What is the Difference Between Settlement and Subsidence

When it comes to property issues, homeowners often encounter two terms that can cause confusion: settlement and subsidence. While both involve downward movement of a structure, they have distinct causes and implications.

Settlement occurs naturally in new buildings as the ground adjusts to support the weight of the structure. This process typically takes place within the first decade after construction.

Subsidence, on the other hand, happens when the soil beneath an existing building’s foundation moves or shrinks, causing the structure to sink.

Understanding the difference between settlement and subsidence is crucial for property owners and potential buyers.

Settlement is generally a normal part of a building’s early life, whilst subsidence can occur at any time and may indicate more serious structural problems.

Recognising the signs and causes of each can help in determining the appropriate course of action for maintaining a safe and stable property.

Understanding Ground Movement

Ground movement can significantly impact buildings and structures. Two common types are subsidence and settlement, which involve downward soil movement but have distinct causes and effects.

Defining Subsidence

Subsidence refers to the downward movement of ground beneath a building when supporting soil moves away. It often results from underground changes like water extraction or mineral removal.

Subsidence can cause severe structural damage and instability.

Cracks from subsidence are typically diagonal and wider at the top. They may appear suddenly and worsen over time.

Subsidence can affect buildings of any age, not just new constructions.

Soil composition plays a crucial role. Clay soils are particularly prone to shrinkage and swelling with moisture changes, increasing subsidence risk.

Defining Settlement

Settlement is the downward movement caused by a building’s weight compressing the soil beneath it. It commonly occurs in new constructions as the ground adjusts to the new load.

Unlike subsidence, settlement usually happens gradually and stabilises over time. It rarely causes significant structural issues unless extreme or uneven.

Settlement cracks tend to be vertical and uniform in width. They often appear within the first decade after construction.

Proper soil preparation and foundation design can minimise settlement effects. In most cases, settlement is considered a normal part of a building’s early life cycle.

Causes and Mechanisms

Subsidence and settlement arise from distinct factors affecting the ground beneath structures. While both can lead to property damage, their underlying mechanisms differ significantly.

Causes of Subsidence

Subsidence occurs when the ground supporting a building moves downwards, often due to soil instability.

Clay shrinkage is a common culprit, particularly during dry spells when moisture is drawn from the soil. Trees and large shrubs near buildings can exacerbate this problem by extracting water from clay soils.

Mining activities can create underground voids, leading to ground collapse and subsidence. Leaking drains or water mains may wash away fine soil particles, causing the ground to sink.

In areas with chalk or limestone bedrock, natural cavities can form and collapse, triggering subsidence.

Climate change and extreme weather patterns contribute to subsidence risk, with prolonged droughts followed by heavy rainfall destabilising soil structures.

Causes of Settlement

Settlement is a natural process that occurs as a building’s weight compresses the soil beneath it. New constructions typically experience some degree of settlement as the ground adapts to the new load.

Poorly compacted soil or inadequate foundation design can lead to excessive settlement.

Alterations to a building, such as extensions or loft conversions, may cause localised settlement due to the additional weight.

Changes in groundwater levels can affect soil stability, potentially leading to settlement. Vibrations from nearby construction work or heavy traffic may also compact soil and trigger settlement in existing structures.

Soil types play a crucial role, with some being more prone to compression than others.

Sandy or silty soils are particularly susceptible to settlement when exposed to varying moisture levels or vibrations.

Identifying Signs and Effects

Subsidence and settlement both involve downward movement of structures, but they manifest differently.

Recognising their distinct signs helps determine the appropriate course of action.

Signs of Subsidence

Subsidence often produces diagonal cracks in walls, typically wider at the top. These cracks may appear suddenly and worsen over time. Look for:

• Cracks around windows and doors
• Rippling wallpaper not caused by damp
• Doors and windows sticking or not closing properly
• Sloping or uneven floors

External signs include:

• Cracks in exterior brickwork
• Separation of extension from main building
• Leaning walls or chimneys

Subsidence can affect properties of any age, often due to soil shrinkage or tree root activity.

Signs of Settlement

Settlement typically occurs in newer buildings as they adjust to their foundations. Signs include:

• Hairline cracks in plaster or brickwork
• Small gaps between skirting boards and floors
• Slight unevenness in floors

These signs usually appear gradually and stabilise over time. Settlement cracks are often vertical or horizontal, unlike the diagonal cracks associated with subsidence.

External signs may include:

• Minor cracks in exterior walls
• Slight separation between window frames and brickwork

Settlement is generally less severe than subsidence and rarely requires major structural repairs.

Assessment and Measurement

Accurately assessing and measuring settlement and subsidence is crucial for determining the extent of structural issues.

Professional surveyors employ specialised techniques and equipment to evaluate ground movement and building displacement.

Surveying for Subsidence

Subsidence surveys involve a comprehensive examination of the property and surrounding area.

Surveyors use precision levelling equipment to measure vertical changes in the building’s position. They may install monitoring stations at key points to track movement over time.

Crack monitoring devices are fitted to measure the width and progression of existing fissures. Surveyors also analyse soil samples to assess ground conditions and moisture content.

In severe cases, boreholes may be drilled to investigate deeper soil layers and potential causes of subsidence.

Tree root mapping can identify vegetation that may be contributing to soil moisture depletion. Drainage surveys help detect leaks or damaged pipes that might be eroding the ground beneath the property.

Surveying for Settlement

Settlement surveys focus on newly constructed buildings or recent extensions. Surveyors use laser scanning technology to create detailed 3D models of the structure, allowing for precise measurements of any movement.

Tilt sensors are installed to monitor changes in the building’s inclination. These devices can detect even slight shifts in the foundation’s position.

Regular measurements are taken over several months to track the rate and pattern of settlement.

