Tougher housing regulations on rental properties have been urged after a warrant of fitness trial failed more than 90 per cent of homes it tested.
Housing advocates and politicians say compulsory minimum standards should be introduced to protect the health and safety of tenants.
The trial assessed 144 properties in Auckland, Tauranga, Wellington, Christchurch and Dunedin, and 94 per cent failed on at least one of the 31 assessment criteria on the checklist.
Darryl Evans, from Mangere Budgeting Services Trust, which advocates for struggling tenants, said he was not surprised by the findings, describing some rental properties as "diabolical".
It was common to find properties with exposed electrical wires and plumbing problems, he said.
Some landlords were reluctant to invest in their properties and many did not know their legal obligations.
He called for mandatory registration of landlords as well as regular assessments for all rental homes.
"I am for a building warrant of fitness, but it does have to include regulators out in the field making sure landlords are meeting a set of criteria."
The trial was conducted by a steering group, which included the University of Otago Wellington, the Green Building Council, the councils of the five cities in which homes were tested and the Accident Compensation Corporation.
It looked at weathertightness, insulation and ventilation, lighting, heating, condition of appliances and building safety.
Property Investors Federation executive officer Andrew King said while some landlords could do better, most were adhering to the Residential Tenancy Act providing safe, sanitary and clean properties.
He acknowledged that many properties failed the test, but "most of those were on small things".
Trial organisers said that although 94 per cent of the inspected homes failed, 36 per cent would require only minor fixes costing between $50 and $150 to pass.