Nearly all of Australia's major capitals rank in the top 25 per cent least affordable markets for middle-income home buyers, according to a survey by United States academics.

The Chapman University Frontier Centre for Public Policy's Demographia International Housing Affordability report focuses on the ability of "median income" households to purchase median-priced homes.

To compare different markets within a country and across the world, it uses a metric called the "median multiple", a ratio of median incomes to median house prices.

Using that criteria, Hong Kong, Sydney and Vancouver are the most unaffordable markets for those buyers.

While the US cities Pittsburgh, Rochester and St Louis are the most affordable.

The survey includes housing markets in Australia, Canada, Hong Kong, Ireland, New Zealand, Singapore, United Kingdom and the United States.

Sydney, Melbourne, Adelaide, Brisbane and Perth all sit in the least affordable 25 per cent of cities in the list of 94 markets included in the study.

"Affordability is disappearing in high-income nations as housing costs now far outpace income growth," the study said.

"The crisis stems principally from land use policies that artificially restrict housing supply, driving up land prices and making home ownership unattainable for many."

Growing problem

For the first time in the study's 20-year history, the authors added a new category for housing affordability: "impossibly unaffordable".

"The term 'impossible' was selected to convey the extreme difficulty faced by middle-income households in affording housing at a median multiple of 9.0.

"This level of unaffordability did not exist just over three decades ago."

Urban planning policies seeking to limit the expansion of urban sprawl and increase the density of cities have placed middle-class sections of society "under siege", the report said.

"The net effect is that land values and house prices have become skewed against the middle class, whose existence depends upon the very competitive land market destroyed by the planning orthodoxy.

"All of the 'impossibly unaffordable markets' in [the report] follow the 'international planning orthodoxy' as do nearly all of the severely unaffordable markets."

In addition to the longer-running causes of housing unaffordability, in the United States, nearly two-thirds of the recent house price "shock" could be attributed to the sudden and significant shift to remote work during the pandemic, according to research by the Federal Reserve and University of California.

In Australia, the latest Bureau of Statistics data show 210,800 dwellings are being built every year.

But for demand to match supply, that figure needs to rise to roughly 240,000 homes.

Analysts told the ABC recently that median-income owners would need to spend around 60 per cent of their gross income to purchase a median-priced property.