Roof gardens proven to cool buildings

ABC News. The World Today.
-Radio Report :  http://www.abc.net.au/news/2012-10-09/roof-gardens-proven-to-cool-buildings/4303394

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ELEANOR HALL: Roof gardens are becoming more prevalent in the world's major cities.

Now a study has found that not only are they building mini-ecosystems, they're also cooling buildings significantly and reducing carbon emissions, as Nicola Gage reports.

NICOLA GAGE: Major cities have inherently been linked to pollution and rising carbon emissions, but 22 stories up on the roof of a building in Adelaide, there's a micro-climate that's returning wildlife to the city.

GRAEME HOPKINS: It's had bees up here collecting honey, it's got birds and we've identified two moth varieties and no doubt the birds have been chasing the moths. So there's a whole ecosystem and this has happened spontaneously on the 22nd floor, so it's quite amazing.

NICOLA GAGE: Landscape architect Graeme Hopkins is the designer of a roof and wall garden project in the city. He says the practice of garden roofs has long been established in Europe, and Australia is beginning to embrace it.

GRAEME HOPKINS: All the real research is from Europe or North America, nothing in the hot, dry climates. So we suspected there were some differences here but we really didn't know what the differences were and designing these roofs, the engineers kept asking us well how much temperature reduction or cooling would be there and we couldn't actually say in a hot dry climate exactly what it was.
So we started off from that point.

NICOLA GAGE: Four native arid grass species and ground covers were used in the study, with three tonnes of soil and pebble mulch. It found all six garden plots reduced temperatures in the roof of the building, one by 42 per cent.
Mr Hopkins says it cooled the building during summer by 2.4 watts per square metre, but after 10 floors there's no measurable impact.

GRAEME HOPKINS: We've developed an insulation factor which is a first time anybody's been able to predict what a green roof will do in a climate. And in the 300 thick substrate, we can reduce the roof temperature by 42 per cent.

In the grated system, we can reduce that by 21 per cent. And so we can use them as predictions in planning new buildings now for energy use.

NICOLA GAGE: The project has also led to gardens growing up the outside of building walls. The findings proved similar results to the roof garden, confirming it insulated the building and reduced inside temperatures.

GRAEME HOPKINS: This is part of climate change adaption and we can reduce temperatures, which means reduce energy which is reduce CO2 or greenhouse gases. This actually is a benefit to people because there's then a connection back to nature and that's been well documented in urban areas.
We need to be connected with that.

NICOLA GAGE: Professor Simon Beecham is from the University of South Australia. He says the roof gardens also reduce flooding, with a decline in storm water run-off.

SIMON BEECHAM: Water is locked up into the soil matrix and held there as soil moisture. So basically the soil gets wet and that volume of water available in the soil can vary from between 25 and 30 per cent of the actual volume of soil.
So this is - it's like a big sponge that when it's dry, it has huge capacity to absorb rain, and so you get for very small rainfall events you get no run-off at all off green roofs.

NICOLA GAGE: Professor Beecham says Adelaide is leading the way in water-sensitive urban design and green roof technology. He says the arid landscape of South Australia makes it essential to improve ways to reduce energy needs.

SIMON BEECHAM: You've got to remember South Australia recycles more water than any other state per capita and that's because of the need - it needs to recycle more water to have more reliable supplies and storm water is one of those supplies and recycled storm water is going to be a very important resource in the future.

ELEANOR HALL: That's Professor Simon Beecham ending that report by Nicola Gage.