Cooling city buildings by using roof gardens

Adelaide in South Australia is leading the way in water-sensitive urban design and green roof technology.

Roof gardens proven to cool buildings ABC Radio The World Today Nicola Gage reported this story on Tuesday, October 9, 2012 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. ….
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.
http://www.abc.net.au/worldtoday/content/2012/s3606696.htm