When the ground sustaining a building moves, cracks may happen. This is sometimes distinguished as subsidence. It is produced by the ground compressing under weight or by clay soils expanding and shrinking with variations in its moisture content.
You will often see cracks in a building, especially in concrete, flooring, brickwork, plasterboard, tiles and around windows and doors. Many cracks are cosmetic and this doesn’t always mean the house is falling apart.
Most buildings will always have some form of settlement after they are built. But if they keep cracking, there may be serious structural issues.
What measure of movement is tolerable?
It may be feasible to compose a footing system to suit all building movements without producing cracking. Still, it is incredibly expensive to perform. Consequently, the Building code of Australia (BCA) has chosen a realistic approach where the footing and slab arrangement must be created and constructed to operate within certain threshold levels.
What are the tolerances for slabs and footings in the BCA?
- Hairline cracks that do not require repair and cracks that are obvious but easily filled and are smaller than 5mm wide are satisfactory and consistent with the requirements of the Standard. Likewise, doors and windows that bind slightly are not uncommon. These problems are deemed a maintenance responsibility of the purchaser.
- Cracks over 5mm wide that need complete or partial replacement of the wall, noticeably bulging walls, and windows and doors that stick and warp, do not satisfy the Standard.
- Hairline cracks not more than 2mm wide meet the requirements of the Standard. Even apparent cracks where the slab has a detectable level change might be satisfactory. The way to examine it is to measure the divergence from a 3m straight edge centred over the gap. If it’s not more than 15mm, the defect is within the satisfactory boundaries of the Standard.
- Cracks more extensive than 2mm, or where the deviation from the straight edge is more significant than 15mm are not inside the Standard – repairing those defects is the burden of the builder or contractor responsible.
Changes in slope
- The QBCC has determined that the local slope change from horizontal or vertical more than 1/100 is not acceptable.
What do I do if I find a potential subsidence problem?
- Get in contact with your builder.
If your house was constructed within the last 6.5 years, you might be covered by home warranty insurance with the QBCC.
- Suppose you are unhappy with the builder’s reply. In that case, you can contact QBCC to lodge a complaint.
- To support your complaint, you can contact Clearcut Building Inspections to perform a structural building inspection and get a comprehensive digital report on your property and where the potential issue may be.
- If your property is older, we can find the problem and point you in the right direction of getting the subsidence rectified.
What will CCBI evaluate during an inspection?
After a grievance about subsidence has been made aware to us, we will send an inspector to evaluate the site:
- The inspector scans to see if the building complies with the BCA, such as any needed control joints in masonry, internal finishes, and movement to joints in stormwater, sewage and site drainage.
- The Inspector will also record any modifications made after construction that may be adding to the movement.
- Maintenance problems such as leaking taps, air conditioning lines discharging close to footings, leaking hot water systems and blocked gutters and downpipes will also be recorded.
- The inspector will record the movement results, including cracking, sticking windows and doors, and any noticeably cracked pipework.
What will CCBI evaluate after the inspection?
The CCBI inspector will assess the information reported on-site to ascertain:
- Whether the subsidence and movement are within the normal range as set out in BCA standards.
- If any maintenance or other concerns should be addressed by the property owner.
- If a plumbing examination is required to check for leaking or broken pipework.
- Whether a specialist, such as an engineer or the QBCC should investigate.