Wall cracks are common in Australian homes, but not all mean something's wrong. Some are harmless signs of natural settling or aging materials. Others? They could signal that your home is shifting or sinking.

So how do you know the difference?

After assessing over 50,000 homes, we've identified the clearest signs that separate cosmetic cracks from structural ones.

We've rounded up the surest signs that tell you if your wall cracks means trouble. Here's what to look for:

Hairline cracks (under 1mm) are often cosmetic. These can be caused by plaster shrinkage or paint drying.

Cracks wider than 3mm may indicate movement in the walls or foundation.

Over 5mm? That's a huge red flag. Get it checked immediately.

Pro Tip: Use a 5c coin or place two credit cards together. If the crack is about the width of the coin's edge or the two cards, or it has appeared suddenly without explanation, it's time for a professional assessment.

Vertical cracks in plaster or corners may be due to natural movement and are often minor.

Stepped cracks in brickwork (following mortar joints) or diagonal cracks above doors and windows often point to foundation issues.

Horizontal cracks are usually more serious and can signal structural stress or wall rotation.

Internal surface cracks (such as hairline cracks in paint or plaster) are more likely to be cosmetic.

Cracks in concrete, external brickwork, slab edges, or near foundation walls are far more likely to be structural.

Cracks near doors and windows are key indicators of wall movement or footing displacement.

If you've patched a crack and it's come back–especially if it's wider than before–it's likely that the underlying issue was never fixed.

What this means: Cosmetic fixes don't work when the structure is still moving. You may be dealing with subsidence.

A crack might be the start of something bigger. Look out for:

Doors or windows sticking or becoming misaligned.

Bouncy or sloping floors.

Gaps between walls and ceilings/skirting boards.

Drainage issues or cracks appearing alongside plumbing.

Cracks can be confusing. Don't stress trying to diagnose it yourself.

Buildfix offers free structural assessments to give you clarity fast. If the crack is structural, wall crack repair with HelicalBar™ reinforces the wall at depth — done in 1–2 days.

With registered structural engineers and over a decade of experience, we'll help you determine whether your home is simply ageing–or if there's something more serious going on beneath the surface.