“Help! My house is subsiding!”

We can’t tell you how many times in a month we get a call from a homeowner expressing concern about cracks in their walls.

“We’re worried our home is subsiding!” is the panicked cry. In fact, people often tell us their house has cracked ‘over the weekend’. It hasn’t. What has happened is that you suddenly start noticing cracks because you’re looking for them and assume that they are all new.

But fear not. Most houses crack – especially if they are more than 30 years old. After all it’s a solid box built on something soft that gets wet, dries out, gets hot and goes cold. There is many a cause of cracked walls, and subsidence is often the least likely. Don’t get me wrong, it is a very real risk for properties, but it may not always be the problem. Single cracks in just one location, and fine cracks and those less than a couple of millimetres wide, are unlikely to be a cause for concern unless they worsen and get larger.

Subsidence? Or settlement?

Subsidence should not be confused with ‘settlement’ which causes the cracks you see in new builds, or new extensions. These cracks can occur for many years after work has been carried out and often where the new work meets the original building. This should always be considered before you cry “subsidence” if you are worried about a new build, or your new kitchen or loft.

Subsidence occurs when one part of a building moves at a different rate to another as a result of a change in the ability of the ground below the foundations to support the weight of your house.  Most often this is because the ground shrinks.

The most common cause of this is tree roots, even tiny ones, which take water from the soil. Your home is more susceptible if built on land with a high water bearing capacity, such as clay content rather than well drained ground such as high chalk or gravel content. The other common cause of subsidence is a broken drain or other underground water leak which can cause soil to be washed away. This situation can be worsened if tree roots get into the broken drains, grow and the pipework cracks further. And everything is worsened in prolonged dry weather which causes the soil to dry out while trees continue to extract water, so subsidence has a greater risk of developing in the summer than the winter.

The extent and nature of cracks

Most surveyors and engineers don’t get too excited about small cracks. We use a crack size scale (below) when advising upon the extent and nature of cracking. This enables a consistent approach understood to other professionals.

  • 0 – Hairline cracks of less than about 0.1mm. These are classed as negligible. No action required.
  • 1 – Typical crack widths up to 1mm. Fine cracks that can be treated easily using normal decoration. Damage generally restricted to internal wall finishes. Cracks rarely visible in external brickwork.
  • 2 – Typical crack widths up to 5mm. Cracks easily filled. Recurrent cracks can be masked by suitable linings. Cracks not necessarily visible externally. Doors and windows may stick slightly and require easing and adjusting.
  • 3 – Typical crack widths are 5-15 mm, or there are several around 3 mm. These cracks require some opening up and can be patched by a mason. Repointing of external brickwork and possibly a small amount of brickwork to be replaced. Doors and windows sticking. Service pipes may fracture. Weather-tightness often impaired.
  • 4 – Typical crack widths are 15- 25mm, but it also depends on the number of cracks. Extensive damage which requires breaking-out and replacing sections of walls, especially over doors and windows. Windows and door frames distorted, floor sloping noticeably. Walls leaning or bulging noticeably and some loss of bearing in beams. Service pipes disrupted.
  • 5 – Typical crack widths are greater than 25mm, but it depends on the number of cracks. Structural damage that requires a major repair job, involving partial or complete rebuilding. Beams lose bearing, walls lean badly and require shoring. Windows broken with distortion. Danger of instability.

What should I do?

Firstly, don’t panic. Cracks caused by subsidence will often be diagonal and wider at the top than the bottom. They will be visible both inside and out and are likely to be found close to doors or windows, or where an extension joins the house.

Have a good look at the cracks and see if there is a pattern or system of cracking. Walls crack in their weakest places – usually at door and window openings. If there is a subsidence problem, these will often go out of square so check that they still open and close properly.

Cracks may also occur where walls meet ceilings and on internal walls above doors. Look outside. Are there trees close by? Lift the inspection chamber lid – is the drain blocked or not draining quickly?

With a pencil, draw a line across the crack and a line at the end of the crack, write the date next to these lines. It’s crude but you can then check if there is ongoing movement – after all, big cracks start as small ones. If there is deterioration over time, then you should consult a building surveyor or structural engineer.

Only then do we suggest notifying your insurance company. They will appoint a loss adjuster who may or may not visit and is likely to request a report from your own surveyor. They may then want to monitor the cracks for deterioration before undertaking investigation works. This process can take a long time – a year is not unusual. Only then will insurers consider what remedial work may (or may not) be required.

So, what else could the cracks be caused by?

As I said, settlement is a big factor in many of the calls we receive, but they can also be caused by changes in seasons.

Dry weather in the summer and wet weather in the winter causes changes to the ground beneath your property and temperature changes cause woodwork, walls and ceilings to contract or swell. For these reasons, cracks often appear wider or narrower at different times of the year.  Thermal cracking is extremely common and rarely a concern in modern buildings. Movement joints are now built in (in fact it’s now a Building Regulations requirement) to allow a building to move without causing damage.

So many different factors can affect the formation of new cracks or changes to them. It is always best to get them checked if you are still worried after reading this or associated articles, just don’t immediately worry the worst-case scenario of subsidence has befallen your property.

Further Reading

For further reading, there is a great article from the Home Owners Alliance which explains fully what subsidence is, how to spot it and what all the potential causes could be: https://hoa.org.uk/advice/guides-for-homeowners/for-owners/subsidence/.

This article from Hunker also explains what you can do to monitor cracks yourself, before seeking professional help: https://www.hunker.com/12610789/how-to-determine-if-the-cracks-in-walls-are-serious.

Full building surveys and single defect surveys

If you are looking to buy a new house, look out for the signs of subsidence and ask if the homeowner has had any problems in the past. Always have a full building survey undertaken if you see the signs of subsidence too.