Subsidence is when the mineral foundation of a building starts to move back and forth and when this occurs in a building that you live in, you might find that cracks begin to form in the walls.
What Causes Subsidence?
When you’ve got cracks showing up in your walls for seemingly no reason at all, it can be easy to think the worst, however, the concrete cracking is generally quite easily explained.
Subsidence is oftentimes directly related to an issue with the clay or soil deposits in the ground beneath the building itself.
When the clay or soil beneath the building begins to wax and wane in size due to the water content, the foundation naturally becomes more susceptible to spatial oscillation.
The Right and Wrong Degree of Movement
Even though subsidence can be a concerning issue, not all foundation movement is necessarily evidence of a significant problem.
Occasionally, certain buildings are intentionally created with footing and slab system implements that are intended to help it move with the flow of clay and soil below, however, the trade-off to this is usually that the system is quite expensive to implement.
In order to approach the cost in a more manageable fashion, the Building Code of Australia (BCA) has established a tiered ranking system of the necessary tolerance levels for different footing system designs.
The more erratic the potential subsidence, the more tolerant the slab system needs to be in order to absorb the fluctuations gracefully.
Footing System Standards for Walls
Generally speaking, cracks in the walls that are less than 5mm wide are generally either going to be unnoticeable or easy to rectify with just a minor amount of filling.
It’s typical for windows and doors to show some slight signs of sticking and these occurrences are typically seen as the building owner’s responsibility.
In the event that cracks exceed more than 5mm, however, then the homeowner may want to consider getting the wall itself replaced before additional and more-concerning cracks can form in the foundation.
Subsidence that requires the most serious degree of intervention will generally be the kind that creates protrusions in the walls and distractingly significant sticking in the walls and/or windows.
Footing System Standards For Concrete Floors
In the event that subsidence cracks in a concrete floor have a straight edge deviation of more than 15mm, the BCA Standard for owner-manageable imperfections have been exceeded.
If the cracks are less than 2mm however, then the cracks are considered to fall within the Standard and possible to be adequately handled at the expense of the building owner.
Floor levels with a local change in slope that exceeds 1/100 are unacceptable and therefore the responsibility of the contractor to address.
Addressing a Slope Issue
If you discover a significant subsidence issue that falls out of the bounds of your responsibility as the owner, then your first priority should be to get in contact with the builder and see whether or not you’re still covered by warranty.
Depending on how satisfying the response you get from the builder is, you might want to arrange an on-site inspection.
What Will Be Inspected?
During the inspection, the inspector will measure up the severity of the distortions to assess the contractor’s adherence to BCA standards. Post-construction changes, maintenance issues, floor level averages and damages from movement will all be taken into account.
After the inspector has finished their inspection, they will determine whether the building owner or the contractor should be made to rectify the issues at hand.
In case of broken pipes, the inspector may also assess whether or not a plumbing test is in order. You may need to reach out to a specialised engineer for further investigation if it is decisively concluded that subsidence damages are neither compliant with BCA Standard nor the fault of the contractor.