Who Is in Charge of a Green Roof?

Wednesday, January 13th, 2016
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People don’t often talk about the task of growing green roofs from basic assets to mature assets, let alone tackling the issue of who is responsible for this big and important task.

As infrastructure which is part of the structure of the building, management of green roof gardens falls to the responsibility of whoever manages the building, whether they are a facility manager, a building manager or the owner.

This management task is very different from merely ensuring that the status quo is maintained, as may be appropriate for the maintenance of, for example, an air-conditioning unit. Growing the value of a green roof asset to maturity is a task that requires vision, responsiveness, creativity and horticultural knowledge as well as knowledge of the maintenance requirements of green infrastructure. It takes sustained focus, drive and leadership.

Knowing what goes into maintaining a green roof is important not just for facility managers to understand but also property developers and architects.

If you are a building owner or facility manager, what you receive at the date a green roof is installed is a brand new garden which has just been planted.

Green roof

Photo: Do it on the Roof

A brand new green roof is a basic asset. It is your job as its owner or manager to grow it to maturity. This also grows the value of the asset, and just what represents value varies from roof to roof. So the first information facility managers and maintenance crews absolutely must obtain is the reason the green roof was created. What is its purpose?

In Australia, people invest in green roofs for over 40 different reasons. Don’t make the mistake of assuming that every green roof has more or less the same purpose!

You need to be proactive in finding out the reason the green roof was created. We often talk to building managers who are uncertain what the answer is when we ask them the purpose of their green roof. This is natural. Green roofs are new in Australia and we are only just beginning to talk systematically about best management practice for green roofs.

Without the vital requirements in the management and maintenance phase becoming common knowledge, project managers in construction cannot be expected to hand over the facts to facility managers. But in the absence of project managers in construction who understand what information it is crucial to hand over to the facility manager at the end of construction, the facility manager or building manager needs to know what information they need, and they have to seek it out.

If the green roof has been around for a while, check the reason people are investing in it. Is it the same reason as it was originally created, or has the purpose of the green roof changed over time?

Once you have ascertained why the green roof was created and why its development from a basic to a mature asset is being invested in, you have your objective: to develop the green roof so it fulfils its specific purpose. At this point you need to check you know how the roof is designed. What are the core strategic functions it is designed to perform, and how will these fulfil the purpose?

The soil (or more often, substrate which performs the core functions of soil) may perform a strategic function in the roof. The chief purpose of the roof may be to cool the room below or cool the ambient air temperature for photovoltaic cells, for example, and the substrate plays a role in serving these purposes by providing a degree of insulation or a sponge which holds water which evaporates, thereby cooling the surrounding air. But for the most part, the substrate is on the roof to provide the plants with what they need.

Green Roof

Green roof and solar panels, T H King Building

Similarly, the support structures beneath the substrate are there to support the growth of a garden in the substrate and to protect the roof membrane from roots and water. They are critical parts of the green roof system and it is vitally important not to damage them, but they don’t, in themselves, perform core strategic functions.

Typical Layers of a Green Roof 

The typical green roof includes structural foundation which provides the structural support for the system, a waterproof membrane, which protects the underlying building from leaks, and a root barrier, to stop roots penetrating the waterproofing and structure of the building. Substrate, generally a mineral-based lightweight substrate, provides plants’ three basic needs: water, nutrients and oxygen. Some, but not all green roofs also include an insulation layer commonly situated immediately above the waterproof membrane. A slip sheet, or separation sheet, used to separate chemically intolerant materials from one another and sometimes for root protection is common, as is drainage to remove excess water from the roof, and a filter fabric, which helps prevent the growing medium from blocking drainage.

The vast majority of the core strategic functions performed by a green roof are performed by the plants and the garden. The really crucial point to grasp here is that the plants and garden generally perform their core strategic functions as a system.

the lush, rich garden with its air of luxury creates the beauty and brand statement that fulfil the purpose of this green roof (Photo: Quentin Bertoux) 

The lush, rich garden with its air of luxury creates the beauty and brand statement that fulfil the purpose of this green roof (Photo: Quentin Bertoux)

Green roof gardens, like any gardens, function as systems in two respects. First, the individual plants and the layout of the garden all work together to create the desired effect. This effect might be productivity for workers who overlook the garden, in which case continual change of colours in the garden may be important, since change and variety trigger improvements in cognitive performance. The desired effect might be to screen wind or an unsightly view, in which case the height at which the plants are pruned and the development of an understory may be all important. Whatever the desired effect, the plants have been most likely selected to work together as a system to create it.

Secondly, the plants in the garden work together because they are part of a living system. The ecological functions of one plant affects another, and in the best garden designs, the plants are selected in part for the way in which they complement one another’s health. In a good garden, each plant is helping the others to flourish. This reduces the intensity of their maintenance requirements, so it is critical to understand this aspect of their relationship with one another. As a general rule of thumb, reducing plant diversity will weaken the health of the plants which remain in the system and make them more susceptible to pests and disease.

Medibank Docklands

Medibank Docklands’ green wall. The variety of its plant species serves both to increase the health and resilience of the wall and to make it more attractive, thereby fulfilling the chief purpose for which the green walls (and for that matter, the green roofs) were installed, namely, to attract talent to the building

The living systems that are vital in gardens – ecological systems – take time to evolve. A garden which has just been planted out does not have highly functioning ecological systems. Even once the individual plants have become established, the ecological system will take time to evolve and reach its full potential, just as the plants need time to grow to achieve the desired level of coverage. To keep you on track, you need a clear plan.

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