MET SURVEYORS

What Is Subsidence?

 

Subsidence generally refers to downward movement of the ground supporting the foundations of a building.

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If part of the ground beneath the property moves or shrinks, the foundation above it may also move.

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This can lead to differential movement within the structure and cracking may develop.

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Possible causes can include:

• Shrinkable clay soils

• Prolonged hot and dry weather

• Mature trees and vegetation

• Leaking underground drains

• Changes in ground conditions

• Poorly compacted ground

• Previous excavation or disturbance

• Inadequate foundations

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Subsidence usually affects part of the building rather than causing the whole property to move uniformly.

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That uneven movement is often what creates visible cracking.

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What Is Settlement?

 

Settlement usually refers to movement that occurs as a building or part of a building adjusts following construction.

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New foundations may compress the ground beneath them slightly.

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Materials may dry and shrink.

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Different parts of a building may settle at slightly different rates.

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A small amount of settlement can therefore be normal, particularly in:

• New buildings

• Recently constructed extensions

• Loft conversions

• Properties that have undergone major alterations

• Areas where new foundations have been introduced

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Settlement does not automatically mean there is a defect.

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The important question is whether the movement is minor and stable or whether it is continuing.

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What Is the Main Difference?

 

The simplest distinction is:

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Settlement usually relates to the building adjusting after construction.

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Subsidence usually relates to movement in the ground supporting the building.

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However, real buildings do not always fit neatly into one category.

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For example, an extension could settle because its foundations are new, while a different part of the property could move because of changes in the soil.

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This is why the pattern and history of the movement need to be considered.

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What Does Settlement Cracking Look Like?

 

Settlement cracking can vary considerably.

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Possible signs include:

• Fine cracks around new extensions

• Cracking at the junction between old and new construction

• Minor cracks around openings

• Small cracks in plaster

• Localised cracking following building works

• Hairline cracks appearing during the first years after construction

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Minor settlement cracks are often relatively stable.

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If the cracking stops changing, it may simply require repair and redecoration.

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However, if cracks continue to widen or repeatedly reopen, further investigation may be advisable.

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What Does Subsidence Cracking Look Like?

 

Subsidence can also produce many different crack patterns.

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Possible signs can include:

• Diagonal cracks around doors and windows

• Cracks wider at one end

• Cracking visible internally and externally

• Cracks becoming progressively wider

• Previous repairs reopening

• Distortion around windows or doors

• Doors and windows beginning to stick

• Movement affecting several connected areas

• Cracks concentrated in one part of the building

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No single crack shape proves that subsidence is occurring.

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The surrounding evidence is just as important.

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Why Is Differential Movement Important?

 

The most significant cracking often occurs where one part of a building moves differently from another.

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This is known as differential movement.

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It can happen for many reasons.

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For example:

• One foundation may be deeper than another

• An extension may have been built many years after the house

• One section may be affected by tree related ground movement

• Different soils may exist beneath different parts of the property

• One part may have been altered structurally

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Cracks can develop where the movement between these sections becomes concentrated.

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Settlement Around Extensions

 

Cracks around extensions are particularly common.

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An extension may have:

• Different foundations

• Different materials

• Different construction methods

• Different loading

• Different ground conditions

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It may therefore move differently from the original property.

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Some initial settlement may occur without indicating a serious structural problem.

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However, cracking should be investigated where it is:

• Wide

• Progressive

• Visible inside and outside

• Associated with distortion

• Reopening after repair

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Can Settlement Happen Years Later?

 

Yes, although movement occurring many years after construction may require closer investigation.

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Normal initial settlement usually happens relatively early in the life of a new structure.

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If significant new movement starts many years later, possible causes may include:

• Changes in ground conditions

• Drainage problems

• Tree growth

• Structural alterations

• Deterioration

• Localised foundation problems

• Subsidence

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The age of the cracking can therefore provide useful evidence.

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Can Subsidence Stop on Its Own?

