New landlord laws mean rental homes have to be insulated.

Rental homes are twice as likely to have poorly-maintained features than owner-occupied ones, according to a new survey.

Those rentals were also twice as likely to smell musty, three times more likely to feel damp, and more likely to have visible mould.

The findings from the Housing Condition Survey, from the Building Research Association of New Zealand (Branz), showed almost a third of rentals were deemed by assessors to have poorly maintained features , compared to only 14 per cent of owner-occupied properties.

ROSS GIBLIN/FAIRFAX NZ Rental homes are more than twice as likely to have poorly maintained features than owner-occupied buildings, according to a new Housing Condition Survey.

Meanwhile, 12 per cent of rentals smelt musty compared to six per cent of owned homes, and just under a third of rentals felt damp, compared to 11 per cent of owner-occupied.

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The survey is the largest of its kind in New Zealand, encompassing 560 standalone and terraced houses, and has been carried out every five years since 1994.

The overall condition of New Zealand housing had improved since the previous survey in 2010. However, Branz research analyst Vicki White said the gap between owner-occupied properties and rentals had remained constant.

"The indication is it is generally the interior and more easily replaced items that are improving to a greater extent than more difficult and expensive features, like roofs and walls."

White said she was shocked by the prevalence of mould, which was visible in nearly half of houses.

But building and construction minister Nick Smith said the results were not surprising.

"This is as a consequence of the owner having a more direct interest in a property's maintenance, doing more self-maintenance, and being able to organise repairs more directly."

The survey also sent a message that landlords could do better, and justified a law change last year that imposed extra obligations on landlords, including making insulation and smoke alarms compulsory, Smith said.

"These law changes will ensure we maintain the momentum of ongoing improvement in the quality of New Zealand homes."

Smith pointed to the overall decrease in poorly-maintained homes as signs of progress.

Those had dropped from 25 to 14 per cent for owner-occupied homes, and 44 to 32 per cent for rental properties.

Branz building performance research team leader Mark Jones said initiatives, such as Warm Up New Zealand, which offered subsidies for insulation, may have contributed to overall improvement.

"The aim is to try and improve our housing stock and get them warmer, drier and healthier. We are hoping some of the areas we highlight and the data we are finding with our House Condition Survey supports the movement in that direction," he said.

The survey rated houses on 49 different features, including foundations, exterior walls, insulation and interior linings.

These were used to place homes on a five-point scale ranging from serious condition – meaning the house required immediate work due to health and safety risks – to excellent, which were typically as-new.

The biggest differences in quality were between interior linings and fittings, as well as exterior doors and windows, all of which were in poorer condition in rented homes.

Rentals were usually older as well, with a larger percentage built before 1980.

Renters were shown to be more transient as well, with only 40 per cent of renters staying in the same home for more than seven years, a figure that jumped to 75 per cent for owners.

The survey noted that a tenant moving out was a good opportunity for landlords to undertake repair work, but this often did not happen if demand was high.

The survey found renters generally regarded their properties to be in worse condition than owners – a reversal of the results from 2010. The Branz report attributed this change in part to media's focus on the quality of rental stock.

Wellington Property Investors' Association president Richard Bacon agreed with this, and saidresidents were feeling more empowered to speak out about poor housing.

He said property maintenance often came down to whether the owner was an "accidental landlord" or a property investor.

Bacon said a rental warrant of fitness (WOF) was not the solution, because monitoring housing stock would create massive overheads for government.

"The new rules on insulation are going to start making a difference, but they don't kick in until July the year after next," he said.

"People are starting to realise that 'just put another jumper on' isn't a way forward."

Tenancy Protection Association Christchurch manager Di Harwood said the survey's findings were no surprise.

"Owner-occupiers are far more likely to maintain their properties, especially if they are living in them, whereas in tenanted homes, the landlords are less likely to want to understand what's going on for tenants."

Harwood said as winter set in, people were realising their homes were damp and cold, and others were finding things like mould appearing.

"Christchurch has a lot of as-is where-is houses which are beng bought cheaply and tenanted out, where conditions are not ideal."

Unlike Bacon, Harwood said a rental WOF would help spot under-par homes, although finding consensus among concerned parties meant the process was taking a long time.

"The fact is, if the WOF was in place, we could identify these homes a lot sooner and deal with issues effectively."