When should I be worried about cracks in walls?

It’s very common to find cracks in walls, and in many cases, they are purely cosmetic and nothing to worry about. However, some cracks can indicate more serious underlying structural issues. Knowing the difference is key to determining when to be concerned and when to simply patch and paint.

Here’s a guide to help you assess wall cracks and when to be worried:

When to Be Worried About Wall Cracks:
The following characteristics often indicate a more serious underlying problem that requires professional assessment:

Width and Progression:

Wider than 5mm (about 1/4 inch):
Cracks that are significantly wider than hairline cracks are more likely to be structural.
Getting wider or longer over time:
If you can see the crack visibly expanding or new cracks forming in the same area, it’s a red flag. Mark the ends of the crack with a pencil and the date, and measure its width periodically.
Goes through the wall:
If you can see daylight through the crack, or it appears on both the interior and exterior of the wall in the same location, it’s a strong indicator of significant structural movement.

Pattern and Direction:

Diagonal cracks (especially “stair-step” cracks):
Cracks that run diagonally or follow the mortar lines in a stepped pattern on brick or block walls are often a sign of uneven settlement or foundation movement. These are among the most concerning.
Horizontal cracks:
While less common, horizontal cracks, especially in basement walls, can indicate significant pressure from the soil outside (hydrostatic pressure) or issues with wall ties.
Vertical cracks (multiple or widening):
While a single, thin vertical crack can be harmless (e.g., plaster drying), multiple vertical cracks on the same wall, or a widening vertical crack, can suggest foundation issues.

Location:

Around doors and windows:

Cracks in walls that radiate diagonally from the corners of door and window frames are often linked to differential settlement or problems with the lintel (the support beam above the opening).

Load-bearing walls:

Cracks in walls that support the weight of the structure above them (load-bearing walls) are always more serious than those in non-load-bearing partitions.

Foundation walls:

Cracks in basement or foundation walls, especially horizontal ones, can indicate significant foundation problems.

Associated Symptoms:

Sticking doors or windows:
If doors and windows that previously operated normally now stick or are difficult to open and close, it suggests that the frame (and potentially the wall around it) has shifted.
Uneven or sloping floors:
Significant floor slopes or dips can be a sign of foundation movement contributing to wall cracks.
Gaps between walls and ceilings/floors:
If you notice new gaps appearing where walls meet the ceiling or floor, it indicates movement.
Visible bowing or bulging of walls:
This is a clear sign of significant structural distress and requires immediate attention.
Dampness or water ingress:
Cracks can allow water to enter the building, leading to dampness, mold, and further structural damage.

Sudden Appearance of Cracks in Walls:

If a significant crack appears suddenly, especially after a period of unusual weather (prolonged drought, heavy rain) or nearby construction activity, it’s a cause for immediate concern.
Common, Less Serious Cracks:
Many wall cracks are simply cosmetic and don’t indicate structural problems. These include:

Hairline cracks (less than 1mm wide): These are very fine cracks, often seen in plaster or drywall, that are usually a result of normal building settlement, plaster drying, or temperature/humidity fluctuations. They can be easily filled and painted over.
Vertical cracks in new builds: It’s common for new homes to experience minor settlement in the first few years, leading to thin vertical cracks that are generally harmless.
Cracks from old nail pops or drywall seams: These are superficial and easily repaired.
Cracks from thermal expansion/contraction: Materials naturally expand and contract with temperature changes, leading to minor cracks.

What to Do if You’re Worried:

If you observe any of the worrying signs mentioned above, it’s crucial to take action:

Monitor the Crack: For smaller cracks, draw a pencil line across the crack at a couple of points, noting the date. Check it regularly to see if it widens or lengthens. You can also use a tell-tale crack monitor (a simple device that shows movement).

Consult a Professional:

Structural Engineer: For any cracks that are wide, diagonal, horizontal, getting worse, or accompanied by other signs of structural movement, a structural engineer is the best professional to consult. They can assess the cause and recommend appropriate repairs.
Chartered Surveyor: A building surveyor (especially one who specializes in structural issues or subsidence) can also provide an initial assessment and advise on the next steps.
Foundation Repair Contractor: If the cracks are clearly related to foundation issues, a specialized foundation repair company may be needed.
Ignoring serious cracks can lead to more extensive and costly repairs down the line, and in severe cases, compromise the safety of the building. Early diagnosis and intervention are always best.