Cyclone Alfred: Which Brisbane homes built to withstand storms

Experts reveal which South East Queensland homes are most at risk from Cyclone Alfred after building codes were overhauled decades ago.

Poorly maintained homes across South East Queensland, and those built before the 1980s in original condition, will be at higher risk of damage from Tropical Cyclone Alfred’s gale-force winds and heavy rain.

Disaster experts confirmed most homes built after 1980 should be able to withstand winds of about 200km/h — the equivalent of those experienced in a low-category-three system – if they had been well maintained.

The strict wind-resistant building standards came from an overhaul of the National Construction Code after Cyclone Tracy’s destruction of Darwin in 1974.

But property owners are warned the unpredictability of the weather system, its intensity and risk of flying debris meant it was not possible to guarantee a home was completely cyclone-proof.

James Cook University Cyclone Testing Station chief engineer David Henderson said Alfred’s anticipated category-two wind speeds were less than those written in the national building code’s minimum design criteria for Queensland homes built after 1980 from Bundaberg to the New South Wales border – an area known as “Wind Region B”.

■ What should I pack? Cyclone safety guide

But he said those same properties were not built to overcome poor maintenance or sustain damage, like from flying debris, or if any wind or rain entered through doors or windows.

“The houses in wind region B are designed for those, crudely, 200km/h wind speeds,” he said.

“The category two storm (Alfred) coming through may have winds in the order of 120 or 140km/h.

“But that spare capacity can be chewed up if you get a broken window or door failing.

“That pressure enters into the building, and now you’ve got that internal pressure pushing up on the roof, as well as all that suction trying to lift the house up by its roofing.”

Housing construction is much more storm-resistant since the ’70s.

Dr Henderson said winds will find the weakest link in the house to try and burst through so proper home maintenance was important.

“A lot of our houses are getting to middle age now, so even though they might be built to the code in the ’80s and ’90s, they’re getting 30 to 40 years old now, and there may not have had enough maintenance done,” he said.

“A modern construction can also be vulnerable to a lot more water coming in because of the large size of windows, and … wind driving rain under our sliding doors and sliding windows and louvres.”

Dr Henderson said the presence of asbestos, used in Queensland construction from the 1940s to the late 1980, could also prove risky.

“Asbestos roofs will be quite old, so there might be real issues with the rusted nails,” he said.

“It could also be that the surface coating has come off, so they’re far more brittle and of course, with the potential damage and breaking of branches, hitting it.”

Natural Hazards Research Australia CEO Andrew Gissing said another threat to Queensland homes was the planting of vegetation near homes not suitable for cyclones.

“It doesn’t really matter what standards your home was built to if you’ve planted a whole bunch of vegetation around the streets and around your home, which is not necessarily suitable for high, strong winds,” he said.

“An experience of Darwin in Cyclone Marcus only a few years ago was they had significant damage because of downed trees.”

Mr Gissing said there would be an opportunity to do detailed engineering studies to identify if there was value in enhancing wind standards for any areas impacted by Alfred.

“Anybody can actually design a fortress, which is pretty robust against a lot of things, it’s also about the whether or not these things are actually affordable and practicable to do,” he said.

“It’s important to make sure that we’re engineering to events which are possible, but maybe rare.”

Originally published as Cyclone Alfred: Which Brisbane homes built to withstand storms