Subsidence and Structural Movement: How to Tell the Difference

If you’re a property owner, chances are you’ve come across subsidence before. Whether you’ve received the home buyer’s report for your prospective first home, or you’re buying the next development property for your growing portfolio, subsidence and structural movement are usually two of the most important issues a surveyor will look for in any property.

However, while they’re similar, it’s important to note that subsidence and structural movement have key differences, and making sure you identify the correct issue is essential to ensure you repair any defects correctly without accidentally worsening them.

In this blog, we’ll help you understand the difference between subsidence and structural movement, what causes each issue, and how our surveyors diagnose these issues within a property.

What Is Subsidence?

Subsidence is the sinking or settling of the ground beneath a building’s foundations. Subsidence often occurs over a long period of time, where a building’s foundations progressively sink deeper into the ground.

Subsidence can be caused by several different factors, including water damage, trees, inadequate drainage, or clay soil shrinkage. It can also be caused by the quality of your foundations, and how well the ground was compacted during construction. Our companion blog, What is Subsidence?, goes into greater detail about subsidence and what causes it.

What Is Structural Movement?

Where subsidence is the movement of the building due to the ground it’s built on, structural movement is movement from within the building itself.

Structural movement is often caused by a failure within a structural component. Lintel and wall tie failure can both compromise the structure of a building. Often, this is the result of defects such as timber decay or penetrating damp, which cause lintels or wall ties to deteriorate. This then allows for movement within the structure.

Why Homeowners Often Confuse Subsidence with Structural Movement and Settlement

Homeowners often confuse subsidence with structural movement and settlement, as their symptoms often overlap.

Settlement happens when a building’s weight compresses the ground slightly after construction. This is expected in almost all properties, especially older ones. Settlement often reaches a natural stopping point within the first few years of construction, but during this period small hairline cracks can form, often around openings like doors or windows. Settlement can also be seen as movement without consequence, as the issues associated with it are usually cosmetic, and do not require extensive repairs besides redecoration to remedy a crack.

Conversely, both structural movement and subsidence involve a greater degree of movement. In the case of subsidence, the property moves along with the ground. In cases of structural movement, the movement is caused by defects in the structure itself, while the ground remains stable.

In both cases, cracks, sticking doors and windows, and sloping floors can all be visual symptoms of movement within a building. This means that misdiagnosis is often very common, and can prove costly if you repair a property incorrectly.

The key takeaway is this: All subsidence is movement, but not all movement is subsidence. Most movement seen in UK homes is structural, and therefore repairable.

The Key Differences Between Subsidence and Structural Movement

To illustrate how similar the symptoms of subsidence and structural movement are, we’ve created a table below:

As you can see, it can be difficult to tell the difference between both issues at first glance. Unless a defect is isolated to one area of your property, such as structural cracking or bulging brickwork, you can easily mistake subsidence for structural movement, or vice versa.

Crack Patterns That Suggest Subsidence

One way that you can tell the difference between subsidence and structural movement is the patterning of cracks within a property.

Subsidence cracking often appears diagonal and tapered (stepped), with one side wider than the other where part of a property has sunk more. Subsidence cracks also tend to appear on both sides of a wall, and a crack outside a property will often be mirrored on the interior wall. Another factor is that cracking may run through bricks themselves, rather than the mortar joint between brickwork.

If left untreated for long enough, subsidence cracks can also show widening or narrowing depending on the season. This usually occurs where the ground swells and settles through the seasons. Subsidence cracking also often expands across the full elevation of a wall.

Crack Patterns That Suggest Structural Defects

In comparison to subsidence cracking, structural defects often show their own form of cracking.

In cases of structural movement, cracking is often horizontal or tapered, and is usually found above openings such as windows or doors. These cracks often from within the mortar joint, rather than the bricks themselves.

Another symptom of structural movement is bulging or bowing walls. This is often the result of cavity wall tie failure, causing one leaf of a cavity wall to weaken under the weight of the structure above it.

