MET SURVEYORS

What Is Subsidence?

 

Subsidence occurs when the ground beneath part of a property moves downwards.

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If the ground supporting the foundations moves sufficiently, the foundations can move with it and this movement may become visible in the building above.

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Subsidence can be associated with factors such as:

• Shrinkable clay soil

• Prolonged hot and dry weather

• Mature trees and vegetation

• Leaking underground drains

• Changes in ground conditions

• Inadequate foundations

• Poorly constructed extensions

• Historic structural alterations

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The presence of any one of these factors does not mean that a property has subsidence.

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They are simply matters that may need to be considered when investigating movement.

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What Are the Main Signs of Subsidence?

 

Possible signs include:

• New diagonal cracks

• Cracks around windows and doors

• Cracks wider at one end than the other

• Cracking visible internally and externally

• Cracks becoming wider over time

• Previously repaired cracks reopening

• Doors and windows beginning to stick

• Gaps appearing around frames

• Uneven or distorted floors

• Movement between an extension and the original building

• Visible distortion to walls or openings

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The significance of these signs depends on their location, extent and whether they are changing.

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Diagonal Cracks Around Doors and Windows

 

Diagonal cracking around doors and windows is one of the signs most commonly associated with structural movement.

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Openings create natural weak points within masonry, which means that movement can become visible there first.

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However, diagonal cracking can also be caused by:

• Lintel movement

• Normal settlement

• Thermal movement

• Poor construction

• Previous alterations

• Movement between different materials

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A diagonal crack should therefore be assessed in the context of the wider building.

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Cracks Wider at the Top or Bottom

 

A crack that changes width along its length may indicate movement between different parts of the structure.

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For example, a crack may be narrow at one end and noticeably wider at the other.

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This does not prove subsidence, but tapered cracking can be more significant than a very fine, uniform crack in plaster.

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If the crack is also increasing in width or appears in several areas, further investigation may be appropriate.

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Cracks Visible Inside and Outside

 

Cracking visible on both sides of a wall may warrant closer attention.

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A fine plaster crack on an internal wall can often be cosmetic.

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Where cracking passes through the wall construction and can also be seen externally, this may indicate that movement affects more than the decorative finish.

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The pattern and location still need to be assessed before conclusions are drawn.

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Cracks That Are Getting Bigger

 

Progressive cracking is usually more significant than an old crack that has remained unchanged for many years.

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You may notice that:

• The crack is becoming wider

• The crack is extending further along the wall

• New cracks are appearing nearby

• A previous repair has opened again

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These changes can indicate continuing movement.

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If you believe a crack is changing, it is useful to record when you first noticed it and take dated photographs.

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Doors and Windows Beginning to Stick

 

Doors and windows that suddenly become difficult to open or close can sometimes indicate movement around their openings.

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Possible signs include:

• Doors catching against frames

• Windows no longer closing correctly

• Gaps developing around frames

• Frames becoming visibly distorted

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However, timber doors and windows can also change with moisture and temperature, so sticking alone does not prove structural movement.

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It becomes more significant when combined with cracking or distortion nearby.

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Gaps Around Windows and Doors

 

New gaps appearing between frames and surrounding walls can indicate movement.

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This is particularly relevant where:

• Gaps have appeared suddenly

• Cracks are also present

• The frame appears distorted

• The problem is worsening

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Movement around an opening may have several causes, including settlement, lintel problems, differential movement and subsidence.

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Cracks Between an Extension and the Original House

 

This is one of the most common concerns we encounter.

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Extensions and original buildings may have different:

• Foundation depths

• Foundation types

• Materials

• Construction dates

• Rates of settlement

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Some movement between old and new construction can therefore occur without there being subsidence.

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However, wider or progressive cracking at the junction should be investigated.

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Particular attention should be paid where the crack is visible internally and externally or where doors and windows nearby are also affected.

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Uneven or Distorted Floors

 

Floor movement can sometimes accompany structural movement.

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Possible signs include:

• Floors becoming noticeably uneven

• Gaps opening at skirting level

• Changes in floor levels

• Localised sinking

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Floor movement can also result from timber deterioration, defective joists, moisture damage or poor previous construction.

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It therefore needs to be assessed alongside the rest of the property.

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Previously Repaired Cracks Reopening

 

A crack that has previously been filled or repaired and later opens again can be important.

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Reopening may indicate that the original cause of the movement remains active.

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If you have photographs or information about previous repairs, this can be useful when investigating the problem.

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Cracks Appearing After Hot Weather

 

Periods of prolonged dry weather can affect some ground conditions.

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Clay soils can shrink as they lose moisture.

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Where a property is founded on shrinkable clay, this can contribute to foundation movement in some circumstances.

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This may be more relevant where:

• Cracks appeared during or after a dry period

• Mature trees are close to the building

• The property has relatively shallow foundations

• Similar movement has occurred previously

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Cracking after hot weather does not automatically mean subsidence, but the timing can form part of the investigation.

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Trees Close to the Property

 

Trees can influence moisture levels in some soils.

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Factors that may be relevant include:

• Species

• Size

• Distance from the property

• Soil conditions

• Foundation depth

• Position of the cracking

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The presence of a tree close to the house does not prove that it is causing movement.

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Where a possible relationship exists, specialist arboricultural advice may sometimes be required.

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Leaking Drains

 

Damaged underground drains can sometimes affect the ground around foundations.

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Where movement occurs close to drainage runs, gullies or inspection chambers, drainage defects may need to be considered.

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Further investigation may include a CCTV drain survey.

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A structural inspection alone cannot establish the condition of underground drainage.

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Is It Subsidence or Settlement?

 

Settlement and subsidence are not the same thing.

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Settlement generally describes movement that occurs as a building or new section of building adjusts after construction.

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Subsidence generally describes downward movement of the ground supporting the foundations.

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An extension, for example, may settle differently from the older building beside it.

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This can cause cracking at the junction without the original property suffering from subsidence.

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The distinction is one reason professional assessment can be useful.

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Does Every Crack Need a Survey?

 

No.

Very fine cracks in plaster are extremely common.

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They may be caused by:

• Drying shrinkage

• Decoration

• Plasterboard joints

• Minor thermal movement

• Normal settlement

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However, advice should be considered where cracking is:

• New

• Widening

• Reappearing after repair

• Visible inside and outside

• Associated with sticking doors or windows

• Affecting several parts of the building

• Accompanied by visible distortion

• Causing concern about possible subsidence

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When Should You Arrange a Structural Survey?

 

A more comprehensive Structural Survey may be appropriate where:

• Cracking affects several parts of the property

• Movement appears widespread

• Several elevations are affected

• Significant distortion is visible

• There is a genuine concern about subsidence

• Previous repairs have repeatedly failed

• A purchaser's survey has raised serious structural concerns

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A wider survey allows the structure to be considered as a whole rather than focusing on one isolated defect.

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When Is a Specific Issue Survey Suitable?

If you have one clearly defined structural concern, a Specific Issue Survey may be more appropriate.

 

Examples include:

• One area of cracking

• A crack above a window or door

• Movement to one wall

• Cracking around a bay

• Movement between an extension and the house

• A localised defect identified in another survey

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Our Specific Issue Survey provides a focused inspection and written report.