An inspection of 25 Tauranga rental homes has found only one to have sufficient insulation, prompting a call for landlords to do more to make "sick houses" safe to live in.
The inspections were carried out by assessors as part of housing warrant of fitness trials across the country.
The Tauranga inspections were undertaken by environmental company Sustainability Options and co-founder Phil Gregg said too many Bay families were living in poverty-like conditions.
The rental housing warrant of fitness trial was conducted by Healthy Housing and looked at the standard of rental properties in Tauranga, Auckland, Wellington, Christchurch and Dunedin. Of the 144 homes inspected, only eight passed the assessment.
About 60 per cent of homes in New Zealand had poor insulation, a figure Tauranga City Council sustainability adviser Michelle Elborn said would be an accurate reflection of the homes in the Bay of Plenty.
Smart Energy Solutions regional manager Carl Vujnovich said a lack of insulation was enough to classify a home as a "sick house".
"There's a lot of properties out there that are traps. They are making people sick for winter," he said.
Toi Te Ora medical officer of health Dr Jim Miller said insulation was an important aspect of a healthy home.
"Insulating homes improves indoor temperature and reduces dampness. Living in cold and damp homes is associated with asthma and respiratory illness. Cold and damp are stressors that can impact on mental health," he said.
"Occupants of cold, difficult-to-heat homes tend to crowd together in an attempt to stay warm. This can be families sleeping in only one room or families spending most of their time in one confined space. Crowding is linked with meningococcal disease, acute rheumatic fever and tuberculosis." Mr Gregg said that during the WOF trial he saw many families living in cold, miserable conditions, which were making them "sick and unproductive in society".
He said more needed to be done to improve living conditions and landlords needed to step up and properly insulate their rental properties.
The Government implemented the Warm Up New Zealand: Healthy Home programme in 2013 to provide subsidies for insulation for people at risk but Mr Gregg said there were still some who did not meet the criteria.
Merivale Community Centre manager Rachel Palmer and Tauranga Grey Power president Christina Humphreys agreed insulation was an issue for the elderly and those struggling to get by, as they could not afford to improve their insulation or heat their homes, leading to health problems.
Tauranga Property Investors secretary Lindsay Richards said it was important tenants communicated with their landlord if the house was cold or damp.
"It's very much a case that unless a landlord's stayed a few nights in a place, you don't know if it's an issue," he said.
Energy and Resources Minister Simon Bridges said more than 300,000 Kiwi homes had been insulated with the help of government subsidies so far, with 6839 of those in the Bay of Plenty.