You notice a crack in the wall of a Perth home you’re considering buying. It measures around 5mm wide.
Is it just cosmetic movement, or could it indicate a major structural problem?
A 5mm wall crack should not be classified as a major structural defect based on width alone. Crack width is an important observation, but an inspector also needs to consider the crack’s location, direction, pattern, whether displacement is present, surrounding building elements and other signs of movement.
For Perth home buyers, the safest approach is not to ignore a 5mm crack—or assume the worst. It should be professionally assessed in the context of the whole property.
Is a 5mm Wall Crack Serious?
Potentially, but the measurement alone doesn’t provide the answer.
A 5mm crack is large enough to deserve closer attention, particularly if it is accompanied by other signs of building movement.
An inspector may consider:
- Where the crack is located
- Whether it is vertical, horizontal, diagonal or stepped
- Whether one side has moved relative to the other
- Whether similar cracking appears elsewhere
- Whether doors or windows are binding
- Whether floors appear uneven
- Whether there is visible distortion or separation
- Whether moisture or drainage issues are present
- The age and construction of the property
A single number therefore shouldn’t be used as a standalone diagnosis.
5mm is a measurement. The significance of the crack depends on the evidence around it.
What Does a 5mm Crack Look Like?
A 5mm opening is usually much more noticeable than a fine hairline crack.
At this width, a Perth home buyer may see it clearly during an open inspection, particularly on:
- Internal plaster or rendered walls
- External masonry
- Around doors and windows
- Near wall junctions
- Above openings
- Along brickwork or mortar joints
However, appearance can be misleading.
A prominent crack in a finish isn’t automatically evidence of major structural failure, while a less dramatic crack in a critical location may deserve further investigation.
This is why photographs and measurements are useful—but context matters more than width alone.
Does Crack Direction Matter?
Yes. The pattern can provide useful information about how different parts of the building may have moved.
Vertical Cracks
Vertical cracking can occur for different reasons depending on the construction, material, location and age of the property.
The inspector should consider whether it is limited to a finish or continues through relevant building elements.
Horizontal Cracks
Horizontal cracking deserves assessment in the context of the wall construction and surrounding conditions.
Its significance cannot be determined simply because it runs horizontally.
Diagonal Cracks
Diagonal cracking, particularly around windows and door openings, can sometimes be associated with movement.
The inspector may look for related cracking or distortion nearby.
Stepped Cracks
In masonry, cracks can sometimes follow mortar joints in a stepped pattern.
A stepped crack should be considered alongside its width, location, displacement and other evidence of movement.
None of these patterns provides a diagnosis on its own.
Where Is the 5mm Crack Located?
Location can be just as important as width.
Consider the difference between a crack in an internal finish and one extending through external masonry.
An inspector may pay particular attention to cracks:
- Around windows and doors
- Through masonry walls
- Near building corners
- At wall junctions
- Around openings
- Between different building materials
- Near areas showing other movement
- In combination with uneven floors or distorted openings
The inspector should determine what can actually be observed and whether further structural assessment is warranted.
For a broader explanation, read our guide to Structural Faults in Perth Homes.
What Other Warning Signs Should Perth Buyers Look For?
A 5mm crack becomes more meaningful when considered with the rest of the property.
Doors or Windows That Don’t Operate Normally
Doors and windows can bind for many reasons.
But where unusual operation occurs alongside significant cracking or visible distortion, the combination may deserve closer assessment.
Uneven or Sloping Floors
Noticeably uneven floors can have multiple causes depending on the property’s construction and age.
If they appear together with cracking or other movement indicators, the inspector can consider whether the observations may be related.
Multiple Cracks
One isolated crack and a pattern of cracking across several parts of a building provide different information.
Distribution matters.
Visible Displacement
A crack where one side appears displaced relative to the other may deserve more attention than a similar-width crack without visible displacement.
Gaps and Separation
Separation around walls, ceilings, cornices, windows, doors or other building junctions can provide additional evidence for the inspector to consider.
Moisture or Drainage Concerns
Water and drainage observations may also be relevant to understanding conditions around a property.
That doesn’t mean moisture automatically caused the crack. It means the building and site should be considered together rather than assessing one isolated symptom.
