LIVING WALLS - improving air quality
image: One Bligh Street Sydney
A green wall (aka VCWV, vertical vegetated complex walls, living wall, vertical garden, eco wall) is a wall, either free-standing or part of a building, that is partially or completely covered with vegetation and, in some cases, soil or an inorganic growing medium. More recently, the larger green walls concept has been utilized with innovative hydroponics technology. The vegetation for a green façade is always attached on outside walls; with living walls this is also usually the case, although some living walls can also be green walls for interior use. For living walls there are many methods including attaching to the air return of the building to help with air filtration.
The concept of the green wall dates back to 600 BC with the Hanging Gardens of Babylon. The green wall was invented by Stanley Hart White at the University of Illinois Urbana-Champaign in 1931-38. White holds the first known patent for a green wall, or vertical garden, conceptualizing this new garden type as a solution to the problem of modern garden design. There are two main categories of green walls: green façades and living walls. Green façades are made up of climbing plants either growing directly on a wall or, more recently, specially designed supporting structures. The plant shoot system grows up the side of the building while being rooted in the ground. With a living wall the modular panels are often made of stainless steel containers, geotextiles, irrigation systems, a growing medium and vegetation.
There are three types of growth media used in living walls: loose media, mat media and structural media.
Loose media
Loose medium walls tend to be "soil-on-a-shelf" or "soil-in-a-bag" type systems. Loose medium systems have their soil packed into a shelf or bag and then are installed onto the wall. These systems require their media to be replaced at least once a year on exteriors and approximately every two years on interiors. Loose soil systems are not well suited for areas with any seismic activity. Reparations are only achieved by re-stuffing soil into the holes on the wall, which is both difficult and messy. Loose-soil systems should not be used in areas where there will be a lot of public interaction as they are quite messy and lose their soil little by little over time. Most importantly, because these systems can easily have their medium blown away by wind-driven rain or heavy winds, these should not be used in applications over 8 feet high. There are some systems in Asia that have solved the loose media erosion problem by use of shielding systems to hold the media within the green wall system even when soil liquefaction occurs under seismic load. In these systems, the plants can still up-root themselves in the liquified soil under seismic load and therefore it is required that the plants be secured to the system to prevent them from falling from the wall. Loose-soil systems without physical media erosion systems are best suited for the home gardener where occasional replanting is desired from season to season or year to year. Loose-soil systems with physical media erosion systems are well suited for all green wall applications.
Mat media
Mat type systems tend to be either coir fibre or felt mats. Mat media are quite thin, even in multiple layers, and as such cannot support vibrant root systems of mature plants for more than three to five years before the roots overtake the mat and water is not able to adequately wick through the mats. The method of reparation of these systems is to replace large sections of the system at a time by cutting the mat out of the wall and replacing it with new mat. This process compromises the root structures of the neighboring plants on the wall and often kills many surrounding plants in the reparation process. These systems are best used on the interior of a building and are a good choice in areas with low seismic activity with small plants that will not grow to a weight that could rip the mat apart under their own weight over time. It is important to note that mat systems are particularly water inefficient and often require constant irrigation due to the thin nature of the medium and its inability to hold water and provide a buffer for the plant roots. This inefficiency often requires that these systems have a water re-circulation system put into place at an additional cost. Mat media are better suited for small installations no more than eight feet in height where repairs are easily completed.
Structural media
Structural media are growth medium "blocks" that are not loose, nor mats, but incorporate the best features of both into a block that can be manufactured into various sizes, shapes and thicknesses. These media have the advantage that they do not break down for 10 to 15 years, can be made to have a higher or lower water holding capacity depending on the plant selection for the wall, can have their pH and EC's customized to suit the plants, and are easily handled for maintenance and replacements. They are the most robust option for a living wall for both exterior applications and for interior applications. They are also the best choice in areas where high-winds, seismic activity or heights need to be addressed in the design. Structural media are superior to the other media for their longevity and high-level of performance in a variety of circumstances. Depending on the installation, they do tend to be more expensive to install, but lower cost to maintain.