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A salty problem for urban houses

G Magazine

society

urban salinity damage

A salt-damaged public building in western Sydney.

Credit: Western Sydney Regional Organisation of Councils

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The Murray-Darling River Basin has had its fair share of salinity problems, but it seems that salty issues are affecting homes as well.

Houses in city areas are at risk of something called 'urban salinity', a salty problem that could, like a cancer, spread through the foundations of homes.

When damp, salty soil comes into contact with bricks or concrete, salts are carried into the porous material where they dry and crystallise, forcing apart the matrix. The problem is that salt attracts water, enabling salt crystals to grow in the material, making the problem severe.

"It does affect existing houses," says Phil Breeze of Master Builders Queensland. "A lot of the telltale signs are - if [the houses are] built in brick, masonry - you see the rising damp that's blowing the bricks out."

Mike Harding of the Housing Industry Association says that "it's anecdotal evidence but it is on the increase".

The problem has been in the making for generations.

Wendy Timms of the Water Research Laboratory at the University of New South Wales says that urban salinity is acute in Australia as its soils are very old. Salt has accumulated near the surface over tens of thousands of years, she says.

Rising groundwater

Western-style agriculture long-ago changed the hydrology of the ecosystem because deep-rooted trees were cut down and replaced with grass and cereals and other crops. This is euphemised to 'poor land management practices'.

With no trees to take it up, surplus water enters the groundwater system. This 'recharge' causes groundwater to rise closer to the surface and produces salinity, explains Melbourne University's Robert White.

White says that many of the groundwaters in rural Australia are saline, although "the last decade of drought has meant that that dryland salinity has ceased to be a big issue".

Colin Berryman of the Western Sydney Regional Organisation of Councils says salinity "certainly is" still a problem in urban areas.

The spread of cities changes drainage patterns. Construction disturbs the upper profile of the soil, and authorities import water from catchments hundreds of kilometres away from where it is used.

Ten to 15 per cent of the volumes of sewers and supply pipes leak, says Timms.

"By changing the way water moves through the landscape - where there may not be a high water table - can bring that moisture to the surface," says Neville Pavan of the NSW Department of Environment, Climate Change and Water. "If there's a salt load in that soil, then it'll come out."

Harding says the Australian Building Codes Committee had a discussion on salinity "five or six years ago" that led to an investigation.

"By doing that, they went to all state councils, local councils, and they came back and got a hell of shock and realised the extent of the damage."

Salty solutions

Remediation is a very expensive process, says Harding.

"My advice would be, don't even bother checking for [salinity before building]," he says. "Just build for a salinity problem. In the [Australian Building Codes Board's] draft regulatory impact statement it's costed at about $210, I think, for a 200-square-metre house."

A high-impact resistance vapour barrier, the plastic membrane placed under the concrete slab, can be used. Harding also recommends installing a more robust damp-proof course at a lower level than normal.

"I think it's an enormous investment at very little cost," he says.

Exposure-class bricks and salt-resistant concrete can also be employed, but there are other things you can fix to lessen the risk of attack.

Leaks from cracked swimming pools, broken gutters and poorly-connected downpipes, unlined water features, leaking taps, and buried pipes that are breached can lead to wet soils.

You can also move your garden away from the house. At an even more basic level, you can replace introduced and water-hungry plant species with native species and control the amount of water you put on them.

But that's no guarantee you're safe. "We don't know where it is and we can't predict it," says Harding. "That's the difficulty that we're having with it."