Houses are cracking in the dry, hot weather, but when should you start to worry?
It starts innocently enough — a hairline crack on, say, the lounge room wall. But, before too long, that annoying little line creeps further down the wall and widens.
“In extraordinary dry times like now, those cracks will widen,” warned Professor Nasser Khalili, the head of geotechnical engineering at the University of New South Wales.
In the vast majority of cases, cracks in houses are caused when the soil underneath the house starts to dry and contract, causing the footing of the house to shift unevenly, which leads the walls to move and crack.
Clay soils are much more susceptible, or ‘reactive’, to changing moisture content than sandy soils because, like a sponge, they soak up or repel water.
“We’ve got this rare occasion now where we’re going without rain, significant rainfall, for months or, in some places,12 months and that means we have long periods where soil, which would otherwise not lose its moisture, is now losing its moisture,” explained Stephen Fityus, a professor of geotechnical engineering at the University of Newcastle.
The Bureau of Meteorology (BOM) has confirmed that last year was Australia’s hottest and driest year on record, with varying parts of Australia having been in drought since 2017.
That heat and dryness is not confined to the atmosphere around us — soil moisture content in December was also “very much below average” in parts of every state and territory except the ACT, according to BOM data.
“Soils continue to be extremely dry along the east coast of New South Wales and the fraction of the state experiencing very much below average soil moisture in December has increased to 48 per cent, compared to 25 per cent in November,” the bureau said in its December drought report.
As the soil beneath us dries up, plants and trees are trying to stay alive, desperately sucking up whatever moisture they can get from the ground, which is drying the soil even more.
“This is an extreme event, and there’s no surprise there’s a correlation to soils around the country being drier than they’ve ever been before and the drought,” said Professor Fityus.
Many Sydney homeowners have noticed new or worse cracks appearing just in the last month or so.
Sandra Eckersley told ABC News that she was disturbed to find the upstairs of her 1891 house in Marrickville had cracked extensively while she was away for a fortnight on a Christmas holiday.
“I’ve had cracks here before, but this is the worst ever. This is extreme.”
Ms Eckersley said the movement has been so extreme that she can only keep her back door closed by locking it.
Meanwhile, further north in Epping, cracks at Sandra Williams’ 1922 home appeared just a few weeks ago.
“The first major crack I noticed was in the brickwork out the front of the house,” she told ABC News.
“It’s about two metres long and about the width of the mortar, it goes around a corner of the house and up the window frame.
“I noticed it a few days before Christmas, the day after that really hot 40-degree day.”
Archicentre Australia managing director Peter Giorgiou said building regulations need to adapt to the warming environment.
“We can’t rely on that seasonal benefit anymore. We’ve got to be a lot more proactive in the way we understand how to manage our buildings in a newly defined era,” he said.
“To that end, the standards we’ve set in the past need to change as well.”
What should you do if your house is cracking?
The ancient Japanese art of Kintsugi, where broken pottery is stuck back together with gold, celebrates the beauty of the cracks.
That is the attitude some experts say homeowners should take about the cracks in their walls.
“If buildings are in areas that are susceptible to shrink and swell, those cracks are non-structural and shouldn’t affect the structural integrity of the building,” said Professor Khalili.
“The usual approach is not to correct them, not to fill them in and patch them because next year again they will reappear in a worse condition.
“They are living buildings — during summer they open, during winter they close.”
The building or engineers department of your local council may be able to provide information about the type of soil your house is built on, or you can check to see if it has a geotechnical investigation of your property done as part of a development permit submission.
Even in areas with reactive soils prone to expansion and contraction, Professor Fityus said there are ways to mitigate against cracking.
“You can build bigger foundations under the house at the start, but that’s expensive,” he said.
However, in an established house, once you have got cracking, it is very hard to stop it.
“You can try to stop the soil from moving, and you can only do that from stopping it getting wet and dry,” Professor Fityus said.
One option is to cut down all the trees on your property.
“But cutting them down can be problematic, because if the tree is established it already has a moisture regime happening and if you cut it down suddenly you’ve got more moisture in the soil than you did before,” he added.
Another option is to put paving all around the house.
“So, if you put a one-metre wide concrete slab around your house and you seal it up against the walls, you move the wet to dry boundary away from right under your walls,” explained Professor Fityus.
“The soil under the path has the same moisture content as the soil under the house and nothing moves right under your walls.”
He said watering lawns is a tricky solution.
“Some people water their lawns to excess and, if you do that, you’re likely to put more water around your house than under it, which will also cause things to move.”
In short, there are no easy fixes and the advice from Professor Fityus is to call in a professional if you are concerned.
“Almost every situation needs to be looked at by someone who knows what’s going on to offer specific advice,” he said.
But all three experts warned of being careful who to get advice from, with some operators biased in favour of using their own product or ‘cure’.
They all agree an independent assessment from a structural engineer or building consultant is a good first step before spending thousands of dollars on any remediation work.