Houzz Roof garden photo: Nest Architects
Author: Chris Knerim
As a building designer who specialises in sustainable design, my mission is to see more of Australian cities transform from a desert of concrete to a sea of green. Green roofs can play a huge part in this. Recent research has shown that green roofs can have huge benefits, and not only to the structure on which they are installed. So why don’t we all have green roofs?
I believe the biggest reason is that some homeowners doubt their technical performance. For instance, a lot of my clients come to me with concerns that green roofs fail because they leak, or that they add additional weight-loading to a roof that a building can’t support. In fact, there is no evidence to suggest green roofs are more susceptible to leaking than normal roofs – some studies show the plants actually help protect the roof from natural weathering.
Let me also assure you that if the work is completed by a qualified and skilled tradesperson, and overseen by a structural engineer, the chances of failure are low. We just need to get proper legislation to make it mandatory that only specific licensed tradespeople can install green roofs. Have a read of the benefits below and you’ll see why installing a green roof is worth your time and money.
WHAT IS A GREEN ROOF?
A green roof – also called a ‘living roof’ – is, in a nutshell, a roof 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 a drainage system.
Green roofs have been around for hundreds of years, contrary to popular misconception that they’re a recent fad, yet recent advances in their execution mean that they are quicker to install, lighter in weight and more robust.
WHY YOU SHOULD LOVE THEM
1. They can save you money
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, reducing runoff. For another, they provide insulation (more on this below) meaning less energy is required for heating and cooling, which therefore leads to significant cost savings.
2. They reduce noise
The multiple layers of soil, plants and trapped layers of air that make up a green roof can reduce external noise from people, machinery, traffic and aeroplanes. This ‘sound insulation’ works in a similar way to the heat insulation they provide; sound waves are absorbed, reflected and deflected.
3. They look nice
Who wants to stare at a reflective roof surface when they can stare 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. They create natural ecosystems
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 in doing so, your green roof is preventing the surrounding environment from being fragmented, and providing visual diversity that can have a positive impact on the community.
5. They insulate a home better
As said previously, 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, geotextile 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. The same applies for summer – the cool air of your air conditioning unit is less likely to escape.
6. They provide 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 CO2 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. They can improve your health
Green roofs also capture fine particles in the air that have been said to cause illnesses such as pulmonary diseases. Green roofs capture these particles primarily due to their irregular surface, in which the particles get trapped and then flow away into the sewers with the rainwater.
8. They reduce flooding
The plants and growing media (soil) of a green roof absorb water that would otherwise become runoff. Research indicates that peak flow rates are reduced by 50-90 per cent compared to conventional roofs.
This means that instead of the rainwater flowing straight off the roof, down the downpipe and into our waterways, the rainwater is absorbed by the plants and soil; which automatically reduces the flow rate of the water into our stormwater systems. Even better, if a rainwater tank is installed then the tank is filled first, before the water flows into the stormwater system.
DID YOU KNOW? Green roofs also help to purify this water. The rainwater flows through the plant and substrate layers before reaching the drain; toxins like zinc and copper sulphate remain in the substrate and out of the water.
9. They reduce ‘heat island’ effect
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, to name a few.
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. And don’t forget the psychological benefits
Lets face it, who wouldn’t prefer to look out a window at a garden rather then a reflective bland roof surface? 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 rather then 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 attraction to their work space and environment.
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