Week 2 - Deceptive Greenery? - "Green" Building

When urbanisation is taking up increasingly more lands,the amount of urban green space is decreasing over the decade. Architects therefore seek to give back greenery to public domain on high buildings. That is the reason of the prosperous of urban green building.

Green buildings here are not referring to the broader concept of sustainable/energy saving buildings, but merely to buildings with green. Generally, there are three categories provided in "green" buildings: green roofs, green sky gardens and green walls. Green wall, as the primary element deciding the building's appearance, being the most controversial one.

Green wall is famous for its lively appearance in urban condition. As time changes throughout the year, the colour, density and shape of the plants change. As a result, green wall is also called living wall. It is claimed to be beneficial - not only to the building tenants as it improves energy efficiency, protects building structure, improves indoor air quality, reduces noise and improves health and well-being, but also to the environment as it increases biodiversity in urban area, reduces urban heat island effect and improves air quality, also provides onsite wastewater treatment (including mitigates storm water runoff).

Artists Impression on Greenwalls in Sydney City

The benefits are attractive, however, it is sometimes questionable to say greenwall is sustainable, when considering the viability and longevity of the wall, we can see the difficulties of maintenance and possibilities of failures.

Living wall maintenance is highly relied on skills from individuals or companies in long run. There are examples that plants on green wall are expected to be replaced every single year because they are expected to die after a year (from a high profile college outside of Philadelphia). This is, no doubt, a very deceptive sustainable option.

In summary, there are two types of failure on green wall:

1. Material Breakdown
2. Plant Mortality, including cultural reasons and physiological reasons (disease, old age)

Choice of material to hold up plants is important. A poor material choice would lead to the failure of green wall. Therefore choice of holding material should provide sufficient strength (compression and tension) to hold up the plant, and also possibly contribute to biological processes to  the plant.  

Cultural reasons mainly refers to lack of education. Over watering or under watering, over fertilising or under fertilising, even temperature, lighting or wind condition change can destroy the green wall. Being delicate, means it needs delicate care to live.

There are heaps of reasons causing living wall failure. Yet, we cannot deny its benefits to the environment. There are methods to avoid green wall failure in reality:

1. Careful choice of material to drain water freely and to avoid anaerobic conditions in the root systems;
2. Careful choice of likeminded plants to avoid different maintenance needs;
3. Careful maintenance to selected plants, including proper amount of water, light and nutrients
4. Careful design with the greenwall area, avoid any elements that could change the micro-climate and affect the wall

I wouldn't say it is deceptive greenery, even though sometimes the maintenance cost excesses our expectation. I believe that with proper selection of material and plant, proper design of the irrigation system and the building, and education to the users, green wall in urban area could be effective in building sustainable cities.






Reference:
http://www.greenroofs.com/content/green-wall-deception-death-of-a-green-wall.htm
http://www.cityforest.com.au/
http://www.greenroofs.org/index.php/about/green-wall-benefits
http://www.greenroofs.com/content/articles/145-Living-Wall-Breakdown-Material-and-Flora-Relationship.htm#.Vy_IzjB96Uk