Do Perth Soil Conditions Cause Wall Cracks?
This is an area where buyers should avoid broad assumptions.
Not every Perth property has the same soil or site conditions.
Ground conditions vary across the metropolitan area and even between individual lots. Building design, foundations, drainage, construction quality, maintenance, alterations and local site conditions can all affect how a home performs.
So it would be misleading to say:
“Perth homes crack because Perth has reactive soil.”
The correct approach is property-specific.
If ground or foundation movement is suspected, the inspector may recommend further assessment based on the evidence observed at that particular home.
Can Perth’s Weather Cause Cracking?
Weather alone shouldn’t be used to diagnose a wall crack.
Perth generally experiences hot, dry summers and cooler, wetter winters. Seasonal conditions can influence moisture and drainage around individual properties, but that does not mean every crack is climate-related.
When assessing cracking, relevant observations may include:
- Drainage around the property
- Water discharge locations
- Moisture-related deterioration
- Building age
- Construction type
- Foundation and structural observations
- Previous alterations
- Crack pattern and distribution
The cause of cracking should be investigated from the available evidence rather than assumed from Perth’s climate.
Is a 5mm Crack Automatically a “Major Structural Defect”?
No.
This distinction is particularly important for home buyers.
A measurement shouldn’t automatically be converted into a contractual or technical classification.
Whether a finding meets the definition of a major defect or has contractual significance depends on more than crack width. The building element affected, severity, cause, consequences and applicable inspection or contractual framework may all matter.
For example:
“The crack is approximately 5mm wide” is an observation.
“This is a major structural defect” is a conclusion requiring appropriate supporting evidence.
A professional inspection should distinguish between the two.
Can a 5mm Crack Be Cosmetic?
It can be, depending on what has cracked and why.
Some cracking can occur in finishes or at junctions without indicating major structural failure.
However, a buyer shouldn’t simply label a 5mm crack cosmetic because:
- The agent says it is normal
- The seller says it has always been there
- The wall has recently been painted
- Similar houses appear to have cracks
- The property is old
Likewise, you shouldn’t automatically conclude that the home has foundation failure.
Assessment comes before classification.
Can Fresh Paint Hide Wall Cracks?
Fresh paint can improve presentation, but it doesn’t tell you the history of the wall.
Previous cracks may have been filled and painted as part of normal maintenance or renovation.
That isn’t automatically suspicious.
However, during a pre-purchase inspection, the inspector may consider whether there are:
- Visible repaired cracks
- Differences in finishes
- Recurring cracking
- Cracking in corresponding external areas
- Other signs of movement nearby
A building inspection is non-invasive, so it cannot guarantee identification of defects that have been completely concealed without visible evidence.
What Will a Building Inspector Do With a 5mm Crack?
A professional inspector should do more than simply photograph it.
Depending on the inspection scope, the process may include:
Record the Location
Where exactly is the crack?
Consider the Width
How wide is the visible opening at the time of inspection?
Examine the Pattern
Is it vertical, diagonal, horizontal or stepped?
Look for Displacement
Has one side visibly moved relative to the other?
Check Surrounding Areas
Are there related cracks, gaps, distorted openings or other movement indicators?
Consider the Building
What is the construction type, approximate age and condition?
Recommend Further Investigation Where Necessary
If the available evidence suggests the crack requires a more detailed structural assessment, that recommendation should be clearly communicated.
This is where an engineer-led building inspection can provide useful context.
Learn more about StructSure’s inspection team on our Our Team page.
Can Thermal Imaging Tell Whether a Crack Is Structural?
No.
Thermal imaging can be useful for identifying thermal anomalies in certain circumstances, but it does not determine whether a wall crack is structurally significant.
Likewise, a moisture meter can provide additional information about moisture conditions in appropriate materials or locations, but it doesn’t diagnose structural movement by itself.
Inspection tools should support professional assessment—not replace it.
Should You Buy a Perth House With a 5mm Wall Crack?
The crack alone cannot answer that question.
Instead, before making your own purchasing decision, try to establish:
What has cracked?
Where is it located?
Is there displacement?
Are similar cracks present elsewhere?
Are other movement indicators present?
Does the inspector recommend further investigation?
What does the rest of the property inspection reveal?
