When assessing cracks in your home, it’s important to focus on the width rather than the length. Here’s a comprehensive guide to understanding and addressing different types of cracks in your Perth property.

Category 1: Small (Minor) Cracks


  • Hairline cracks < 0.1 mm
  • Fine cracks < 1 mm, including cornice cracks


These cracks are typically caused by the settlement of walls onto foundations or movements in the building due to temperature or moisture changes.

Impact and Repair:

Small cracks are usually cosmetic and don’t require specific repairs. A simple patch and paint job is often enough to fix these.

Category 2: Medium Cracks


  • Cracks from 1 mm to 5 mm


Medium cracks can be visually concerning but are often due to settlement or vibratory actions in newer homes. In older homes, these cracks might signal the beginning of more severe issues. Additionally, water concentration around footings from unconnected downpipes can cause subsidence and wall cracking.


Impact and Repair:

Generally, these cracks can be patched and painted. However, it’s crucial to monitor for significant changes over 6-12 months. Preventative measures should be taken if the cracking worsens or if contributory factors like rusting lintels or water ingress are identified. Digital photography can help monitor changes over time by providing a reference point.

Category 3: Large (Moderate to Severe) Cracks


  • Cracks from 5 mm to 25 mm


These significant cracks can result from various issues, such as:

  • Footing and concrete pad problems (subsidence)
  • Water ingress and moisture in walls
  • Concrete cancer and rusting lintels
  • Impact damage
  • Roof frame or other load-bearing problems
  • Water concentration around footings


Impact and Repair:

These cracks require immediate attention. Small cracks need filling to prevent water ingress, while severe cases might need a structural engineer’s assessment. Remediation plans should be enacted promptly.

Australian Standards

Refer to Australian Standard and Guides to Australian Standards and Tolerances for guidance on dealing with cracked walls, ceilings, and floors.

Maintenance and Repair Responsibilities

New Homes:

During the maintenance period, builders typically repair all cracks. Post-maintenance, unless a construction defect is identified, property owners are responsible for repairing small and medium cracks. Builders in WA will address large cracks within the 6-year defect liability period if construction-related.


Older Homes:

Beyond 6 years, the responsibility shifts to the property owner. Follow these steps:

  • Small cracks (Category 1): Patch, paint, and monitor for changes.
  • Medium cracks (Category 2): Patch, paint, monitor closely, and address contributory causes.
  • Large cracks (Category 3): Act immediately. Identify the cause and create a remediation plan. Seek advice from a Registered Builder or Structural Engineer.

Repairing Cracks

Hairline Cracks:
Use acrylic sealant, applied directly over the crack and smoothed with a moist finger. The sealant remains flexible and keeps the crack hidden.

Medium Cracks:
Apply plasterboard patching cement. Dampen the crack first, undercut the edges for better adhesion, and follow package instructions before painting.

Joins Between Different Materials:
Use a flexible sealant for gaps around door frames, architraves, cornices, and skirting boards. Choose a product that is easy to apply, paintable, durable, and water-cleanable.


A Perth building inspector will be able to diagnose the problem and suggest further ways to repair it in a way that it does not become a recurring problem. Another indicator to keep an eye out for is nail popping. Are there any nails or screws that are visibly popping out of your walls? This could signal foundational damage or a structural issue.

At BCI WA, we want you to feel safe and secure in your own home. To find out more about our building inspection reports or if you have any questions regarding potential problems in the structure of your home, feel free to contact us.