Almost every home develops a crack somewhere. Most are harmless, but some are an early warning that the foundation beneath your home is moving. Knowing the difference can save you a lot of money and stress. Here is how to read the cracks in your walls, and when it is time to get expert advice.
Cracks that are usually harmless
Fine hairline cracks in plaster, cornices and paint are common as a home settles and as materials expand and contract with temperature and humidity. Thin, stable cracks that do not change over months are generally cosmetic. The key word is stable: if a crack is not growing, it is far less likely to be structural.
Cracks worth worrying about
Some patterns point to structural movement rather than surface shrinkage. Watch for:
- Stepped or diagonal cracks following the mortar joints in brickwork
- Cracks wider than about 5mm, or cracks you can fit a coin into
- Cracks above doors and windows, or frames pulling away from the wall
- Cracks that appear on both the inside and outside of the same wall
- Any crack that is visibly getting longer or wider over weeks and months
These often appear alongside other symptoms such as sloping floors and sticking doors, which together suggest the foundation is settling unevenly.
Why walls crack in the first place
The most common cause across South East Queensland and Northern NSW is reactive clay soil that swells when wet and shrinks when dry, driving constant movement beneath the slab. Poor drainage and plumbing leaks that soften or wash away supporting soil, and large trees drawing moisture from the ground, are also frequent culprits. For a deeper look at each, see our page on cracks in walls.
A simple test: watch, measure, then ask
If you find a crack that concerns you, mark each end with a pencil and note the date, or photograph it next to a ruler. Check it again in a few weeks. If it is growing, or if you are seeing several of the warning signs above, it is worth having it qualified with facts rather than guessing. Our complimentary Home Check-up is a no-pressure way to find out whether what you are seeing is cosmetic or structural, and what to do about it.