ENGINEERING PRACTICE | 31 AUGUST 2026
Cracks in Buildings: When Should You Be Concerned?
Not every crack signals structural failure, but every crack has a story worth understanding..
Not every crack signals structural failure, but every crack has a story worth understanding.
Few things worry a building owner faster than discovering a crack in a wall, slab, beam or column.
The immediate question is usually: Is the building safe?
There is no useful answer based on appearance alone. Some cracks are superficial and result from normal shrinkage, temperature changes or movement of finishes. Others may indicate settlement, excessive structural movement, overloading or deterioration that deserves immediate investigation.
The important question is therefore not simply whether a crack exists, but why it formed, where it is located, how it behaves and whether it is still changing.
1. A Crack Is a Symptom, Not a Diagnosis
Concrete shrinks as it dries. Materials expand and contract with changes in temperature. Foundations may settle. Structural members deflect under load. Different materials connected together may move differently.
Any of these can produce cracking.
This is why looking at a crack and immediately declaring it either “harmless” or “structural” can be misleading. The engineer must first understand the mechanism that produced it.
Much like a warning light on a dashboard, the crack draws attention to something that has happened. The investigation determines what that something is.
2. Many Cracks Are Non-Structural
Some of the most common cracks occur in finishes rather than in the structural system itself.
They may result from:
- shrinkage of plaster or concrete;
- inadequate curing;
- thermal expansion and contraction;
- movement between masonry and reinforced concrete;
- poor workmanship;
- minor differential movement; or
- inadequate provision of movement joints.
Fine cracks in plaster, for example, may be unsightly without materially affecting the safety of the building.
That does not mean they should simply be ignored. Their cause should still be understood, particularly where they recur after repair.
3. Some Cracks Deserve Closer Attention
Concern increases when cracking occurs in structural members or develops in a pattern associated with significant movement.
Examples include diagonal cracking around doors and windows, substantial cracks in beams or columns, cracking associated with visible foundation settlement, separation between structural elements, and cracks accompanied by noticeable distortion of floors, walls or openings.
A crack that continues to widen is particularly important.
Doors suddenly refusing to close, floors developing noticeable slopes, walls separating at junctions or several cracks appearing together may provide additional clues that the problem extends beyond the surface finish.
In such circumstances, simply filling the crack is not an adequate response.
4. Crack Width Matters, But It Is Not the Whole Story
It is tempting to judge seriousness by width alone: a tiny crack must be harmless while a large crack must be dangerous.
Engineering assessment is more nuanced.
The location, orientation, depth, pattern and progression of the crack can be just as important as its width.
A relatively narrow crack occurring at a critical location in a structural member may warrant investigation, while a more visible crack confined to plaster may have little structural significance.
The crack therefore has to be considered within the behaviour of the structure as a whole.
5. The Pattern Can Tell a Story
Cracks often leave clues about the forces or movements that produced them.
A diagonal crack may suggest a different mechanism from a vertical one. Repeated cracks occurring at similar positions may indicate systematic movement. Fine interconnected surface cracks may point towards shrinkage or finishing problems.
The surrounding construction is equally important.
What materials meet at the cracked location? Is there a beam, column, opening or foundation below it? When did the crack first appear? Was there recent construction nearby? Has the building use or loading changed?
The crack itself is only one piece of the evidence.
6. Is the Crack Still Moving?
One of the most useful questions is whether the crack is active or dormant.
A dormant crack resulted from movement that has substantially stopped. An active crack continues to change because the underlying cause remains.
Where appropriate, cracks can be measured, photographed and monitored over time. Dates and crack widths can be recorded so that subsequent observations are compared with actual measurements rather than memory.
This simple exercise can reveal whether the situation is stable or developing.
7. Do Not Repair the Crack Before Understanding the Cause
The instinctive response to a crack is often to fill it, plaster over it and repaint the surface.
That may produce a beautiful wall for a few weeks.
If the underlying cause remains, however, the crack will often return.
More importantly, premature cosmetic repair may conceal useful evidence that would have helped determine what caused the cracking.
The correct sequence should therefore be:
Investigate the cause → assess its significance → address the cause where necessary → repair the crack.
Not the other way around.
8. When Should an Engineer Be Consulted?
Professional assessment is advisable where cracks are widening, recurring or appearing suddenly; where they occur in important structural elements such as beams or columns; where there are signs of foundation movement or significant deformation; or where the cause simply cannot be confidently established.
An engineer will normally consider much more than the crack itself. The structural arrangement, foundation conditions, loading, construction history, surrounding defects and progression of the cracking may all form part of the assessment.
In some cases, monitoring may be sufficient. In others, further investigation, testing or structural intervention may be necessary.
Conclusion
Cracks are common in buildings, and their presence should neither automatically cause alarm nor automatically be dismissed.
The sensible response lies between those two extremes.
Observe the crack. Consider its location and pattern. Establish whether it is changing. Look for associated signs of movement. And where its significance is uncertain, obtain competent professional assessment before carrying out cosmetic repairs.
A crack should not be judged by how frightening it looks, but by what caused it and whether that cause is still active.Eng. Benson Kioko Muange
Civil/Structural Engineer
Managing Director, Mutwii Engineering & Management Consultants Ltd.
31 August 2026