MET SURVEYORS
Expert Advice on Property Matters
House Subsidence: Causes, Warning Signs and What to Do Next
Subsidence Can Be Serious, But Not Every Crack or Uneven Floor Means Your House Is Subsiding
House subsidence is one of the most worrying structural problems a homeowner can face.
Cracks appearing in walls, doors beginning to stick, floors becoming uneven or an extension appearing to move can all raise concern that the ground beneath the property is changing.
However, these symptoms can also be caused by settlement, thermal movement, poor construction, drainage problems, structural alterations or defects in the floor itself.
The first step is therefore not to assume the worst.
The important questions are:
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What has moved?
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Why has it moved?
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Is the movement still active?
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Is the problem localised or more widespread?
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What level of investigation is justified?
Met Surveyors can advise whether the appropriate starting point is a Specific Issue Survey from £695 + VAT, a Crack Monitoring Programme from £1,395 + VAT, or a wider Structural Survey.
What Is House Subsidence?
Subsidence generally refers to downward movement of the ground supporting part of a building.
If the ground beneath a foundation moves, the foundation above it may also move.
This can lead to differential movement within the structure and visible defects such as:
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Wall cracking
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Distorted openings
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Sloping floors
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Movement around extensions
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Gaps around frames
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Reopening previous repairs
Subsidence often affects one part of a building rather than causing the whole property to move evenly.
It is this uneven movement that can create visible cracking and distortion.
What Causes Subsidence in Houses?
There are several possible causes.
Common factors include:
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Shrinkable clay soil
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Prolonged hot and dry weather
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Mature trees and vegetation
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Damaged or leaking drains
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Poorly compacted ground
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Inadequate foundations
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Previous excavation
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Historic structural alterations
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Different foundation depths
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Poorly constructed extensions
More than one factor can sometimes be involved.
Clay Soil and Subsidence
Clay soil can change volume as its moisture content changes.
During prolonged dry weather, clay can lose moisture and shrink.
Where a property is founded on shrinkable clay, this can sometimes contribute to foundation movement.
The risk may be greater where:
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Foundations are relatively shallow
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Mature trees are nearby
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Dry weather continues for a prolonged period
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Ground conditions vary across the site
However, the presence of clay does not mean that a property will automatically suffer from subsidence.
Trees and House Subsidence
Trees can influence ground moisture, particularly in clay soils.
A mature tree can draw substantial amounts of water from the surrounding ground.
Factors that may be relevant include:
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Tree species
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Height and maturity
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Distance from the building
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Root spread
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Soil type
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Foundation depth
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Location of cracking
A nearby tree does not prove that it is responsible for movement.
Where necessary, specialist arboricultural advice may be recommended.
Can Leaking Drains Cause Subsidence?
Yes, in some circumstances.
Damaged underground drains can affect the ground around foundations.
Leakage may soften or wash away surrounding material, depending on the local ground conditions.
Where movement occurs close to drainage runs, further investigation may be appropriate.
This can include a CCTV drain survey.
What Are the Warning Signs of House Subsidence?
Possible signs include:
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New diagonal cracks
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Cracks around doors and windows
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Cracks wider at one end
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Cracking visible inside and outside
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Previously repaired cracks reopening
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Doors and windows beginning to stick
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Gaps around window or door frames
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Sloping or sinking floors
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Cracked concrete floors
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Cracked screeds or tiles
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Movement between an extension and the original house
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Distortion to walls or openings
No single sign confirms subsidence.
The overall pattern needs to be considered.
What Do Subsidence Cracks Look Like?
Cracks associated with structural movement can vary considerably.
They may be:
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Diagonal
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Vertical
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Stepped through brickwork
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Wider at one end
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Visible internally and externally
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Concentrated around openings
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Reappearing after repair
The shape of the crack is only one part of the evidence.
Its age, location, width and whether it is changing are often more important.
Are Hairline Cracks a Sign of Subsidence?
Usually not on their own.
Hairline cracks are common in plaster and may result from:
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Drying shrinkage
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Decoration
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Temperature changes
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Plasterboard movement
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Minor settlement
More concern may be justified where cracks are widening, recurring or associated with other movement.
