The insurance industry says many homeowners are reporting huge variations in assessments of how much it will cost to rebuild their homes.
Major changes to home insurance policies, which came into effect in June, now mean homeowners must calculate their new policies.
They can work out how much it will cost to rebuild their home by using online calculators, getting their home assessed by surveyors or accepting the default sum from their insurer.
Insurance Council operations manager Terry Jordan says the big differences in estimates are mainly down to the insurers not knowing what sorts of materials are in a home.
"People know more about their house and they know what the quality of it is," says Mr Jordan.
He says the insurer might assume it's an average house when it is above average, or premium, quality and the calculator will show the difference straight away.
Mr Jordan says people should assess whether the default sum and the online calculator sums are fair amounts, before going to a quantity surveyor.