Canterbury District Health Board is urging landlords with earthquake-damaged rental properties to make sure tenants' health is not put at risk.
The warning comes as investors buy and rent out homes that have been written off by insurers.
A Canterbury medical officer of health, Alistair Humphrey, says it's important the rental housing shortage is not exploited by landlords renting damaged and potentially unhealthy properties to desperate tenants.
Dr Humphrey says landlords are responsible for making sure their houses are heated, insulated and ventilated properly.
He says if the properties are not, tenants are more likely to suffer from cardiovascular and respiratory problems, colds, influenza and poor mental health.