Cracks in walls: when to worry and when not to

Every house cracks. Materials shrink, settle and move with temperature, and most of what owners notice is cosmetic. But some cracks are telling you something, and the difference is usually identifiable.

What generally is not a concern

Hairline cracks in drywall at corners of windows and doors
Fine vertical cracks in a foundation wall that have not changed
Cracks that appeared shortly after construction and stopped

What warrants a look

Stepped cracks in masonry following the mortar joints in a staircase pattern — these usually indicate differential settlement
Horizontal cracks in a foundation wall — often the most serious, because they can indicate lateral pressure pushing the wall inward
Cracks wider than about 3mm, or wider at one end than the other
Doors and windows that have started sticking alongside new cracking
Anything that is visibly changing

Movement matters more than width

A wide crack that has been stable for twenty years is often less concerning than a narrow one that opened last month. The question an engineer is trying to answer is not how big it is but whether it is still moving — which is why monitoring over weeks or months is sometimes part of the assessment.

How the cause gets established

The pattern of cracking, its location, the soil conditions and the age and construction of the building together usually point to the cause: settlement, expansive soils, water, a removed or altered load path, tree roots, or original construction. The remedy depends entirely on which.

What to do now

Photograph it with a ruler or coin for scale and date the photo. If it changes, you will have a record. That single habit tells an engineer more than a description ever will.