Vertical gardens: everything you need to know about green walls

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Modern cities have plenty of problems, one efficient way to respond to some of the problems, is by making walls made of plants. These are sometimes called vertical gardens or green walls.

They provide a natural protection against noise pollution and smog. They also help us save energy by providing insulation, help keep the building cool in the summer and provide natural fibre protection. And that is not all: these natural walls also affect our well-being,  Just looking at these green covered walls soothes our eye and our mind, increasing the value of the building.

Let’s have a look at what green walls actually are. There are many kinds of green walls, all easily adaptable to different architectural and modular surfaces. You can opt for partial or total covering of the exterior – standing walls – walls of containment – or closing.

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Green walls can be achieved on large panels or modular assembly structures; thus incorporating the characteristics of the walls, while ensuring that the doors and windows can open. Modern architecture constructs these green walls for two different purposes: the ventilated wall; ideal for covering the outer walls of tall buildings, or sound-absorbing walls, designed solely to ensure acoustic isolation and to beautify noisy areas; such as stairs, cross-roads, highways, and railroads.

1) Ventilated facade

The technique of assembling panels which are already overgrown with plants is the most commonly used technique to make plant walls. This technique assures sustainability. It takes approximately 12 months from the beginning of plant growth until the final installation. In general plants are grown and placed in the support structures (selected plants are grown in nurseries).
This process ensures a uniform distribution of green surface for a whole year.

The panels are usually made ​​of oxidized aluminum sheet, with knots and creases to let plants grow and grooves to allow water to circulate. The posterior part of the panels is water-tight, so no risk of moisture  seeping through to the walls of the building. In addition, the modules are attached to the walls with  a moisture-resistant and weatherproof aluminum grid serving as a support.

To ensure ventilation and thermal-acoustic insulation, it is necessary to leave a space between the panel and the wall. The plants are generally located on a sub-layer, made of polypropylene felt. This layer contains a core of peat and perlite: this is a kind of volcanic rock that retains moisture and recreates the natural habitat for the growth of plants: a technique that is well known to hydroponic people.

2) Sound-absorbing barriers

These are freestanding barriers, providing support for one or both sides. They are particularly effective against noise and promote urban design near stations and highways. The structure is formed by steel studding, already welded to the metal framework, on which the panels are installed. There is one light under layer that helps to retain water and provide nutrients necessary for all grafted plants.

They do not take up too much space. (13.3 cm thick for single-detached and 22cm for two-sided), making them easily adaptable to any type of surface and location.

Now that we have seen the various benefits of green walls and the various techniques for making a perfect infrastructure for green walls, we now need to address issues relating to choosing the plant species that are most suitable for making a green wall. In order o do this we must consider the type of noise you want to block, maintenance and the cost of production.

Regarding plants, it is good to choose the variety that requires minimal maintenance,  plants that need little care and sporadic interventions during the year. Another important feature, the plant must be easily attached to the supporting structures, so climbing plants, bushes and shrubs are preferred.

Hotel Pershing Hall, Paris

A spectacular green wall – Hotel Pershing Hall, Paris

The most used plants are classified in two categories:

  • microterme variety (grass ), resistant to cold but do not produce heat.
  • macroterme variety (weeds and grass), good for providing insulation and mimicking warm climates at low temperatures area, it loses its color periodically and then turns green again in the spring.

When choosing plants, you must also take into account various factors, including the geographical area of ​​the building (exposure to sun, wind, direction, etc. ) , the watering needs of the plant species, and the type of facilities and undercoats selected for the support structure of the plant.

The green cover must be installed in a favorable environmental and climatic conditions. It is important to monitor the plant’s growth and adaptation, especially in the first 8-12 months.

Proper irrigation and fertilization are mandatory, irrespective of the varieties of selected plants.

The easiest way is to use an automated system that is incorporated into the building walls. There should be water reserves arranged horizontally at various levels of the wall. These reserves are connected to vertical tubes that are spread across the support structure, distributing plant nutrients. If the facility has an irrigation system in a closed cycle, the water used is rainwater harvested and stored in tanks, at the foot of the wall, can be used.

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Now it is time to discuss the crux of the matter. That is the overall cost for such a green wall.

The final price is determined by multiple factors, such as: materials for the structure, irrigation system, sub- layer material. For example, a green facade of 2 meters, with irrigation ponds and a support structure in aluminum would cost around 420-450 Euros per square meter. Too much? Your choice!

JANE

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