As Victorians prepare to rebuild the 2,029 homes destroyed in the deadly Black Saturday bushfires, the CSIRO is warning that the new national bushfire building standard is inadequate.
A month after the fires, the Victorian Government announced that it was fast-tracking the introduction of the new national bushfire building standard.
Premier John Brumby called it a tougher standard that would help Victorians rebuild in the safest way possible.
The standard is already in force in Victoria and the ACT and will be introduced in other jurisdictions by May next year.
But the CSIRO’s leading researcher on bushfire-related building design has told ABC Radio’s AM that based on the scientific evidence, the new standard offers less protection for residents in bushfire-prone areas than the previous standard.
The CSIRO’s Justin Leonard says the revised standard now in force in Victoria removes or weakens some crucial material and design requirements for buildings in bushfire-prone areas.
“Like the removal of the need to protect raised floors on some buildings and the types of materials you might be required to use for these floors,” he said.
“Also, there’s a lessening for the requirements for gaps and vents that allow a greater chance of ember entry and ignition inside roof spaces, wall cavities and the interior of the house.
“The other main [concern] is around the loosening of requirements for the combustibility of materials that would be used on the outside of a house.”
Under the new standard, new buildings throughout Victoria are to be assessed on what is known as their bushfire attack level, and graded on a scale of one to six: no risk to extreme risk.
Mr Leonard says most of the homes being rebuilt will be assessed as being at the lower end of the risk scale, because they are not close enough to vegetation to be highly susceptible to radiant heat.
And despite the CSIRO’s advice to the Standards Committee, Mr Leonard says those lower risk categories are just where the standards have been weakened, leaving new homes susceptible to ember attack in particular.
“Ember attack is not only just the flying, burning embers, but there’s a lot of fine fuel that’s in the air, and it accumulates and deposits all around structures, and can get in and under structures,” he said.
“There’s also a low-level flame spread over horizontal surfaces, and that low-level flame can burn up to and under structures, so we certainly have a lot of concern around those design details of the structure.”
Mr Leonard is encouraging Victorians who are planning to rebuild homes razed in the fires to go further than just satisfying the new building standard.
“Gain a further understanding of the specific ways bushfires can ignite structures, and look at the whole system,” he said.
“Look for the little details and weak points in their overall design, and build a greater confidence around the types of building design decisions they end up making in the rebuild process.”