The catastrophic flooding that devastated south-east Queensland and northern NSW is now the fourth most expensive disaster in the nation's history, according to the Insurance Council of Australia (ICA).

Figures released today show the estimated insurance cost of the natural disaster has climbed by almost $1 billion in the last month.

The total cost is now put at $4.3 billion, although ICA chief executive Andrew Hall has previously told the ABC the actual damage bill was likely to be significantly higher.

"You add into it the under insured, people who don't have insurance, who opted out of the flood cover for example and then we've got public infrastructure on top of that," he said.

The ICA said 20 per cent of claims had now been closed, and almost $1 billion had been paid to policyholders so far.

The most expensive weather event on record, according to ICA figures, was the Sydney hailstorm of 1999, which resulted in $5.57 billion in insured losses.

Next was Cyclone Tracy in 1974, with losses estimated at more than $5 billion, and Cyclone Dinah in 1967 at $4.69 billion.

Lismore's billion-dollar rebuild

The figures were released as the Lismore City Council published its own report on the floods, which estimated more than $350 million worth of damage to council assets.

The repair bill for roads and bridges alone was thought to be $200 million.

Lismore City Council General Manager John Walker said the cost of rebuilding the broader community would be close to $1 billion.

He said the document would be used to lobby state and federal governments for financial assistance to rebuild the city and its surrounds.

"The report provides an historical record of what happened during and after the floods," Mr Walker said.

Resilience NSW roasted

Meanwhile, witnesses at a NSW parliamentary inquiry have criticised the performance of Resilience NSW, the body tasked to help communities rebuild and lead disaster and emergency efforts from prevention to recovery.

"Resilience NSW has been found wanting at every level," Lismore MP Janelle Saffin told the inquiry.

Lismore City councillor Elly Bird, who has been heading up a community group known as Resilient Lismore, also spoke of her frustration.

"I asked who my point person was and I was given a generic email address for Resilience NSW, and every email I sent to that address went unanswered," she said.

"I had an offer from the Surf Lifesaving Club to send 1,000 volunteers into Lismore to work alongside us to support our community.

"All they needed was an email from Resilience NSW saying that they approved it.

Tweed MP Geoff Provest was asked about the performance of Resilience NSW at today's inquiry sitting in Murwillumbah.

"I still have faith in Resilience (NSW), although I think some of their processes need to be refined," he said.

"I'm not as critical of them, I think it was their first big disaster since the bushfires down south.

"In all honesty, I think they tried their very best."

The inquiry will now move to western Sydney, and is due to report back to the NSW Parliament in early August.