Greening the Rooftops

Green roof

It’s great to see sustainable garden practices becoming the norm such as growing our own food, composting food and garden waste onsite and harvesting water through tanks and grey water systems. These practices are not only good for our health and wellbeing but they contribute significantly to maintaining a healthy environment.

But there is new technology and innovative thinking in the sustainable garden space that needs to be embraced particularly as we see the effects of climate change with future forecasts of reduced rainfall and temperature rises already coming true.

Green roof technology has been thriving in Europe for a very long time. In both London and Paris, legislation now exists that ensures all new builds must have either a green roof or solar panels.

In Australia, green roof technology is still in its infancy but Melbourne University and Melbourne Water have been working together over the past 10 years researching and making advances in this area. They have been testing the types of growing media and plants that can thrive in our climate.

Normal soil is not used on a green roof as its composition makes it very heavy. Instead a mix of mineral or rock based materials that are lightweight are used so that it provides good drainage, holds water and nutrients and does not break down readily. They’ve also tested the best type of plants that survive in quite harsh conditions, as a roof can get very hot and is exposed to higher winds.

I learnt all about this innovation whilst studying in recent years and now that I have the opportunity to build my own home I’m including a green roof into the design to improve the performance of the building.

The advantages of a green roof are significant as it will:

  • Reduce energy costs through its insulating qualities – keeping the building cool in summer and holding the heat in during winter
  • Extend the life of the roof by providing protection from the elements
  • Assist in reducing the heat bank caused by many concrete buildings (this is particularly an issue in urban areas)
  • Increase biodiversity by providing food and shelter for bird and animal life
  • Remove pollutants from storm water runoff as the roots of the plants act as a filtering system ensuring contaminants do not enter the waterways.

A green roof can either be extensive or intensive.

An extensive green roof has a thin layer of growing media (50 – 200mm deep) that sits on top of a system including waterproofing, drainage and a root barrier. The plants used are generally a ground cover or low growing. An intensive green roof has a deeper layer of growing media and will support growing trees. These types of green roofs are considered a garden, as there is enough depth in the soil to grow more significant plants. More information is available through My Home.

Green roof

The intensive green roof at Melbourne University at the Burnley campus

With our new home we have designed an extensive green roof. It has been an interesting process involving our building designer, engineer, builder and green roof expert. Interesting in terms of marrying old building technology with new. It has meant changing mindsets and fortunately for us we are working with a great team of open-minded willing participants.

green roof

An intensive green roof provides your property with another garden space to enjoy

The best learning from the experience so far has been that it is much simpler to achieve a green roof than first expected. Essentially the design treats our flat roof like a large box gutter with a 2-degree slope. The way the layering of the system works, it ensures that when there is heavy rainfall, the water will penetrate the system easily, flowing slowly down to the shallow channel at the lowest point of the roof, and then exiting through the storm water pipe. This makes my engineer very happy, as it doesn’t exceed his weight computations even when it is wet!

We are still a little way off from putting our green roof into action but I can’t wait to gain the benefits of reduced energy bills and living in a home with a comfortable temperature all year round whilst contributing positively to environment at the same time.