This gives you much more useful information than deciding based solely on “5mm”.
A Pre-Purchase Building Inspection in Perth can assess the crack alongside other accessible parts of the property.
What If the Crack Is Found After You’ve Made an Offer?
If you’re purchasing through a private sale in WA and your offer has already been accepted, check the wording of your Offer and Acceptance (O&A) and any relevant building-inspection special condition.
Don’t assume that finding a 5mm crack automatically gives you the right to:
- Cancel the contract
- Require repairs
- Reduce the purchase price
- Delay settlement
Your options depend on your contract and the nature of the inspection findings.
If you’re uncertain about your contractual position, seek advice from an appropriately qualified legal or settlement professional.
For more context, read Negotiating After a Building Inspection: How to Use Your Report.
What If You Find the Crack Before a Perth Auction?
This is where timing becomes especially important.
If you notice significant cracking in a property you’re considering bidding on, consider arranging the appropriate inspection before auction day.
WA auction purchases operate differently from conditional private sales, so buyers should complete relevant due diligence before bidding.
Read our guide to Building Inspection Before Auction in Perth: What Buyers Should Know for the complete process.
What If the House Is Being Sold “As Is”?
An “as is” sale makes understanding the property’s condition particularly important.
Don’t assume that visible cracking will necessarily be repaired before settlement.
The contract and sale terms need to be understood before you commit.
For more information, read Buying an “As Is” Property in Perth: What Every Buyer Must Know.
What Should You Do If You See a 5mm Crack at a Home Open?
Don’t panic and don’t ignore it.
Use this simple process:
1. Take note of the location.
Remember where you saw the crack and whether similar cracking appears elsewhere.
2. Don’t diagnose it yourself.
Width alone doesn’t establish the cause or significance.
3. Arrange an appropriate building inspection.
Tell the inspector about your specific concern.
4. Read the entire report.
Don’t assess the crack in isolation from the rest of the property.
5. Follow recommendations for further assessment.
If a more detailed structural investigation is recommended, consider completing it within the relevant buying timeframe.
6. Check your contract.
If you’ve already made an offer, understand how your O&A deals with building-inspection findings.
For a complete inspection checklist, see What Does a Building Inspection Cover in Perth? A Buyer’s Checklist.
Frequently Asked Questions
Is a 5mm crack in a wall serious?
A 5mm crack deserves professional assessment, but width alone cannot determine whether it is a major structural defect. Location, pattern, displacement and other signs of movement should also be considered.
What size wall crack is considered structural?
There isn’t a single crack width that automatically proves a structural defect in every building. Crack width is one observation among several that need to be considered.
Should I worry about a 5mm crack in brickwork?
A visible 5mm crack in masonry should not be ignored. Its pattern, location, displacement and surrounding building conditions should be professionally assessed.
Are wall cracks common in Perth homes?
Cracking can occur in Perth properties for various reasons, but the significance varies considerably. Avoid assuming a crack is normal simply because other homes have similar-looking cracks.
Does a diagonal crack mean foundation problems?
Not automatically. Diagonal cracking can have different causes. The crack and surrounding building need to be assessed before attributing it to foundation movement.
Can a building inspector determine why a wall is cracking?
An inspection can assess visible evidence and provide professional observations. Where the cause or structural significance cannot be adequately established within the inspection scope, further specialist investigation may be recommended.
Can thermal imaging identify structural cracks?
No. Thermal imaging identifies temperature patterns and is not a tool for determining whether a crack is structurally significant.
Should I get an inspection before buying a house with visible cracks?
If cracking concerns you, an independent pre-purchase inspection can help assess the crack in the context of the accessible condition of the property.
Book an Engineer-Led Building Inspection in Perth
A 5mm wall crack is a reason to investigate—not a reason to immediately assume structural failure.
The width matters, but so do the crack pattern, location, displacement, surrounding building elements and other evidence across the property.
StructSure provides engineer-led Pre-Purchase Building Inspections Perth to help buyers better understand significant accessible building findings before making their own property decisions.
If you have already noticed cracking at a Perth property, mention it when booking so the inspector knows about your specific concern.
Building Only — $299
Standard Building + Pest — $499
Premium Building + Pest — $699
Call StructSure: +61 422 370 505
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