The "conservative" estimate only covers remediation of water leaks, fire safety breaches, structural failure and combustible cladding in units built since 2009.

It does not include legal costs, audit schemes or increased insurance premiums, or any defected buildings older than 10 years.

The construction union, which commissioned the research, says the cost assessment is staggering.

"Tens of thousands of families, many of whom have purchased their first home, are now stuck with the crippling cost and mental anguish of owning homes that they may not be able to live in, are unsafe and cannot afford to repair," the CFMMEU's Dave Noonan said in a statement on Monday.

Most of the costs relate to buildings in NSW, followed by Victoria and Queensland, with flammable cladding the biggest expense.

"Our analysishighlights that the cost to Australia will be substantial," the Equity Economics report said.

Australian Associated Press