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And if they do not want to judge that by a property’s CV or an online calculator, that could come with a very large valuer’s bill.

All of the country’s insurers are changing their policies from "total replacement value", where the insurer pays out whatever is required to rebuild a home, to "agreed value" policies, where a set payout is determined and agreed on by the property owner and the insurance company.

Already, new AA Insurance customers are on the new style of policy and the rest of the country’s insurers will start switching renewing customers over the next couple of months.

The move gives companies more certainty about what they would have to pay out in the event of a natural disaster. The country’s largest insurance group, IAG, said reinsurance costs had doubled because of the Canterbury earthquakes.

IAG's New Zealand chief Jacki Johnson said reinsurance costs had risen to 15% of gross written premiums  in the first half of 2013 from around 8% in 2010. That cost was being passed on to consumers.

"Insurers [have been] told to step in line with other countries because, with Canterbury, they will have no idea of the total cost of the rebuild until it is finished and that is because of the total replacement policies," said Insurance Council chief executive Tim Grafton.

But Auckland Property Investors Association president David Whitburn said many property investors could be left vulnerable by the move. He said few would want to pay to have a registered valuer look at all their properties and a lot of people would take the DIY approach. “There will be a lot of guesstimates.”

He said some would end up under-insured and some would pay too much. “There will be a mix. I am worried that a lot of people will grossly under-insure.”

The fine print of many home loans stated that owners had to have sufficient insurance to rebuild a property in the event of total loss. Whitburn said that meant some property owners could end up in breach of their contracts and the banks had a track record of calling back such loans.

Consumer New Zealand warned it almost always cost more to replace a house than what it would sell for. Payouts would need to include the cost of clearing a site. Demolition can add a lot to a rebuild.

Terry Naylor, of the Property Institute, said his organisation, which represents valuers, had talked to insurers about absorbing the $500 cost of a valuation but had been unsuccessful.