Cracks Around Doors and Windows
Openings are common locations for movement to become visible.
Possible signs include:
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Diagonal cracks from corners
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Cracks above lintels
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Cracks below windows
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Distorted frames
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Doors or windows sticking
Possible causes include settlement, lintel movement, structural alteration, differential movement and subsidence.
Sloping or Uneven Floors
Floor movement can also be an important sign.
Possible symptoms include:
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Floors developing a slope
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A noticeable change in level between rooms
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Localised sinking
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Concrete slabs cracking
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Screeds breaking up
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Repeatedly cracked tiles
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Gaps beneath skirting boards
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Doors dragging across the floor
However, floor movement does not automatically mean the foundations are subsiding.
A concrete slab may settle independently of the main walls, while suspended timber floors can move because of deteriorated joists or supports.
Cracked Concrete Floors
A cracked floor can result from:
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Shrinkage
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Poorly compacted fill
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Settlement beneath the slab
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Thermal movement
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Drainage issues
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Foundation movement
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Subsidence
Particular attention may be needed where:
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One side of the crack is higher than the other
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The floor has visibly dropped
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The crack is widening
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Wall cracking is also present
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Several connected areas are affected
Movement Between an Extension and the Main House
Extensions frequently move differently from the original building.
The extension may have:
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Different foundations
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Different foundation depths
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Different materials
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Different ground conditions
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Been built many years later
Cracking at the junction can therefore be caused by differential settlement without necessarily indicating major subsidence.
Wider or progressive movement should be investigated.
Subsidence After Hot Weather
Cracks may sometimes become more noticeable after prolonged dry weather.
This can be relevant where the property is built on shrinkable clay soil.
Possible signs include:
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New cracks after a dry summer
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Existing cracks becoming wider
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Movement close to mature trees
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Cracking concentrated in one part of the house
Hot weather is not itself proof of subsidence.
It is simply one factor that may contribute to ground movement.
Subsidence or Settlement?
Subsidence and settlement are different.
Settlement generally describes movement as a building or part of a building adjusts after construction.
Subsidence generally refers to downward movement of the ground supporting the foundations.
For example, a newer extension may settle slightly without the original house suffering from subsidence.
Understanding the distinction is important because the appropriate response can be very different.
Can Subsidence Stop?
Yes, movement can sometimes stabilise.
For example:
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Drainage may have been repaired
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Ground conditions may have changed
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Historic movement may no longer be active
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Seasonal movement may reduce
This is why evidence of previous cracking does not necessarily mean a property is still moving.
Where the position is uncertain, monitoring may be useful.
How Do You Know Whether Subsidence Is Active?
One inspection may identify signs of movement but not always establish whether the movement is continuing.
Possible evidence of active movement includes:
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Cracks widening
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New cracks appearing
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Previous repairs reopening
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Doors becoming progressively harder to open
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Increasing distortion
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Floors continuing to move
Where the position remains uncertain, a Crack Monitoring Programme may be appropriate.
What Is Crack Monitoring?
Crack monitoring records movement across selected cracks over time.
Monitoring gauges are installed and baseline measurements taken.
The same points are then measured during scheduled return visits.
This can help establish whether cracks appear:
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Stable
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Continuing to move
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Increasing
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Seasonal
Met Surveyors offers Crack Monitoring Programmes from £1,395 + VAT when upgraded during an initial Specific Issue Survey.
A standalone programme starts from £1,695 + VAT.
Why Start With a Specific Issue Survey?
For one localised concern, the most sensible starting point is usually a Specific Issue Survey from £695 + VAT.
This allows us to inspect the affected area and assess the likely cause.
Examples include:
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One diagonal crack
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One wall showing movement
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Cracking around one opening
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Movement around a bay
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Cracking between an extension and the house
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One localised floor problem
Monitoring may not be necessary.
If monitoring is recommended during that visit, the instruction can normally be upgraded while we are already on site.
Save £300 by Upgrading to Crack Monitoring on Site
Where monitoring is appropriate, the initial inspection can become the first stage of the monitoring programme.
