Your sum insured is the single most important number in your house insurance policy. Get it wrong and you could be tens or even hundreds of thousands of dollars short after a major event. Here is how to work it out properly.
Your sum insured is the maximum amount your house insurer will pay out if your home needs to be rebuilt from scratch. It is the ceiling on your policy - if the cost to rebuild exceeds your sum insured, you pay the difference out of your own pocket.
When you take out or renew house insurance in New Zealand, you nominate your sum insured amount. This is not a number your insurer sets for you. It is your responsibility to get it right, and most insurers make this very clear in their policy documents.
Almost all house insurance policies in NZ are now "sum insured" policies. This replaced the old "full replacement" model, where insurers promised to rebuild your home regardless of cost. The shift happened after the Canterbury earthquakes exposed the massive financial risk that open-ended replacement policies created for insurers. Under a sum insured policy, the rebuild cost is capped at the amount you nominate - so accuracy matters enormously.
The Sorted.org.nz house insurance guide has a clear explanation of how sum insured policies work and why getting the number right is so important.
Underinsurance is one of the biggest problems facing New Zealand homeowners. It means your sum insured is lower than what it would actually cost to rebuild your home. If a total loss occurs - fire, earthquake, landslip - you are left with a shortfall that can run into hundreds of thousands of dollars.
The Canterbury earthquakes brought the scale of the problem into sharp focus. Thousands of homeowners discovered their sum insured was not enough to cover the real cost of rebuilding. Some were short by $100,000 or more. With construction costs surging after the earthquakes due to demand for labour and materials, the gap widened further.
More recently, building costs across New Zealand have continued to climb. Materials, labour, consents, and compliance costs have all increased significantly since 2020. A sum insured figure that was accurate five years ago could be well below today's rebuild cost.
The Insurance Council of New Zealand (ICNZ) has repeatedly highlighted underinsurance as a systemic risk. Their research indicates that a significant proportion of NZ homeowners have a sum insured that would not cover the full cost of rebuilding their home at today's prices.
The consequences are straightforward. If your home is destroyed and the rebuild costs $650,000 but your sum insured is only $450,000, you are responsible for the $200,000 gap. That gap could mean taking on new debt, downsizing, or not being able to rebuild at all.
Why getting your sum insured right is critical
This is the single most common source of confusion around sum insured, and it leads directly to underinsurance. Your sum insured should be based on the rebuild cost of your home - not its market value, not its rateable value, and not what you paid for it.
Market value is what a buyer would pay for your property on the open market. It includes the land, the location, the neighbourhood, the views, proximity to schools, and dozens of other factors that have nothing to do with the physical structure. In Auckland, Wellington, and other high-value areas, land often makes up 50-70% of a property's market value. That land value is irrelevant to your sum insured.
Rebuild cost is what it would cost to demolish what remains of your home and build a new one of similar size, quality, and specification on the same site, to current building code standards. It includes materials, labour, professional fees, council consents, and a range of other costs we will cover in detail below.
In some cases, the rebuild cost is lower than the market value - particularly in areas where land is expensive. In other cases, especially rural or remote locations, the rebuild cost can actually exceed the market value because of the expense of transporting materials and tradespeople to the site.
Your local council's rateable value (RV or CV) is not a reliable guide either. Council valuations are done for rating purposes and are typically several years out of date. They are not designed to estimate rebuild costs.
The Consumer NZ house insurance guide explains this distinction clearly and is worth reading if you are unsure about the difference.
Calculating your sum insured does not need to be guesswork. There are tools and professionals that can help you arrive at a solid figure. Here is a practical approach.
Step 1: Estimate your base rebuild cost. Start with the floor area of your home in square metres and multiply it by a per-square-metre rebuild rate. As a rough guide, rebuild costs in New Zealand in 2025/2026 typically range from around $2,500 per square metre for a basic build to $4,500 or more for a high-specification home. A standard three-bedroom home of around 150 square metres might have a base rebuild cost of $450,000 to $600,000, depending on the quality of finishes and fittings.
Step 2: Add demolition and site clearance costs. Before you can rebuild, the damaged structure needs to be demolished and the site cleared. This can cost $20,000 to $50,000 or more, depending on the size of the home, the materials involved, and whether there is asbestos or other hazardous materials to deal with.
