Given the historical and natural significance of its positioning, the redevelopment of the Clock Tower Precinct – and in particular the construction of No 1 Silo – is guided by the latest global requirements for environmentally sustainable construction, as governed by the Green Building Council of South Africa.
Covering over 200 linear meters, and equalling a total of 500m², this is the first time in South Africa that construction site hoardings play host to vertical gardens on this scale. Third-party advertising has also been incorporated into the design and installation, resulting in a living, three-dimensional and impactful visual display.
“The concept of vertical gardens, or living walls, is capturing the imagination of urban space designers worldwide. However, it is still a relatively novel concept here in South Africa,” says Alana Robertson of ACR group, responsible for the development, installation and maintenance of this green initiative.
The ‘green hoarding’ initiative is collaboration between the V&A Waterfront’s development team, horticultural experts Greennaissance and the ACR Group, the green consultants on the project.
“The living wall basically constitutes a simple layer of irrigation cloth affixed to the hoarding boards,” she says. “Pockets, cut into the cloth and containing only the minimum required amount of soil, provide a solid footing for plants to establish and grow from,” Robertson explains. The water-conducting irrigation cloth, manufactured from non-degradable deconstructed acrylic textiles, allows for plant roots to firmly spread through the fibres and to absorb water and nutrients.
Robertson explains that the composition and functioning of the irrigation cloth can be compared to a layer of algae or moss covering forest rocks or tree trunks. “All the exchange between plant, water and atmosphere takes place through the irrigation cloth, rendering a soil-free solution and adding to the relative simple concept of vertical gardens,” she says.
The cloth is irrigated via a simple plastic tube incorporated into the top section of the material, and a diluted nutritive solution is added to the irrigation flow. Watering occurs three to five times daily for between one to three minutes, depending on the weather conditions and the stages of plant growth. Plants were carefully selected based on their ability to withstand severe climate and environmental conditions. “Proximity to the ocean, aptitude to sun and shade exposure, as well as the effects of construction had to be considered,” says David Gent of Greennaissance. The different species also had to bear the same growth characteristics and maintenance requirements. “Water-wise, indigenous plants and succulents have been selected as far as possible due to their sturdy growth and natural resilience levels,” Gent says.
The long-term sustainability of these plants was also a key consideration. The vertical gardens will remain in this position for the next two years up until the conclusion of this development phase. Once this construction phase has concluded, the panels will be removed and the gardens will be repositioned elsewhere.
These vertical gardens not only enhance the aesthetic qualities of the construction site, but also actively contribute to the improvement of the immediate environment. The leaf surfaces and irrigation cloth trap dust and pollutants emitted by nearby industries, vehicles and the construction process.
Once trapped, the dust is decomposed by water and micro-organisms into chemical elements that are absorbed by the plants. In addition, micro rubber fragments from tire wear on the roads along the hoardings are carried away in puddle spray and deposited on the lower sections of irrigation cloth.
“We have been able to keep water usage to a minimum,” Robertson says. Depending on the plant types, weather conditions and time of year, a typical vertical garden requires between 0.5 to 3 litres of water per m² per day, which is low compared to watering requirements for parks and other gardens.
Simply Green Issue 2 2012
Irrigation of gardens are, and will become even more of, a concern. Between water restrictions and the price of water, which will just increase and increase, I doubt people will be able to continue attend their gardens as desired. The recycling of grey water makes perfect sense for irrigation purposes – you can keep your garden, beautiful as is, without having to use extra municipal water or having to store harvested rainwater in water tanks for irrigation purposes at a later stage.