This means we can establish the baseline while already at the property.
Specific Issue Survey: from £695 + VAT
Crack Monitoring Programme upgraded during the initial visit: from £1,395 + VAT total
Standalone Crack Monitoring Programme: from £1,695 + VAT
This saves £300 + VAT compared with arranging the monitoring programme separately later.
When Is a Structural Survey More Appropriate?
A wider Structural Survey may be more suitable where:
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Cracking affects several rooms
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Several elevations are affected
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Floors are visibly moving
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Several doors or windows are distorted
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Significant previous repairs have reopened
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There are multiple areas of movement
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The cause is uncertain
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There are wider concerns about the structure
This allows the property to be assessed as a whole rather than focusing on one localised defect.
What Further Investigation Might Be Required?
Depending on the evidence, further investigation may include:
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Crack monitoring
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Level monitoring
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CCTV drainage inspection
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Trial holes
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Foundation investigation
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Ground investigation
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Soil testing
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Arboricultural assessment
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Structural engineering input
Not every property requires every investigation.
The scope should always be proportionate to the evidence.
Does Subsidence Always Need Underpinning?
No.
Underpinning is only one possible structural remedy.
Other outcomes may include:
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Drainage repairs
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Tree management
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Monitoring
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Local structural repair
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Crack repair
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Foundation strengthening
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No major structural work where movement is historic and stable
The cause should be established before major structural work is considered.
What If the House Has Already Been Underpinned?
A previously underpinned property is not automatically a bad property.
The important questions are:
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Why was underpinning required?
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Which part of the house was affected?
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When was the work carried out?
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Who designed it?
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Was Building Control involved?
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Is documentation available?
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Was the property monitored afterwards?
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Has further movement occurred?
Good documentation can be very important when assessing historic structural work.
Buying a House With Subsidence
If you are buying a property with a history of subsidence or visible movement, try to obtain as much information as possible.
Useful documents include:
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Structural reports
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Building Survey reports
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Monitoring records
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Insurance documentation
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Drainage reports
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Arboricultural reports
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Underpinning records
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Building Regulation documentation
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Repair invoices and guarantees
Where the problem is unresolved, further structural investigation should ideally take place before exchange of contracts.
What About Insurance?
If you believe your property may be suffering from subsidence, check your buildings insurance policy and its notification requirements.
Where a historic claim exists, insurance documentation can provide useful information about:
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Cause
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Extent of movement
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Monitoring
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Remedial works
Met Surveyors provides independent structural advice but does not replace any investigation required by an insurer.
Should You Repair Cracks Straight Away?
Not always.
If a crack may be useful evidence of structural movement, it can be better to photograph and record it before carrying out cosmetic repairs.
Repeatedly filling a crack without understanding the cause can simply hide the symptom.
Where movement is uncertain, monitoring may be more useful before final repairs are carried out.
What Should You Do If You Suspect House Subsidence?
Start by recording what you can see.
Useful information includes:
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When you first noticed the problem
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Whether the cracks are changing
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Whether cracking is visible inside and outside
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Whether doors or windows are sticking
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Whether floors are sloping
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Whether there are mature trees nearby
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Whether drainage problems are known
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Whether cracks have been repaired before
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Whether extensions are affected
Take clear photographs.
Then seek advice about the appropriate level of investigation.
Which Service Do You Need?
For one localised structural concern:
Specific Issue Survey from £695 + VAT
For one localised concern where we need to establish whether movement is continuing:
Crack Monitoring Programme from £1,395 + VAT when upgraded during the initial visit
For widespread cracking, multiple affected areas, significant movement or broader structural concerns:
Structural Survey quoted according to scope
Concerned About House Subsidence?
You do not need to diagnose the problem yourself.
Send Met Surveyors:
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The property address
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Photographs of the cracking or movement
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A brief description of the problem
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When you first noticed it
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Details of any previous repairs
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Photographs of sloping or sinking floors
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Information about extensions
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Any previous structural or survey reports
We can advise whether the appropriate starting point is a Specific Issue Survey, Crack Monitoring Programme or wider Structural Survey.
