Australian home values have fallen for six straight months, down 5.2% from their March 2026 peak. None of that tells a homeowner what it now costs to rebuild. The two figures move independently, and this renewal season they are moving in opposite directions.
That divergence reaches the client as a single line on a renewal notice. A home insurance renewal arrives each year showing a sum insured that has gone up, but nothing on that document says which benchmark did the lifting, or whether it has kept pace with what a builder now charges.
Insurers are explicit that the increase is not a guarantee. Allianz tells customers it raises the sum insured automatically at renewal unless they ask it not to, and also advises them to check their home's replacement value themselves each year before renewing. Other insurers and brokers give similar advice.
Martin Birch (pictured), principal of Agrisurance in Sydney, said falling property values have made that annual check far easier to skip.
"The real danger is that homeowners mistake falling sale prices for a reason to reduce their cover," Birch said to Insurance Business. "Falling house prices can mask a growing insurance gap."
Values are falling in a way that invites exactly that reading. Cotality's Home Value Index fell 1.1% in September, a sixth consecutive monthly decline that left national values 5.2% below their March peak. The Reserve Bank of Australia (RBA) has lifted the cash rate by 100 basis points over 2026, to 4.60% effective September 30, with its next decision due on 3 November.
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The reassurance published alongside those falls measures something else again. In its Financial Stability Review on 1 October 2026, the RBA said that in a scenario involving a uniform 20 per cent fall in housing prices from current levels, only around 5 per cent of mortgages would fall into negative equity. That is a loan balance set against a sale price. It carries no information about whether the same house is insured for enough to be rebuilt.
The divergence Birch describes is arithmetic rather than judgement.
"CPI measures inflation across household goods and services; the building cost index tracks the labour and materials needed to construct a home," he said.
"Insurance Council analysis shows building costs rose around 30% over the five years to March 2026, compared with CPI of about 24%."
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Those comparative figures come from the Insurance Council of Australia's (ICA's) analysis of Cotality's Cordell Construction Cost Index. Six percentage points over five years reads as marginal. Compounded on a sum insured carried forward untouched across that period, it is not.
Birch expects the gap to widen rather than close.
"If inflation puts renewed pressure on construction costs, that gap could widen – leaving homeowners facing a total loss with insufficient funds to rebuild," he said.
His position is that indexation cannot substitute for assessment, whatever rate it runs at.
"The key is to review replacement costs at renewal, rather than 'assume' that a CPI adjustment will keep cover adequate," he said.
The timing sets up a conflict. Clients are absorbing a year of rate rises, watching their largest asset lose value on paper, and arriving at renewal looking for savings. The most available saving in a home policy is a lower sum insured.
"For brokers, the renewal conversation must go beyond premium: a cheaper policy offers little comfort if the saving leaves the client unable to rebuild," Birch said.
He is explicit that he means a formal valuation rather than an online estimate and that the economics justify the expense.
"This means obtaining proper replacement cost valuations by a qualified professional – the cost of this will outweigh the downside of getting the sum insured wrong," he said.
A falling market takes nothing off the price of a slab, a roof or a licensed trade. It only makes it easier to believe that it might have.