Another factor in structural cracking is the location of a defect. Often, cracking from structural movement is isolated to a specific defect and elevation (for example, cracks around a window or sinking of some floorboards in one floor but not another).

Why Lintels, Wall Ties, and Timber Decay Are Often Mistaken for Subsidence

Lintel damage, wall tie failure, and timber decay are mistaken for subsidence because they all cause cracking. We often associate subsidence with cracks by default, without having the symptoms of cracking checked before coming to that conclusion.

In the case of lintels, repair or replacement will likely resolve the issue of movement within a structure. This may also involve repairing the defect(s) around an opening to prevent a lintel from deteriorating again.

Similarly, cavity wall tie replacement can prevent the collapse of the leaves of a cavity wall. In extreme cases, it might be necessary to support the upper elevations of a building to allow for a wall to be rebuilt alongside installing new wall ties, while repairing any defects that may have caused the original wall ties to fail.

Finally, timber repairs will likely be required in cases of timber decay. This might only require fungicidal treatment in the case of minor decay, but could require splicing or complete replacement of structural timbers if a case of wet rot or dry rot is severe enough to compromise the integrity of a building.

How Professionals Diagnose the Difference (What a Survey Looks For)

Upon visiting a site, a surveyor will often require access to a full property to ensure a thorough and complete structural repair survey can take place. They will often look for the following signs to correctly identify whether cracking is down to structural movement or subsidence:

• The location of cracking within a property.
• The pattern, width, and progression of these cracks.
• The location of any external defects and moisture sources that might be causing the cracks to form, or causing the issue causing the cracks.
• The history of the property (when it was built, as well as when any major alterations were made such as extensions or remodelling).
• How long the defects have been monitored since they were first formed or noticed.

Building a property profile in this way allows a surveyor to correctly diagnose what type of movement defect a property is suffering from.

Why Incorrectly Assuming Subsidence Can Cost You Thousands

Whenever we see a crack, it’s easy to put the blame at subsidence’s door. However, doing so often leads to expensive and unnecessary structural engineer reports and insurance claims that go nowhere.

By assuming the worst, it also limits your options. Often, simpler repair solutions such as lintel repair, wall tie replacement, or crack stitching are adequate for repairing damage caused by subsidence, without the need for demolishing and rebuilding sections of a structure.

When diagnosing your property, it’s always best to have a structural repair surveyor assess your property in the first instance. Structural repair surveys are often more cost-effective than extensive repairs, and will provide a diagnosis and ideal treatment bespoke to your property or situation.

What to Do If You Notice Cracks or Movement in Your Property

If you notice cracks or movement in your property, don’t fill and monitor them blindly. Book a specialist structural repair survey to have your property professionally assessed. Early diagnosis of an issue opens your repair options while preventing major rebuilding costs.

FAQs

How do I Know if Cracks are Subsidence?

Subsidence cracking often appears diagonal and tapered (stepped), can appear wider on one side, can appear on both sides of a wall, and may run through bricks rather than the mortar joint.

Are all Wall Cracks Caused by Subsidence?

No. Subsidence causes cracks, but cracks can be caused for several other reasons, including structural movement, external defects, or settlement.

Can Structural Movement be Repaired?

Yes, structural movement can be repaired in several ways. Common repair methods include lintel repairs, crack stitching, or cavity wall tie replacement. You should have your property surveyed by a structural repair specialist prior to beginning any repair work to ensure the issue has been diagnosed correctly.

Does Subsidence Always Affect Foundations?

Yes, subsidence typically affects the foundations of a property. In severe cases, subsidence cracking can extend across several elevations of a property.

Who Should Assess Cracks in my House?

You should have a structural repair surveyor assess and diagnose any significant cracks in your property. If your property is suffering from the effects of structural cracking, you can book a survey to have one of our specialists attend your property.