Help! There are cracks in my building

What does it mean and what do I do about it?

The first thing you need to do is not panic! There are numerous reasons that can cause a building to crack, and it is unlikely that cracking needs to be dealt with immediately, as most houses are very robust.

The Building Research Establishment categorises cracking into six different categories, ranging from hairline cracks of less than 0.1mm and large structural cracks of greater than 25mm.

Small cracks are generally nothing to be concerned about. Typically, we would take several larger cracks over 3mm more seriously, and we would become concerned that cracking might need structural remedial work if we identified cracks in excess of 25mm wide, as this is normally where the real trouble starts.

In our experience, cracking can be caused by a number of factors including thermal movement, freeze/thaw action, impact damage, settlement, subsidence or ongoing movement. 

Here, we draw on the expert knowledge of our team at Harrison Clarke to look at each of these causes of cracks in more depth and explain our recommended action in each case.


Thermal movement

This is, by far, the most common cause of cracking that we see when we are carrying out building surveys. Thermal movement is particularly prevalent in new or refurbished buildings, especially those with a lot of timber components. Cracks caused by thermal movement are usually hairline in nature, and are caused by the natural expansion and contraction of building elements.

A crack in the brick wall of a building.

Often, but not always, this type of cracking is worse at upper floor levels. This is because buildings are normally less rigid on upper floors as they have less weight holding them in place. It is, therefore, very common to see this type of crack appearing extensively in loft conversions, particularly as new building materials are acclimatising to being in a heated environment.

This type of cracking can also be exacerbated by high moisture levels, as this can affect the way that finishes perform.


It is rare that structural work will be required to fix cracks like this – we simply advise that they are filled before your next redecoration.


Freeze/thaw action

This type of crack tends to develop externally and is most common through the mortar joints in the brickwork. If the mortar pointing on your house is old and slightly degraded, it will take on more water than it should, which can freeze in the joints between the bricks. As this can dislodge the mortar pointing, and look quite dramatic, it can cause alarm but it is usually superficial and not as bad as it looks.

Sometimes, the freeze/thaw effect can also cause cracks in the actual brickwork.

Our first remedy for addressing this type of crack, unless we identify other contributing factors, is usually to repoint the affected area of brickwork in a suitable mortar, and to replace any cracked bricks. Repointing can also address other issues, such as internal damp and humid environments.


Impact damage

It can be hard to diagnose ‘impact damage’ from a one-off inspection. Of course, if a property owner has driven their car through the porch, the cause of the impact damage will be very clear! In less obvious circumstances, a little detective work and quizzing the homeowner about recent events can usually find the cause, for example we often see quite significant cracking resulting from the vibration during the installation of windows and doors. Often, this cracking doesn’t worsen for years, and it causes no problems but, due to freeze/thaw action, this type of cracking can sometimes deteriorate, allowing water ingress or internal cracking to develop. 

Sometimes, when it is not clear if damage has been caused by impact, we recommend a period of monitoring to ensure that the problem is not caused by something more serious, such as movement to the foundations. Without this monitoring, we cannot be absolutely sure of the cause of the movement but we do, of course, use our experience to estimate the most likely cause. We set out the risks of each of these potential causes and detail what type of work might be required in the future.

This type of cracking can be almost any size, and we advise on remedial work accordingly, depending on the specific case.



Settlement cracking is caused by sections of the building’s foundations moving at a slightly different rate to the rest of the building, before coming to a rest in a new position. We often see this happening where there have been historical drainage defects previously fixed, or after a new extension has ‘bedded in’.

As with many cracks, we cannot one hundred per cent confirm that a building has settled, without first observing it over a monitoring period. The key issue with settlement is ensuring that the cracking has stopped worsening. When we are sure that the building has stopped moving, we can address its knock-on effects, such as addressing the cracking and adjusting the windows and doors.


Subsidence or ongoing movement

Subsidence cracking is similar to settlement cracking, but with one crucial difference – the building is continuing to move. This is common if, for example, part of the building is slowly migrating down a slope, or if the causes of movement have yet to be addressed, such as the drainage, or large tree roots causing changes in the soil conditions.

Often, this type of movement will create the largest cracks, and can sometimes be responsible for cracks greater than 25mm wide, which is a serious cause for concern. A common remedy for subsidence can include underpinning to the foundations, which is expensive work that will definitely need a construction professional to take care of it for you.

Another type of ongoing movement can be caused by roof spread – where weaknesses in the roof structure can cause outer walls to bulge. This is often the result of replacing a lightweight slate roof with concrete tiles and will require roof strengthening works before the cracking can be addressed. These roof strengthening works can be expensive and tricky to fix so, again, it is a job for a construction professional.


How do I know whether my property has settlement or subsidence?

Following our recent heatwave, more people than usual have contacted us with queries relating to cracks in buildings which appear to be caused by movement that is a hybrid of settlement and subsidence. This seems to be driven by soil drying out and contracting, allowing foundations to move in unexpected ways. We even viewed one building, underpinned following the 1976 heatwave, that has now cracked in exactly the same areas as it did during the 1976 heatwave. We confirmed this by comparing the new cracking with the engineer’s report from nearly 50 years ago.

If you think that your cracking might be connected to the heatwave, we suggest that you wait for a couple of months, and a decent amount of rainfall, to see if your building returns to normal, which we would expect to be the case for many buildings. Whilst you are likely to be left with some minor cracking, this is most likely to be cosmetic only and not something that needs structural repair. 

So, if the cracking only appeared soon after the heatwave started, and has not developed into cracks that are at least 3mm wide, sit tight for a while. However, if waiting will cause you a lot of worry, do contact a surveyor, like our team at Harrison Clarke, straight away to give you peace of mind.


I am worried about cracks in my property. Who can I contact for an expert opinion?

If you have any concerns about the cracks in your building, and what might be causing them, our expert and experienced team of Chartered Building Surveyors will be very happy to help you. They are all well versed in building pathology and will be able to assess the cause of your crack, or direct any further investigation as necessary.

Call them on 023 8155 0051, or email us at so that we can talk through your situation and answer any questions you may have.

At the time of writing, we have a total of 59 reviews across Trustpilot and Google. We are proud to say that they are all 5 star ratings across the board.

Tim Clarke, Director at Harrison Clarke chartered surveyors.

About the author

Tim Clarke,


Tim set up Harrison Clarke Chartered Surveyors in July 2017 following a series of public and private sector surveying roles, having previously worked for the University of Cambridge, Rund Partnership, Goadsby, and CBRE. 

Tim has degrees in building surveying, construction project management, and business administration.

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