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The Cause Of Wall Cracks

Understanding the cause requires consideration of a large number of factors

The Cause Of Wall Cracks

Understanding the cause requires consideration of a large number of factors, and is the first step in making any assessment as to the seriousness and cost of repairing wall cracks.
Some of the most common causes of cracking are:

The impact of foundation soils

Some level of soil excavation is usually required when a home is first built. Depending on the type of home you have, will determine how much excavation work needs to be carried out. Some types of homes require more disruption to the soil than others in the course of their construction.

Disturbed soil will compact and settle with time, which can cause a wall to crack. This process can take months or even years to occur. Natural settling will often cause narrow vertical cracks as opposed to big jagged cracks.
Minor settling is a normal process that occurs over time. However, significant downward motion in the soil under a wall may create more serious structural faults. Significant faults can occur when soil is washed away (an example is sudden flooding or slowly over time during a gradual leak),when soil compacts too much or collapses. A powerful example of this is sink holes.

Reactive Soils

A reactive soil is a type of soil that contracts when it is dry and dramatically expands when moist. A good example of a reactive soil is clay. Examples of non-reactive soil types include bedrock, gravel and sand. To assist in identifying whether the soil on your property is reactive and could be a contributing factor to cracking, soil testing should be undertaken.

Changes occurred by nature and the environment

Intense climate and seasonal changes, such as flood and drought, can cause dramatic contraction and expansion of the soil. Wall cracking can also occur when the water table changes deep below a property.
While earthquakes and earth tremors are infrequent events in Australia, these can also contribute to wall cracks appearing.

Construction and excavation work in your area

If you live in an area where there is a lot of construction work happening, such as a new housing estate, or if you live in close proximity to a quarry then this can be the cause of wall cracking.

The vibration of heavy machinery, excessive mechanical compaction of the soil or blasting (the use of explosives to excavate) can all cause your walls to crack.

If the wall cracking appears during or following construction in your area, you should seek an urgent assessment of the cracks and legal advice.

Design or extension work

If your property was poorly designed (whether it is the initial construction or an extension which has been added), this can cause wall cracking.

The cracking can occur because of too much weight on a load-bearing wall, inferior or faulty building materials, or under-engineered footing design.

Surrounding the property

Blocked or leaking pipes, garden sprinklers or blocked gutters can all cause wall cracks as they can have the effect of saturating or even washing away soil.

Trees can also have invasive root structures that can contribute to wall cracking. It is best to only have small bushes or shrubs in close proximity to your walls. Apart from destructive roots, trees can also contribute to wall cracking by removing water from the soil and affecting the soil’s moisture content.

If you remove a large tree from an area in close proximity to your walls, this can also cause cracking as it can destabilise the soil in the space previously occupied by the root system. It can also lead to changes in the moisture levels of the soil or settling over time.


Nothing lasts forever, and building materials are no exception. Weathering, gravity, poor maintenance or rotting can all take their toll on building materials.

When building material starts to age, its structural integrity might be undermined causing it to succumb to gravity. This can cause wall cracks to appear. If steel reinforcements in concrete starts to rust and degrade following exposure to moisture and salt, this can also cause cracking.

Next steps

Don’t be complacent. Take photos and document wall cracks. We recommend including a ruler in the frame of the photo so you can easily compare and track the progress of any cracks over time.

According to QBCC Standards & Tolerances Guide 2016 and Australian Standard AS2870, cracks in concrete slabs 2mm or greater and those in masonry or plasterboard walls 5mm or greater (3mm or greater when in groups) may be deemed to be defects.

If the cracks in your walls are the sizes mentioned above, or if you have any concerns about smaller cracks, we recommend that you contact a qualified building inspector for an assessment of the possible cause and severity of the cracks in your walls. They will be able to provide you with a plan of attack and estimate the possible costs of repairs.

Protecting your family’s safety and your financial investment is paramount, and it is important that you take their advice seriously and follow through within the recommended timeframes.

Need to identify the cracks in your wall? Read our article on “Cracks in Buildings. How Serious Are They?

Concerned about cracks in your walls? Contact BeSafe Property Inspections to discuss your wall crack concerns on(02) 9410 3740 or via our website.

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