How to Calculate Your Home's Sum Insured in NZ (2025): The Rebuild Cost Method

How to calculate your house sum insured in NZ using rebuild cost, demolition, professional fees and an inflation buffer — and how to check whether your current figure leaves you underinsured.

On almost every house policy in New Zealand, there is a single dollar figure that decides how much your insurer will ever pay to rebuild your home. It is called the sum insured, and since the market moved away from open-ended "full replacement" cover, setting that figure has become the homeowner's job, not the insurer's. Get it right and a total loss is covered. Set it too low and you carry the shortfall yourself.

This article explains what the sum insured has to cover, why rebuild cost is different from market value, how the common calculators work, and how to sanity-check your own figure before renewal. It is general information, not advice about your situation.

TL;DR: Your house sum insured is the most your insurer will pay to rebuild ², so it needs to cover the full rebuild cost — structure, demolition, debris removal, professional and consent fees, code-compliance upgrades and GST — not your home's market or rating value ⁹. A rebuild calculator like Cordell Sum Sure is the usual starting point, and most owners add an inflation buffer because rebuild costs can move sharply over a multi-year rebuild.

What does 'sum insured' actually mean on an NZ house policy?

The sum insured is the dollar amount written on your policy schedule as the maximum your insurer will pay to repair or rebuild your home after a claim ². Cover stops at that number. If the actual cost of rebuilding comes in higher, the difference is yours to fund.

This matters because of a structural change in the New Zealand market. Following the 2010–2011 Canterbury earthquakes, insurers moved away from open-ended "total replacement" or "full replacement" cover — where the insurer simply rebuilt your home whatever it cost — to fixed sum-insured cover for most house policies. That shift took hold across the market in roughly 2013 to 2016 ¹. Under the older model the insurer carried the risk of getting the rebuild figure wrong. Under sum-insured cover, the homeowner sets the number, so the responsibility for accuracy sits with you ¹.

The practical consequence is simple: an accurate rebuild estimate is now part of owning a home, not a box the insurer ticks for you. If the figure on your schedule has drifted below today's rebuild cost, you are underinsured, often without knowing it.

Why is rebuild cost different from market value and rating value?

Three numbers get attached to a house, and they measure different things. Confusing them is the most common reason people set their sum insured wrong.

• Market value is what a buyer would pay for the property today — house, land and location together. It is driven by the property market.
• Rating value (RV) or capital value (CV) is the council's valuation for setting rates. It is a mass-assessment figure, usually a few years old, and again includes land.
• Rebuild cost is what it would cost to demolish the existing home and reconstruct it on the same site, including site works, professional fees and bringing the build up to current building rules ⁹.

Your sum insured needs to reflect rebuild cost, not market or rating value ⁹. The two can sit a long way apart in either direction. A modest home on expensive land may have a high market value but a much lower rebuild cost, because you are not rebuilding the land. An older or architecturally complex home can be the reverse: cheap on paper but costly to reconstruct to modern standards. Using market value or RV as a shortcut for your sum insured is how homes end up either over- or under-insured.

Source: MoneyHub NZ; general insurer guidance ⁹. Rebuild cost is the figure your house policy is built around — not market or rating value.

How do you use a rebuild calculator like Cordell to set your figure?

For most homeowners the starting point is an online rebuild calculator. The one the major insurers point to is Cordell Sum Sure, an automated rebuild-cost estimation platform run by Cotality (formerly CoreLogic). It estimates a residential replacement cost from construction-industry cost data ⁵.

Both Tower and Vero direct customers to the Cordell calculator. Vero describes it as an independent online tool that estimates a rebuild cost from typical costs for homes with similar materials and features once you enter your address ⁴. Tower uses Cordell Sum Sure and notes that the estimate it produces already includes professional fees, demolition, removal of debris and GST ³. Kiwibank likewise points customers to Cordell Sum Sure to calculate their sum insured ³. So if you have a recent calculator estimate, several of those forgotten costs may already be built in — but it is worth confirming which, rather than assuming.

How it works in practice:

1. You enter your address, and the tool pulls known characteristics of the home where available.

2. You confirm or adjust details — floor area, number of storeys, construction materials, roof type, garaging, and features such as decks or a second bathroom.

