When constructing a sustainable building, there are many options for materials, but there’s one option that’s totally green and totally cool. Vegetative walls date back to the ancient days, and now the technology that supported the wonder of Babylon’s hanging gardens is beginning to sprout up all over the world.

Vegetative roofs are relatively common in the green construction business. A living wall is similar, but stands vertically. It has a root system that tracks the entire wall. A green façade is what you would call an ivy covered trellis where the roots climb a wall in one direction. Trellis systems can be used to build green walls, if multiple growth points are used.

 "Living wall" at the Marks & Spencers Norwich store after 18 months of extensive redevelopment the revamped store opened in September 2011. Photo by Evelyn Simak.

Plants of living walls can either be supported by recirculation water (delivering nutrients directly to the roots of the plant material) or it can use soil (or another growing material). Walls that use growth media will require small containers to house the soil-like materials and the plant it sustains.

Vertical walls that use media can support beneficial micro-organisms. They can also hold water, which can require less irrigation. However, when constructing a green wall that lives on media, it is important to allow for free drainage and plenty of oxygenation to protect your plants against harmful pathogens that thrive in anaerobic conditions.

Hydroponic designs must also provide highly aerated systems at the roots. If the plant root becomes too hot or is denied oxygen, it will not survive. Also, it’s important to keep reservoirs clean in order to protect against root rot.

So other than looking really cool, what’s so special about a green wall? Well, for starters, plants can remove harmful pollutants in the air – both inside and out.

The truth is we’re pretty sensitive to our air quality. Poor indoor air quality can cause something called “sick building syndrome” resulting in a variety of health problems like asthma, coughing and fatigue. This can affect productivity of employees and quality of life for residents. Indoor plants can clean Benzene, Formaldehyde and Trichloroethylene from the air, and there are also positive psychological effects from being exposed to indoor plants.

When implemented outside, green walls offer a lot of benefit to urban areas. Plants can reduce smog and air born particulates, reducing the urban heat island effect; and like vegetated roofs, green walls can be built to grow edible plants!

Before jumping on the green wall bandwagon, it’s important to confront the fact that vertical gardens require additional energy and water. One of the challenges about building a vegetative wall is that it is composed of living material and needs more care than a traditional wall.

Some critics question the sustainability of the walls, due to the amount of maintenance, energy and equipment needed to keep it flourishing.

 The ultimate goal, for exterior walls, is to connect plants to an environment in which they can become a self-sustaining, organic part of the urban environment. For more information, you can read The Vertical Garden: From Nature to City by Patrick Blanc, one of the pioneers in the field. Also, George Irwin is a field expert who has written extensively on green walls.

Having her fair share of construction management jobs, Kristie Lewis - the author of this column- considers herself an expert on the subject and regularly writes about it. Send your questions and feedback to her at Kristie.lewis81@gmail.com.  

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