Green walls are a rapidly developing sector of horticultural technology; particularly for urban horticulture. In Singapore for instance, there is now legislation requiring developers to build green walls. In many other big cities around the globe, the use of green wall technology has become an important component of government environmental management.
Hydroponic technologies are very appropriate for use in green walls. Even non hydroponic green walls still utilize many of the same technologies as what have been developed for hydroponics.
How Difficult is it to Build a Green Wall?
A typical green wall could have the following components:
- Structural support for containers that plants are growing in (e.g. a metal frame attached to a wall, a free standing framework, or brackets on a wall)
- Containers which can be attached to the structure (e.g. nft channels, or pots filled with potting media)
- An irrigation system to supply water to each plant.
The overall weight of a system (including plants, potting media and water), needs to be well supported by the structure. Taller green walls can have a greater weight, and if exposed to wind far more stress lower walls.
Where Do You Build It
Green walls and roofs can either be:
- Built off-site, then moved onto a site as a series of modules; and quickly assembled, all on the same day; or
- Built on-site.
Building on-site can be more disruptive, particularly if the building is already occupied, but it can also have significant advantages. For instance, discrepancies in building façades and irregular shapes may be more easily addressed. Whilst measurements and photographs may assist with pre-planning, some difficulties of installation will only become apparent once on-site. For instance, it may be discovered that the surface of a wall is crumbly or extremely solid making it difficult to drill into. This might result in a new approach to securing frameworks or an alteration to the materials used.
For roof gardens on properties which are retrofitted it is likely that access to the roof will be minimal - perhaps through a narrow fire escape. In such cases it will prove too difficult to move large frames and pre-planted containers to the site directly. Materials will need to be transported to the site and the garden created in situ. Older buildings may have narrower door frames and passageways, again limited the size of materials being transported. In some cases access may be possible using a cherry picker.
For tall apartment blocks, scaffolding may need to be erected before constructing or installing green walls. For new buildings materials and complete modules may be lifted by crane to roof tops.
Modular systems are often easier to maintain. They often have standardised containers of plants grown in an off-site nursery, which can be brought in to replace any dead or unsightly plants, as required. Growing the plants in modules at nurseries means that they are mature enough i.e. hardened off before installation and are better able to withstand the environmental transition.
If we consider a similar modular system applied to roof gardens, then a roof may be covered by low growing succulents grown in standard sized trays. Periodically, trays can be swapped and poorly performing plants relocated to a nursery where they can be cared for and rejuvenated. Each tray may be supported within a horizontal modular framework.
When you consider window boxes, they are often comprised of three parts; the sleeve, which is typically of a decorative wooden appearance, the inner plastic box which supports the plants and is suspended inside the sleeve, and a drip tray which sits beneath the plastic box. This type of arrangement allows for new window box displays, perhaps highlighting seasonal colour, to be planted off-site and then the inner boxes are swapped over. The same applies for simple green walls which are made from a series of plastic window boxes housed within a framework.
Of course where only a small number of plants and trays need to be installed or changed, it is possible to take the materials to the site and do the planting there.
Dealing with Weight
There is potential for the weight of a roof or vertical garden to damage the structure that supports it. Even a vertical garden attached to a fence can collapse if the fence was never built to be strong enough to hold the weight of large hanging baskets hanging off it.
You may need to consult an engineer, or strengthen a structure. For instance, the brick facade of a house may need reinforcing with a layer of concrete render before fixing to the wall. Where feasible you might even replace a structure with something more suitable. For instance, a wooden fence could be replaced with a brick wall.
Dead load of a roof – a green roof system which is saturated with water in the root zone is considered part of the 'dead load’ along with the actual structure of the roof and any permanent fixtures such as air conditioning equipment
Live load of a roof – includes snow and water from rain or irrigation that is in excess of the saturated potting media.
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