Some renters are sweltering in unhealthy conditions over summer, prompting calls for new standards for air-conditioning and insulation to keep tenants alive.
Rental homes regularly exceed safe temperature limits and, on average, cracked 30C degrees for one in six days over summer, research by advocacy organisation Better Renting has found.
Night-time temperatures were high enough to impair sleep almost half the time, the temperature tracking research report released on Thursday shows.
Adam McFillin rents a home with his partner and baby in Yeerongpilly in Brisbane's south, where the indoor temperature topped 36C and was above 25-30C for more than two-thirds of the summer.
He says he's so worried about the heat he's losing sleep, and it's affecting his mental health.
"These old houses are like living in a tent - if it's hot outside it's hot inside, if it's cold outside it's cold inside," he said.
Rosa Hicks, who rents with housemates in South Fremantle, Western Australia, has no ceiling insulation and no air-conditioning.
"The temperature in my room didn't drop below 30 degrees for days," she said.
"My cat struggled and I had to keep giving him ice packs and wet flannels."
Australian Council of Social Service head Cassandra Goldie said millions of people on low incomes were getting sick or dying because they couldn't afford higher energy bills, and were unable to install measures to keep their homes cool in summer.
Better Renting executive director Joel Dignam said high indoor temperatures were a threat to health.
"Almost eight million people rent across Australia - that's a huge number of people who can't install ceiling insulation, put in a ceiling fan, or set up air-conditioning," Mr Dignam said.
More than 100 organisations have joined Better Renting in calling for governments to implement enforceable minimum energy efficiency standards for rental properties.
Adelaide GP Kate Wylie said she was concerned about the heat-related risk to patients as the climate changes, because it increased the risk of heart attacks and strokes.
Better Renting worked with 50 households to track summer temperatures in their rental homes and found safe temperatures of 25C were exceeded for more than nine hours a day on average.
Risk from heat begins to increase above 25C, and healthy building standards recommend 30C should be exceeded only one per cent of the time, Mr Dignam said.
Australian Associated Press
Sign up for our newsletter to stay up to date.