Sydney's housing crisis has reached an alarming new threshold with a key measure revealing it now takes more than two average full-time wages to affordably service a loan for a typical city home.

The Housing Industry Association's housing affordability index, which measures the capacity of households to service mortgages, shows Sydneysiders must fork out $4,729 per month, or nearly $57,000 a year, to service a standard mortgage on an averaged-priced home in the city.

That is more than 30 per cent of the earnings of a Sydney household with two average full-time wages – the portion of income widely accepted to be a manageable housing repayment.

"House buyers in Sydney now require more than double the average income in Sydney to be able to afford the averaged-priced house in that market," the report said.