A green wall is a wall partially or completely covered with vegetation that includes a growing medium,
such as soil. Most green walls also feature an integrated water delivery system. Green walls are also
known as living walls or vertical gardens.
Such walls may be indoors or outside, freestanding or attached to an existing wall, and come in a
great variety of sizes. As of 2015, the largest green wall covers 2,700 square meters (29,063 square
feet or more than half an acre) and is located at the Los Cabos International Convention Center, a
building designed by Mexican architect Fernando Romero for the 2012 G20 Los Cabos summit.
Green walls have seen a recent surge in popularity. Of the 61 largescale outdoor green walls listed in
an online database provided by greenroof.com, 80% were constructed in or after 2009 and 93% dated
from no later than 2007. Many Iconic green walls have been constructed by Institutions and in public
places such as Airports and are now becoming common, to improve the aesthetics. For example:
Edmonton International Airport(Canada), Changi International Airport (Singapore) & Chhattrapati
Shivaji International Airport (Mumbai, India)
While Patrick Blanc is sometimes credited as having developed the concept in the late 1980s, the
actual inventor is Stanley Hart White, a Professor of Landscape Architecture who patented a green
wall system in 1938.
Green wall at the Universidad del Claustro de Sor Juana in the historic center of Mexico City.
A wall of living plants designed by Patrick Blanc at Caixa Forum near Atocha station, Madrid.
A green wall (mat media) in a children's museum, Kitchener, Ontario, Canada
Green walls are often constructed of modular panels that hold a growing medium and can be
categorized according to the type of growth media used: loose media, mat media, and structural
Loose medium walls tend to be "soilonashelf" or "soilinabag" type systems. Loose medium
systems have their soil packed into a shelf or bag and are then 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. Repairs can only
be made by restuffing soil into the holes on the wall, which is both difficult and messy. Loosesoil
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 winddriven 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 uproot
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. Loosesoil 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. Loosesoil systems with physical media erosion systems are
well suited for all green wall applications.
Mat type systems tend to be either coir fiber 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 and 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 recirculation 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.
The Green Wall in Sutton High Street, Sutton, Greater London
Structural media are growth medium "blocks" that are not loose, nor mats, but which 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
replacement. They are the most robust option for a living wall in both exterior and interior applications.
They are also the best choice in areas where highwinds, 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.
There is also some discussion involving "active" living walls. An active living wall actively pulls or
forces air through the plants leaves, roots and growth medium of the wall and then into the building's
HVAC system to be recirculated throughout the building. A problem with these systems is that building
code still requires all the standard air filtration equipment that would have to be installed anyway,
despite the living wall's installation. This means that active living walls do not improve air quality to the
point that the installation of other air quality filtration systems can be removed to provide a cost- savings. Therefore, the added cost of design, planning and implementation of an active living wall is
still in question. With further research and UL standards to support the air quality data from the living
wall, building code may one day allow for our buildings to have their air filtered by plants.[citation
The area of air quality and plants is continuing to be researched. The majority of the research cited is
from NASA's studies performed in the 1970s and 1980s by B.C. Wolverton. There was also a study
performed at the University of Guelph by Alan Darlington. Other research has shown the effect the
plants have on the health of office workers."The Effect of Indoor Foliage Plants on Health and
Discomfort Symptoms among Office Workers". Retrieved 20101223..
An indoor green wall in an office in Hong Kong.
Green walls are found most often in urban environments where the plants reduce overall temperatures
of the building. "The primary cause of heat buildup in cities is insolation, the absorption of solar
radiation by roads and buildings in the city and the storage of this heat in the building material and its
subsequent reradiation. Plant surfaces however, as a result of transpiration, do not rise more than 4–
5 °C above the ambient and are sometimes cooler."
Living walls may also be a means for water reuse. The plants may purify slightly polluted water (such
as greywater) by absorbing the dissolved nutrients. Bacteria mineralize the organic components to
make them available to the plants. A study is underway at the Bertschi School in Seattle, Washington
using a GSky Pro Wall system, however, no publicly available data on this is available at this time.
Living walls are particularly suitable for cities, as they allow good use of available vertical surface
areas. They are also suitable in arid areas, as the circulating water on a vertical wall is less likely to
evaporate than in horizontal gardens.
The living wall could also function for urban agriculture, urban gardening, or for its beauty as art. It is
sometimes built indoors to help alleviate sick building syndrome.
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