• Joe Bleasdale

PKS Explains: Why Do Buildings Crack?

Cracks in a building can look unsightly to property owners and potential buyers, and, if left untreated for a long time, or by not acting quickly enough, can begin to affect the structural integrity of the building. Here, we explain what might be behind it, and how we can advise on preventing it from affecting your assets.

Why do cracks form in a property?


The most common causes of cracking are:

  • Ground movement – buildings and structures move all the time due to natural processes beneath the foundations, such as soil movement through subsidence and settlement, clay shrinkage, land slips, and vibration frequencies. Most of this is undetectable, but if the material is unable to accommodate this movement over long periods of time, cracks can start to form.

  • Foundation failure – concrete and soft clay brick erode over time due to chemical contaminants.

  • Decay of the building fabric – woodworm and rust are the most common causes.

  • Moisture and damp – this can cause building materials to expand and contract, especially if vegetation is allowed to grow in faulty and / or damaged drains.

  • Thermal movement – this is when seasonal temperature increases, and decreases cause the building materials to expand and contract.

  • Inherent defects – structures built over 100 years ago suffer from normal wear and tear, and some suffer due to an absence of foundations.

  • Suspended structures such as floors that deform under load.

  • Tree rot growth.

How serious can cracking get?


The Building Research Establishment (BRE) classifies cracks in low-rise buildings according to length, width, and depth, as well as shape, and has provided a number system detailing what repair work might be required for each class.


0 = “Hairline cracks”

These cracks are the most common and least serious. They appear in most buildings, particularly in plaster, which is extremely sensitive to thermal movement. They are less than 0.1mm in width, and no repair action is required.


1 = “Fine cracks”

These are usually indistinguishable from hairline cracks but can be up to 1mm in width. Likewise, they are generally found on internal wall finishes, and are easily treated by painting over.


2 = “Easily-filled cracks”

These often appear as stepped cracks in joints of the building, such as beds of cement between bricks, which could indicate structural movement. They may not be visible from outside, but can be up to 5mm in width, and while they can be masked by suitable linings, door and windows may need to be adjusted to prevent sticking.


3 = “Cracks that require opening up”

Once a crack is as much as 15mm in width, this could be a sign that structural components have failed, and the building has significant stresses. These vertical cracks can affect the property’s weather tightness and service pipes, and external brickwork may need to be repointed or replaced.


4 = “Extensive damage”

When a crack reaches 25mm in width, windows and door frames start to become distorted, and walls lean and bulge. This may be an indication of foundation movement, particularly if a crack is larger at one end, which can be used to determine the direction of this movement. Repairing this would require breaking-out and replacement of sections of the wall.


5 = “Structural damage”

If a crack is larger than 25mm in width, this is when a property can start to become dangerous, particularly if they are horizontal, as this indicates that a wall may be failing completely. At this point, beams start to lose their baring, walls require shoring, and the structure becomes unstable. Major and costly repair works would be required to sort this out.

Initial steps to help resolve cracking


When it comes to buildings cracking, new builds may be more ahead of the game. While they have a natural advantage through not having been around as long, architects and engineers are designing new properties with preventative measures to keep cracks out in future, such as choosing materials that are resistant to movement, and flexible joints.


For buildings that have been around longer, it is important to know if the cracks are caused by the fabric of the building itself, for example, a poor grade of cement, or by an external factor such as thermal movement or subsidence. It should also be established whether the cracking is one-off or progressive, because if it deteriorates further unchecked, it could increase the cost of potential repairs.


Some cracks can be pasted over with cosmetic decoration and plastering, but if they are large, or increasing in size, in the case where they are being caused by problems that are likely to persist, they may require more invasive repairs. In many cases the building insurance on the property may cover the expense of repairing the damage. The insurance company may send a qualified engineer or surveyor employed by them to investigate the cause of the cracking and to establish if the cracking is progressive or not. This will involve an initial survey of the property, then a series of monitoring the cracking over a period of time (usually 6 to 12 months). This is all dependent on the type of policy you have.


Prince Krofa & Sons surveyors can help with an independent detailed report in understanding the causes of cracking and recommend effective remedies. If you are struggling to contain cracks in your property, we thoroughly recommend seeking expert advice.


To contact us and / or book a survey, visit this page. You can also sign up to our newsletter, and follow us on Facebook, Instagram, and LinkedIn to read more about our services and recent findings.