A healthy vegetation:
In vertical garden the plants gets more exposure of sunlight and air circulation as it grows upwards, which results in a healthy garden.
- The plants even help to reduce stress:
Many studies have found the Physiological effect of Plants in reducing the physical signs of stress and promote access to vegetation for having a greater positive human health impact.
- It’s aesthetically pleasing:
You can incredibly transform the wall or any empty space into something aesthetically pleasing and creatively stimulating by vertical gardening. It gives a soothing natural beauty and makes a great impact on the visualize.
Disadvantages:
- Cost:
Green walls are a luxury item costing between $900 - $1,500 per square meter, however the new systems take a lot of the hard work out of the construction of green walls so there is a decreasing installation cost.
- Maintenance:
Green walls are very labour intensive to maintain, usually you have an average of 50 plants per square metre. Keeping soil intact on a vertical living system looks easy, but in reality cleaning up the soil that falls out every day because your plants are growing. You will also need to regularly replace plants that have died or are root bound.
Sources
https://www.naava.io/editorial/what-are-green-walls
https://iopscience.iop.org/article/10.1088/1755-1315/44/3/032016/pdf
https://dergipark.org.tr/en/download/article-file/308530
https://www.bebee.com/producer/@claire-cardwell/the-pros-and-cons-of-green-walls-by-claire-cardwell