Poor housing is causing preventable injury and disease that is estimated to cost New Zealand up to $164 million a year in hospital admissions and accident compensation claims.
The annual cost, which falls between $129 million and $164 million, arises from homes that are cold, damp, mouldy or in dangerous disrepair, according to data gathered by Wellington researchers.
The study found that homes that are damp or mouldy cause sickness that leads to more than 35,000 nights being spent in hospital each year, costing around $35 million.
"However, that $35 million does not include, for example, costs of time lost from work or school while patients are in hospital," said one of the researchers, Dr Lynn Riggs, of Motu Economic and Public Policy Research. "Nor does it include GP visits or pharmaceutical costs."
Nearly 2000 nights in hospital were due to homes being cold, at a cost of more than $2 million a year.
And preventable injuries caused by homes in disrepair cost ACC more than $100 million a year, the researchers found.
The research was presented today at the Public Health Summer School at the University of Otago, Wellington.
This follows the Government's announcement yesterday that new healthy-homes standards will be introduced for rental homes. They will include requirements for rentals to have a heater, a minimum thickness of ceiling and floor insulation, and moisture-removal fans.
Also presented at the summer school were the new international guidelines on healthy housing.
One of the authors of the guidelines, Professor Philippa Howden-Chapman, of the University of Otago, said they were a world first which brought together the most recent evidence to provide practical recommendations on how to improve housing.
"We are hopeful the guidelines will assist in helping to turn around the type of preventable health costs identified in this latest research."
Riggs said that in the 12 months to March 2015, 15 per cent of owner-occupied homes were reported to be cold, in contrast to 35 per cent of rental homes.
"Three per cent of owner-occupied homes were damp or mouldy compared to 12 per cent of rentals."
Twenty-one per cent of New Zealanders reported their house was always or often cold.
Household crowding caused more than 3500 nights in hospital a year, costing nearly $5 million, the researchers said. Ten per cent of New Zealanders lived in crowded housing.
"While it is expensive to fix problems with housing," Riggs said, "not fixing them is also costly. Previous research has estimated broader societal costs from home falls alone at over $5 billion per year."
Riggs told the Herald after her presentation that the hospital and ACC costs were a low estimate for the overall health cost of poor housing.
She said future work would give a clearer picture of the true health costs by including GP visits, pharmaceutical costs, lost work, and social costs.
For instance, the hospitalisation cost that could be directly attributed to cold housing was only $2.3 million, but "there were a lot of things related to cold that were hard to link directly to hospitalisations", which were likely to emerge from the GP and pharmaceutical research.