Green Roofs - Myths

Myth 1: Green roofs are too expensive

It is undeniable that Green roofs present higher construction costs than a conventional roof. While the higher initial investment may limit the short term economic return, the long term returns can be excellent with green roofs improving tenant amenity, reducing maintenance and running costs, significantly extending roof life and potentially increasing the lettable area, value and marketability of a property.

Myth 2: Green roofs leak

Often conventional roofs leak as they age, due to damage by ultraviolet light and weather. Green roofs do not make the situation worse; instead they may improve a roof because greater attention is paid to having a high quality, impermeable barrier and the barrier is then protected from U.V. light, extremes in temperature and other environmental damage by the vegetation.
It is suggested that in the rare cases they do leak, this may largely be due to poor roof construction, and not the green roof system itself.

Myth 3: The physical structure of the many buildings prevents the establishment of green roofs.

Another common misconception is that additional structural support is always required in order to install a green roof. However, green roofs are designed based on the structural capability of the building, not the other way around.

Green roofs range from lightweight extensive roofs such as that on the Ford Motor Company building (in Michigan USA) covering 4.5Ha with only 25mm of growing media, to much deeper, heavier roof gardens.

In larger buildings, the weight of the green roof becomes even less of an issue as it becomes a smaller percentage of the total weight that must be borne by the building. View examples

A structural engineer should be consulted before any green roof is implemented.

Myth 4: Isn’t better to have solar panels on a roof, rather than a green roof?

There is a common misconception that a building can either have a green roof or solar/photovoltaic panes. It is possible to have both; in fact there is considerable evidence from Germany that the use of solar and green roofs provide duel benefits in terms of energy production and energy saving.

Solar panels at a roof level are known to work more efficiently when installed on a green roof rather than on a conventional surface. Green roofs can reduce fluctuations of temperatures at the roof level and help maintain a more efficient climate around the photovoltaic panel increasing the panel’s efficiency.

Myth 5: Most of Australia is experiencing drought; we don’t have enough water for green roofs

Depending on the types of plants and the types of soil some green roofs may not need to be watered and survive on just rainfall. This is why the research being undertaken by Melbourne University into the types of plants and substrates which can survive without water is so critical. Depending upon the services of the building, green roofs may be watered sparingly using recycled grey water from bathroom fixtures or even using water from the mandatory testing of fire sprinkler systems.