Is This Crack Dangerous?
Not all cracks mean your house is falling down. Use our free diagnosis tool to see if you need a structural engineer.
Select the shape of your crack:
Thin Vertical
Hairline width, straight up/down.
Zig-Zag / Stair Step
Follows mortar lines like stairs.
Wide Gap (>5mm)
Can fit a coin in it / see daylight.
The 3 Types of Cracks Explained
Hairline: Usually cosmetic. Caused by plaster drying or thermal expansion.
Stair-Step: The classic sign of subsidence. Bricks don’t break easily; mortar does. This shape means the wall is twisting or dropping.
Horizontal: The most dangerous. Means pressure is pushing the wall inwards.
Frequently Asked Questions
Can I just fill the cracks?
Only if the movement has stopped. Filling a crack on a moving foundation is like painting over rust—it will come back. Underpinning stops the movement first.
Why do cracks open and close?
Reactive clay soil swells in rain (closing cracks) and shrinks in drought (opening cracks). This “breathing” fatigues your foundation.