Step 3: Add professional fees. You will need an architect or designer, a structural engineer, possibly a geotechnical engineer, a surveyor, and a project manager. Council consent fees also fall into this category. Professional fees typically add 10-15% to the base rebuild cost.
Step 4: Factor in council consents and compliance. Building consent fees, resource consent fees (if required), development contributions, and inspections all add up. These vary by council but can total $10,000 to $30,000 or more.
Step 5: Account for building code upgrades. If your home was built decades ago, a rebuild must meet current New Zealand Building Code standards. This could mean higher-specification foundations, better insulation, updated electrical and plumbing, improved accessibility, and seismic design requirements. These upgrades add cost that was not part of the original build.
Step 6: Include an inflation buffer. Construction costs can rise between the time you set your sum insured and the time a rebuild actually happens. It can take 12 to 24 months or longer from a major event to the start of construction. Adding a 5-10% buffer for cost escalation is worth considering.
Step 7: Consider site-specific factors. Difficult access, steep sites, retaining walls, special foundations, and remote locations all increase rebuild costs. If your property has any of these characteristics, factor in the additional expense.
The Natural Hazards Commission (NHC) website has useful resources on understanding rebuild costs in the context of natural disaster recovery.
Follow these steps to arrive at an accurate figure
Multiply your home's floor area (sqm) by a per-square-metre build rate. Use an online calculator or get a builder's estimate for your area and home type.
Include the cost to demolish the damaged structure, remove debris, and clear the site ready for rebuilding. Allow $20,000 to $50,000 or more.
Architect, engineer, surveyor, and project management fees. Typically 10-15% of the base rebuild cost.
Building consent, resource consent (if needed), development contributions, and inspection fees. Allow $10,000 to $30,000+.
A rebuild must meet current code. Older homes may need significantly better foundations, insulation, wiring, and seismic design.
Construction costs rise over time. A 5-10% buffer accounts for cost escalation between setting your sum insured and starting the rebuild.
Steep sites, difficult access, retaining walls, or remote locations all add cost. Factor these in if they apply to your property.
Many homeowners underestimate their sum insured because they only think about the basic construction cost. A full rebuild involves a lot more than just bricks and timber. Here is a breakdown of the costs that should be factored into your sum insured.
The table below outlines the main cost categories and gives a rough indication of what each might add. These are indicative ranges only - actual costs depend on your location, the size and type of your home, and market conditions at the time.
| Item | Typical Cost Range | Notes |
|---|---|---|
| Base construction cost | $2,500 - $4,500+ per sqm | Depends on size, quality, and specification of the home. High-end homes can exceed $5,000 per sqm. |
| Demolition and site clearance | $20,000 - $50,000+ | Removing the damaged structure, debris, and hazardous materials like asbestos. |
| Architect / designer fees | 5 - 10% of build cost | Required for design, plans, and building consent documentation. |
| Structural and geotechnical engineering | $5,000 - $20,000+ | Structural design, foundation design, and site investigation reports. |
| Council building consent fees | $5,000 - $15,000+ | Varies by council and project value. Includes inspections and code compliance certificate. |
| Resource consent (if required) | $5,000 - $20,000+ | May be needed depending on zoning, site coverage, or heritage overlays. |
| Project management | 3 - 5% of build cost | Coordinating the rebuild, managing contractors, and overseeing quality. |
| Surveyor fees | $2,000 - $5,000 | Boundary pegs, setting out, and as-built surveys. |
| Building code upgrades | Varies widely | Bringing the rebuild up to current NZ Building Code standards - insulation, wiring, seismic, accessibility. |
| Temporary accommodation allowance | Included in most policies | Check your policy - this is usually a separate benefit, not part of sum insured. |
| Inflation / cost escalation buffer | 5 - 10% of total | Accounts for rising costs between the event and the start of construction. |
| Site-specific costs | Varies widely | Retaining walls, difficult access, steep sites, special foundations, remote locations. |
Underinsurance rarely happens because homeowners deliberately choose a low sum insured. It usually happens because of honest mistakes and misunderstandings. Here are the most common ones.
