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10 reasons to love green roofs

By Chris Knierim, National President, Building Designers Association of Australia

As a building designer who specialises in sustainable design, my mission is to see Australian cities be transformed from concrete deserts to seas of green. Green roofs are a great way to start the transformation, with homes becoming their own small oases. Recent research has shown that green roofs can have huge benefits, and not only to the structure on which they are installed. 

A green roof also called a “living roof”  is a roof is a surface that fosters the growth of vegetation, either partially or completely, in a soil-covered, waterproof membrane that’s accompanied by a root barrier and drainage system. Contrary to the popular misconception that they’re a recent fad, green roofs have been around for hundreds of years. Recent advances in the installation process mean they are now quicker to install, lighter in weight, and more robust.

1. Money savings
Green roofs have been shown to increase the value of a property due to their cost-saving abilities. For one thing, they absorb and redirect rainwater by reducing runoff. For another, they provide insulation, meaning that less energy is required for heating and cooling, therefore leading to significant cost savings.

2. Reduced noise
The multiple layers of soil, plants and trapped layers of air that make up a green roof can reduce the external noise of people, pets and traffic. This sound insulation works in a similar way to the heat insulation they provide; sound waves are absorbed, reflected and deflected.

3. Aesthetics
Who wants to look at a reflective roof surface when they can gaze in wonder at a beautiful natural roof garden instead? Of course, the environmental positives are undeniable, but even if that isn’t your objective, you’ll benefit from the aesthetic aspects of having an extended garden space.

4. Biodiversity
Green roofs attract flora and fauna back to the area by creating their own mini ecosystems, which increase biodiversity. It’s fantastic to watch the insects, especially the bees, pollinating the plants – and even better knowing that your green roof is preventing the surrounding environment from being fragmented. Imagine the positive impact on the community that all those green roofs, with diverse species of plants, can have.

5. Improved home insulation
As mentioned, by installing a green roof, you can increase a home’s thermal performance. Through the multiple layers that make up a green roof – waterproofing membranes, water storage cells, geo-textile protection fabrics, soil media and the foliage of plants – heat is less likely to escape through the roof. Yes, this will reduce your energy bills, but it will also keep the heat in during winter. Conversely, the same applies for summer – the cool air from your air-conditioning unit is less likely to escape.

6. Cleaner air
Green roofs reduce air pollution and greenhouse gas emissions associated with mechanical energy production. The plants in a green roof actively work to deliver cleaner air by removing particulate matter and gaseous pollutants. For instance, they absorb carbon dioxide gases, which are a huge contributor to global warming, and other pollutants, including sulphur dioxide, nitrogen oxides, carbon monoxide and ground-level ozone from the air.

7. Improved health and wellbeing
Green roofs also capture fine particles in the air that have been said to cause illnesses, such as respiratory and pulmonary diseases. Green roofs capture these particles primarily due to their irregular surface, in which the particles get trapped and are then washed away into the sewers with the rainwater.

8. Reduced flooding
The plants and growing media (soil) of a green roof absorb water that would otherwise become run-off. Research indicates that peak flow rates are reduced by 50–90% compared to conventional roofs. Even better, if a rainwater tank is installed, then the tank is filled before water flows into the stormwater system. Green roofs also help to purify water. The rainwater flows through the plant and substrate layers before reaching the drain and acts like a filter so toxins like zinc and copper sulphate are leached out of the water.

9. Mitigate the ‘heat island’ effect
The heat island effect refers to the increased temperatures found in our built-up urban areas, compared to the surrounding rural regions. The phenomenon is a huge concern for our cities, causing increased air-conditioning costs, pollution, and even heat-related illnesses such as respiratory difficulties, heat cramps and exhaustion, and heat strokes. In densely developed areas, green roofs can reduce the heat island effect by removing heat-conducting roof surfaces, like concrete or brick, and replacing them with heat-absorbing “living” layers that also provide shade for the hot air.

10. Psychological benefits
Let’s face it, who wouldn’t prefer to look out a window at a garden rather than a bland, reflective roof? Consider this not only in the home environment, but also in the work environment. You don’t need government-funded research or a team of scientists to work out that people would prefer to look out at a garden than at a plain rooftop. I’ve seen the natural, mood-boosting benefits firsthand when installing greenery around office spaces, whether it be a green roof or a vertical garden. It’s an instant positive attraction to the workspace and environment.

This story was originally published in the March 2018 edition of Facility Perspectives, Vol 12, No 1. 

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