Rising energy costs are the latest problem for renters living in "brutal" conditions over winter, research shows.
Researchers tracked temperature and humidity - key to mould growth - in more than 70 rental homes nationwide through June and July and found the homes were routinely below safe temperature levels.
The Cold and Costly report, released on Tuesday, calls for Australian governments to introduce minimum energy efficiency standards for rental properties to better protect renters.
"Renters told us about getting sick more often, about a constant state of worry over energy costs, and an unending battle against mould and damp," said Joel Dignam, head of advocacy group Better Renters.
But many aren't choosing between a cold home and expensive bills - they end up with both.
"Many of the homes in this study were so substandard that even when people chose to run their costly, inefficient heaters, they were still unable to get warm," the report said.
Nor were they able to make changes to weatherproofing, insulating, and energy systems.
Cold temperatures in substandard housing have been linked with higher blood pressure, reduced immunity, more intense asthma, and greater incidence of mental illness.
"The data paints a frightful picture of the brutal conditions people are facing in their homes," Mr Dignam said.
Across Australia, indoor temperatures were below healthy levels three-quarters of the time.
A comparison group of owners in energy efficient homes barely recorded temperatures below a key safe level of 18 degrees, at less than five per cent.
NSW had the highest average humidity of any jurisdiction, with 83 per cent of recordings above 60 per cent and more than half above 70 per cent relative humidity.
The high humidity explained the ongoing mould problems in many NSW rental homes, the report said.
South Australia was the second-highest, also risking persistent mould on floors, walls and ceilings.
Tasmanian renters had the greatest amount of time below 18 degrees. At 91 per cent, this was over 21 hours per day below the recommended minimum healthy temperature.
Although Tasmania spent more time in cold temperatures, on average ACT renters were colder indoors than anywhere else.
NT was a mixed picture with Darwin enjoying relatively manageable temperatures and humidity, while Alice Springs renters were below 18 degrees for most (89.5 per cent) of the time.