Load testing may be conducted to assess the bearing capacity of the soil and foundation system. This involves applying controlled weight to specific areas and measuring the resulting displacement.

Surveyors also inspect the building for visual signs of settlement, such as stepped cracks in brickwork or misaligned windows and doors. They carefully document these observations to establish a baseline for future comparisons.

Impact on Property and Construction

Subsidence and settlement can significantly affect buildings and construction projects.

These ground movements lead to distinct issues that require different approaches for prevention and mitigation.

Subsidence and Property Damage

Subsidence often causes severe damage to existing structures. It typically results in diagonal cracks in walls, particularly around doors and windows. These cracks tend to be wider at the top and may be visible both inside and outside the property.

Subsidence can also cause doors and windows to stick, as the building’s frame becomes misaligned. In extreme cases, it may lead to sloping floors and visible tilting of the entire structure.

Insurance policies generally cover subsidence-related damage, but claims can be complex and time-consuming. Addressing subsidence often requires substantial interventions, such as underpinning the foundation or stabilising the soil beneath the property.

Settlement in New Constructions

Settlement is a common occurrence in newly built structures. It usually manifests as minor, uniform cracks in plaster or brickwork within the first few months after construction.

These cracks are typically hairline and vertical, appearing above doors and windows or where walls and ceilings meet. They result from the building’s weight compressing the soil beneath its foundations.

Most settlement occurs within the first year of construction and is considered normal. Builders often account for this by incorporating expansion joints and flexible materials in the construction process.

While settlement rarely causes significant structural issues, excessive or uneven settlement may indicate poor soil compaction or inadequate foundation design. In such cases, remedial work might be necessary to prevent long-term problems.

Regional Considerations

Northern Ireland’s counties experience varying degrees of subsidence risk due to their distinct geological characteristics. Local factors play a crucial role in determining the likelihood and severity of ground movement issues.

Subsidence in County Antrim

County Antrim faces unique subsidence challenges due to its diverse geology. The area’s basalt bedrock, formed by ancient lava flows, provides stability in many regions.

However, pockets of clay soil and areas with a history of mining activity present increased risks.

Coastal regions, particularly around Larne and Carrickfergus, may be more susceptible to subsidence due to erosion and changing sea levels.

Urban centres like Belfast have seen instances of subsidence related to ageing infrastructure and underground voids.

Property owners in County Antrim should be aware of potential risks, especially in areas with known geological vulnerabilities or historical mining activity.

Subsidence in County Down

County Down’s subsidence profile differs from its northern neighbour. The county’s geology includes a mix of sedimentary and metamorphic rocks, which can influence ground stability.

Areas near the Mourne Mountains may experience localised subsidence due to weathering and erosion of granite formations.

Coastal towns such as Newcastle and Warrenpoint face risks from coastal erosion and potential sea level changes.

In urban areas like Bangor and Newtownards, subsidence issues often stem from poorly compacted fill material or changes in soil moisture content.

Rural parts of the county with peaty soils may be prone to gradual settlement over time.

Local authorities in County Down actively monitor high-risk areas and implement measures to mitigate subsidence impacts on infrastructure and properties.

Mitigation and Repair

Addressing subsidence and settlement issues requires different approaches due to their distinct causes.

Prompt action and appropriate techniques can minimise damage and restore structural integrity.

Addressing Subsidence Issues

Tackling subsidence often involves underpinning the affected area. This process strengthens the foundation by extending it to more stable ground.

Concrete underpinning is a common method, where concrete is poured into strategically excavated sections beneath the structure.

Tree root barriers may be installed to prevent moisture extraction from soil near the building. In cases of clay soil shrinkage, a technique called rehydration can be employed. This involves injecting water into the ground to restore soil moisture levels.

Repairing cracks caused by subsidence typically requires specialist attention. Flexible fillers are often used to allow for future movement. In severe cases, rebuilding affected walls might be necessary.

Managing Settlement Problems

Settlement issues are generally easier to address than subsidence. For minor settlement cracks, applying suitable fillers or grout can be effective. It’s crucial to sand the repaired area before repainting to ensure a smooth finish.

In new buildings, allowing time for natural settlement is often the best approach. However, if settlement persists or worsens, soil improvement techniques may be necessary. These can include compaction or the use of soil stabilisers.

For older properties with historical settlement, structural reinforcement might be required. This could involve adding steel beams or braces to support weakened areas. Regular monitoring is essential to detect any further movement.

Legal and Insurance Perspectives

Subsidence and settlement have significant implications for property owners, insurers, and legal matters. These issues can affect insurance coverage, claims processes, and property valuations in distinct ways.

Subsidence and Insurance Claims

Subsidence is typically covered under standard buildings insurance policies in the UK. Insurers often require a specialist survey to confirm subsidence before approving a claim.

The excess for subsidence claims is usually higher than for other types of damage, often around £1,000.

Claims can be complex and time-consuming, involving monitoring periods to assess ongoing movement. Insurers may cover costs for underpinning or other structural repairs if deemed necessary.

Properties with a history of subsidence may face higher premiums or struggle to obtain coverage from mainstream insurers.

Settlement and Property Value

Settlement is generally not covered by insurance as it’s considered a natural occurrence. This can impact property values, particularly for newer buildings still experiencing settlement.

Buyers’ surveys often highlight settlement issues, potentially leading to price negotiations. Severe settlement problems may deter potential purchasers or require costly remedial work.

Mortgage lenders might request additional surveys or guarantees before approving loans for properties with significant settlement.

Legal disputes can arise if sellers fail to disclose known settlement issues. Buyers may seek compensation if undisclosed problems are discovered post-purchase.

Proper documentation of settlement history is crucial for property transactions to proceed smoothly.