Subsidence Cracks: All You Need to Know

Discovering cracks in the walls of your home can be unnerving. For many, a crack running along an internal wall will immediately raise concerns about the stability of their home. While not every crack will be a sign of serious structural problems, certain types of internal subsidence cracks are an early warning sign that your home’s foundations may be shifting.

Understanding the difference between harmless hairline cracks and more serious subsidence cracks inside your home is essential. In this post, we explor the different types of cracks which can be a sign of structural issues and what steps you should take if you suspect you have interior wall subsidence cracks.

5 Signs Your Home Might Have Subsidence

Before we get into the fine details, here are 5 common signs that your home may have subsidence issues. If in doubt, call a professional. Our subsidence repair method, using resin injection, means repairs can be carried out in as little as a day.

	Reason	Subsidence Ltd advice on action needed
1	You see cracks internally and externally in the same part of the property, particularly at the base of the property	We would advise that you contact us and we will triage your property to advise you on next steps.
2	You have sloping floors and the floor is a concrete raft or slab	We would advise that you contact us and we will triage your property to advise you on next steps. If your floors are timber then contact a local builder for further advice.
3	Your doors and windows are misaligned and are starting to jam.	We would advise that you contact us and we will triage your property to advise you on next steps. We will either help you or advise you to speak to a local builder once we have done the triage.
4	Your porch, conservatory or extension is moving away from the main part of the property.	We would advise that you contact us and we will triage your property to advise you on next steps.
5	You are seeing cracks upstairs at ceiling level, but no signs downstairs.	We would advise that you either speak to a local builder or a strutural engineer first for advice. If they state it is subsidence then please contact us for further advice!

How to Identify Internal Subsidence Cracks

Internal wall cracks can vary in size, shape and location. Some will be harmless and nothing to worry about, caused by natural plaster shrinkage, damp drying or even temperature changes. However, subsidence cracks are usually quite distinctive and here’s what to look for:

Location

The position of a crack will give you a good idea of its cause. For example, subsidence cracks on internal walls are often found near structural weak points, such as window frames and door frames or ceiling corners. If you notice several cracks running along the same wall, this can also be an indication of structural movement rather than a cosmetic issue.

Direction

The angle of a crack is another key factor. Diagonal cracks are often a common sign of structural damage, as well as cracks with a stepped pattern. Whereas, straight vertical cracks are more typical of plaster drying. If you see zigzagging or branching cracks, they may be early internal signs of subsidence, and it’s important not to ignore them.

Size

The size and width of a crack can also influence whether it’s serious. Narrow, hairline cracks under 5mm are usually less concerning and often just cosmetic. However, larger cracks that are wider than a 10p coin may be a sign of subsidence. Any cracks that continue to grow over time are particularly worrying as they may suggest your property’s foundations are shifting.

Appearance

The appearance of a crack is the final giveaway. When it comes to subsidence cracks inside the home, they often look irregular when compared to surface cracks from minor plaster issues. They are often wider at the top than at the bottom and can be jagged or stepped. A big red flag is if cracks reappear after being filled or decorated, especially in the same location.

Categories of Cracks

The Building Research Establishment (BRE) has identified six categories of cracks which linked the width and number of cracks to the type of repair that was appropriate.

Damage categories with descriptions of typical damage. Ease of repair in italics.

0 – Hairline cracks of less than about 0.1 mm which are classed as negligible. No action required.

1 – Fine cracks that can be treated easily using normal decoration. Damage generally restricted to internal wall finishes; cracks rarely visible in external brickwork. Typical crack widths up to 1 mm.

2 – Cracks easily filled. Recurrent cracks can be masked by suitable linings. Cracks not necessarily visible externally; some external repointing may be required to ensure weather-tightness. Doors and windows may stick slightly and require easing and adjusting. Typical crack widths up to 5 mm.

3 – Cracks that 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. Typical crack widths are 5 to 15 mm, or several of, say, 3 mm.

4 – 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, some loss of bearing in beams. Service pipes disrupted. Typical crack widths are 15 to 25 mm, but also depends on number of cracks.

5 – 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. Typical crack widths are greater than 25 mm, but depends on number of cracks.

To quote the BRE: “In general, categories 0, 1 and 2 with crack widths up to 5 mm can be regarded as ‘aesthetic’ issues that require only redecoration. Categories 3 and 4 can generally be regarded as ‘serviceability’ issues, that is, they affect the weathertightness of the building and the operation of doors and windows. Category 5 presents ‘stability’ issues and is likely to require structural intervention.”

You can access the full text on the BRE page: Assessing cracks in houses.

What To Do Next

If you are worried about cracks in your property or home, it’s important to take action. Check out our blog on how to fix subsidence cracks. Ignoring internal subsidence cracks will likely result in further damage and more costly repairs in the future. Here’s what you should do next:

Monitor the cracks – Keep an eye on their width, direction, and length. You can use remote laser monitoring tools like SUBCHECK to track any changes too.

Check for additional signs – Look for other common signs of subsidence, such as doors and windows sticking, sinking or sloping floors, or skirting boards separating from walls.

Get professional advice – If cracks are wider than 5mm, diagonal, or getting worse over time, contact a specialist like Subsidence Ltd.

At Subsidence Ltd, we specialise in identifying and repairing subsidence cracks, and we have decades of experience. Our engineers know how to spot the early internal signs of subsidence and can stabilise your foundations with cutting-edge resin injections. We offer full inspections and surveys to determine the cause of the cracks, using professional monitoring methods to track movement and confirm whether you have subsidence issues.

Our 10-year warranty can provide peace of mind and ensure your property remains stable for years to come. This warranty reflects the confidence we have in the resin injection method and the standard of service we provide.