Greenroofs.com: In the Shadow of the Vertical Garden, By Lars Kronborg Bak

Publisher's Note: Lars contacted me last May and told me about how over the last few years he had conducted some R & D in his spare time involving green walls and a green matrix. He says he has no commercial interest in this application - he's interested only in the environment and hopes others can be inspired to go further. I asked him about obtaining a patent. He replied "It takes a lot of time, energy and money to follow that road. I think instead of protecting a product “people/company” should focus on being and doing the best instead. Being available freely on the Web, he says the information is "free for everyone. So, all in all, I would prefer to see some green walls soon." Editing has been kept to a minimum to retain the flavor of his writing style.

Green roofs are great; they cool off buildings and look great as well. But let us not stop at the roof, let us start at the roof and continue the greening of the urban landscape with green living walls. Of course, we “green-people” think green walls looks great – but besides how they look they can provide some important functions by cooling off the buildings and reducing the urban heat island effect. Most certainly they can also serve as a buffer for rainwater and handle greywater through vertical reed bed systems.

In the future, I don't believe modern cities will look like some scene from a science fiction movie but rather they will be green and natural. Not only because we want to, but because we have to. In this article I will present a basic technique for a vertical growth medium/green wall. I hope it can provide some inspiration.

Over time, many systems have been developed for green roofs, but how about greenwalls and living walls?

The technique used for green roofs is not easy to adapt to the façades of buildings since the limiting factor is often the slope or angle of the roof. If the roof is flat or the slope is below a certain angle, often between 30-45 degrees, the current known and accepted solutions provide satisfactory results.

If the angle of the roof slope is above 45 degrees, problems will start to arise getting a well functioning green roof to become established. Roof slopes approaching the vertical at 90 degrees become almost impossible using existing solutions - it is therefore necessary to develop a specific technique for this purpose.

For planting façades there are a number of useful climbing plants, but these can "only" climb as near as 25 meters. Many modern high buildings are way above 25 meters. In addition, the types of climbing plants can also be limited – e.g. if there is a need or wish to use specific plants, such as evergreens, etc.

The benefits of green walls are not only for aesthetics’ sake, but can also provide shade and cooling for solar heating. Over time there has emerged a number of products for green walls - some consist of simple trays hanging with soil and others work with hanging textiles (nonwoven, etc.). I will not evaluate these methods, but only describe the basic technique in my proposal for a vertical planting technique.

But why vertical planting?

Vertical planting provides interesting opportunities for new architecture. But in addition to a new method with new textures which can be added to the wide variety of common building materials, a vertical planting can provide another possibility - namely the possibility of shading and cooling. And particularly chilling is a great need in many modern cities, where cooling often occurs through highly energy-consuming air conditioning. Solar heating of large cities is also known as the concept of the Urban Heat Island.

As a way to reduce this heat many buildings are constructed with green roofs – in order to limit heat from the sun. But a larger area can be greened if green vegetation gets extended to the façades. A larger surface area with green vegetation will provide more shade to the building and therefore provide more cooling.

Another interesting angle could be the possibility of wastewater treatment. Perhaps vertical vegetation could act like a type of reed bed system offered as an option for local treatment of wastewater from the building before it gets diverted to sewers. A façade planting may also, like a green roof, act as a buffer so rainfall is not delivered directly to the sewer system but is delayed. This feature could be used as part of the solution to overloaded sewer systems and greater future rainfall.

The technique used

A good product is often characterized by a simple solution. Many considerations and requirements for operation are analyzed and designed in a simple but effective technique. I have therefore concentrated on two basic elements – 1) tensile strength and 2) growth medium of high quality.

One of the basic techniques which I have used is Nonwoven airlaid. As the name indicates this is airflow of fibers that are assembled and made into fiber mats. The basic technique consists of a backbone which can handle the weight of planting and allows a vertical installation. The carrying element is "embedded" into a fiber matrix that can serve as growth media for the green vegetation. This combination achieves a high tensile strength in the whole growth medium extent. In Table 1, the principle is demonstrated.

