In my article on biological buildings, I wrote about the concept of considering the building fabric as a living bio-membrane. Whilst greening of roofs is now a well established and accepted technology, green walling is relatively under-developed, especially in the UK. Yet for every roof there are four walls and on a large building this can be a considerably bigger surface area than the roof. Green walls have a number of advantages, the principle one being a reduction of thermal loading on the building fabric; others include heat island reduction (in urban situations), stormwater attenuation, noise reduction, ecological enhancement, air purification and psychological well being of urbanites. Further potentials include rainwater harvesting, urban food production and greywater filtration.
Perhaps the most important reason for the long term development of green walls/biomembranes is that they could help to visibly restore the connections between the built environment and the natural, between mankind and nature. If we are to survive climate change and impending energy decline, we need to radically change the way we relate to the world. Blurring the boundaries between the natural and manmade environments increases our interaction between the two and this is the only way in which we can adapt to an uncertain future.
There a three main methods of vertical greening:
- use of self clinging plants climbing directly on walls
- the use of climbing supports
- the provision of a vertical growing medium with plants growing directly within this
self clinging plants
This is the easiest and most traditional way of growing plants on walls. With ivy (Hedera), this can occur unintentionally in the UK from neglect. species such as Parthenocissus, Hydrangea (climbing) and Hedera will spread vigorously by means of aerial rootlets. This brings about fears of damage to building fabric, but in fact, research has shown this occurs much less often than commonly believed. A more obvious problem is keeping climbers from encroaching onto windows, and once the plant has surrounded a window frame, regular pruning is required. However, for new or commercial buildings, Insurance Companies definitely don't like self clinging plants!
This method is ideal, however, for large blank walls, especially North facing. It is very cheap and no structure is required other than a planting bed and perhaps irrigation.
climbing supports
Modern climbing supports are very different from the traditional wooden trellis one sees in gardens. Climbers are capable of reaching 20 - 30 metres in height and so can cover huge amounts of urban wallspace. Apart from self-clinging plants, described above, many (in fact most) climbers are twiners, or use tendrils which cling to whatever is at hand. These plants need something to help them and this is usually provided in the way of mesh screens or panels (right), or cabling systems.
These structures are extensive in area but lightweight and relatively cheap to use. the main disadvantage may be the wait for climbers to obtain height during the first few years after installation. Again, irrigation may be required.
vertical wall panels
The most sophisticated method of vertical greening is through the use of vertical growing medium placed upon the wall surface. This gives a totally different feel as the plants used are not climbers but small, creeping herbaceous perennials, ferns, grasses and small shrubs. This system required an irrigation/hydroponics system to be built into the structure and is therefore the most costly and complicated to design and install.
Offsetting this is the fact that the thermal reductions on the building are the largest, giving a potential saving on the cost of heating and cooling the building. Also this system has a huge visual impact and most projects to date (such as those pioneered by Patrick Blanc) have effectively been “art” installations.
This subject fascinates me to such an extent that I have set up a company to design and install green walls in the UK (or anywhere) call BioTecture Ltd (www.biotecture.uk.com). There is a big future here and we have built our first trial wall and are already looking at some very exciting projects with architects and developers. Watch this space...