Using market value or purchase price. As covered above, these figures include land value and bear little relationship to rebuild cost. A $1.2 million property in a high-land-value suburb might only cost $500,000 to rebuild - but equally, a $400,000 property in a rural area might cost $500,000 to rebuild due to transport and access costs.
Not updating after renovations. If you have added a new bathroom, extended the kitchen, built a deck, or converted the garage, your rebuild cost has increased. Many homeowners complete renovations and forget to update their sum insured. A $80,000 kitchen renovation means your sum insured should increase by at least that amount, plus the associated professional fees and consents for that portion.
Not accounting for cost inflation. Building costs in New Zealand have risen sharply in recent years. A sum insured set in 2020 could easily be 30-40% too low by 2026. If you set your sum insured and never review it, you are almost certainly falling behind.
Forgetting demolition and professional fees. The base construction cost is only part of the picture. Demolition, site clearance, architect fees, engineering, consents, and project management can add 20-30% to the total. Leaving these out means your sum insured is immediately too low.
Not considering building code changes. Building standards evolve. If your home was built in the 1970s or 1980s, a rebuild to current code will cost significantly more than what it cost to build originally. Better insulation, modern wiring, seismic bracing, and improved foundations all add expense.
Ignoring site-specific costs. Hillside properties, homes with difficult access, properties requiring retaining walls, or homes in remote areas all cost more to rebuild than standard suburban homes on flat sections. These factors need to be reflected in your sum insured.
The Settled.govt.nz website has helpful information about property risks and considerations that can affect rebuild costs.
You do not have to calculate your sum insured from scratch. Several tools and services can help you arrive at a reliable figure.
Online sum insured calculators. The most widely used tool in New Zealand is the Cordell Calculator, powered by CoreLogic. It uses data about your home's size, construction type, age, and features to generate an estimated rebuild cost. Many NZ insurers either use the Cordell Calculator directly or offer their own version based on similar data. Tower, AMI, and other major insurers have online calculators built into their quote process.
Quantity surveyors. For the most accurate estimate, a registered quantity surveyor can assess your specific property and produce a detailed rebuild cost report. This is especially worth considering for architecturally designed homes, heritage properties, homes with unusual construction methods, or high-value properties. A quantity surveyor report typically costs between $500 and $1,500 depending on the complexity of the property. The New Zealand Institute of Quantity Surveyors can help you find a registered professional.
Builder estimates. Getting an informal estimate from a local builder or building company can provide a useful cross-check. Ask what they would charge per square metre to build a home of similar size and quality in your area. This is not a formal quote, but it gives you a ballpark figure grounded in current local market rates.
Your insurer. When you apply for or renew your house insurance, most insurers will flag if your nominated sum insured seems unusually low or high based on their data. Some will actively prompt you to review the figure. Take these prompts seriously - your insurer has a good sense of rebuild costs in your area.
The Consumer NZ website regularly publishes guidance on sum insured calculators and how reliable they are. It is worth checking their latest assessment.
Setting your sum insured is not a one-off exercise. Building costs change, your home changes, and the gap between your sum insured and reality can widen quickly if you do not stay on top of it.
Review at every renewal. When your house insurance renewal comes through, do not just auto-renew at the same sum insured. Check whether building costs in your area have moved. Many insurers will apply an automatic inflation adjustment, but these adjustments are often conservative and may not keep pace with actual cost increases.
Update after any major work. If you have done renovations, extensions, or significant upgrades, recalculate your sum insured immediately. This includes new kitchens and bathrooms, room additions, garage conversions, new decking, and any work that increases the floor area or specification of your home.
Watch for market signals. If you hear that building costs are rising sharply - as they did across New Zealand post-Covid and after Cyclone Gabrielle - that is a prompt to check your sum insured. Industry publications, news coverage, and your insurer's communications can all signal when costs are moving.
Keep records. Maintain a file with your home's floor plans, a list of major features and finishes, records of renovations, and your most recent sum insured calculation. This makes it much easier to update your figure each year and provides useful documentation if you ever need to make a claim.
The Sorted.org.nz insurance guides include practical checklists for annual insurance reviews that may be helpful. For more on how house insurance works overall, see our guides on what house insurance covers and how EQC works.
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