Cracks in your house: which ones matter and when to call an engineer

Cosmetic cracks vs structural cracks

Fine, hairline cracks in plasterboard, cornices and render are usually caused by normal shrinkage, temperature change and minor seasonal movement. They are mostly a maintenance issue.

Cracks become more concerning when they are wider, keep growing, run diagonally from the corners of doors and windows, step through brick mortar joints, or appear together with sticking doors and uneven floors.

Warning signs worth an inspection

• Cracks that are getting wider or longer over weeks or months
• Diagonal or stepped cracks in brickwork, especially near corners and openings
• Doors and windows that start to jam or no longer close properly
• Gaps opening between walls and floors, ceilings or skirting boards
• Cracks in the slab together with floors that feel out of level
• New cracking after heavy rain, a long dry spell, a leaking pipe or nearby excavation

Common causes in Brisbane and South East Queensland

Reactive clay soils are common across Brisbane, Ipswich, Springfield and parts of the Gold Coast. These clays swell when wet and shrink when dry, which can move footings and slabs unevenly.

Other frequent causes include poor site drainage, leaking stormwater or sewer pipes, large trees drawing moisture from the ground, uncontrolled fill, nearby excavation or retaining wall movement, and footings that were not designed for the actual site classification.

What an engineer checks

• Crack pattern, width and direction, and how they relate to each other
• Floor levels and wall verticality to understand the movement pattern
• Drainage, plumbing, trees and surrounding ground conditions
• Footing type and, where needed, soil testing or a site investigation
• Whether movement is likely to be ongoing and what repair approach suits it

What you can do now

Take dated photos with a ruler or coin next to the crack so changes can be tracked. Fix obvious leaks and make sure water drains away from the house. Avoid patching cracks before they have been assessed, as this hides how the movement is developing.

Every house and site is different. A site-specific inspection by a qualified engineer is the only reliable way to confirm the cause and the right repair.