Dodgy imported products are being found on building sites across Auckland, including electrical wiring, toughened safety glass shower doors and roofing tiles.
In the most recent cases, three homes had to be rewired and another eight were retiled after building inspectors uncovered materials that were not up to code.
The problems come as a severe housing shortage drives a building boom across Auckland that has seen one in three work sites fail council inspections because of shoddy workmanship.
Products associated with weathertight systems have also been reported as substandard.
The scale of the problem is unknown but concerns are serious enough to have prompted probes by the Ministry of Business, Innovation and Enterprise (MBIE), Auckland Council and the Commerce Commission.
In February, more than $1 billion of residential building work was consented - up 40 per cent on the same period last year.
Auckland Council building control manager Ian McCormick highlighted one case where 100mm waste pipes were sold for $1 a metre, about a tenth of the normal retail price.
Mr McCormick said with building advancing at a growing pace, the council was keeping a vigilant eye on builders and tradespeople for non-complying products.
He would not name any of the tradesmen suspected of using dodgy products or the sites involved, but said the council was working with the MBIE and trade bodies to verify products and investigate issues.
"We understand that these types of products are not being sold through major retailers, but rather they are being imported privately," he said.
Mr McCormick said about eight houses had to be reroofed after asphalt tiles were substituted with an imported product which council inspectors were not satisfied complied with the building code.
Building products needed an endorsement or marking to show the manufacturer complied to a recognised certifying body.
In the past year, the council had carried out 134,000 building inspections, of which a third failed.
MBIE determinations and assurance manager John Gardiner said the ministry was working to determine how significant the problem of dodgy materials was.
There had always been background noise and allegations of non-compliant products, he said, but complaints had recently got louder.
MBIE asks people to report building product compliance issues to a dedicated email address.
"We have done some investigations, primarily to get some more information. One of the challenges that we have got is that ... it is very easy to make an allegation but without supportive evidence," he said.
As well as products identified by Auckland Council, MBIE had heard about compliance issues with weathertight systems, including membrane products and flashing plates, and a toilet.
Mr Gardiner said MBIE had the power to issue warnings and take disciplinary action against licensed trades people. Only licensed builders could do consented work.
A Placemakers spokeswoman said it was focused on selling quality materials with manufacturer warranties.
"The majority of building materials we stock are sourced domestically, although a small percentage are imported. For imported products we use our professional sourcing office in Shanghai which has robust quality assurance processes," she said.
Meanwhile, the Commerce Commission is investigating whether some steel mesh products used for concrete floors, driveways and pathway slabs meet standards.
Last month, Steel & Tube agreed to sell only seismic-reinforcing steel mesh which has been independently tested, similar to an undertaking entered into with Euro Corporation.
The commission is also investigating whether Timber King, a small building supplies company in Mt Wellington, sold steel mesh that did not meet the standard.