3. The calculator returns an estimated rebuild figure based on typical costs for comparable homes ⁴.

The accuracy of the output depends entirely on the accuracy of what you enter. A calculator estimate is a reasonable starting point for a standard home, but it is an estimate, not a quantity surveyor's report. For a home that is large, unusual, heritage, or on a difficult site, a professional rebuild assessment is often worth the cost.

What costs do people forget (demolition, site works, professional fees, code upgrades)?

People tend to picture the cost of the new building and stop there. A real rebuild after a total loss involves a sequence of costs before and around the construction itself, and these are exactly what gets missed when someone guesses a figure or reuses an old one.

• Demolition and debris removal. The damaged structure has to be cleared and disposed of before anything new goes up.
• Site works and access. Clearing the site, temporary services, and getting machinery and materials in — more involved on a sloping or hard-to-reach site.
• Professional and consent fees. Architects or designers, engineers, council consent fees and project management. On a full rebuild these add up.
• Code-compliance upgrades. A rebuild must meet the current Building Code, not the standard the house was originally built to. Older homes can need upgrades to foundations, bracing, insulation, plumbing and wiring that the original never had.
• GST. Often overlooked when people estimate a "build cost" in their head.

The reassuring part is that a Cordell Sum Sure estimate is designed to include professional fees, demolition, removal of debris and GST already ³. The catch is the special features a generic calculator does not capture. MoneyHub notes that a calculator estimate excludes things like a difficult or sloping site, so owners should add for those themselves ⁹. Long driveways, retaining walls, extensive landscaping, high-end fittings, solar systems and the like can all push the real rebuild above a standard estimate.

Figure: What a $600k house sum insured really has to cover

Source: Cordell Sum Sure methodology; Insurance Council of New Zealand (ICNZ) guidance ³⁵. A sum insured is not just the new building — it is the whole job from clearing the site to a consented, code-compliant home, plus a buffer for cost movement over the rebuild period.

The point of the figure is that the headline number on your schedule is doing far more work than "the cost of a new house." It has to absorb the demolition, the fees, the code upgrades and the GST, and still leave room for prices to move while the work is done.

How much inflation buffer should you add for a multi-year rebuild?

A rebuild is not instant. After a major event there can be a queue of work, materials and labour shortages, and a build that takes many months or even years. Your sum insured is generally fixed at renewal, so it needs to be high enough to still cover the cost when the work actually happens — which is why many people deliberately build in a buffer above the bare calculator figure.

The size of a sensible buffer depends on where construction-cost inflation sits, and that moves on its own cycle. As at early June 2025 the readings had cooled sharply. Stats NZ's Capital Goods Price Index showed residential building costs rising about 1.4% in the March 2025 quarter — the smallest quarterly lift in two and a half years ⁶. The Cotality (CoreLogic) Cordell Construction Cost Index recorded only about 1.0% annual growth in the year to the March 2025 quarter ⁷.

But low current readings are not the whole story, and this is the trap. That same Cordell index has a long-run average of around 4.2% a year, and it peaked at about 10.4% in late 2022 ⁷. So over a multi-year rebuild, costs can run far above today's quiet numbers. For context, general consumer price inflation (CPI) was 2.5% in the year to the March 2025 quarter ⁸ — a reminder that rebuild costs run on a separate cycle from headline inflation and can diverge sharply from it year to year.

Source: Stats NZ Capital Goods Price Index and Consumers Price Index, March 2025 quarter; Cotality (CoreLogic) Cordell Construction Cost Index, March 2025 quarter ⁶⁷⁸. Construction-cost inflation moves on its own cycle and can run well above headline CPI over the years a major rebuild takes.

There is no single "correct" buffer, and the right margin depends on your home, your region and the current cost cycle. The general idea is to set the figure so it still covers a full rebuild if construction costs rise meaningfully before and during the work — not just at today's lowest reading. This is one area where a conversation with an adviser or a quantity surveyor is genuinely useful.

How do you check whether your current sum insured is too low?

You do not need a major event to find out you are underinsured — you can pressure-test the figure now.

