The surge in P-contaminated homes has been likened to being potentially as costly to homeowners as the leaky home crisis. Photo / Dean Purcell

As Kiwi homeowners spend millions each year fixing P-contaminated houses, a drug detection expert has opened up on how to spot a drug house in your neighbourhood.

The surge in P-contaminated homes - badly damaged from their use as P labs or from previous inhabitants' personal use of methamphetamine - has been likened to being potentially as costly to homeowners as the leaky home crisis.

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And the costs aren't just the massive sums related to clean-up operations - which can top the $100,000 mark for a total refit - but also the severe health problems including to the neurological and respiratory system, as well as skin disorders, inflicted on residents unknowingly living in a former P pad.

As more and more Kiwi owners pay the price of former residents' meth use, one of New Zealand's biggest drug testing companies has revealed some of the biggest tell-tale signs to alert prospective house buyers to a property's nefarious past, or residents if a P lab was operating in their area.

Kirk Hardy, chief executive of the Drug Detection Agency, said there were several "property and people indicators", including:

• Chemical odours and dead vegetation around a section,

• An increase in visitors, combined with houses being outfitted with elaborate CCTV systems,

• Visible stains on curtains, walls and ceilings,

• Waste including empty medicine packaging, paint thinner containers and coffee filters with white or red powdery substances, and

• Tenants who only pay with cash.

And Hardy advised would-be home owners to door knock neighbours of homes they were considering buying to check on the background of the people who previously lived there.

"Neighbours will tell you a lot of information that real estate agents won't."

Hardy said it was important to keep in mind that a P lab could appear in any suburb.

"You've had meth labs in the Metropolis, you've had meth labs on Paritai Drive - it transcends all homes," he said.

"This is big business, let's make no bones about it. It's a big risk for big reward."

Methamphetamine has been a scourge in New Zealand since 2003.

It has ruined lives and its addicts have been responsible for crimes which have shocked the nation.

This week police said a man who allegedly led them on a 120km pursuit from Auckland's North Shore to the Waikato, taking a man hostage, had told them he had swallowed 3mg of meth.

"[Methamphetamine] has been around for a long, long time ... but it certainly seems to have resurfaced over the last 12 or 18 months in a big way," Hardy said.

His company tests about 2080 homes a year for traces of meth, with about 20 per cent coming back positive.

Last week it was revealed that almost a quarter of the 19 homes featuring in a year-old Housing New Zealand development in Christchurch had tested positive for P.

Given a water supply and a heat source were the only basic requirements for meth manufacture, Hardy said campervans and motel rooms were also used by drug makers.

As well as testing properties for meth residue, the Drug Detection Agency also runs workplace screenings across 22 industries throughout the nation.

While positive tests for drug use were dropping, Hardy said there had been an increase in failed tests for P.

Hardy's company conducted 120,000 workplace staff tests last year. The national rate for positive tests for all drugs was 6.19 per cent.

In the forestry sector, almost 20 per cent of all positives were for meth - up from 11.4 per cent in 2014.

Transport industry workers had a 4.9 per cent rate of failing drugs tests conducted by the Drug Detection Agency.

Methamphetamine made up 9.14 per cent of all positive tests, up from 5.5 per cent in 2014.