Green roofs and walls are slowly taking root.
A small number of city roofs and walls are sprouting lush foliage, and they’re attracting lots of attention. “Everybody is getting excited by them. I think it’s time to rethink city-wide design,” says Green Roofs Australia vice president, Ben Nicholson. His organisation is holding its annual conference at Melbourne University’s Burnley campus from September 23 to 25.
Mr Nicholson says although green roofs are an old technique, the modern systems were developed in Germany just three decades ago. Plants grow in lightweight soils over waterproof and root-repellent layers on the roof. They can range from extensive (inaccessible and low-maintenance) to intensive (abundant and high-maintenance, more like a roof garden).
Either way, they act as a sponge for stormwater, reduce urban heat radiation and boost biodiversity. They can also double the lifespan of roofing materials and reduce the need for heating and air-conditioning indoors.
That’s an enticing list, but so far in Australia, green roofs are only gradually moving into commercial and residential use. Mr Nicholson warns against putting on “green bling” that won’t stand the test of time. “There’s a lot of research to be done to establish which species will thrive locally over the long term.”
The other big catch is the cost of retrofitting on existing homes. Mr Nicholson says that an extensive green roof can weigh four times the load-bearing capacity of most roofs. “So before you’ve even started the retrofit, there can be huge costs in getting the building ready to host a green roof. It’s much easier to design a new home with a green roof. Our rooftops could then be sites for urban agriculture or habitat creation – as well as improving the view.”
Sydneysider Jock Gammon’s business, Junglefy, is working on a green roof for the Melbourne City Council. He estimates that an extensive green roof on a new home will cost between $180 and $220 per square metre. There’s a lot to keep in mind, including the roof capacity, plant selection and rainwater runoff arrangements. “Do the consultation and designs at the beginning of your building project,” he advises.
If you’re dedicated to gardening on high, but you’re not planning to build from scratch, then a green wall is the best bet.
Junglefy sells a range of vertical garden products, including ecoVert, a self-contained system that will help you grow herbs and veggies up the wall. It starts at $625, plus an optional mains or solar-powered watering system. The plants shoot from pockets of coconut fibres, not soil, and feed from organic fertilisers. “It’s designed for apartment dwellers and people with small courtyards who hadn’t previously grown things,” Mr Gammon says.
For a lower-tech food-producing wall, try espalier fruit trees. With pruning and training, you can grow the trees in flat patterns against a trellis or fence – it’s a tried and tested method, in use since at least the Middle Ages.