Table 1 - Principle of the Fiber Forming

Figure 1: Materials.
To the left are rock wool fibers and the right white plastic fibers. These fibers are mixed together and mixed vigorously for the forming technique.
The amount shown is illustrative and not the actual ratio.

Figure 2: Airflow.
The red arrow indicates the direction of air.
From above, airflow of fibers is blown through a dense network. Under the network air is sucked out under a high vacuum. The network retains the fibers from the air flow and creates a matrix of fibers. Notice the black coarse net. This is superimposed meshed network and is "embedded" in the fiber matrix. The coarse network provides a high tensile strength and strength.

Figure 3: Shaping Process.
This shows the structure of fibers at mid-term, the black network is now half
filled with the yellow rockwool fibers.

Figure 4: Completed forming.
The coarse network is now completely filled with fiber and ready for
thermobinding in the oven.

Figure 5: Binding Process.
The process ends in a special oven where heated air is led through the fiber matrix. The special plastic fiber melts and binds the fibers together.

Figure 6: Completed Process.
Completed fiber matrix with the internal network and rockwool fibers.

In Table 1 above a highly flexible network is embedded in the growth medium. This network causes a high tensile strength in all directions and allows a vertical installation, for example on façades. The network also supports a green growth in a way so all roots are free to evolve in the whole growth medium extent.

But how do you get the system up a façade? In Table 2, Figure 7 the principle of the vertical mounting is illustrated.

Table 2 - Principle of the Vertical Mounting

Figure 7: Mounting Principle.
In the illustration the network is displayed without fibers.
Profile Rail (A) is mounted vertically on the vertical façade.
Horizontal sections (B) are pushed through the profile of the rails and the network.
The network and the number of horizontal bars across all affect the ultimate strength.

Figure 8: Test Subject.
Example of growth of grass in the vertical stand.

Figure 9: Transformation.
Mounting the grass can be done in several ways - e.g. on a chair by Verner Panton. Besides getting a special chair, I had simultaneously tried different angles and mounting techniques.

The idea of the vertical garden should not only focus on the facade planting technique. Breaking the usual framework and providing new aesthetic opportunities are both interesting and relevant.

Depending on the types of applications, i.e. where large areas are to be covered by green vegetation, further optimization should be achieved through more pilots tests - including water and fertilization techniques, and a screening of suitable plants. This is not a product that can be purchased on the market currently. But my work can hopefully inspire and motivate interested parties to optimize the method further for a commercial product. A further optimization requires, in addition to skills, capital - a pilot plant for fiber forming can easily cost 300,000 Euros. Furthermore, add costs for optimization of the product itself and the adjustment of molding equipment for its industrial manufacture.

My background for this interest is due to a multi-experience with fiber technology as a laboratory technician. I have participated in public and private R & D projects, including development of environmentally friendly products made from plant fibers. The very idea of developing a vertical growth media came to me during study of landscape architecture (change of career). The green knowledge I gained seemed natural to combine with my knowledge of fiber technology.

Crucially, my employers have been very sympathetic to my ideas, allowing experimental equipment available for my own R & D. Unfortunately, these development environments exist no longer in Denmark, therefore I publish my results on the Internet. Perhaps others can see the excitement in the method and the possibility for a new green technology?

Lars Kronborg Bak
Landscapearchitect, mdl.

Lars Kronborg Bak (*1971) holds a Master degree in Landscape Architecture from the University of Copenhagen, Denmark (2008). Before he studied landscape architecture he was a laboratory technician (Kold College, Odense 1995) working with plant fiber technology in public/government and private R&D projects from 1997-2006. His main focus in that area was the environmental benefits in forming plant fiber in composites instead of the use of plastic, etc. Lars Kronborg Bak is currently working for Fredericia Municipality in in south-central Denmark. Contact Lars at: lkb@greenspace.dk and visit his website: www.greenspace.dk/greenmatrix.

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