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New Zealand’s Green Roofs

22-Oct-2013 | Contributed by: Guest Author

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Green (or living) roofs are roofs that have plants growing on them either for environmental benefits, or as an elevated garden. Essentially, they take a space that is not usually used and make it useful, and often aesthetically pleasing.

They have been popular in Europe for some time, but have been popping up across New Zealand, mostly in cities. Green roofs act as insulation for a building, reducing energy costs, and improve air quality in the area, as well as helping with storm water management by absorbing storm water and reducing runoff. Not only that, but green roofs have been shown to last twice as long as conventional roofs because the vegetation protects the roof from weather and from UV rays.

Green roofs do cost more upfront, as they often require professional design that takes into account the roof’s structure, as well as the vegetation. However, a green roof is an investment that can have economic benefits in the long run. Green roofs can increase the value of a property, particularly if the green roof is accessible as a rooftop garden (creating extra floorspace), and the reduction of energy costs, and the longer lasting time can pay the roof off over time.

They do not necessarily need as much maintenance as you would think either. The University of Canterbury’s Dr Aisling O’Sullivan and Dr Tonny de Vries have been investigating green roof benefits in Christchurch, and have discovered that irrigation of green roofs is not necessary. After eighteen months, their green roofs have never been irrigated, and are thriving.

Dr Aisling O’Sullivan researching a green roof system.

Green roofs range from intensive to extensive. Intensive green roofs can include trees, walkways, and shrubs, and are essentially rooftop gardens. They as less popular because the soil depth needs to be deep, they are heavy, and require a very strong supporting roof.

Extensive roofs usually consist of native ground cover, and are not made to spend time on. The soil depth required (5 – 15cm) is much smaller, making them lighter. They still usually require reinforcement of the roof to support it, particularly if the roof is sloping, but are easier to set up. 

If you are considering setting up a green roof on your house, you may need to reinforce your roof, and you will need to consider the slope of your roof. Lower slopes, or flat roofs work best. You can select a lightweight soil, and choose low maintenance, drought resistant, shallow rooted plants. Plants can include ground covers, sedums, herbs, succulents, and grasses. Your roof will require a waterproof membrane to be placed over the roof (this must both prevent water and roots from getting to the roof below), and on top of that a drainage layer (this can include the simple use of gravel, or a plastic drainage system). The soil can be placed next, with the vegetation planted into the soil.

Green roofs can be beneficial in cities, as they help decrease pollution, and in rural New Zealand they are incredibly aesthetically pleasing, blending the building in with the natural environment, making them an eco-friendly option for all buildings.

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