It is designed to ease Auckland traffic congestion by adding new motorway lanes between Manukau and Papakura as well as a shared pedestrian and cycle path.

NZTA senior manager project delivery, Chris Hunt, said that while the construction passed through a "narrow, live motorway corridor with neighbouring properties close by", the agency and its contractors worked hard to be a good neighbour.

Contractors had to meet strict "resource consent" conditions and carry out regular monitoring, such as by measuring vibration levels.

Gaylene Smith says her house has suffered $500,000 worth of damage because of the work being done on the motorway. Photo / Diego Opatowski

The agency was also "investigating on a case by case basis whether or not vibration from the construction work has caused damage to properties in Conifer Grove", Hunt said.

So far all reports had concluded vibration levels in the suburb were "comfortably below the guideline values", he said.

The contractor could not be reached yesterday but NZTA told the Herald questions for the firm should also be directed to the roading agency.

Auckland Council said it was not aware of any complaints relating to the motorway project but it would need to investigate further this week.

Smith said she first noticed cracks in the walls of her two-storey timber home and its fibre cement cladding after the roadworks started up.

Initially her insurance company agreed to cover the claim after she lodged it in February 2017.

However, one year later the company reversed its decision, she said, claiming the policy did not cover vibration damage.

In between, the company received an estimated $500,000 repair bill for Smith's home, while its engineer's report found cracks in the walls were most likely caused by machinery operating on the nearby motorway project.

A second insurance report was inconclusive, saying most of the cracks in Smith's home appeared to pre-date the roadworks but vibrations from the construction may have reopened them.

Smith took the company to the insurance ombudsman but lost her bid to force it to honour the claim.

Attempts by the Herald to reach the insurance company yesterday were unsuccessful.

Fellow Conifer Grove residents Mark Heaslip and Liz Lloyd, who live in nearby streets Kamulla Court and Corolu Place, said they faced similar hurdles.

Neither the contractor nor NZTA had accepted responsibility for cracks in Heaslip's spa pool or the walls of Lloyd's home. Both homeowners claim the damage was caused by the roadworks.

Dianne and Cliff Walker say they've fought NZTA on many issues arising from the project. Photo / Diego Opatowski

Brylee Drive resident Dianne Walker said her insurance company was still investigating whether cracks in her home were caused by the motorway construction.

She had also battled the contractor and NZTA on a range of other issues.

Last winter, flood waters swept into her backyard and those of her neighbours, which she said was caused by the roadworks.

Her back fence was also knocked down by work crews, allowing a pet dog to escape onto the motorway, she said. She now feared her young children could do likewise.

While she managed to get partial compensation for the flooding and fencing, Walker said the contractor had been so hard to deal with that most other Conifer Grove residents simply gave up.

University of Waikato geotechnical engineering lecturer Dr Ali Shokri said he could not conclusively say what caused the damage without a site visit.

Vibration was a possible, but unlikely cause, he said. Another possible explanation was changing water levels caused by contractors draining or increasing water depending on the soil in the area.

"You can get some sort of different balance in terms of load on the foundations. So one side of the building falls down and the other side stays up and it causes a crack inside the wall. That's one possibility."

He said the issue would be easier to prove for older homes as they had been there longer. Subsidence was more expected with newer homes, but depended on the soil type.

"If they have this building for 20 years and nothing happened and then [damage occurs] suddenly, overnight or after a year, after the road works, there could be some linkage and most probably because of water levels changing, shrinkage, and then cracks."

Meanwhile, Smith said her fight wasn't over. She was now contemplating hiring a lawyer.

"I'm sure some people are giving up because there is a cost involved at fighting this, but I can't afford to give up, I have to keep fighting," she said.

"I've gotta keep a roof over my family's head."