Some mistakes in insurance are loud.
Others are silent. They sit quietly inside the policy for years, causing no trouble at all… until the day you actually need protection.
Declaring the wrong square meterage is exactly that kind of mistake.
It looks small. It feels harmless.
And it can become very expensive.
When arranging home insurance, many people say something like:
“It’s roughly this size.”
Insurance does not like the word roughly.
Risk is never approximate.
Why Square Meterage Matters So Much
Home insurance is not based on market value.
It is based on reconstruction cost.
The real question insurers ask is simple:
“If this building were destroyed today, how much would it cost to rebuild it exactly as it is?”
That calculation rests on three pillars:
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Square meterage
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Construction type
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Build quality
If the square meterage is wrong, everything else collapses mathematically.
The insurer collects less premium.
The homeowner lives with less protection.
And when a claim happens, nobody is happy.
The Most Common Error: Net vs Gross Area
This is where most problems begin.
Homeowners usually declare net square meters.
Insurance calculations often require gross square meters.
Net area is what you live in:
Living room, bedrooms, kitchen.
Gross area includes:
Walls, columns, balconies, sometimes even shared structural space.
The difference can easily be 15–30%.
A home believed to be 120 m² may actually be 150 m².
That means the insured value is already 20% too low.
The mistake does not show up when the policy is issued.
It shows up when the claim is paid.
The Underinsurance Rule No One Likes
There is a clause in insurance policies that few people read and many people regret:
Underinsurance.
In simple terms:
If your home should be insured for 3 million but you insured it for 2 million,
you are automatically considered underinsured by one third.
Even if the damage is only 300,000,
the insurer applies the same ratio and reduces the payment accordingly.
Fire, flood, earthquake.
The cause changes.
The mathematics do not.
“But I Didn’t Do It on Purpose”
This argument is very human.
Insurance, however, is technical.
Loss adjusters look at:
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Actual square meterage
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Declared square meterage
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The difference
Intent usually does not matter.
Incorrect information, even if innocent, leads to the same result.
That is why wrong square meterage is the most expensive innocent mistake in home insurance.
Apartments vs Detached Houses
The risk is especially high in:
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Older apartment buildings
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Homes with enclosed balconies
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Houses extended over time
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Roof terraces and attic conversions
Title deeds often do not match the real structure anymore.
Insurance follows the physical reality, not the paperwork.
“My Neighbor Paid Less for the Same Building”
A familiar sentence.
But you do not know:
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Which square meterage they declared
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Which construction class they selected
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Which coverages they removed
Same building does not mean same risk.
Insurance does not work on copy-paste logic.
How to Get Square Meterage Right
The safest approaches are:
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Checking architectural plans or permits
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Using gross square meterage
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Declaring slightly higher if unsure
Over-insuring is rarely a real problem.
Under-insuring almost always is.
The Conclusion: Cheap Policy, Expensive Lesson
A home insurance policy with wrong square meterage looks fine on paper.
In real life, it fails when tested.
Nobody notices before a loss.
After a loss, it is too late.
Home insurance is not purchased to feel safe.
It is purchased to stay standing after something goes wrong.
And staying standing starts with one simple thing:
the correct square meterage.
This is not a detail.
It is the foundation.
