According to realestate.com.au, a modest bathroom needed a second, unexpected renovation within weeks of the first — a reminder that even routine building work can blow past initial cost estimates once trades, materials and compliance requirements are factored in. That gap between what a homeowner expects a job to cost and what it actually costs is the same gap that quietly undermines building insurance across Australia. When rebuild costs rise faster than a policy's sum insured, the difference is not covered by the insurer — it is worn entirely by the homeowner.
A building sum-insured figure is meant to reflect the full cost of demolishing a damaged property and rebuilding it to an equivalent standard, including labour, materials, permits, and often temporary accommodation. Most policies are set at inception based on a calculator estimate or a builder's quote at the time, and many insurers apply an automatic indexation each year to keep pace with inflation. The problem is that standard indexation is usually pegged to a general cost index, not to the specific, often volatile, movements in trades labour and building materials pricing that Australia has experienced in recent years.
This matters because construction costs do not move in a straight line. Material shortages, trade labour scarcity, and compliance upgrades (bushfire construction standards, updated wiring rules, accessibility requirements) can all push actual rebuild costs well above a generic indexed figure. A policy that was accurately priced three or four years ago can quietly fall thousands of dollars short of a genuine rebuild quote today, even though the homeowner has been paying premiums the whole time and assumes they are fully covered.
The core risk is structural, not accidental: sum-insured figures are recalculated on average trends, while actual rebuild costs are driven by localised trade availability, material specification and compliance upgrades — three variables that rarely move in lockstep with a standard indexation formula.
For homeowners and investors alike, the practical takeaway is that "insured" and "adequately insured" are not the same thing. A policy can be current, premiums can be paid in full, and a claim can still leave the policyholder short of the cash needed to complete the actual rebuild, particularly on older homes with non-standard finishes or additions that were never formally valued.
How Underinsurance Plays Out at Claim Time
Underinsurance becomes visible at the worst possible moment — after a total loss, when a builder's quote for full reinstatement comes in above the policy limit. Some insurers apply what is known as an average or co-insurance clause, where if the sum insured is found to be materially below the true rebuild cost, the payout on even a partial claim can be reduced proportionally, not just capped at the sum insured. This means underinsurance can hurt policyholders on smaller claims too, not only on total losses.
The renovation example from realestate.com.au is a useful illustration of how quickly costs can shift within a single project, let alone across the years between a policy's inception and a claim. A bathroom that needed re-work within weeks shows how trade quality, material specification and compliance issues can force costs upward without warning. Scale that unpredictability across an entire dwelling and the case for regularly checking a sum-insured figure becomes clear.
For property investors managing multiple dwellings, the risk compounds. A portfolio of properties insured years apart, each indexed differently, can leave an investor with wildly inconsistent cover levels — some adequate, some significantly short — without any single trigger event to prompt a review. Investors relying on standard fixed vs variable mortgage structures to fund their holdings should treat an annual insurance review with the same discipline as a rate review, since a shortfall in rebuild cover is effectively unhedged balance-sheet risk.
Recalculating Cover: What Homeowners Should Actually Do
The most reliable way to check for underinsurance is to obtain a fresh building replacement estimate, either through an insurer's own online calculator, a quantity surveyor, or a licensed builder familiar with current local trade rates. This is particularly important after any renovation, extension, or upgrade — a new kitchen, a second storey, or even a pool and associated fencing can materially change the true rebuild cost without the policyholder ever notifying the insurer.
Older homes present a specific complication. Character features such as ornate cornices, hardwood flooring, or heritage-style facades can cost significantly more to reinstate than a standard modern equivalent, and generic calculators often assume like-for-like modern materials rather than period-accurate replacement. Homeowners with older or architecturally distinct properties should treat the default calculator figure as a starting point, not a final answer, and seek a more detailed quote where the property has non-standard features.
Strata properties add another layer of complexity, since the building sum insured is typically managed by the owners corporation rather than the individual lot owner. Owners in strata schemes should confirm their strata title arrangements clearly separate building cover (held at the corporation level) from contents and improvements cover (held individually), since gaps between the two are a common and preventable source of disputes after a claim.
Practical Implications for Buyers, Owners and Investors
For anyone currently buying a property, the settlement period is the ideal moment to establish an accurate, independently sourced rebuild estimate rather than accepting a default insurer calculation. This is a natural complement to the work already done during buyer's agent engagements or building and pest inspections, since both processes generate detailed information about a property's condition and construction that feeds directly into an accurate sum-insured figure.
Existing owners should treat a sum-insured review as an annual task, ideally timed to coincide with a policy renewal, rather than something only revisited after a major event. Anyone who has renovated, extended, or upgraded services since their policy began should assume their current figure is out of date until proven otherwise. For those weighing up how insurance costs interact with broader financing decisions, tools like REAStats can help contextualise regional cost trends alongside property market data.
Investors managing several properties should build a rolling schedule of rebuild-cost reviews rather than relying on blanket indexation across a portfolio, since the compliance and material cost drivers behind underinsurance rarely apply evenly across different property ages, locations and construction types. A modest amount of time spent on this each year is inexpensive relative to the exposure of a shortfall discovered only after a total loss.
Ultimately, underinsurance is a slow-moving risk that rarely announces itself until a claim is underway. Reviewing sum-insured figures against genuine current rebuild quotes, rather than relying solely on automatic indexation, remains the single most effective step Australian property owners can take to close this gap. For a comprehensive overview, see our Property Insurance Guide.
This article was produced with AI assistance and reviewed for accuracy. Content is for informational purposes only and does not constitute financial or property investment advice.