 

Sometimes movement may stabilise.

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For example, ground conditions may change seasonally.

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Historic movement may have stopped many years ago.

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However, you cannot assume that a crack has stabilised simply because it is not visibly changing from day to day.

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In some cases monitoring may be necessary to establish whether movement is continuing.

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Is Settlement Less Serious Than Subsidence?

 

Not always.

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Minor settlement is often less concerning than active subsidence, but severe settlement can still cause significant structural problems.

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Likewise, some historic subsidence may have stabilised and no longer be active.

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The seriousness depends on:

• Extent of movement

• Cause

• Whether movement is continuing

• Parts of the building affected

• Foundation conditions

• Structural consequences

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The terminology alone does not determine the level of risk.

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What About Heave?

 

Heave is another form of ground movement.

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Instead of moving downwards, the ground moves upwards.

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This can happen where soil gains moisture and expands.

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In clay soils, for example, removing a large mature tree can sometimes allow the ground to regain moisture and expand.

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Heave is different from both settlement and subsidence, but it can also lead to cracking and structural movement.

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What About Thermal Movement?

 

Not all movement originates in the foundations.

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Building materials expand and contract as temperatures change.

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This can cause cracking, particularly where:

• Long walls lack movement joints

• Different materials meet

• Extensions join older buildings

• External temperatures vary significantly

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Thermal movement is another reason why cracks should not automatically be labelled as subsidence.

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Can Poor Construction Cause Similar Cracks?

 

Yes.

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Cracking can result from:

• Inadequate lintels

• Poor masonry bonding

• Defective structural alterations

• Inadequate foundations

• Lack of movement joints

• Poor workmanship

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These defects may resemble movement associated with settlement or subsidence.

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A proper inspection therefore considers the construction as well as the crack itself.

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How Can You Tell Whether Movement Is Active?

 

Active movement may be suggested by:

• Cracks becoming wider

• Cracks extending further

• New cracks appearing

• Previously repaired cracks reopening

• Increasing distortion

• Doors or windows becoming progressively harder to operate

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Photographs can help establish whether visible changes are occurring.

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In some cases, formal crack monitoring may be recommended.

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Should You Measure the Cracks?

 

Recording the width of a crack can be useful, but measurements should be treated carefully.

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Movement can be affected by:

• Temperature

• Seasonal moisture changes

• Decoration

• Plaster movement

• Different measuring points

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A single measurement tells you little on its own.

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What matters more is whether a consistent pattern of change develops over time.

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Does the Age of the Property Matter?

 

Yes.

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Older properties may contain historic cracks that have been present for decades.

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Victorian and Edwardian buildings may have experienced minor movement over a long period.

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A crack that has remained unchanged for many years may be less concerning than one that has recently appeared and is widening.

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Similarly, new buildings may experience some initial settlement.

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The age and history of the building should always form part of the assessment.

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When Should You Be Concerned?

 

Professional advice should be considered where:

• Cracks are widening

• Several cracks have appeared

• Movement is visible internally and externally

• Doors or windows are sticking

• Floors appear distorted

• Repairs repeatedly reopen

• Cracking affects an extension

• Several areas of the property are affected

• Movement appears to be continuing

• You are concerned about possible subsidence

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Which Survey Is Appropriate?

 

The correct survey depends on how extensive the concern is.

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Structural Survey

A wider Structural Survey may be appropriate where:

• Cracking is widespread

• Several elevations are affected

• Significant distortion is visible

• There are multiple possible causes

• Subsidence is suspected

• The overall structure requires assessment

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A broader inspection allows the property and pattern of movement to be considered together.

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Specific Issue Survey

 

Where there is one clearly defined area of concern, a Specific Issue Survey may be more appropriate.

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Examples include:

• One crack above a window

• Cracking to one wall

• Movement around a bay

• Cracking between an extension and the house

• A localised structural defect

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Our Specific Issue Survey concentrates on that particular concern and includes a written report with recommendations.