Since the Canterbury earthquakes, most insurers have moved to fixed sum policies for home rebuilds

to shed the risk of having to rebuild a client's home whatever the cost. With the cost of building materials continuing to rise, however, the amount homes are covered for may no longer be enough.

Research from building products database EBOSS has revealed that the cost of building materials rose by more than a third over the past 12 months.

"And to be honest it doesn't really matter what type of material [it] is – the increases are fairly constant across the different categories,” said EBOSS managing director Matthew Duder, who expected costs to climb at least a further 10% over the next six months.

Insurance Council chief executive Tim Grafton said homeowners should ensure their cover was appropriate.

"We're in a very high inflationary environment and particularly with respect to building costs and building supplies, some of those are in double-digit inflation territory, so that would have a dramatic effect on the cost of rebuilding your house if the very worst happened,” he said.

While some insurers had a 10% buffer in place for sum-insured policies, the buffer may not be enough in the current market, Grafton told RNZ.

Tower Insurance chief executive Blair Turnbull said the environment has changed rapidly.

"We certainly feel we have a responsibility to make sure that the cover that we have in place for our customers matches the asset,” Turnbull said. “That's why we provide tools that are accumulating a lot of data or grabbing data in real time to best reflect the value of that asset.”