Living walls the next way to stay cool

As power bills soar in unison with summer temperatures, Australian homeowners are fast coming around to the idea of passive cooling.

Better insulation, double glazing, tree shading and even rooftop sprinklers are in the mix when it comes to cheap and efficient ways to beat the heat.

But there's another concept gaining traction: living walls, also known as green walls or vertical gardens.

These walls are made up of upright panels covered in vegetation housed in pots, felt pockets or planter boxes and irrigated on structures attached to a wall.

While previous University of South Australia research showed installing green walls can reduce household temperatures by up to 12 degrees Celsius during the hottest summer days, a new study takes the finding a step further.

Experiments comparing living walls with porous concrete pavement systems show the latter are, at best, just 15 per cent as effective at cooling, according to UniSA professor Simon Beecham.

In the worst cases, they're only four per cent as effective.

Researchers measured the evapotranspiration rates of the two as porous concrete absorbs stormwater, unlike conventional concrete or asphalt.

"Both living walls and porous concrete roads are now being investigated for their ability to cool the urban environment," Prof Beecham said.

"Evaporation of water from porous concrete occurs after rainfall and this results in the ambient air temperature decreasing.

"This process is more enhanced by living walls because the vegetation transpires water for much longer. Also, living walls are irrigated more frequently than it rains."

Living walls can be installed in homes, car parks, sub-divisions, public sites and commercial and industrial areas, as well as being used in road and multi-storey building construction.

They are designed to reduce flood risks, improve water quality, moderate temperature and enhance biodiversity.

Unlike systems that involve roots planted in the ground, the stems, leaves and flowers on green walls are contained in planter boxes and irrigated rather than relying on rainfall.

With planter boxes $500-$700 a square metre, they're yet to take off in Australia but researchers say over time the energy savings will more than outweigh outlays.

Then UniSA PhD student Rosmina Bustami conducted a nine-month experiment in 2018 in Adelaide exploring the potential energy savings of vertical gardens on west-facing external house walls.

She compared temperatures on a 144-pot living wall with one without plants, recording up to 12 degrees difference.

An automated irrigation system watered the pots twice daily in summer and once every two days in winter.