• Run a current calculator estimate. Put your address and accurate details into Cordell Sum Sure and compare the result with the figure on your schedule ³⁴. A large gap is a flag.
• Check what your figure is based on. If your sum insured was set off your market value or rating value, it may not reflect rebuild cost at all ⁹.
• Account for special features. Add for anything a generic calculator misses — a sloping or difficult site, long driveways, retaining walls, premium fittings ⁹.
• Factor in cost movement since you last set it. If the figure has not been touched in a few years, construction inflation over that period may have left it short ⁶⁷.
• Consider a professional assessment for non-standard homes. Large, complex, heritage or architecturally unusual homes are where calculator estimates are least reliable.

If your sum insured turns out to be below a realistic modern rebuild cost, you are exposed to an underinsurance shortfall — the gap between what it costs to rebuild and what your policy will pay. That shortfall is the part of a claim no one else carries. For how this interacts with the public natural-hazard scheme, see [domestic insurance basics](blog-post-title-domestic-insurance), and for general house-cover principles see [our guide to house insurance](blog-post-house-insurance).

How often should you review your sum insured?

A sum insured is not a set-and-forget number. A reasonable habit is to review it at every annual renewal, and again whenever something changes the rebuild cost of your home — a renovation, an extension, a new deck or garage, a kitchen or bathroom upgrade, or the addition of solar.

Between renovations, the main driver is construction-cost inflation, which is exactly why reviewing at renewal matters even when nothing about the house has changed. A figure that was accurate three years ago may quietly have fallen behind. Many insurers apply an automatic inflation adjustment at renewal, but that adjustment is a general index, not a check of your specific home, so it is worth confirming the result still reflects a realistic rebuild.

This kind of review fits naturally alongside the rest of your protection. New homeowners in particular are juggling several covers at once; the order to think about them is set out in [protecting a new mortgage](protect-new-mortgage-which-cover-first-nz).

Smiths Financial does not provide advice on property valuation or quantity surveying. This is general information only — for a precise rebuild figure on a complex home, an appropriately qualified professional such as a quantity surveyor can help.

Frequently asked questions

What should my house sum insured be based on in NZ? It should be based on the rebuild cost of your home — what it would cost to demolish the existing house and reconstruct it on the same site, including demolition, site works, professional and consent fees, code-compliance upgrades and GST. It is not your home's market value or its council rating value ⁹.

Is rebuild cost the same as my home's market value? No. Market value includes the land and reflects the property market; rebuild cost is only the cost to reconstruct the building. The two can differ substantially in either direction, so using market value or rating value as your sum insured can leave you over- or under-insured ⁹.

What does the Cordell Sum Sure calculator include? According to Tower, a Cordell Sum Sure estimate already includes professional fees, demolition, removal of debris and GST ³. It is an address-based estimate using typical costs for comparable homes ⁴. It generally excludes special features such as a difficult or sloping site, so owners should add for those ⁹.

How much inflation buffer should I add to my sum insured? There is no single correct figure. Construction-cost inflation moves on its own cycle — as at early June 2025 it had cooled to around 1.0–1.4%, but the Cordell index has a long-run average near 4.2% and peaked around 10.4% in late 2022 ⁶⁷. Because a rebuild can take years, many people set their figure so it still covers the cost if construction prices rise meaningfully during the work.

How often should I review my house sum insured? A common approach is to review it at every annual renewal, and again after any renovation, extension or significant change to the home. Construction-cost inflation can erode an old figure even when the house itself hasn't changed ⁶⁷.

What happens if my sum insured is too low when I claim? Your insurer will pay up to the sum insured on your schedule and no more, so any rebuild cost above that figure falls on you ². That underinsurance shortfall is the main risk you can control by setting an accurate, current rebuild figure.

This article is general information only and is not personalised financial advice. It does not take into account your particular financial situation, goals or needs. Before acting, consider whether it's right for you and seek advice tailored to your circumstances. Craig Smith Business Services Ltd (FSP712931), trading as Smiths Financial, holds a Class 2 licence issued by the Financial Markets Authority and is a member of the Financial Dispute Resolution Service (FDRS). Smiths Financial does not provide advice on property valuation or quantity surveying. This is a summary only — whether an insurance claim is paid, and how it is settled, depends on the policy terms, conditions, exclusions and your disclosure, so always read the policy wording. Construction-cost and inflation figures are correct as at 4 June 2025 and can change. Written by Henry Smith, Financial Adviser; reviewed by Craig Smith, Principal Adviser. Last reviewed 4 June 2025.