The Child Poverty Action Group (CPAG) has recently called for a warrant of fitness for rental properties because of rising rents, overcrowding and what it says are poor and deteriorating rental properties.

NZ Property Investors’ Federation executive officer Andrew King said his organisation supported improving rental properties, but there were better ways to do it than with a WOF.

"A WOF is expensive, which will do nothing to help rental prices or overcrowding" King said. "Insulation is one part of providing a healthy home, but heating and ventilation are also critical elements. If tenants can't afford to turn on heating now, how will a WOF help them?"

He said a recent study showed rental prices in New Zealand were lower than they have been in the past.

In 1985, rents amounted to 42% of household income, but in 2014 this has fallen to 32%.

A June 2014 study showed that it is $136 per week cheaper to rent than to own the average New Zealand home.

King said University of Otago studies showed fuel poverty and overcrowding were major factors in the health of families in predominantly low-income households. “A WOF will make these matters worse. Any proposals to improve the living conditions of low-income families need to take into account all of the factors involved. Proposals should aim to have a minimal effect on increasing rental prices and address all the challenges that low-income families face.”