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23 Apr 2019

Sustainability is the buzz word of our times and ‘green’ or ‘living’ walls tick a lot of eco boxes. In its most basic form, a green wall can be created by planting that climbs upwards, attaching itself to the surface of the wall for support and nutrition. This is a scenario that can strike fear into the heart of many a structural engineer as, on a large scale, vegetation can undermine the integrity of a building and cause serious damage. Their preference may be for the next step up in the green wall concept. This is termed ‘indirect greening’ where plants are grown up a trellis or wires creating an air space between the plants and the wall – an ‘engineered’ design in its most basic form.

The big boy of the green wall world is the ‘Living Wall System’ in which irrigated planting modules are fixed onto a frame and separated from the building with an air gap and a membrane. Exponents herald how such projects combat air pollution by the trapping of harmful particles on leaves and enthuse about their insulating properties which can lead to energy savings by keeping a building warmer in winter and cooler in summer. Other positives include the increase in biodiversity, sound insulation and, in some cases the simple addition of ‘wow factor’ that enhances the human experience. A restaurant which installs a green wall for instance, can see a boost in profits. In short what’s not to like about something that does so much to create a healthier urban environment?

It is a well-known fact that Structural Engineers get a little twitchy about anything either growing up or being added to a building. Will construction materials be damaged and the structure weakened as a result? Loading is another factor high on the engineers’ checklist – how much does any addition to the building weigh? Which plants have been chosen? Planting and the structures holding it, plus the irrigation system, must be carefully chosen and environmental loads such as snow, wind and rain must also be considered. Green walls and roofs appear to have many life enhancing qualities -and may even actively protect a building from the ravages of poor weather and pollution – but, in large scale projects, only if the structural engineers’ calculations add up too.