As the final zoning decisions are announced for the Port Hills, CHARLIE GATES examines the care needed and the risks involved in demolishing hillside homes.

Red-zoned homes on the Port Hills will have to be cautiously demolished for fear of triggering deadly landslips or rockfalls.

Demolition of hillside homes in the residential red zone will take longer than those on the flat, the Canterbury Earthquake Recovery Authority (Cera) has warned.

Cera residential red-zone security manager Brenden Winder is urging private demolition companies to be cautious of rockfall risks.

He said demolition contractors working for insurance companies would be given safety advice.

"There are cross-boundary risks that are broader than the site you are working on.

"We want to alert people to the fact that if you have a house on a property and you are going to demolish it, that is permitted, but neighbours could be affected," he said.

"You could set off a landslip. The hazard could be 150 metres long and 200 metres wide and you could be standing on top of it and not even know it."

Demolition firms working for Cera will start work once geotechnical and engineering assessments are completed.

"It is a much smaller volume but likely to be a more complex demolition. Port Hills demolitions are likely to take longer," Winder said.

"There is a lot of work that needs to go into how we will approach those demolitions.

"We need quite a lot of geotechnical and engineering advice before those demolitions start. The last thing we want is for demolition people to go in and have an avoidable accident."

Private security guards patrolling the Port Hills' red zones would also have to be cautious, Winder said.

Cera spends $1000 a day on private security guards who patrol residential red zones to prevent burglaries and arson.

"The security teams don't go into any properties in the Port Hills. There are life-risk issues, which is different to the residential red zones on the flat," he said. "We don't want to put our boys in any risk, so we will have safety protocols about putting people in those areas. Some of the buildings up there are not in great shape.

"We don't want them to go into those buildings unless there is a very good reason."

Inspector Richard Bruce said the Port Hills were challenging because of "risks in the hill areas". He said regular police and community patrols would help keep the area safe.

- © Fairfax NZ News

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