Evidence of structural movement and subsidence within a property
All houses crack sometimes. Very often cracks in old houses and old plaster walls are due to regular thermal and moisture changes in the structure and brickwork and are not a cause for worry. New plaster walls will often develop cracks too.
We’re here to help to explain what subsidence is, when you should be worried, and what you can do about it.
What is subsidence?
Subsidence occurs when one part of a building moves at a different rate to another. This is caused by a change in the ability of the ground below the foundations to support the weight of your house.
Often this is because the ground shrinks. If your house is very old, its foundations could also be shallow and encourage subsidence.
Subsidence can affect all types of house whether detached or mid terrace. However, cracks in a mid-terrace or semi detached house may not be subsidence, but could potentially be caused by work undertaken by your neighbour. For this reason, a Party Wall Agreement needs to be made for any work you or they might do that could affect neighbouring walls or foundations.
What’s the difference between subsidence and settlement?
Subsidence shouldn’t be confused with other ground movement types such as heave (upward movement of the ground beneath a building when soil expands); landslip (downward movement on sloping ground); and settlement (which usually happens within the first 10 years of a house or extension being built).
What can cause subsidence?
There are a number of things that can contribute to subsidence, with the most notable ones being:
- Tree roots: they absorb water from the soil beneath, leading to shrinkage and drying.
- Homes built on land with high water-bearing capacity: land with a high clay content is more susceptible to causing subsidence compared to well-drained ground like high chalk or gravel.
- Broken drains or underground water leaks: Drain problems and leaks can result in soil erosion. This can be exacerbated if tree roots infiltrate the damaged drains and cause further cracks in the pipework.
- Prolonged dry weather: the soil dries out while trees continue to extract water. Subsidence poses a greater risk of occurring during summer months compared to winter.
What is subsidence damage?
Subsidence will often create diagonal cracks that will be wider at the top than the bottom. They will be visible both inside and out and are likely to be found around 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. Single cracks in just one location, and fine cracks less than a couple of millimetres wide, are unlikely to be a cause for concern unless they worsen and get larger.
The effects of subsidence can be dramatic. The images here show what subsidence damage can look like.
How can I tell if cracks are getting bigger?
Remember, most houses have small cracks, especially if they are more than 30 years old. After all, a house is a solid box built on something soft that gets wet, dries out, gets hot and goes cold. In most cases, it is nothing to worry about and can easily be resolved. So, before you contact your insurer or even a chartered surveyor in Kent or London like Collier Stevens, a simple marking on your wall will help you assess whether the cracks on your wall are increasing over time. This will indicate if they are something you should have investigated further by a professional.
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 get in touch with our building surveyors in London and building surveyors in Kent for a single defect report.
Can subsidence be fixed?
Yes, but the cost of remedial work will vary depending on the cause of the subsidence. It is likely you will need to claim on your buildings insurance. After you’ve had a building survey, and if we find there is subsidence, you should notify your insurance company.
Your insurer will appoint a loss adjuster who may or may not visit and is likely to request a structural engineer report. 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. Insurers will not consider what remedial work may (or may not) be required until this process has completed.
Underpinning is often used to fix problems with subsidence where the cause of the problem cannot be eliminated; this means building new foundations underneath the existing ones.
Getting to the cause of the problem early is the best solution though – this means that repairs to your house foundations may not be needed at all. For example:
- If tree roots taking water from the soil are the cause of your subsidence, consider removal with the advice of a specialist.
- If there are leaking drains meaning there is too much moisture beneath your property, get them repaired.
Can subsidence be prevented?
It can take many years for subsidence to show any effects on your house. Unfortunately, it is difficult to prevent subsidence, especially if it is based on the soil type beneath your house.
Here are some of the things you can do to prevent subsidence:
- Plant trees at a distance from your property to avoid excessive water absorption from the soil.
- If trees are too close, consider pruning or removing them to prevent water depletion.
- Be cautious when removing trees, as disrupting the root system could worsen the issue.
- Seek professional advice before removing trees or shrubs suspected to be causal factors.
Conduct annual checks on your property, focusing on pipework, gutters, and drainage systems to prevent blockages and flooding.
How do surveyors check for subsidence?
Many householders become alarmed about cracks and worry unnecessarily. That is why it is essential for a diagnosis to be made by experienced building surveyors or engineers.
A chartered surveyor will review the pattern and location of cracking, consider external factors such as trees or drains and provide an accurate assessment.
Surveyors 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 is 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.
After a survey has indicated subsidence may be a likely cause for the cracks, you will need a structural engineer to produce a detailed report that will tell you the extent of any subsidence, what repairs are needed and how much they will cost.
Is subsidence dangerous?
Yes, if you have a level 5 crack.
However, to get to the point of level 5 without noticing over a period of time would be rare. By the time it got to this point, you and your neighbours would likely have been moved to temporary accommodation so it couldn’t pose a threat.
An immediate impact or earthquake might cause a level 5 crack immediately, and you should vacate the property.
Can you get a mortgage on a house with subsidence?
If a house is subsiding and the issue has not been resolved you are unlikely to get a mortgage on it.
If there is a history of subsidence that has been rectified, then it will be easier to get a mortgage.
When you are buying a house we always recommend a survey so that signs of subsidence can be spotted by a professional surveyor like us.
Should I buy a house with structural movement?
You could buy a house with structural movement.
If you buy a house that has historic subsidence that has been fixed with underpinning, it is likely the foundations will be very strong, so the risk is far less.
Whether you should buy a house that has current subsidence issues is completely up to you and your pocket.
Remember though, if you can’t get a mortgage you would need to be a cash buyer, or get a bridging loan. You would be responsible for repairing the issues out of your own pocket. Whether the cost of the house versus what you spend to repair it and its predicted value at the end is worth it, is for you to decide.
As we have said before – always get a chartered surveyor or structural engineer to assess the level of structural movement and what work might be needed to fix it.
Do you have to declare subsidence when selling a house?
Yes. If you are selling a house that has a history of subsidence, then you should inform the buyers and provide evidence of work completed to rectify it.
Full building surveys and single defect surveys
If you’re 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. We have surveyors in Folkestone and property surveyors in London, as well as building surveyors in Kent and Thanet. Get in touch to learn more about our building survey services.
Steven Way
Steven Way BSc MIHEEM MFPWS MRICS is the Practice Principal and is a Chartered Building Surveyor. With over 35 years as a practicing surveyor, Steve has a wealth of experience and expertise in both residential and commercial building surveying, party wall advice and disabled access auditing. He has also built his reputation as an expert witness.